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Location of the study site. (a) The location of the Garonne River; (b) the location of the simulated area; (c) the location of the alluvial soil, Monbéqui site, and piezometers.
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Numerous studies have pointed out the importance of groundwater and surface water interaction (SW–GW) in a river system. However; those functions have rarely been considered in large scale hydrological models. The SWAT-LUD model has been developed based on the Soil and Water Assessment Tool (SWAT) model; and it integrates a new type of subbasin; wh...
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... Garonne River has a drainage area of about 51,500 km 2 and a length of 525 km at the last gauging station not influenced by tidal (Tonneins). The average annual rainfall is around 900 mm [20]. The study area is located in the middle of the Garonne River, between Toulouse and the confluence with the Tarn River ( Figure 2). The width of the floodplain is 2-4 km. The coarse alluvium of 4-7 m (sand and gravel) eroded from the Pyrenees Mountains during the past glacial periods overlie an impermeable molassic bedrock [21]. A series of terraces exists in the floodplain, and the higher terrace delimits the floodplain. Field studies show that the impermeable substratum of the higher terrace is placed above the topographical surface of the floodplain, and the floodplain is disconnected from the larger scale upland aquifer [21]. The middle terrace, which is around 2 km wide, is cultivated and rarely flooded (every 30-50 years). The lower terrace, with a width of a few hundred meters devoted to poplar plantations, is flooded every year or every two years. The riparian zone is flooded almost every year and has a width of 10-100 m ...
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... observed daily discharges at the Portet gauging station ( Figure 2c) were applied as input data to represent the river water discharges from the upstream area. The nitrate concentration in the river water was considered as a constant 1.13 mg·L −1 (N-NO 3 − ), which was given based on the nitrate concentrations measured at the Blagnac station (located downstream of