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Ground Water Discharge of Agricultural Pesticides and Nutrients to Estuarine Surface Water
Abstract
This research investigated the transport of land-applied nutrients and pesticides from unconfined aquifers to tidal surface waters of Virginia's coastal plain. Ground water, estuarine surface water, ground water discharge, upland soil, and offshore sediment samples were collected from May 1992 until February 1993 from four agricultural sites. Samples were analyzed for inorganic nitrogen and phosphorus and five pesticides: atrazine, cyanazine, alachlor, metolachlor, and carbofuran. Pesticides from aqueous samples were determined by liquid-solid phase extraction followed by gas chromatography-electron capture detection (GC-ECD) and/or by pesticide-specific immunoassay. Soil and sediment samples were analyzed by extraction and gas chromatography/mass spectrometry (GC/MS). Nutrient measurements indicated that fertilizer nitrogen was moving from the ground water to the surface water, and nitrogen fluxes across the sediment-water interface were correlated with fresh water discharge rates. Mean nitrate-N flux was 2.48 mg/m2hr, with a maximum value of 30.98 mg/m2hr. Pesticides were detected in more than half of the upland soil samples, in approximately 40 percent of the ground water samples, and in just under 20 percent of the seepage meter samples. Pesticides were not detected in any of the offshore sediment samples or surface water samples. Alachlor and metolachlor were detected in upland soil samples at concentrations ranging from 10 to almost 500 μg/kg. All five pesticides were found in ground water samples at concentrations generally below 1 μg/L, with alachlor, atrazine, and metolachlor most frequently found. Alachlor, atrazine, cyanazine, and metolachlor were detected in water discharging across the sediment-water interface and entering estuarine waters at concentrations ranging from 0.05 to 0.5 μg/L. These levels were generally consistent with the amount of dilution due to the mixing of fresh ground water and saline pore waters prior to discharge across the sediment-water interface. Based on all positive detections of pesticides in ground water discharge, which represented approximately 18 percent of all samples, average flux rates of cyanazine, metolachlor, alachlor, and atrazine were 0.32, 0.37, 0.80, and 1.12 μg/m2hr, respectively. These findings indicate that submarine ground water transport of both nutrients and pesticides does occur, and this transport route should be considered when implementing agricultural management practices. The levels of nitrogen transport to surface water appears significant. The overall levels of pesticide movement through ground water, although generally quite low, represent a transport route that is commonly neglected in watershed management.
... The discharge of ground water to coastal marine environments such as bays, estuaries, and lagoons may represent an important transportation process for pollutants including excess nutrients, from shallow sediments to overlying surface waters. The importance of such a phenomenon has gained increased recognition in recent years because studies have shown that submarine discharge of water transports nutrients from agricultural lands (Simmons 1992, Gallagher et al. 1996 and residential septic tanks (Weiskel and Howes 1992) to coastal marine waters. This nutrient flux has lead to poor water quality and eutrophication of near shore ecosystems (Nixon 1986, Corbett et al. 2000. ...
... The movement of water represents one of the primary controls of the distribution of pollutants in estuaries (Gallagher 1996, Martin et al. 2000. Water budgets of estuaries are routinely determined by measuring the volumes of surface water runoff, atmospheric deposition, and evapotranspiration in the area. ...
... Ground water flux rates have been the focus of several studies in the past (e.g. Gallagher et al. 1996b., Li et al. 1999), but the associated nutrient fluxes have rarely been measured. Quantifying nutrient fluxes requires knowing nutrient concentrations within the water column, shallow sediments, and the discharging ground water. ...
... Discharges similar to those observed in Eckernförde Bay were reported for the Great South Bay off New York (Bokuniewicz 1980), coastal bays of New England (Valiela et al. 1990), Chesapeake Bay (Gallagher et al. 1996;Reay et al. 1996), and the northeastern coastal Gulf of Mexico (Rasmussen 1998). At least in some cases, these discharge rates also included the effect of recirculated seawater (Taniguchi et al. 2002), whereas the pore water composition is essentially unaffected by recirculation of seawater for muddy sediments of Eckernförde Bay. ...
... Discharges similar to those observed in Eckernförde Bay were reported for the Great South Bay off New York (Bokuniewicz 1980), coastal bays of New England (Valiela et al. 1990), Chesapeake Bay (Gallagher et al. 1996;Reay et al. 1996), and the northeastern coastal Gulf of Mexico (Rasmussen 1998). At least in some cases, these discharge rates also included the effect of recirculated seawater (Taniguchi et al. 2002), whereas the pore water composition is essentially unaffected by recirculation of seawater for muddy sediments of Eckernförde Bay. ...
Submarine groundwater discharge (SGD) from subseafloor aquifers, through muddy sediments, was studied in Eckernförde Bay (western Baltic Sea). The fluid discharge was clearly traced by 222 Rn enrichment in the water column and by the chloride profiles in pore water. At several sites, a considerable decrease in chloride, to levels less than 10% of bottom-water concentrations, was observed within the upper few centimeters of sediment. Studies at 196 sites revealed that Ͼ22% of the seafloor of the bay area was affected by freshwater admixture and active fluid venting. A maximal discharge rate of Ͼ9 L m Ϫ2 d Ϫ1 was computed by modeling pore water profiles. Based on pore water data, the freshwater flow from subseafloor aquifers to Eckernförde Bay was estimated to range from 4 ϫ 10 6 to 57 ϫ 10 6 m 3 yr Ϫ1. Therefore, 0.3-4.1% of the water volume of the bay is replaced each year. Owing to negligible surface runoff by rivers, SGD is a significant pathway within the hydrological cycle of this coastal zone. High-resolution bathymetric data and side-scan sonar surveys of pockmarks, depressions up to 300 m long, were obtained by using an autonomous underwater vehicle. Steep edges, with depths increasing by more than 2 m within 8-10 m in lateral directions, equivalent to slopes with an angle of as much as 11Њ, were observed. The formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents. Fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread, but easily overlooked, pathway affecting the cycle of methane and dissolved constituents to coastal waters of the Baltic Sea. For coastal areas, Sonrel (1868) reported the discharge of freshwater from submarine springs and speculated on their use and risks for sailors. Since then a few studies have considered the importance of fluid discharge from sediments for nutrient budgets of coastal environments, formation of offshore plankton blooms, hydrological cycles, or the release of trace elements and gases such as radon from the seafloor deduced that the quantity of submarine groundwater discharge (SGD; here taken as fresh plus salt water) represented 40% of the river input into the study area. Although these figures probably overestimate the contribution of submarine seepage 1 Corresponding author (mschlueter@awi-bremerhaven.de). Acknowledgments We thank the captains and crews of RVs Littorina, A. v. Hum-bold, and Alkor for their support during several cruises. We are grateful to W. Lemke and J. Harff from the Institute of Baltic Research (IOW, Warnemünde) for providing the vibro corer system. Jayne Wolf-Welling is gratefully acknowledged for improving the English text. We thank DeBeers Marines/Maridan for conducting the AUV dives. Application of GIS was supported by Dr. A. Schäf-er. The paper benefited from the comments and suggestions of two anonymous reviewers. This research was funded as part of the EU shared cost project Sub-GATE (contract no. ENV4-CT97-0631).
... These gradients were estimated at mid-to-low tide, and would be expected to vary tidally as observed elsewhere in this region (Beck et al. 2016). Groundwater discharge was calculated according to the Darcy equation (v = K h [dh/dl]), assuming a regional hydraulic conductivity (K h ) of 0.001 cm/s (Gallagher et al. 1996;McFarland and Bruce 2006;Robinson et al. 1998). A seepage face of 5 m width was estimated. ...
... Nutrient concentrations in groundwater at the living shoreline sites (Figure 14.5) were consistent with other observations in the Chesapeake Bay region but were generally lower within the brackish marsh groundwater samples than observed elsewhere (Beck et al. 2016;Gallagher et al. 1996 . Results of the current study also matched previous work showing low NO x − and high NH 4 + concentrations in suburban/urban land use types (Reay and Simmons 1992 and references therein). ...
... Chemical and physical properties such as solubility, adsorption, degradation, and volatilization determine the potential of pesticides to contaminate groundwater (Chin and Weber, 1988;Davidson, 1995). Many studies have described pesticide movement in groundwater (e.g., Zhang et al., 2009;Rendón-von Osten and Dzul-Caamal, 2017), including the presence of the ubiquitous herbicide glyphosate (Magga et al., 2008) but few have documented their transport across the landocean interface to the coastal ocean through SGD (Gallagher et al., 1996;Almasri, 2008). ...
... The GLY that enters Faga'alu Bay each day via baseflow and coastal SGD is likely diluted relatively quickly as it enters a large body of water and mixes offshore. Gallagher et al. (1996) found low concentrations of pesticides across coastal sites in Virginia, but detected none in the offshore surface water or sediment samples. The chronic effects of the GLY itself are suggested not to be a factor on reef health, as its dilution and degradation are relatively rapid in open water (Schuette, 1998). ...
It is increasingly recognized that groundwater discharge in the form of stream baseflow and submarine groundwater discharge (SGD) plays an important role in contaminant transport. This study seeks to demonstrate the importance of groundwater flow for the distribution and transport of selected pesticides and nutrients in the Faga'alu aquifer on the island of Tutuila in American Samoa. Field measurements, including seepage runs and analysis of stream and groundwater for pesticides and nutrients, were combined with hydrological modeling. Selected analytes were glyphosate (GLY), dichlorodiphenyl-trichloroethane (DDT), imidacloprid, and azoxystrobin for pesticides and chemical species of nitrogen, phosphate, and silicate for nutrients. Hydrological flow and transport models of the aquifer were built to simulate groundwater flow and to provide estimates of GLY and dissolved inorganic nitrogen (DIN) fluxes. Stream baseflow was responsible for 59% and SGD for 41% of groundwater flow to the bay, which totaled 6,550 ± 980 m³/d in the dry season when surface runoff was negligible. DDT was found in 85% and GLY in 100% of tested samples. SGD and baseflow thus delivered 9 ± 2 g/d of DDT, 0.9 ± 0.2 g/d of GLY, 570 ± 100 g/d of DIN and 840 ± 110 g/d of dissolved inorganic phosphorus (DIP) into Faga'alu Bay. While all pesticide levels are below environmental limits, their presence in baseflow and SGD, which discharge continuously year-round, result in sustained fluxes of GLY and DDT to the reef. The presence of DDT in groundwater decades after its last application confirms its long-term environmental persistence.
... [2] Submarine groundwater discharge (SGD) has been recognized recently as a significant water and material pathway from land to ocean [Moore, 1996;Burnett, 1999;Burnett et al., 2001], and has stimulated studies from both hydrological and coastal oceanographic communities [Li et al., 1999;Hussain et al., 1999;Smith and Zawadzki, 2003;Burnett et al., 2003;Chanton et al., 2003]. Recent field work revealed that SGD contains submarine fresh groundwater discharge (SFGD) and recirculated saline groundwater discharge (RSGD) [Gallagher et al., 1996;Li et al., 1999;Taniguchi et al., 2002Taniguchi et al., , 2003a, and that there are tidal effects on SGD [Taniguchi, 2002;Kim and Hwang, 2002]. Because SGD is difficult to detect and quantify, there are still many uncertainties in understanding the subsurface processes. ...
... They found the ratio of SFGD to total SGD ranged from 1% to 29% in Osaka bay, Japan. Ratios of SFGD to SGD were also estimated in other studies to be 35% using seepage meters and salinity measurements by Gallagher et al. [1996], 10% using 222 Rn and 226 Ra measurements by Hussain et al. [1999], and 4% using numerical simulations by Li et al. [1999]. However, temporal and spatial variations of SFGD/ SGD ratios and process of the variations are still not clear. ...
Relationships between submarine groundwater discharge (SGD) and the freshwater-saltwater interface are evaluated by continuous measurements of SGD rates, conductivity and temperature of SGD, and resistivity measurements across the coastal aquifer. Our measurements show that the processes of SGD differ between the offshore and nearshore environments. SGD and submarine fresh groundwater discharge (SFGD) rates were largest just landward of the saltwater-freshwater interface. SGD variations landward the saltwater-freshwater interface had negative correlations with tidal variations, because of the connections of terrestrial groundwater in the land and the ocean. SGD in the nearshore can be explained mainly by connections of terrestrial groundwater, while offshore SGD rate is controlled mostly by oceanic process such as recirculated saline groundwater discharge.
... [3] A variety of methods have been employed to determine groundwater flux rates across the sediment-water interface. Seepage meters have been used to determine groundwater seepage rates into lakes [Lee, 1977;Fellows and Brezonik, 1980;Woessner and Sullivan, 1984;Cherkauer and Zager, 1989], estuaries [Gallagher et al., 1996;Robinson et al., 1998], and coastal environments [Giblin and Gaines, 1990;Cable et al., 1997]. Groundwater seepage rates have also been determined based on hydraulic head gradients [Woessner and Sullivan, 1984;Cherkauer and Zager, 1989;Robinson et al., 1998;Uchiyama et al., 2000] and by detecting tracers in surface waters [Hussain et al., 1999;Moore, 1999]. ...
... [4] Quantification of benthic seepage fluxes is important because aquifers and sediments can act as sources of contaminants to surface waters [e.g., Gallagher et al., 1996;Zelewski et al., 2001]. This is indicated by concentration gradients of dissolved metals in sediment pore waters in estuaries Flegal, 1997a, 1997b] and coastal zones [Ciceri et al., 1992], which show that metals flux from sediments to surface waters in some settings. ...
Nonconservative excesses of dissolved metals in northern San Francisco Bay indicate that there are internal sources of metals within the bay. We quantified groundwater seepage and bioirrigation rates in this area to determine their roles in transporting dissolved metals from benthic sediments to surface waters. We deployed seepage meters and collected sediment, pore water, and bottom water samples at three sites. We determined seepage rates from seepage meters and modeled the transport of water through the sediment using pore water data to constrain rates of diffusion, advection, and bioirrigation. A groundwater flow model incorporating sediment physical properties and local topography constrains more regional seepage estimates. The seepage meters indicate upflow rates from 7 to 56 cm yr−1 in March and April 1999 with some large (≤50 cm yr−1) daily fluctuations that greatly exceed predictions based on sediment physical properties and tidally induced pore pressure variations. During this period, results from modeling pore water chemical data are consistent with a small bioirrigation rate (
... Pesticides typically enter estuaries via freshwater runoff. However, groundwater from submarine springs and seeps may also be sources of pesticides and may locally modify estuarine salinity (Gallagher et al. 1996;Cuevas et al. 2018). Pesticides can add to the burden of other stressors including varying salinity already influencing euryhaline species (Delorenzo 2015;Cuevas et al. 2018). ...
Agricultural activity within coastal watersheds results in estuaries becoming the receiving environment for pesticide inputs. In estuaries, salinity can alter insecticide responses of exposed crustaceans. The acute toxicity of environmentally relevant doses of chlorpyrifos and imidacloprid were examined using the euryhaline amphipod Gammarus lawrencianus at 20 and 30 Practical Salinity Units (PSU). Responses were recorded every 24 h until an incipient (threshold) L(E)C50 was reached. For chlorpyrifos, LC50 ranged from 0.1 to 0.5 µg/L and was two-fold higher at 30 vs. 20 PSU at all time-points over the 96 h exposure. Imidacloprid immobility EC50 ranged from 4 to 40 µg/L over the 144 h exposure. An effect of salinity was only observed at 48 h and the EC50 values showed 1.4 times more potency at 20 PSU compared to 30 PSU. Measured concentrations of both compounds did not differ between salinities. Acetylcholinesterase activity in chlorpyrifos exposed amphipods showed no salinity effect at 96 h. We conclude that salinity level alters G. lawrencianus susceptibility to chlorpyrifos exposure, but not imidacloprid.
... The hydraulic properties of coastal aquifer systems are relevant to various hydrogeological, hydro-ecological, and engineering problems, such as seawater intrusion (Carr, 1969;Kuan et al., 2012;Werner et al., 2013), submarine groundwater discharge (Moore, 1996;Taniguchi, 2002;Prieto & Destouni, 2011;Wang, Doan, et al., 2018;Wang, Chen, et al., 2018), migration of contaminants and/or nutrients (Chan & Mohsen, 1992;Gallagher, Dietrich, Reay, Hayes, & Simmons Jr, 1996;Uchiyama, Nadaoka, Roelke, Adachi, & Yagi, 2000), and stability of coastal engineering structures (Farrell, 1994). Although mass transport in a coastal aquifer system can be controlled by many processes, such as advection, dispersion and reaction, understanding the hydraulic properties of a coastal aquifer system is of fundamental importance when evaluating advection. ...
Determination of the hydraulic properties of coastal aquifer systems has important implications that are related to the issues such as seawater intrusion, submarine groundwater discharge, migration of contaminants, assessment of water resources, and geotechnical engineering. Over recent decades, many analytical solutions that consider different types of coastal aquifer systems or models have been developed. These solutions can be used as a theoretical basis for the tidal method that characterizes the hydraulic properties of a coastal aquifer system using hydraulic response measurements in an observation well or wells induced by tidal waves in the ocean. The hydraulic properties of an aquifer can be estimated through fitting a series of time‐dependent changes of hydraulic head detected in an observation well to those calculated based on theoretical solutions. For simplicity, most theoretical solutions only consider one tidal component and idealized boundary conditions, although in reality multiple tidal components exist simultaneously and boundary conditions can be more complicated. For practical applications of the tidal method and to increase its reliability, multiple tidal components should be considered and models considering more complicated boundary conditions should be developed. In addition, methods that can determine both the hydraulic conductivity and storage coefficient, rather than only the hydraulic diffusivity, that is, the ratio of hydraulic conductivity to storage coefficient of coastal aquifer, should be developed. Cautions should be taken into account when using the tidal method because earth tides and changes in local atmospheric pressure may induce similar tidal fluctuations in the hydraulic head within inland observation wells.
This article is categorized under: Science of Water > Hydrological Processes
Science of Water > Methods
... A 1985 study detected 20 different pesticides in ground water with the herbicide Atrazine being the most common (Mostaghimi et al., 1993). A sampling of Virginia's coastal plain in 1992-1993 found pesticides (atrazine, cyanazine, alachlor, metolachlor, and carbofuran) absent from surface waters of the Bay and offshore sediments, but present in upland soils, groundwater and in groundwater emerging into the estuary (Gallagher et al. 1996). Streams and ground water of the Potomac River basin sampled in 1992 -1996 had measurable amounts of 12 different pesticides (Ator et al. 1998). ...
The end of World War II brought DDT and other organic pesticides to Chesapeake Bay agriculture. These new insecticides and herbicides supported the industrialization of farming that primarily produced feedstock for the manufacture of animal-based foods. The widespread use of these new chemicals constituted a war on nature with the intent of poisoning non-human animals that ate crops and weeds that competed for land, space, light, nutrients, and water. The pesticides tended to fail as the artificial selection they imposed on their targets promoted the evolution of resistant pests. In the 1960s, herbicides replaced insecticides as the dominant pesticide. Genetic engineered pesticide resistant corn and soybean facilitated the marketing of the generalist herbicides glyphosate, and later dicamba. The genetically engineered crops and pesticide dominate the animal feedstock agriculture in the region. Years of pesticide use have contaminated water, soils, fish and wildlife. The pesticides threaten both human health and that of the environment. Adopting sustainable organic agricultural practices can end the war on nature and help recover the health of the Chesapeake Bay ecosystem and that of its people.
... Characterization of the hydraulic properties of coastal aquifer systems has important implications that cover a number of research topics, such as geotechnical engineering (Farrell 1994), assessment of water resources (Jha et al. 2008;Befus et al. 2017;Singaraja, Chidambaram, and Jacob 2018), submarine groundwater discharge (Moore 1996;Taniguchi 2002;Prieto and Destouni 2011), seawater intrusion (Carr 1969;Kuan et al. 2012), and migration of contaminants, nutrients, and land-sourced solute (Chan and Mohsen 1992;Gallagher et al. 1996;Uchiyama et al. 2000;Liu, Jiao, and Luo 2016). Although several direct hydraulic testing methods, such as the use of permeameters or seepage meters, slug test, tracer test, pumping test, and a few indirect methods, such as grain-size analysis (Michael et al. 2003;Millham and Howes 1995), are available, the tidal method is simple and inexpensive, and can obtain compatible results with the pumping test (Carr and Van Der Kamp 1969). ...
Determination of the hydraulic properties of a coastal aquifer system with lower cost and acceptable accuracy has practical implications. Although many theoretical solutions have been developed over recent decades, most of them assume that an aquifer system extends inland and subjected a single-frequency tidal fluctuation on coastline boundary. In addition, only one hydraulic parameter, i.e., the hydraulic diffusivity, of an aquifer can be obtained in most cases. In this paper, the solution of groundwater response in a leaky confined coastal aquifer to dual frequency tidal fluctuations has been established. The new solution was then used as an example to discuss the applicability and limitations of using tidal fluctuations for determining coastal aquifer hydraulic properties. Our study illustrated that ocean tides could only transport to a limited distance towards inland depending on the coastal aquifer hydraulic properties. The tidal method is applicable only when changes in the hydraulic head within in a monitoring well can be detected with an acceptable accuracy. Both the hydraulic diffusivity and leakage can be identified from the monitored hydraulic heads. By incorporating the use of aquifer thickness, the transmissivity and storage coefficient of a perfectly confined aquifer can also be simultaneously estimated.
... The pressure to produce enough food has had a worldwide impact on agricultural practices such as intensification that needs an expansion of irrigation and a massive use of fertilizers and pesticides. These practices poorly managed can lead to contamination of surface and groundwater by nutrients and pesticides (Gallagher et al. 1996;Fischer et al. 2003;Brodie and Mitchell 2005;Mitchell et al. 2005;Gilliom 2007;Hildebrandt et al. 2008;Schult 2016a,b). In urban and industrial areas, the production of waste and its mode of disposal is one of the activities that generate large quantities of pollutants that will be found in the natural environment without inadequate treatment and can reach groundwater (Han et al. 2016). ...
The present study aimed to evaluate the suitability for drinking purpose of shallow groundwater near the Béni-Mellal wastewater treatment lagoon based on various physicochemical, heavy metals, and bacteriological parameter analyses. The physicochemical results revealed that some of the samples do not comply with the Moroccan and/or WHO standards for drinking water. Parameters including turbidity, TH, Na⁺, Li⁺, Ba²⁺, Ca²⁺ (∼47.1% of samples), Cd (∼52.9% of samples), Fe (∼82.4% of samples), Pb (∼58.8% of samples), T. coliforms, and E. coli exceeded the drinking limits. The statistical analyses revealed that the shallow groundwater chemistry is mainly controlled by geogenic and anthropogenic sources. For quality assessment, using the Moroccan groundwater assessment grid, the values of EC and Cl–, NO3–, NH4⁺, oxidability, and E. coli, fixed as pollution indicators, showed that most of the wells showed medium-to-poor quality, 14% of them have a very poor water quality, and 20% of them belong to the bad water quality. According to geometric and arithmetic DWQI values, the groundwater quality was frequently fair to good, needing treatment or at least disinfection before public consumption. A sensitivity analysis results indicated that Fe, Cd, Cr, Pb, and E. coli have an important impact on the DWQI computing.
... Although representing a potential risk for environmental and human health, pesticides are not much in the focus of groundwater-related matter fluxes until now. However, Gallagher et al. (1996) reported several pesticide species in groundwater discharge into Chesapeake Bay (Virginia & Maryland, USA). ...
The discharge of groundwater into surface water bodies is a hidden, but significant pathway for the input of water and matter into lakes, rivers, estuaries and the coastal sea. Since groundwater is most often characterized by higher levels of nutrients or heavy metals, its discharge has often a crucial effect on the surface water body´s chemistry and the ecosystem health as well as on the related ecosystem service supply. For instance, groundwater-derived nutrient inputs are essential to fuel primary productivity, but if critical thresholds are exceeded groundwater-derived nutrient inputs can cause eutrophication, which may trigger harmful algal blooms or the creation of oxy-gen minimum zones – a serious threat to aquatic life.
This thesis focuses on quantifying submarine and lacustrine groundwater discharge by applying environmental tracer based methods with emphasis on radionuclide (radon and radium isotopes) and stable water isotope (δ18O, δ2H) techniques. These tracers are suitable for determining groundwater discharge as they show distinct concentra-tion and isotope ratio gradients between groundwater and the receiving surface water. Four studies are presented in this thesis:
(1) The quantification of the response delay of the mobile radon detector RAD7 applied for radon-in-water mapping.
The response delay of the mobile radon-in-air detector RAD7 is determined for two detection set-ups (radon extraction via RADaqua and via a membrane module) as well as for a range of water flow rates. For the membrane module the response delay is less pronounced compared to the RADaqua. For instance, at a water flow rate of 1 l min-1 the peaks of the instruments recordings lag behind the radon-in-water concentrations by ~10 min for the membrane module and by ~18 min for the RADaqua. Further, it was demonstrated that faster water flow rates decrease the response delay. An algorithm is presented that allows the inverse calculation of radon-in-water concentrations from RAD7 records for the described detection set-ups and water flow rates. Thus, it allows a more precise localization of radon-in-water anomalies and, consequently a more precise localization of groundwater discharge areas.
(2) Determination of submarine groundwater discharge into a large coastal bay (False Bay, South Africa)
SGD consists generally of two components: (a) fresh terrestrial SGD (FSGD) driven by the inland hydraulic gradient and (b) seawater re-circulation (RSGD) through the coastal aquifer driven by seaward effects such as tidal pumping. A bay-wide radon mapping resulted in identification of a SGD site, where subsequently detailed investiga-tions were conducted. At this SGD site a salt and a radon mass balance were applied consecutively for determining FSGD and total SGD, respectively. RSGD was inferred from the difference between FSGD and total SGD. For the radon mass balance, new approaches for calculating the radon degassing and mixing loss were proposed. The tracer mass balance revealed median FSGD of 2,300 m³ d-1 or 0.9 m³ d-1 per m coastline and median RSGD of 6,600 m³ d-1 or 2.7 m³ d-1 per m coastline. The FSGD rate was val-idated using (a) a hydrological model for calculating the groundwater recharge rate and (b) a groundwater flow model for delineating the subsurficial FSGD capture zone. This validation supported the tracer based findings. The relevance of this study is foremost the presentation of new methodological approaches regarding the radon mass balance as well as the validation of FSGD under consideration of hydrological and hydrogeological information.
(3) Differentiation of fresh and re-circulated submarine groundwater discharge in an estuary (Knysna Estuary, South Africa). Knysna Estuary is a more complex system than False Bay since besides seawater, FSGD and RSGD also river water mixes within the estuary. Both FSGD and RSGD were differentiated by applying a mixing analysis of the estuary water. For this purpose, an end-member mixing analysis (EMMA) was conducted that simultaneously utilizes radon and salinity time series of estuary water to determine fractions of the end-members seawater, river water, FSGD and RSGD. End-member mixing ratio uncertainty was quantified by stochastic modelling (Monte Carlo simulation) under consideration of end-member characterization uncertainty. Results revealed highest FSGD and RSGD fractions in the estuary during peak low tide. Median fractions of FSGD and RSGD were 0.2 % and 0.8 % of the estuary water near the mouth over a 24 h time-series. In combination with a radon mass balance median FSGD of 46,000 m³ d-1 and median RSGD of 150,000 m³ d-1 were determined. By comparison to other sources, this implies that the SGD is a significant source of dissolved inorganic nitrogen (DIN) fluxes into the estuary. This study demonstrates the ability of EMMA to determine end-member fractions in a four end-member system under consideration of end-member uncertainty. Further, the importance of SGD for the water and DIN budget of Knysna Estuary was shown.
(4) Quantification of groundwater discharge and water residence time into a groundwater-fed lake (Lake Ammelshainer See, Germany).
The presented approach utilizes the stable isotopes of water (δ18O, δ2H) and radon for determining long-term average and short-term trends in groundwater discharge rates. The calculations were based on measurements of isotope inventories of lake and groundwater in combination with climatic and isotopic monitoring data (in precipitation). The results from steady-state annual isotope mass balances for both δ18O and δ2H are consistent and reveal an overall long-term average groundwater discharge that ranges from 2,800 to 3,350 m³ d-1. These findings were supported by the good agreement of the simulated annual cycles of δ18O and δ2H lake inventories utilizing the de-termined groundwater discharge rates with the observed lake isotope inventories. However, groundwater discharge rates derived from radon mass balances were significantly lower, which might indicate a distinct seasonal variability of the groundwater discharge rate. This application shows the benefits and limitations of combining δ18O/δ2H and radon isotope mass balances for the quantification of groundwater con-nectivity of lakes based on a relatively small amount of field data accompanied by good quality and comprehensive long-term meteorological and isotopic data (precipitation).
This thesis presents important methodological achievements with respect to radon and stable water isotope mass balances, uncertainty quantification, geochemical differentiation between FSGD and RSGD and validation of FSGD. Further, first SGD estimates are reported for False Bay and Knysna Estuary in South Africa.
... Significant levels of some of these contaminants are commonly more a reflection of historical than ongoing activities (e.g., Sanger et al. 1999). Tidal marshes and their creeks commonly have higher levels of heavy metals than other estuarine waters (Gallagher et al. 1996). ...
The purpose of this document is to highlight recent scientific literature that compares functions of diked common reed wetlands – the most extensive wetland type in the Greenbelt and hereafter abbreviated as Phragmites -- to those of the following wetland types:
1. Restored or natural emergent wetlands dominated by Spartina patens and S. alterniflora (cordgrass) marsh – hereafter abbreviated as Spartina – which are supported hydrologically by exchange of estuarine tidal surface waters, and
2. Restored or natural palustrine mixed emergent and shrub wetlands (e.g., Typha, Scirpus, Carex, Salix) – hereafter abbreviated as PEMS -- which are supported hydrologically by a varying array of non-tidal water sources.
The comparison of these particular types is of interest because invasion of tidal marshes by Phragmites has been widely demonstrated to cause a decline in plant diversity (Roman et al. 1984, Chambers 1999, Keller 2000) and because Spartina and other marsh types are proposed as substitutes for Phragmites in the context of wetland restoration and enhancement programs. However, apart from the widely-acknowledged botanical impacts, the ultimate effects of Phragmites dominance are the subject of debate, with some scientists opining that functions [such as]:
“support of higher trophic levels, enhancement of water quality and sediment stabilization… are not diminished when a tidal wetland becomes dominated by Phragmites, provided that tidal flooding is retained” (Chambers et al. 1999)
whereas others have condemned the invasion by Phragmites, asserting or implying that it causes fundamental changes which can only be damaging to estuarine systems (Roman et al. 1984).
While much of the debate has focused on the relative merits of Phragmites vs. Spartina, much less research has been done to directly compare either of these with other wetland types (i.e., palustrine emergents) prevalent in the northeastern United States. Thus, as a reflection of the published literature, this review focuses mainly on the Phragmites vs. Spartina issue. Also, it must be noted that few studies of Phragmites marshes have distinguished functional differences between diked vs. undiked Phragmites. Indeed, some do not even report if the studied marsh is completely diked, partly restricted, or undiked.
... The presence and hydraulic con- ductivity of fringing reefs can strongly influence the location and in- tensity of freshwater discharge, which may deliver nutrients but also pollutants to the oceans (e.g. Gallagher et al., 1996;Bratton 2007;Moore, 2010;Knee and Paytan, 2012;Wang et al., 2014;Moosdorf et al., 2015). Nutrient input can strongly influence the ecology of the reef and adjacent lagoons, e.g. by promoting algal blooms, which subdue coral growth and lead to reef degradation (Naim, 1993;Lapointe, 1997;Dadhich et al., 2017). ...
Geological heterogeneity of the subsurface, caused by both discrete features and spatially distributed hydraulic conductivity fields, affects the flow of coastal groundwater. It influences the shape and the position of the interface between saltwater and freshwater, as well as the location and flux rate of freshwater discharge to the ocean. Fringing reefs lead to a bimodal regime of freshwater discharge, with discharge at the beach face and through deeper, submarine springs. Impermeable vertical flow barriers (dykes) lead to an impoundment of fresh groundwater and a compartmentalization of the aquifer but also to a delayed expulsion of saline water. Spatially distributed conductivity fields affect the shape of the interface and the geometry of the saltwater wedge. Higher effective conductivities lead to a further landward intrusion of the wedge toe. These flow characteristics can be important for groundwater extraction, the delineation of protection zones and the assessment of contaminant transport to coastal ecosystems.
... The infiltration of seawater by waves and tides alters the salinity distribution in the beach aquifer, the directions and rates of groundwater flow, and the rates of submarine groundwater discharge (SGD) (Michael et al., 2005;Vandenbohede and Lebbe, 2005;Robinson et al., 2007;Li et al., 2008). As a result of this infiltration, seawater circulating through beach aquifers can comprise a significant portion of SGD (Gallagher et al., 1996;Robinson et al., 1998;Boehm et al., 2006;Sieyes et al., 2008). Furthermore, mixing between through-flowing freshwater and circulating saltwater in the beach aquifer has been shown to impact biogeochemical processes that affect the transport of land-derived solutes to the sea (Charette and Sholkovitz, 2002;Kroeger and Charette, 2008;Santos et al., 2008;Spiteri et al., 2008;Loveless and Oldham, 2009;Santoro, 2009). ...
... Although SGD-related transport of pesticides into coastal waters is clearly possible, few studies have reported pesticide concentrations in discharging groundwater or SGD-related pesticide fluxes. One study (Gallagher et al., 1996) reported alachlor, atrazine, cyanazine, and metolachlor concentrations of 0.05-0.5 μg l −1 in groundwater discharging into the southern Chesapeake Bay. ...
This chapter provides a review of the current state of knowledge on submarine groundwater discharge (SGD) and the associated fluxes of nutrients, trace metals, microbes, pharmaceuticals, and other terrestrial constituents to coastal waters. We review methods of estimating SGD, present flux estimates from different locations worldwide, and discuss how various hydrogeologic features such as topography, aquifer substrate, climate, waves, and tides affect SGD. We discuss the range of nutrient and metal concentrations observed in groundwater and their relationship to land use, and explore the chemical changes that nutrients and metals undergo during their seaward journey through the aquifer. Climate change is likely to affect both the quantity and the quality of SGD, and we investigate these effects, which are only beginning to be studied. The chapter concludes with a discussion of active areas of SGD research, including expanding the geographic scope of SGD studies; characterizing and reducing the uncertainty associated with SGD measurements; understanding the behavior of nutrients, metals, and other pollutants in the subterranean estuary; and modeling SGD on a global scale.
... Although SGD-related transport of pesticides into coastal waters is clearly possible, few studies have reported pesticide concentrations in discharging groundwater or SGD-related pesticide fluxes. One study (Gallagher et al., 1996) reported alachlor, atrazine, cyanazine, and metolachlor concentrations of 0.05-0.5 μg l −1 in groundwater discharging into the southern Chesapeake Bay. ...
... The impact of surface and groundwater interactivity on herbicide concentration was measured by Verstraeten et al. ( 1998 ), and according to the results, the concentrations of one-half to one-fi fth of herbicides decrease in groundwater. Gallagher et al. ( 2007 ) investigated the transport of land-applied nutrients and pesticides from uncon fi ned aquifers to the tidal surface waters of Virginia's coastal plain; the study revealed that the levels of nitrogen contaminating the surface water was signi fi cant and overall levels of pesticide movement through groundwater, although generally quite low, represented a transport route that is commonly neglected in watershed management. An integrated numerical model was developed to estimate the fl ow and chemical transport between an integrated surface-subsurface hydrologic system (Van der kwaak 1999 ). ...
According to the hydrological cycle, after rainfall infiltration becomes high and once the soil pores become saturated, surface runoff begins. The infiltrated water is added to the groundwater and depressions and canals are utilized to store or drain out excess water. Because surface water and groundwater have the same source, their quality is related, but the physiochemical properties of the soil layers and geological characteristics of the catchments also influence the quality of water in the surface and ground. Many scientific studies have established that surface water is not as pure and fit for drinking as groundwater. Groundwater is free of turbidity, suspended impurities, and organic and inorganic micropollutants. This reactive nature of water is almost neutral. Although groundwater is affected by dissolved metals (like arsenic, iron, etc.), volatile organic compounds and toxic gases, but the intensity of groundwater pollutants varies with location and surrounding geophysical and ecological structures. In most of the places people use groundwater for drinking without adopting any means of purification. If the source is free of organic and inorganic pollutants and if the metal and gaseous concentrations are low, then the ground/surface water can easily be used for drinking or washing purposes without much threat to human health. But if the surface water contaminates the source through leakage or accidental removal of the impervious layers, then it may contaminate the source, and use of the contaminated groundwater could cause affect public health. The present study attempts to predict the quality of groundwater with the help of surface water quality parameters along with some climatic and geophysical parameters. The study utilized neurogenetic models for predicting the quality of groundwater. The results show that predictions of pH and chlorine levels based on the parameters was found to be more accurate and reliable than the prediction of any other quality variables. Thus it can be concluded that if surface water and groundwater are mixed, the pH and turbidity will undergo the most dramatic change among all other quality variables. © 2013 Springer Science+Business Media Dordrecht. All rights reserved.
... Enhanced permafrost thawing may also increase ground water discharge. Submarine groundwater discharge (SGD) has been recognized as an important factor influencing coastal zones and significant source of contaminants to the marine environment (Gallagher et al. 1996;Szymczycha et al. 2013). ...
In this paper we discuss local impact of breaking waves on production of sea salt aerosols and hence on the change of aerosol size distribution and particle optical properties. Our studies were made between 17 and 27 July 2012 at the Coastal Research Station (CRS) in Lubiatowo on the Polish Baltic coast. During the studies aerosol optical depth was measured using Microtops II sun photometers and AERONET and MODIS data were used to support the further analyses. We show that with the local wave breaking phenomenon the aerosol optical depth may increase by a magnitude of even one order and that the ensemble of aerosol particles may shift from the dominating fine mode to coarse mode (sea salt). Such shift may have a strong local impact on the radiative forcing and hence on a local climate.
... Enhanced permafrost thawing may also increase ground water discharge. Submarine groundwater discharge (SGD) has been recognized as an important factor influencing coastal zones and significant source of contaminants to the marine environment (Gallagher et al. 1996;Szymczycha et al. 2013). ...
The Arctic is particularly vulnerable to environmental changes connected to climate change. Most of assessments of the climate change impact to the Arctic environment concentrate on direct effects to the marine and terrestrial ecosystems. There is little understanding of numerous indirect effects of global change and their impact on cycle of different compounds e.g. man-made substances. The global change effects will not always be predictable but may be abrupt. Environmental changes connected to climate change will influence contaminant transport and migration within the Arctic marine ecosystem. Main effects of global change will be visible through changes of large scale contaminant transport pathways e.g. air mass transport, ice transport, marine currents transport and the changes of in situ environmental conditions e.g. changes of pH, temperature, oxygen content. In this review article we describe major environmental factors that may influence global transport of contaminants and migration of contaminants within the arctic ecosystem elements. We also discuss possible further changes in contaminant sources and distribution within the Arctic related to global changes.
... Numbers refer to Table ISince the areal ratio of recharge to discharge is typically about 100, this may explain the two orders of magnitude difference between SGD and groundwater recharge rates. However, the SGD rates observed by direct measurements may also be greater because these estimates may include recirculated seawater in addition to the fresh groundwater component (Gallagher et al., 1996; Li et al., 1999). Comparison of reliably measured SGD values with calculated values from water budgets or modelling (fresh water only) may be able to evaluate the extent of the recirculated seawater component. ...
Submarine groundwater discharge (SGD) in the coastal zone is recognized as a potentially significant material pathway from the land to the ocean. This chapter provides an overview on several methodologies used to estimate SGDs. Measurements of SGD using “manual seepage meters” show that consistent and reliable results can be obtained if one is aware of and careful to prevent known artifacts. New “automated seepage meters” help understand the hydrological and coastal oceanographic processes with longer-term and higher-resolution measurements. Direct measurements of SGD by seepage meters and piezometers in local areas may be scaled up to a regional basis by use of natural geochemical and geophysical tracers. Water balance estimates, although useful for rough estimates, are usually not very precise because the uncertainties in the various terms used to construct the balance are often on the same order as the groundwater discharge being evaluated. Estimates of SGD via analytical and numerical methods depend mainly on the evaluations of the thickness of the aquifers and representative hydraulic conductivities, of which well-constrained values are usually difficult to obtain.
... The problem has been the ability to quantify the magnitude of SGD. Measured discharge is areally heterogeneous and often greater than the discharge calculated from water budgets and ground water flow models (e.g., Gallagher et al., 1996;Robinson and Gallagher, 1999;Moore, 1996;Li et al., 1999;Belanger and Walker, 1990;Pandit and El-Khazen, 1990; Martin et al., 2002;Martin et al., 2004). ...
... Seepage meters were developed originally by engineers studying leakage of canal bank linings (Israelson and Reeve 1944) but were largely ignored by the scientific research community until the 1970s when Lee (1977) demonstrated their effectiveness in evaluating groundwater seepage along shorelines. Since then, different forms of the seepage meter have been used with varying degrees of success in many freshwater and marine environments (e.g., Bokuniewicz 1980Bokuniewicz , 1992Prepas 1989, 1990;Belanger and Montgomery 1992;Reay et al. 1992;Libelo and MacIntyre 1994;Cable et al. 1996;Gallagher et al. 1996;Taniguchi and Fukuo 1996;Cable et al. 1997a,b;Corbett et al. 2000;Chanton et al. 2003;Cable et al. 2004). The simplicity of seepage meter design and deployment makes the device simultaneously attractive for field work and the bane of the researcher. ...
Seepage meters, like most benthic flux chamber techniques, come with inherent concerns about how their presence may alter the environment and flow regimen of the benthic boundary layer and underlying sediments. Flow due to wave and current movement across topographic features induces a downward and upward flow field within the sediments surrounding the feature. We found this Bernoulli-induced flow is a real, but maybe minor, component of measured advection using seepage meters. This study was conducted in a Florida coastal lagoon to test the physical forcing mechanisms that may influence seepage measurements from sediments. Calculated Bernoulli seepage was within the measured background (∼1 to 2 cm day-1) expected from seepage meters when a plastic barrier beneath the device is used to inhibit natural seepage contributions. Nearby seepage measurements made with Lee-type seepage meters placed directly in the sediments ranged from 1 to 12 cm day -1. Thus, when seepage flow is very slow from sediments, Bernoulli-induced seepage may obscure the measurement. However, this study demonstrates that seepage in the Indian River Lagoon must be driven by forces other than Bernoulli-induced (pumped) flow. Suggestions for these forcing mechanisms highlight the uncertainty of the water source(s) in seepage measurements. In these Florida lagoon sediments, bioirrigation and terrestrial groundwater inputs are the most likely drivers, depending on distance from shore, benthic community composition, and continental recharge. Seepage measurements can be an excellent measure of advection in shallow-water marine sediments if Bernoulli-induced seepage is taken into account either experimentally or calculated based on local hydrographic and meteorological data. © 2006, by the American Society of Limnology and Oceanography, Inc.
... It was two decades later that the environmental and ecological impacts of groundwater discharge were highlighted (Johannes 1980;Bokuniewicz, 1980). Field studies later show the role of groundwater discharge as a transport mechanism of nutrients and residual pesticides from agriculture intensive land sources (Simmons et al. 1998;Gallagher et al., 1996) and residential septic tanks (Giblin and Gaines, 1990;Weiskel and Howes, 1992;Harris, 1995;Harman et al., 1996) ROBERTO S. SORIANO ...
A field study of a 350m sand dune aquifer system has been carried out on the northern part of New South Wales, Australia. Bundled piezometers and monitoring wells were installed to measure fluid electrical conductivity and hydraulic heads. A FEFLOW model was developed to incorporate the varying head and salinity conditions on the model boundary.
Model results show the dynamic flow patterns of the groundwater caused by the tide and enhanced by the wave activity near the coast. Vertical head measurements and field observations were used to constrain the model parameters. Model simulations established the interaction of the sand dune aquifer with rainfall recharge, regional influx from nearby marsh and tidal creek. A geologic formation of low permeability significantly modified the groundwater flow patterns. A conceptual model, which features flow and salinity structure in the coastal sand dune was developed.
... The infiltration of seawater by waves and tides alters the salinity distribution in the beach aquifer, the directions and rates of groundwater flow, and the rates of submarine groundwater discharge (SGD) (Michael et al., 2005;Vandenbohede and Lebbe, 2005;Robinson et al., 2007;Li et al., 2008). As a result of this infiltration, seawater circulating through beach aquifers can comprise a significant portion of SGD (Gallagher et al., 1996;Robinson et al., 1998;Boehm et al., 2006;Sieyes et al., 2008). Furthermore, mixing between through-flowing freshwater and circulating saltwater in the beach aquifer has been shown to impact biogeochemical processes that affect the transport of land-derived solutes to the sea (Charette and Sholkovitz, 2002;Kroeger and Charette, 2008;Santos et al., 2008;Spiteri et al., 2008;Loveless and Oldham, 2009;Santoro, 2009). ...
The intertidal zone of coastal aquifers is a dynamic region of mixing between saline surface water and fresh groundwater. Groundwater circulation in this zone is affected by complex forcing mechanisms that operate on a range of timescales and can regulate chemical fluxes to marine environments. We evaluated wave swash-induced infiltration and associated flow dynamics in the unsaturated region of two sandy beach aquifers with differing wave conditions and beach morphologies. High frequency (5 Hz) moisture and pressure sensors were used to measure fluctuations in water content, water table elevation, and hydraulic gradients in the swash zone at mean lower low water, mean sea level , and mean higher high water. Water content in the unsaturated region of the swash zone responded to wave overtopping and swash infiltration, with a rapid rise in water content followed by a slower decline. Swash-induced unsaturated infiltration rates, calculated from water content response, were lowest near low tide and increased up the beachface with inflow highest near high tide at both sites, consistent with an increase in water table depth up the beach. Unsaturated infiltration at the wave dominated beach was 1.6 m3/m per tidal cycle at the wave-dominated beach and 0.4 m3/m per tidal cycle at the tide-dominated beach. Saturated pore pressure measurements show that a water table mound formed as a consequence of swash infiltration that migrated up the beach during rising tide, leading to divergent seaward/landward groundwater flow. The results demonstrate the significant and spatially variable effects of wave swash on moisture dynamics in the unsaturated zone of beach aquifers, and show that these effects depend on wave conditions and beach characteristics. Results have implications for understanding transport and reaction of solutes in this biogeochemically active zone.
... Maximum part of the recharge advances towards the sea as a freshwater front that is subsurface groundwater discharge due to low aquifer storage and high transmissivity (Gallagher et al., 1996). Surface water is absent on the island and groundwater is the only source of freshwater. ...
The study evaluates movement of the saltwater interface and ionic composition in the atoll aquifer system in response to natural recharge in Western Indian Ocean (WIO). Sea level rise owing to climate change is expected to have substantial impacts on the world's population living on or near the coast over the next century ( and ). Change in sea level is predominantly linked to inundation and saltwater intrusion in coastal aquifers (Döll, 2009). However the change in precipitation pattern as a possible clause for seawater intrusion is poorly established and is due for substantial studies. The Intergovernmental Panel on Climate Change (IPCC) report (2007) that projects the global sea level rise of 18 to 59 cm from 1990 to the 2090s, along with an unspecified amount that could come from changes in the large ice sheets covering Greenland and Antarctica, depicts a relatively much lower regional sea level rise in the WIO. In addition, the report signifies a reduction in annual precipitation rate in this region in agreement with past historical data. This characterizes the WIO region as a potential critical zone under the influence of climate change (i.e. less sea level rise, high reduction in rainfall pattern) unlike most of its neighboring regions. The WIO region is a home to hundreds of coral islands and is inhabited largely. Despite its purported importance, tracing of the aquifer geometry under the influence of climate change has not been reported much. Application of hydro-chemical analysis to delineate the climate change impacts has even been rare. Androth island of Lakshadweep archipelago has been chosen as the study area. The study establishes that hydro-chemical evidences have a high degree of correlation between groundwater aquifer geometry and rate of precipitation. It depicts that decreasing trend in precipitation in the WIO region would result in seawater intrusion and significant shrinkage of aquifer geometry. The study determines the control of precipitation pattern over the aquifer geometry by systematic analyses of hydro-chemical data. The conceptual analyses include surface plots, correlation analysis, ionic exchange and ionic ratio techniques, and multivariate data analyses. The study comprises two precipitation conditions derived from observed field data: (1) rainfall 30% below yearly average and (2) rainfall 30% above yearly average. The result shows shrinkage of around 54.91% from 82.64% (scenario 2) to 27.63% (scenario 2) in good quality water reserves. The study highlights the importance of aquifer boundary conditions in the context of climate change. The analyses clearly indicate that the decreasing trend in rainfall would severely impact the existence of fragile island aquifer systems of the Lakshadweep archipelago.
... Additional estimates of SGD and seepage flux on a global scale, though quite limited, were presented by Burnett et al. (2001) and Taniguchi et al. (2002). Despite the wide range of variability in SGD calculations (depending on techniques, sediment type, location, etc.), which can vary from 0.01% to 80% of the total river flow, the importance of SGD in the global water cycle is unquestioned because of the high ratio of SGD to surface runoff (e.g., Bokuniewicz, 1980;Gallagher et al., 1996;Schlüter et al., 2004). For the Polish coastline alone (500 km), the total value of groundwater discharge to the Baltic Sea was calculated to be approximately 1.45 km 3 yr −1 (Kryza and Kryza, 2006), while estimations of 4.4 km 3 yr −1 were reported by Peltonen (2002) for the whole Baltic Sea. ...
The discharge of groundwater into the sea affects surrounding environments by changing the salinity, temperature
and nutrient regimes. This work reports the spatial effects of a submarine groundwater discharge
(SGD) on the abundance and structure of the meiofaunal community in the shallow area of Puck Bay (Baltic
Sea). Several field expeditions in the years 2009 and 2010 found that low-saline groundwater escapes into
the bay from permeable, sandy, near-shore sediments. The SGD literature has grown rapidly during the
current decade; however, the effects of this type of disturbance on the shallow sandy bottom fauna have
thus far been little studied. We provide evidence that the discharge of groundwater has a clear effect on
meiofaunal assemblages in the research area. This effect was reflected in a significant decline of certain
meiofaunal taxa, mainly nematodes and harpacticoids, as well as in altered patterns of temporal distribution
and small-scale (vertical) zonation of meiofaunal assemblages. Overlooking submarine groundwater discharge
processes may lead to serious misinterpretations of ecological data. It is clear that groundwater
discharge phenomena should be considered in future scientific studies.
... It has been shown, for example (Slomp and van Cappellen, 2004), that high nutrient concentrations in fresh groundwater are likely derived from watershed sources, while remineralization processes cause high nutrient concentrations in saline groundwaters. As a consequence, some nitrogen species and P may be significantly elevated in coastal groundwater relative to river water, and the stoichiometry of N/P in submarine groundwater most often diverges drastically from the Redfield ratio (16:1) (Capone and Bautista, 1985;Lapointe et al., 1990;Valiela et al., 1990;Weiskel and Howes, 1992;Gallagher et al., 1996;LaRoche et al., 1997;Herrera-Silveira, 1998;Corbett et al., 1999Corbett et al., , 2000Miller and Ullman, 2004). ...
A suite of naturally occurring radionuclides in the U/Th decay series (222Rn, 223,224,226,228Ra) were studied during wet and dry conditions in Tampa Bay, Florida, to evaluate their utility as groundwater discharge tracers, both within the bay proper and within the Alafia River/estuary — a prominent free-flowing river that empties into the bay. In Tampa Bay, almost 30% of the combined riverine inputs still remain ungauged. Consequently, groundwater/surface water (hyporheic) exchange in the discharging coastal rivers, as well as submarine groundwater discharge (SGD) within the bay, are still unresolved components of this system's water and material budgets.
... Recently, efforts have begun to couple land use activities, groundwater discharge, and surface water quality. Consequently, a growing body of research has implicated submarine groundwater discharge (SGWD) as a significant source of fresh water, nitrogen and pesticides to coastal waters and more specifically to the Chesapeake Bay system (Simmons, 1989;Libelo et al., 1991;Simmons et al., 1991;Reay et al., 1992;Gallagher et al.,1996). ...
Recent research has indicated that submarine groundwater discharge (SGWD) is a significant component of the hydrologic cycle in coastal plain regions, and that discharged groundwater can be contaminated with nutrients and pesticides. Although discharge has been measured directly on a local level, a convenient method for determining the spatial distribution of SGWD on a regional scale using readily available data is needed. A geographic information systems (GIS) was applied to the problem of regional-scale determination of SGWD and nutrient loads for the Eastern Shore of Virginia. Computerized data layers included land use, hydraulic gradient and soil permeability. The GIS model was used to predict spatial distribution of SGWD as well as the contaminant flux from nearshore agriculture and on-site waste treatment technologies. Comparison with field data indicated excellent agreement for SGWD, but only moderate agreement for contaminant fluxes. The GIS model predicts that 90% of the impact from nearshore land use occurs in the southwestern quadrant of the Eastern Shore. The model identified areas susceptible to contamination through discharge to a resolution of about 33 meters, showing that GIS can function as a local as well as regional management tool
... The diffuse discharge of ground water to estuaries and the coastal oceans may represent a flow path for solutes to the overlying water column (Johannes 1980;Simmons 1992;Bokuniewicz 1980;Capone and Bautista 1985;Gallagher et al. 1996;Robinson et al. 1998;Moore 1999;Robinson and Gallagher 1999). Although ground-water discharge can originate from a variety of sources, in part it includes water discharging from onshore fresh-water aquifers that flows offshore under pressure from hydrostatic head (Cooper 1959;Glover 1959;Church 1996;Li et al. 1999). ...
The construction and operation of a multi-level piezometer (multisampler) designed to collect pore water from permeable sediments up to 230 cm below the sediment-water interface is described. Multisamplers are constructed from 11/2 inch schedule 80 PVC pipe. One-quarter-inch flexible PVC tubing leads from eight ports at variable depths to a 11/2 inch tee fitting at the top of the PVC pipe. Multisamplers are driven into the sediment using standard fence-post drivers. Water is pumped from the PVC tubing with a peristaltic pump. Field tests in Banana River Lagoon, Florida, demonstrate the utility of multisamplers. These tests include collection of multiple samples from the permeable sediments and reveal mixing between shallow pore water and overlying lagoon water.
... To model the groundwater discharge process at the field scale, the tide and associated boundary conditions along the beach must be included in the model. Field studies also show groundwater discharge to be a source of nutrients and pesticides from agricultural lands (Simmons et al., 1992;Gallagher et al., 1996), and residential septic tanks (Gablin and Gaines, 1990;Weiskel and Howes, 1992). ...
Since the 1950s, numerous publications of analytical studies of tidal wave propagations in coastal aquifers have been appeared. This paper reviews the following aspects: importance of tidal effects in studies of coastal areas, analytical studies of tide-induced groundwater flow and related case studies. Finally several important open problems in analytical studies of tide-induced groundwater flow are proposed.
... Herbicide-resistant corn and the companion herbicide may provide an additional tool for managing weeds in no-tillage systems. Using herbicide-resistant corn may also reduce the need for residual herbicides such as atrazine, alachlor, and metolachlor, which are confirmed ground and surface water contaminants (Blanchard and Donald 1997;Donald et al. 1998;Gallagher et al. 1996). Glyphosate, glufosinate, imazethapyr, and imazapyr are broad-spectrum herbicides that may be used for weed control in their respective type of herbicide-resistant corn. ...
Field studies were conducted to evaluate corn vigor reduction, weed control, corn yield, and economic returns in a no-till system with various herbicide strategies using full and reduced rates of acetochlor and atrazine with glyphosate, glufosinate, or imazethapyr + imazapyr in their respective type of herbicide-resistant, no-tillage corn. Crop vigor reduction due to herbicide injury was 10% or less with all treatments. A burndown plus a full label rate of a residual herbicide applied early preplant (EPP) generally provided less than 80% control of giant foxtail, common waterhemp, and common cocklebur but usually greater than 85% control of common ragweed and common lambsquarters. Two-pass strategies generally provided greater than 85% control of all species evaluated. Early postemergence, mid-postemergence (MPOST), and late postemergence strategies generally provided inconsistent and poor overall weed control. EPP-MPOST strategies generally provided lower weed control than strategies using acetochlor or atrazine EPP followed by a postemergence application. Corn yield and net economic returns followed a similar trend as weed control, with strategies that provided greater than 80% weed control showing minimal crop vigor reduction and high grain yields. Two-pass strategies with residual herbicides generally provided the highest yields, economic returns, and low coefficients of variation (CV) of net income. Although EPP strategies provided similar economic returns as some of the two-pass strategies, they had higher CVs, implying greater risk to economic return.
Meteoric groundwater discharge (MGD) to coastal regions transports terrestrial freshwater and nutrients that may alter coastal ecosystems by supporting harmful algal blooms. Estimation of MGD-driven nutrients is crucial to assess potential effects on coastal zones. These estimates require a reliable assessment of MGD rates and pore water nutrient concentrations below subterranean estuaries. To estimate nutrient delivery into a subterranean estuary in the Indian River Lagoon, FL., pore water and surface water samples were collected from nested piezometers along a selected transect on five sampling episodes. Groundwater hydraulic head and salinity were measured in thirteen onshore and offshore piezometers. Numerical models were developed, calibrated, and validated using SEAWAT to simulate MGD flow rates. Lagoon surface water salinity exhibits no spatial but mild temporal variation between 21 and 31. Pore water salinity shows tremendous variation in time and space throughout the transect except in the middle region of the lagoon which exhibits uniform but elevated salinities up to 40. Pore water salinity as low as that of freshwater happens to occur in the shoreline regions during most of the sampling episodes. Both pore water and surface water show remarkably higher total nitrogen TN than total phosphorus TP concentrations and most TN is exported as NH4, reflecting the effect of mangroves on the geochemical reactions that reduce NO3 into NH4. Nutrient contributions of pore water and lagoon water exceed the Redfield TN/TP molar ratio in all sampling trips by up to a factor of 48 and 4, respectively. Estimated TP and TN fluxes receives by the lagoon via MGD are 41-106 and 113-1478 mg/d/m of shoreline. The molar TN/TP ratio of nutrient fluxes exceeds the Redfield ratio by a factor of up to 3.5 which indicates the potential of MGD-driven nutrients to alter the lagoon water quality and support harmful algal blooms.
Coastal beaches are the most important part of the marine environment and are highly influenced by the interactions taking place between groundwater and surface water of any form. Generally, the purity index of the groundwater is based on the concentration of Total Dissolved Solids (TDS) in it. Analytical solutions are the best tools for groundwater flow and transport modeling. However, contaminant transport along the sloping coastal beaches with complex boundaries cannot be addressed with available analytical solutions. In the present study, new analytical models are developed for groundwater flow and contaminant transport for sloping coastal beaches with continuity and tidal boundary conditions. To assess the performance of the new analytical solution and to validate the range of aquifer parameters, numerical simulation is performed using Du-Fort Frankel (DFF) Scheme. Numerical experimentation is carried out using the Tchebycheff and L2 norms. It is observed that the new analytical solution for the contaminant transport gives acceptable results over the wide range of the aquifer parameters. To show the effectiveness of the developed models, two case studies from Indian coastal aquifers namely, Kalpakkam, Tamil Nadu, and Bhavnagar, Gujarat are considered. The profiles of the contaminant concentration are obtained to study the TDS behavior along these complex coastal beaches in the spatiotemporal directions. The results are compared with numerical model results and found to be satisfactory. The combined effect of the initial rainfall and rainfall decay constants showed a significant impact on the concentration of TDS. TDS concentrations are observed to be varying highly with the variation in the tidal constituents and bed slope.
This book chapter includes the study of submarine groundwater discharge (SGD) across various coastlines and related nutrient fluxes to the coastal oceans. SGD represents an essential pathway of materials like carbon, nitrate, phosphate, silicate, and trace metals between land and sea. Global DOC and DIC Fluxes through SGD studied across different mangrove climatic zones indicate that the area of tropics accounted for 71% and 81% of DIC and DOC fluxes, respectively. Subtropics contributes 29% and 19% respectively, while the contribution of temperate region is even less than 1% for both the parameters. An increase of about 38% in SGD nitrogen input between 1950 and 2000 has been observed in global coastal water and is estimated to increase by 22% between 2000 and 2050. The rise in nitrogen is not followed by an equivalent increase in phosphate and silicate, suggesting that nitrogen is the primary nutrient affected by SGD. The increase in nitrogen is mainly due to the anthropogenic contamination of the certain aquifer, which in turn modify the Redfield ratio where the N/P ratio exceeds the river system revealing that human activities can change N-limited coastal primary production to P-limited one. The Indian coastline is mainly composed of red, yellow, and alluvial soils, which are poor in nutrients. Hence Indian farmers use excessive fertilizers to obtain a better yield. Which plays a significant role in controlling nutrient dynamics in groundwater. SGD-derived trace metals are also equal to or higher than the river fluxes and contribute approximately 10% of total trace elements to the oceans.
The influx of fresh groundwater and re-circulated sea water into coastal ecosystem occurs through the submarine groundwater discharge (SGD). Measurement of salinity, radium tracers (²²⁴Ra, and ²²⁶Ra isotopes) and nutrients in estuarine water, coastal surface water and groundwater during December 2019 estimated the SGD and associated nutrient fluxes near the Karameniyar estuary (Gulf of Mannar) and surroundings of the Manapad region at southern part of Tamil Nadu state in India. The presence of excessive radium tracers revealed that the SGD was contributing to Ra desorption from the sediments and enrichment in the coastal waters. We estimated SGD of approximately 0.03–0.59 m³ m⁻² d⁻¹ for the Manapad region and relatively more homogeneous but comparatively less values in the Karameniyar estuary (0.03–0.34 m³ m⁻² d⁻¹). Higher average values of dissolved inorganic nitrogen (DIN; 43.62 μmol L⁻¹) and soluble reactive phosphate (SRP; 1.848 μmol L⁻¹) suggested greater influence of SGD on the overall coastal water nutrient budget. This study also indicated simultaneous occurrence of fresh and saline SGD in this region.
This review of studies that quantified fluxes with seepage meters in marine settings in the last decades shows the historical evolution of this device and the knowledge acquired during this period. Coastal environments are differentiated from freshwater settings due to water salinity and the effects of tides and waves that have important implications for the measurement approach and generated results. The framework in which seepage meters have been used in marine settings has evolved in parallel to the understanding of submarine groundwater discharge. This review of seepage meter research shows: an uneven distribution of studies in the world with some densely-studied regions and an absolute lack of data in other regions; a dominance of studies where only seepage meters were used compared to studies that combined seepage meter measurements with values determined with radioactive tracers or hydraulic calculations; and a variety of publication outlets with different focuses (hydrology, oceanography or multidisciplinary). The historical overview of the research conducted with seepage meters shows the wide range of seepage meter applications – from simply measuring fluxes at local scales to larger studies that extrapolate local results to estimate fluxes of water, nutrients, and other solutes at regional and global scales. A variety of automated seepage meters have been developed and used to better characterize short-term groundwater-seawater exchange, including the effects of waves and tides. We present recommendations and considerations to guide seepage meter deployment in marine settings, as seepage meters are still the only method that quantifies directly the interaction between groundwater and surface water.
India has a very long coastline compared to other countries in the world and is considered as the backbone of our national economy. One-fourth of the country’s population lies in this region; the most fertile agricultural land is situated in this area, and it occupies the most potential aquifer systems of the country which faces multifaceted complex problems like seawater intrusion, land use/land cover changes, climate change, and human-induced anthropogenic problems like discharge of sewage effluents, agricultural, salt pan, and aquacultural activities. It is also highly vulnerable to extreme events, such as storms, which impose substantial costs on coastal communities. Numerous rivers enter to the coast that tends to form estuaries and mixes with sea which includes a huge complex ecosystem. The population density increases the risks and vulnerability of the coastal states. The anticipated sea level rise by climate changes affects the coastal aquifers which push the freshwater–seawater interface and makes the shallow aquifers saline. Rivers are the major contributory of the pollution in the coast whereas all rivers are polluted due to industrial effluents and sewage disposal. The various studies on different aspects of hydrogeochemical approach explain the degradation of coastal regions and also various mitigations to overcome these problems.
The book integrates the fundamental factors that determine current and future impacts of biofuels production on water supply and demand in the context of climatic changes. The effects of biofuels production on ground water quality with increasing water scarcity are examined, and the utilization of water sources in the commercial scale production of biofuels are sketched, covering the complete route from growing of crops to biorefinery. Biofuel's chemical composition, characteristics and uses as fuel in terms of water consumption are also investigated. Overall, the diversity of biomass, various technological approaches and microbial contribution are reviewed.
Learning objectives on this topic are presented by means of a series of tables and figures in order to guide both professionals and students. The present manuscript deals with biofuel and bioenergy courses and is therefore invaluable to students. The book provides thorough coverage of all industrial aspects of biofuels production, including impacts of climate change and water availability. It will play vital role for industry employees involved in product development, production management, quality management and helpful source to those studying for professional qualification. Academics involved in teaching elements of the subject and persons involved in an environment regulatory capacity would be able to take advantage from this book.
Biofuel in particular, together with the rising demands for food, have the highest prospects for an increase in agricultural water withdrawals. The water-biofuel relationship is being recognized as backbone of the factors fundamental for the future sustainable supply of water and biofuel. A better understanding of the subject is essential to adopt superior technologies that may improve use of water for biofuel production in efficient way. This chapter presents prospective and future trends of the water-biofuel relationship and impacts of additional water usage in future increased biofuel production. The importance of technological innovation to save water and future impacts on water quantity and especially on water quality will be assessed in terms of safe keeping the environment. The obligation of reusing wastewater and application of undiluted wastewater to grow feedstock for biofuel to save freshwater resources will be analyzed.
Biofuel production process use fresh water collected mainly from surface water flows or from underground natural reservoirs for different activities and it became contaminated with organic and inorganic pollutants. Waste water quality returned to soil and to surface water flows is very poor. To produce one liter of ethanol, 10–17 L of water are consumed. Biofuel production plants are water intensive and there is an upward trend in water consumption. The chapter will describe agricultural and industrial activities involving current water consumption during biofuel production. Major steps of lifecycles for biofuel production pathways: bioethanol from sugarcane molasses and cellulosic feedstock, Biogas from distillery spent wash and Biodiesel from various sources will be evaluated regarding water consumption. The amount of irrigation water used in growth of biofuel feedstock and water consumption for biofuel production through various processing technologies will be analyzed. The vital importance of water management during the feedstock production and conversion stage of the biofuel’s lifecycle will also be discussed.
Worldwide intensive demand of biofuel as a substitute to fossil fuels has sparked a debate about their advantages especially concerns about human health. Potential health impacts of biofuel are linked to biochemical and chemicals applied in biofuel production processes. Such caustic chemicals are highly hazardous for human health. Other impacts of biofuel come through water pollution; air pollution and use of agrochemicals and pesticides to raise the feedstock. Incomplete burning of sugarcane leaves or residues may results in toxic compounds formation and fine particulates are emitted into atmosphere. The chapter summarizes the basic health effects of biofuel from agriculture cultivation of feedstock to production processes.
Disinfection with aggressive chemicals like chlorine or ozone is normally the last step in purifying drinking water. Many water systems intentionally leave residual disinfection agents in the water after exiting the plant so it travels throughout the distribution system. The most common disinfection method is some form of chlorine such as chlorine gas, sodium hypochlorite, chloramines or chlorine dioxide. The water must sit in the clear well to ensure that the water is in contact with the disinfectant for a minimum amount of time because it takes time to inactivate the harmful microbes. The disinfection of water is of utmost importance of the treatment process. In a water treatment plant at Raipur, there are a large number of zonal overhead reservoirs. The water from the river Hooghly is collected by pumps and then delivered to the inlet well by adding the chemical solutions such as chlorine, alum and poly-electrolyte. The dose of gaseous chlorine is regulated by the clarifloculator and chlorine analyzer before pumping out clear water in the water treatment plant. The dedicated feeder line (19 km away from West Bengal State Electricity Board Falta Substation) travels along a distance of 50 km and is again stored into two underground reservoirs at Boosting Stations I and II. Chlorine is further administered for effective disinfection of water at the consumer point. The main objective of this study is to check the time rate of propagation of chlorine concentration (disinfectant) that has been traveled in a pipe network distribution system with the help of EPANET. In this study, the time rate of propagation of chlorine concentration has been modeled in the age of water throughout a distribution system and also the rate of reaction of decay of chlorine concentration has been calculated using zero order kinetics with a first order decay. The results conclude the propagation of chlorine concentration is decreasing with time not only for short term but also for long term decay. Thus the very less amount of chlorine is required to administer here for further effective disinfection of water to the consumer point by another twenty seven (27) zonal overhead reservoirs.
The Dead Sea hypersaline water system is unique in terms of its unusual
geochemical composition, rapid lake level changes and water composition
of the brines discharging along its shoreline. The Dead Sea can be used
as a natural lab for studying groundwater-seawater interaction and
saline water hydrological circulation along the aquifer-sea boundary. It
provides an opportunity to follow the geochemical processes along a flow
path from the lake into the aquifer and back into the lake. The lake
level has been dropping since the 1960's due to human interference in
its water budget, reaching a rate of 1 m/yr in recent years. Saline
water circulation in coastal aquifers may be a major process that
governs trace element mass balances in coastal areas. This study uses
radium isotopes in order to quantify the lake water circulation in the
Dead Sea aquifer. There are four naturally-occurring radium isotopes,
with half-lives ranging from 3.7 days to 1600 years which are chain
products of uranium and thorium isotopes. Radium isotopes are usually
enriched in saline groundwater and therefore are good candidates for
estimating seawater or hypersaline lake water circulation in the
aquifer. Compared to most natural water bodies, the Dead Sea is
extremely enriched in radium and barium, where both 226Ra and 228Ra
activities and Ba concentration (145, 1-2 dpm/L and 5 mg/L,
respectively) are 2-3 orders of magnitude higher than in ocean water,
whereas the salinity of the Dead Sea is only 10 times higher. Circulated
Dead Sea water in the aquifer contains decreased concentrations of 226Ra
(60 dpm/L), Ba (1.5 mg/L), Sr (300 relative to 340 mg/L in the Dead Sea)
and Sulfate (250 relative to 392 mg/L). We suggest that the low 226Ra
and Ba concentrations are due to precipitation of barite and celestine
from the supersaturated Dead Sea water on entering the aquifer. 228Ra
and the shorter-lived 224Ra and 223Ra, which have much lower activities
in the Dead Sea (up to 1.8, 3 and 0.8 dpm/L, respectively), are enriched
in the circulated Dead Sea water (up to 25, 100 and 30 dpm/L,
respectively) due to recoil and desorption. This implies that the
circulation of Dead Sea water in the aquifer removes 226Ra and
contributes 228Ra, 223Ra and 224Ra to the lake. Therefore, a major
source with relatively high 228Ra/226Ra ratios is added to the Dead Sea
mass balance. Following a flow path of saline water from the Dead Sea
inland, barium and 226Ra decrease gradually and 228Ra increases
gradually. This provides a method for calculating the DS mass balance,
groundwater age or velocity and the rate of barite and celestine
precipitation. 228Ra ages are around 2 and 13 yrs at 10 and 80 m from
the shore inland, respectively. With this velocity (5-6 m/yr), the first
order precipitation rate constant is 0.23 1/yr. Based on 226Ra and 228Ra
mass balances in the Dead Sea, the calculated amount of Dead Sea water
circulation is 200-300 million m3/yr, which is of the same order of
magnitude as all other known Dead Sea water sources at present (160-340
million m3/yr) and therefore is a significant component in the Dead Sea
mass balance.
The challenge of improving water quality is a growing global concern, typified by the European Commission Water Framework Directive and the United States Clean Water Act. The main drivers of poor water quality are economics, poor water management, agricultural practices and urban development. This paper reviews the extensive role of non-point sources, in particular the outdated agricultural practices, with respect to nutrient and contaminant contributions. Water quality monitoring (WQM) is currently undertaken through a number of data acquisition methods from grab sampling to satellite based remote sensing of water bodies. Based on the surveyed sampling methods and their numerous limitations, it is proposed that wireless sensor networks (WSNs), despite their own limitations, are still very attractive and effective for real-time spatio-temporal data collection for WQM applications. WSNs have been employed for WQM of surface and ground water and catchments, and have been fundamental in advancing the knowledge of contaminants trends through their high resolution observations. However, these applications have yet to explore the implementation and impact of this technology for management and control decisions, to minimise and prevent individual stakeholder’s contributions, in an autonomous and dynamic manner. Here, the potential of WSN-controlled agricultural activities and different environmental compartments for integrated water quality management is presented and limitations of WSN in agriculture and WQM are identified. Finally, a case for collaborative networks at catchment scale is proposed for enabling cooperation among individually networked activities/stakeholders (farming activities, water bodies) for integrated water quality monitoring, control and management.
Consumption of pesticides associated foods increased in recent decades in Bangladesh. Most of the pesticides come from paddy, as rice is the main food items here and about 70 % pesticides are used only on paddy fields. Water samples of paddy fields and Kaliganga River of Manikganj district were analyzed to provide base line data on cypermethrin, chlorpyrifos and diazinon residue by using high performance liquid chromatography. Levels of Cypermethrin, chlorpyrifos and diazinon detected in the paddy field water samples were (0.605 ± 0.011 μg/L), (0.06 ± 0.001 μg/L) and (0.039 ± 0.002 μg/L), respectively. 0.11 ± 0.003 μg/L of cypermethrin and 0.012 ± 0.0006 μg/L of chlorpyrifos were also identified in the water samples of Kaligonga River. Diazinon residue was not detected in the river water samples. The detected concentrations of pesticide residues in the river water were below the accepted maximum residue limit (MRL) value of drinking water (0.1 μg/l) adopted by the FAO/WHO Codex Alimentarius Commission. Cypermethrin and chlorpyrifos were chosen for decontamination through rice bran, as it was found in river water. Two gm rice bran could easily decontaminated 95.6 % and 96.4 % of cypermethrin and chlorpyrifos. The result of this study showed that pesticide residue was detected in water samples were below the MRLs value, which can easily be decontaminated through absorption of rice bran.
We reviewed data concerning phytoplankton production, chlorophyll a, and associated physical and chemical variables from 63 different estuarine systems. Data were analyzed statistically to test hypotheses regarding algal productivity and factors regulating temporal patterns. Prior to statistical analysis, estuarine systems were classified into four groups based on criteria of physical circulation and geomorphology. Analysis of grouped data indicated that algal production and biomass were consistently high in warm periods of the year in a broad spectrum of estuaries and that ratios of available nitrogen to phosphorus were low during periods of high production, except in highly eutrophic systems. In general, phytoplankton production and biomass exhibited weak correlations with a variety of physical and chemical state variables, perhaps indicating the significance of rate processes as opposed to standing stocks in regulating these important features of estuarine systems. A six-year time series of measurements of algal production and chlorophyll a at stations in middle Chesapeake Bay exhibited considerable year-to-year variability, with a three-fold range in peak values. Summertime maxima were strongly related to annual loadings of both nitrogen (N) and phosphorus (P) but annual production appeared to be sustained primarily on recycled nitrogen and phosphorus. To generalize from these findings, N and P loading rates were estimated for 14 different estuarine systems, and a significant positive relationship was obtained between phytoplankton production and nitrogen (but not phosphorus) inputs.
This paper presents evidence of a seasonal shift from P to N as the nutrient limiting the accumulation of algal biomass in Chesapeake Bay. Following the winter/spring maximum in freshwater runoff, (1) the ratio of dissolved inorganic nitrogen to soluble reactive phosphorus (DIN/PO4) was greater than the N/P of algal biomass; (2) alkaline phosphatase activity was high; (3) phosphate turnover times were short; (4) ammonium turnover times were long; and (5) growth rates of phytoplankton were stimulated by additions of phosphate but not by additions of ammonium or silicate. During the period of low runoff in summer, all indicators reversed, and N limited algal growth rates. Silicate concentrations also showed evidence of biological depletion in spring, which may have limited diatom abundance. Due to the concordance of all indicators at large and small scales, we argue that phytoplankton growth rates exert primary control over biomass accumulation. We conclude that P and Si limit the accumulation of algal biomass along the major axis of Chesapeake Bay in spring, whereas N limits algal accumulation in summer, similar to the conclusions of D'Elia et al. (1986; Can. J. Fish. Aquat. Sci. 43: 397-406) for the Patuxent subestuary. Controlling eutrophication of the Bay and its subestuaries will require basin-specific management practices for both N and P reductions in influent waters. Such management efforts will provide ecosystem tests of nutrient limitation on a scale similar to those successfully conducted in lakes.
This report is the first in a series of non-technical publications on the USGS National Water-Quality Assessment (NAWQA) Program. The purpose of these publications is to describe key findings from the individual investigations and to relate those findings to water-quality issues that are of regional and national concern. By disseminating this information, the USGS seeks to increase awareness of water-quality concerns when considering the Nation's environmental issues. Extensive agricultural land use on the Delmarva Peninsula has introduced nitrate and pesticides to ground water. This study has helped identify where the contamination is most likely to occur. The pattern of contamination depends on a number of factors, including crop type, geology, soils, land use, and ground-water flow. An understanding of these factors is critical to those individuals who make decisions about crop-management practices, land-use planning, and water management. Facilitating data exchange among water-resource managers in agencies at the federal, state, and local levels is a major mission of the NAWQA Program. -from Authors
The movement of nitrates into the groundwater of the southern and eastern states of the USA, is of particular importance and concern. To understand and explain the reasons for the movements, research has been undertaken on the effects of the geology, methods of aquifer recharge and the regional hydrology. Further influencing factors identified, include agricultural management, soils and landforms. As a result of the research, simulation models can be produced and management recommendations made. -R.C.Medler
Oxygen and nutrient fluxes across the sediment-water interface were measured over an annual cycle in the turbid portion of the Patuxent Estuary. Benthic respiration rates ranged from 0.5 to 4.1 g O2 m–2 d–1 and were positively correlated with temperature and primary production. Net fluxes of ammonium (NH4+) and dissolved inorganic phosphorus (DIP) ranged from –105 to 1584 μg-at N m–2 h–1 and 1 to 295 μg-at P m–2 h–1 respectively. These rates, which were positively correlated with temperature, are among the highest yet reported in the literature. Fluxes of nitrate plus nitrite were small during summer when water column concentrations were low, but high and directed into the sediments during winter when water column concentrations were high. In general it appears that nutrient fluxes across the sediment-water interface represent an important source to the water column in summer when photosynthetic demand is high and water column stocks are low and, conversely, serve as a sink in winter when demand is low and water column stocks high, thereby serving a “buffering” function between supply and demand. A simple budget of sediment-water exchanges and storages of nitrogen indicated that, of the total particulate nitrogen deposited annually onto the sediments, about 34% was returned to the water column as NH4+, 41% was stored as particulate nitrogen in the sediments and, by difference, we estimated that the remaining 24% was denitrified. We also observed considerable uptake of nitrate by the sediments during winter months (1.1 g-at m–2 y–1), suggesting an additional source of annual denitrification, since this nitrate uptake was not accompanied by ammonium release back to the water column. The ecological implications of these large nutrient fluxes are discussed in terms of sources and sinks of nutrients, as well as couplings with carbon productivity.
To meet increasing demands for data on pesticide transport to groundwater, residues of selected pesticides, EDB, atrazine, butylate, aldicarb, and fenamiphos were monitored in shallow goundwater beneath a Bonifay sand in the southeast Coastal Plain near Tiftaon, GA. Pesticides in tile outflow from the treated area were also monitored along with pesticide residue in soil. Low concentrations of atrazine and butylate were present in wells at depths of 1.0 m, 1.5 m, and 2.4 m beginning with the second year (1984) of the study. Fenamiphos was detected in only one well throughout the study. However, EDB and aldicarb moved readily to groundwater and in the tile outflow. Results were generally as would be predicted considering chemical properties of the pesticides. However, in these studies we found that aldicarb was very rapidly converted to the sulfone derivative which was the dominant species in well water and tile outflow. Some researchers have found aldicarb sulfoxide to be the dominant metabolite in soils. Others have also found fenamiphos to be transformed to a persistent sulfoxide form which is mobile in soil. Since we found little fenamiphos or its metabolites in groundwater and tile outflow, we speculate that degradation occurs rapidly in our soils. Fenamiphos translocation observed in soil suggested the presence of the more mobile metabolites in soil. Masses of pesticide transported from the treated area were computed using concentrations and estimated water budgets. Comparing leaching losses from the root zone estimated using GLEAMS simulation with groundwater transport shows that <10% of the leaching losses were actually transported from the treated area in shallow groundwater during the observation period. The difference evidently remained in storage or was adsorbed or degraded in transport.
Nitrogen balances were measured for a moderately well-drained and a poorly drained soil in the North Carolina Coastal Plain to evaluate the effect of drainage on the fate of unutilized fertilizer N. Approximately one-half of the fertilizer N applied to each soil was not utilized by the crop.
Most of the nitrogen lost by surface runoff from both soils was organic nitrogen associated with the sediment. However, there was a measurable increase in loss of nitrogen from fertilized plots as compared to unfertilized plots. The poorly drained soil (27% organic matter) had approximately 50% less surface runoff than did the moderately well-drained soil (2% organic matter). However, the concentration of N in runoff from the poorly drained soil was almost twice as great resulting in nearly identical N losses from the two soils. Much of the total surface loss of N from corn (Zea mays L.) occurred during the first few months after planting.
During the winters after the 1972 and 1973 harvests, an average of 46 kg NO3-N/ha moved from the moderately well-drained soil by subsurface drainage. A portion of this loss entered surface waters directly via tile outlets. The remainder was thought to enter a shallow aquifer and is believed to ultimately move with the water to nearby surface streams. It is unlikely that denitrification removed significant amounts of N from the moderately well-drained soil.
An average of 16 kg NO3-N/ha was removed from the poorly drained soil by subsurface drainage during the two winters. The smaller loss from the poorly drained soil was thought to result from denitrification of residual NO3 in the shallow ground water.
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The dispersion of salts produced by reciprocative motion of the salt-water front in a coastal aquifer induces a flow of salt water from the floor of the sea into the zone of diffusion and back to the sea. The head losses that accompany the landward flow tend to lessen the extent to which the salt water occupies the aquifer.
Laboratory and field tests revealed that there was an anomalous, short-term influx of water into plastic bags after they were attached to seepage meters. At Narrow Lake, Alberta, the anomalous, short-term (30 min) influx of water averaged 237 ml to bags that were initially empty, but the anomaly was effectively eliminated when bags were prefilled with 1000 ml of water before they were attached to seepage meters. The impact of the anomaly on calculated seepage rates was greatest when seepage rates were low, eg. 0.3 ml m-2 min-1. The anomaly may be due to mechanical properties of the bag, and it may be alleviated by partially filling bags before they are attached to seepage meters. -from Authors
In recent years, there has been increased concern over pollution of groundwater by NO3-, yet little is known about microbial N transformations below the crop rooting zone. This study investigated the importance of microbial denitrification below the crop rooting zone of conventional and no-till corn plots. The soil was a well-drained Matapeak silt loam located in the Atlantic Coastal Plain. Plots were sampled in 30- and 60-cm depth increments down to the water table, which occurred at ca. 420 cm. Total viable bacteria and numbers of denitrifying bacteria decreased exponentially with increasing soil depth down to 150 cm. From 180 cm to the top of the water table total bacterial numbers were very low (< 100 organisms/gram). No CO2 production activity was observed below the 180-cm depht in unamended soil incubated aerobically at 25°C for 24 h. Anaerobic incubations with added NO3- and glucose showed no denitrifying activity below the 180-cm depth. These results indicate that C levels below the rooting zone in this well-drained, low organic matter soil are too low to support anaerobic conditions necessary for denitrification or to sustain a microbial population. Therefore, denitrification is not a mechanism of significant NO3- loss below the crop rooting zone at this location. Surface tillage practices had little influence on microbial activity below the root-zone.
Much of the runoff from agricultural fields in the southeastern Coastal Plain is carried to a stream channel system in a shallow phreatic aquifer. This subsurface runoff often passes through a band of riparian forest before becoming streamflow. It is hypothesized that the riparian ecosystem acts as a nutrient sink and reduces the concentrations and loads of nutrients in the shallow aquifer before the nutrients reach the stream channel. Concentrations and loads (kg/m ² ) of NO 3 ‐N, NH 4 ‐N, organic N, dissolved molybdate‐reactive P 1 total P, Ca, Mg, K, Cl, and SO 4 ‐S were measured in shallow phreatic wells at 37 locations on an agricultural watershed near Tifton, Ga. Total water volume moving off the watershed in subsurface flow was < 1% of streamflow with corresponding small amounts of nutrients. Nitrate‐N, Ca, and Mg had significantly higher concentrations in field wells than in forest or streamside wells. Concentrations of Cl were not reduced as water moved from field to forest. Processes within the riparian zone apparently converted primarily inorganic N from fields (76% NO 3 ‐N, 6% NH 4 ‐N, 18% organic N) into primarily organic N in streamside wells (10% NO 3 ‐N, 14% NH 4 ‐N, and 76% organic N). Concentration differences between field and forest wells indicated the riparian forest's ability to act as a sink for NO 3 ‐N, Ca, Mg, K, and SO 4 ‐S. Due to their role as nutrient sinks, riparian forests are important in maintaining stream water quality on agricultural watersheds.
Nutrient concentration changes were measured in surface runoff and shallow groundwater as they moved through a small cropland watershed in Maryland. From surface runoff waters that had transited c50 m of riparian forest, an estimated 4.1 Mg of particulates, 11 kg of particulate organic-N, 0.83 kg of ammonium-N, 2.7 kg of nitrate-N and 3.0 kg of total particulate-P per ha of riparian forest were removed during the study year. An estimated removal of 45 kg.ha-1/yr-1 of nitrate-N occurred in subsurface flow as it moved through the riparian zone. The cropland appeared to retain fewer nutrients than the riparian forest and probably incurs the majority of its nutrient losses in harvested crop. The dominant pathway of total-N loss from the riparian forest seemed to be subsurface flux. Total loss of P from the riparian forest appeared almost evenly divided between surface and subsurface losses. Nutrient removals in the riparian forest are of ecological significance to receiving waters. Coupling natural systems and managed habitats within a watershed may reduce diffuse-source pollution. -from Authors
A regional study of the areal and depth distribution of pesticides in shallow groundwater in the Delmarva Peninsula of Delaware, Maryland, and Virginia was done to (i) relate the pesticides detected to landscape and shallow subsurface features, and (ii) evaluate aquifer vulnerability and the potential contamination of drinking-water supplies. Water samples collected at 100 wells from 1988 to 1990 were analyzed for concentrations of 36 pesticides, four metabolites, and other constituents. The most commonly detected residues were atrazine, cyanazine, simazine, alachlor, metolachlor, and dicamba. Concentrations were low; few exceeded 3 μg L-1. Most detections correlate with the intensive use of these herbicides in three widely distributed and commonly rotated crops-corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and small grain-particularly if grown in well- drained soils. Most detections occurred in samples collected from shallow wells screened within 10 m of the overlying water table. The shallow depth distribution of most residues is consistent with their suspected history of use (ca. 20 yr), and patterns in shallow groundwater flow in the surficial aquifer in the study area. The areal and depth distributions of detectable residues in groundwater did not correlate with a vulnerability index, nor any of the component scores developed to estimate that index using the DRASTIC method. The shallow depth of most detections also indicates why few samples from water-supply wells in this study had measurable concentrations of pesticides; most supply wells are deeper than 10 m below the water table. The low number of contaminated samples from supply wells implies that deep groundwater currently (1992) used for drinking generally does not contain detectable pesticide residues.
Waters from 21 wells and two springs located in a typically farmed, mostly agricultural Pennsylvania watershed were analyzed for 11 pesticides, NO3, Cl and PO4. Among the pesticides selected according to a farm use survey, only atrazine was commonly found but at extremely low concentrations ranging from 3 ng/l to 1.11 μg/l. Atrazine appeared in 74% of cropland wells at least once in a three sampling sequence designed to sample several major groundwater recharge periods. No alachlor, metolachlor, carbofuran, terbufos, chlorpyrifos, or fonofos was found. Cyanazine was found intermittently in two wells. With only one record of application, simazine was found at least once in 32% of the cropland wells, but at extremely low concentrations. Neither 2,4-D nor dicamba were found in the one sampling analyzed. The frequency and extent of corn production expressed as Corn Production Intensity (CPI) was strongly related to atrazine concentrations. The highest atrazine concentrations were nearly always associated with continuous corn production. Atrazine concentrations over time varied greatly by well and followed several distinct patterns. Sampling time relative to major groundwater recharge periods affected these concentrations, but a predictive relationship was not apparent.
Increased nutrient levels in surface streams and eutrophication of some Coastal Plain waters has led to inquiries about both the amount and control of nitrate losses from agricultural fields. Nitrate concentrations in shallow groundwaters beneath cultivated fields and in the drainage waters from those fields were examined to determine the fate of nitrogen lost to drainage waters. From a Middle Coastal Plain watershed where well-and moderately well-drained soils dominate agricultural fields, 10 to 55 kg ha-1 yr-1 NO3-N moved from the fields in subsurface drainage water. However, most fields are bordered by forested buffers between the cultivated areas and streams which consist of poorly and very poorly-drained soils covered by dense vegetation. The evidence strongly indicated that a substantial part of the nitrate in the drainage water was denitrified in the buffer strip and that assimilation by vegetation was insignificant. Buffer strips of < 16 m were effective for inducing significant losses of nitrate before drainage water reached the stream. A field containing subsurface drainage tubing which emptied into open ditches moved more nitrogen into surface water than those fields without subsurface drainage improvements. From a Lower Coastal Plain watershed, a dense clay layer below the surface horizon reduced subsurface drainage resulting in total losses from the field of only 6 to 12 kg ha-1 yr-1 NO3-N. These losses were mostly in surface runoff. The extensive floodplain of the natural stream had a high capacity to reduce large quantities of N but the low total loss from the watershed is largely a result of low input to the drainage water from nonpoint sources. Soils included in this study were Typic Paleudults, Arenic Paleudults, Aquic Hapludults, and Aeric Paleaquults.
Unexpectedly high frequencies of positive responses have been observed in ELISA screening for alachlor in private rural wells, when samples were analyzed using the EnviroGard Alachlor Plate Kit. The majority of positive responses are false positives with respect to alachlor. In the false positive samples which have been tested, most of the positive response appears to be due to the ethane-sulfonate metabolite of alachlor. The concentrations of ES are relatively high, even in samples collected months after alachlor application, suggesting that ES is relatively persistent and mobile in soil. Additional studies of ES are warranted, and ELISA alachlor screens may be useful in its study.
The frequency of occurrence of alachlor and several other agrichemicals in water from private, rural domestic wells was determined for all counties in the United States where alachlor is sold. The three-stage, stratified, unequal probability selection procedure yielded water samples from 1430 wells in 89 counties. Of the estimated 6 million existing private domestic wells in the target area, less than 1% have detectable levels of alachlor. Similar occurrence frequencies were found for metolachlor and simazine. Atrazine was the most commonly detected pesticide in the alachlor use area with an occurrence frequency near 12%. Concentrations of all detected pesticides in rural well water are very low and are rarely expected to exceed any health-based standard. The occurrence of nitrate/nitrite, however, is more common. Over 50% of the wells in the alachlor use area have detectable levels of nitrate/nitrite. Nearly 5% exceed the 10 mg/L maximum contaminant level for nitrate/nitrite (expressed as total nitrogen). The occurrence of all chemicals is correlated with various measures of chemical use near the well and with measures of groundwater vulnerability. The likelihood of finding other agrichemicals in a well is significantly increased when nitrate and atrazine are also present.
Alachlor, atrazine, cyanazine, metolachlor, and metribuzin were measured at six sites during 1984 and 1985 in large subbasins within the Cedar River, IA. A computer model separated the Cedar River discharge hydrograph into groundwater and overland-flow components. The concentration of herbicides in the river when groundwater was the major flow component was less than 1.0-mu-g/L and averaged 0.2-mu-g/L. The maximum concentrations of herbicides occurred when overland flow was the major component of river discharge, exceeding 50-mu-g/L for total herbicides. About 6% of the annual river load of atrazine was transported with the groundwater component, while 94% was transported with overland flow. From 1.5 to 5% of the atrazine applied during the year was transported from the basin. Atrazine concentrations in the river increased according to the discharge divided by the drainage area. This correlation indicates that rivers with large normalized 2-year peak flows have the potential to transport large concentrations of herbicides. A diagrammatic model of nonpoint-source transport of herbicides was developed that suggests that sorbed transport from fields occurs during episodes of overland flow with rapid dissolution of herbicides downstream.
Great South Bay (New York) is a large lagoon on the northeast coast of the United States. The flow of groundwater across the floor of Great South Bay has been reported to account for as much as 2/3 of the total freshwater inflow. In situ measurements of this seepage flow have been made along four offshore transects in the Bay. These measurements show that the flow rate decreases rapidly offshore; within 30 m of the shoreline, the submarine outflow rates were typically 40 l (day m2)−1 and decreased to less than 10 l (day m2)−1 at a distance of 100 m from shore. The Bay floor at the study locations was sand or silty sand with vertical intrinsic permeabilities ranging from 14 to 78 darcys.The flow rate across the Bay floor may be described by an exponentially decreasing function. The flow distribution may, therefore, be specified with two parameters—the flow value at the shoreline, A, and a ‘decay’ constant, c, that governs the rate of decrease of the flow offshore. The calculated total flows along the four transects were 2·1 × 103, 1·1 × 103, 8·5 × 103 and 3·9 × 103 l (day m)−1. Between 40% and 98% of this flow enters the Bay within 100 m from shore. The total flow of groundwater across the Bay floor was calculated to be about 2 × 108 l day−1 or 10–20% of the total freshwater inflow.
Surface water, groundwater, and groundwater discharge quality surveys were conducted in Cherrystone Inlet, on Virginia's Eastern Shore. Shallow groundwater below agricultural fields had nitrate concentrations significantly higher than inlet surface waters and shallow groundwater underlying forested land. This elevated nitrate groundwater discharged to adjacent surface waters. Nearshore discharge rates of water across the sediment-water interface ranged from 0.02 to 3.69 liters·m−2·hr−1 during the surveys. The discharge was greatest nearshore at low tide periods, and decreased markedly with increasing distance offshore. Vertical hydraulic heads, Eh, and inorganic nitrogen flux in the sediments followed similar patterns. Nitrate was the predominant nitrogen species discharged nearshore adjacent to agricultural land use, changing to ammonium farther offshore. Sediment nitrogen fluxes were sufficient to cause observable impacts on surface water quality; nitrate concentrations were up to 20 times greater in areas of groundwater discharge than in the main stem inlet water. Based on DIN:DIP ratios, nitrogen contributions from direct groundwater discharge and tidal creek inputs appear to be of significant ecological importance. This groundwater discharge links land use activity and the quality of surface water, and therefore must be considered in selection of best management practices and water quality management strategies.
The Delmarva Peninsula is an extensively farmed region in which nitrate from commercial fertilizers and poultry has entered
the ground water and streams. The peninsula contains forested wetlands in a variety of settings, and their size and location
are a result of the surrounding hydrologic and soil conditions. Three regions, here referred to as hydrogeomorphic regions,
were selected for study. Each region has characteristic geologic and geomorphic features, soils, drainage patterns, and distribution
of farmland, forests, and forested wetlands. In all three regions, forested wetlands generally occupy poorly drained areas
whereas farmlands generally occupy well-drained areas. The three hydrogeomorphic regions studied are the well-drained uplands,
the poorly drained uplands, and the surficial-confined region. The well-drained uplands have the largest amount of farmland
and the smallest amount of forested wetlands of the three regions; here the forested wetlands are generally restricted to
narrow riparian zones. The poorly drained uplands contain forested wetlands in headwater depressions and riparian zones that
are interspersed among well-drained farmlands. The surficial-confined region has the smallest amount of farmland and largest
amount of forested wetlands of the three regions studied. Wetlands in this region occupy the same topographic settings as
in the poorly drained uplands. Much of the farmland in the surficial-confined region was previously wetland. Nitrate concentrations
in ground water and surface water on the peninsula range widely, and their distribution reflects (1) the interspersion of
forests among farmland, (2) hydrogeologic conditions, (3) types of soils, and (4) the ground-water hydrology of forested wetlands.
The well-drained uplands had higher median nitrate concentrations in ground water than the poorly drained uplands or the surficial-confined
region. The highest nitrate concentrations were in oxic parts of the aquifer, which are beneath well-drained soils that are
farmed, and the lowest were in anoxic parts of the aquifer, which are beneath poorly drained soils overlain by forested wetlands.
The effect of forested wetlands on water quality depends on the hydrogeologic conditions, extent of farming, and type of soils.
The three regions contain differing combinations of these factors and thus are useful for isolating the effects of forested
wetlands on water quality.
Key Wordswater quality-forested wetlands-hydrology
Direct measurements of groundwater seepage show the importance of subaqueous discharges as sources of fresh water and of dissolved
chemicals to lakes and the coastal ocean. The rate of seepage decreases rapidly offshore; an analytical solution was developed
that describes the discharge as Ki(In(coth πxk/4l))/k where i is the hydraulic gradient, K is the vertical hydraulic conductivity,l is the aquifer thickness, x is the distance from the shoreline, and k2 is K divided by the horizontal hydraulic conductivity. In addition to variations due to the inhomogeneities in the aquifer,
seepage into the coastal ocean involves some recirculation of the salt water. In Great South Bay, New York measured fluxes
were as great as 150 I m−2 d−1. The discharge near the shore was typically 50 I m−2 d−1, decreasing to 30 1 m−2 d−1 at a distance of 100 m offshore. Secondary convection due to an unstable density structure at the sediment-water interface
may also be superimposed on the seepage distribution. Fingers of salt should be capable of carrying marine water many decimenters
downward against the fresh groundwater advection. As a result, care must be exercised in interpreting direct measures of seepage
flux to recognize the contribution of recirculated seawater.
An assessment of developing eutrophic conditions in small temperate lagoons along the coast of Rhode Island suggests that
in such shallow, macrophyte based systems the response to nutrient enrichment differs from that described for plankton based
systems. The nitrogen loadings per unit area of the salt ponds are 240–770 mmol N per m2 per year. Instead of the high nutrient concentrations, increased phytoplankton biomass and turbidity, leading to eventual
loss of benthic macrophytes described for such systems as the Chesapeake, Patuxent and Appalachicola Bay, nutrient enrichment
of the Rhode Island lagoons has led to increased growth of marine macroalgae. The increased macroalgal growth appears to alter
the benthic habitat and a shift from a grazing to detrital food chain appears to be impacting important shellfisheries. As
more extensive areas of organic sediments develop, geochemical cycling changes, resulting in higher rates of nitrogen remineralization
and accelerated eutrophication. The major sources of nitrogen inputs to the salt ponds have been identified and a series of
management initiatives have been designed to limit inputs from present and potential development within the watersheds of
the lagoons.
A regional assessment of non-point-source contamination of pesticide residues in ground water was made of the San Joaquin Valley, an intensively farmed and irrigated structural trough in central California. About 10% of the total pesticide use in the USA is in the San Joaquin Valley. Pesticides detected include atrazine, bromacil, 2.4-DP, diazinon, dibromochloropropane, 1,2-dibromoethane, dicamba, 1,2-dichloropropane, diuron, prometon, prometryn, propazine and simazine. All are soil applied except diazinon.Pesticide leaching is dependent on use patterns, soil texture, total organic carbon in soil, pesticide half-life and depth to water table. Leaching is enhanced by flood-irrigation methods except where the pesticide is foliar applied such as diazinon. Soils in the western San Joaquin Valley are fine grained and are derived primarily from marine shales of the Coast Ranges. Although shallow ground water is present, the fewest number of pesticides were detected in this region. The fine-grained soil inhibits pesticide leaching because of either low vertical permeability or high surface area; both enhance adsorption on to solid phases. Soils of the valley floor tend to be fine grained and have low vertical permeability. Soils in the eastern part of the valley are coarse grained with low total organic carbon and are derived from Sierra Nevada granites. Most pesticide leaching is in these alluvial soils, particularly in areas where depth to ground water is less than 30m. The areas currently most susceptible to pesticide leaching are eastern Fresno and Tulare Counties.Tritium in water molecules is an indicator of aquifer recharge with water of recent origin. Pesticide residues transported as dissolved species were not detected in non-tritiated water. Although pesticides were not detected in all samples containing high tritium, these samples are indicative of the presence of recharge water that interacted with agricultural soils.
Seepage flux can be measured and samples of groundwater flowing into lakes and estuaries collected by enclosing an area of bottom with a cylinder vented to a plastic bag. The method has the advantage of not requiring measurements of permeability of bottom sediments. Seepage velocities from −0.1–2.58 µ m s ⁻¹ were measured in Minnesota and Wisconsin lakes and in Nova Scotia and North Carolina estuaries.
Where seepage inflow was rapid (0.4–0.8 s ⁻¹ ), water collected with the seepage meter was chemically similar to water from wells on the same flow path, and the distribution and chemistry of the seepage concurred with a theoretical flow net. The rate and direction of seepage flux were correlated with water surface elevation during a tidal cycle.
Atrazine, alachlor, and cyanazine exhibited maximum concentrations of about 1000-6000 ng/L in the Minnesota River in 1990 and 1991, resulting from precipitation and runoff following the application period. Transport of these herbicides to the river occurs via overland flow or by infiltration to the drainage networks. Suspended sediment, SO42-, and Cl- concentrations were used as indicators of transport mechanisms. The atrazine metabolite, DEA, was present in the river throughout the year. The ratio of DEA to atrazine concentration was used to calculate an apparent first-order soil conversion rate of atrazine to DEA. Half lives of 21-58 d were calculated for 1990 and 1991, respectively. The longer conversion rate in 1991 results from rapid flushing from the soil and minimum exposure to soil microorganisms. Total flux of herbicide to the river was 1-6.5 t, with over 60% of this loading occurring during the month of June. Loading to the river accounts for less than 1.5% of applied herbicide.
An indirect enzyme-linked immunosorbent assay (EIA) for metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamid e) detection in river water and soil was developed using serum obtained from rabbits immunized against the acid of metalaxyl ((N-(2,6-dimethylphenyl)-N-(methoxy-acetyl)-DL-alanine methyl ester) conjugated to bovine serum albumin. The assay had a linear working range from 1 to 50 ng/ml with a mean I50 value of 13.6 ng/ml and a lower detection limit of 2.0 ng/ml. Both the mean interwell and interassay coefficients of variation were less than 4% over the range of the standard curves for samples which had been prepared in phosphate buffered saline (PBS), river water, or soil extract. Assay cross-reactivity to the following four structurally related chloro-acetanilide pesticides were: propachlor (0%), metazachlor (0%), alachlor (23%), and metalaxyl (5,000%). Mean recoveries of metolachlor in spiked (2.0 to 32.0 ng/ml range) PBS, river water, and soil extract were 102%, 103%, and 110%, respectively. Soil samples were taken over a 56-d period from field plots treated with metolachlor and analyzed by GC and EIA. The correlation coefficient for comparison of the two methods was 0.96 with the slope of the linear regression line being 0.78. Furthermore, no statistical difference (P less than 0.05) was found between the dissipation curves of metolachlor derived from GC data versus EIA data.
At least 17 pesticides have been found in ground water in a total of 23 states as a result of agricultural practice. These results have been obtained through three different types of monitoring studies: large-scale retrospective, small-scale retrospective, and small-scale prospective. The first two types of studies survey areas where the pesticide(s) in question has already been used. The third type of study is an intensive field study where the pesticide is applied and monitoring begins at time zero. Often, soil core data are at least as important as ground water data. The ability to draw meaningful conclusions from large-scale studies is greatly diminished unless the studies have a statistical, stratified design. The purpose of this paper is threefold: to describe the three study types; suggest guidelines for groundwater sampling, soil sampling and well construction; and update the data summary of pesticides in ground water from agricultural practice.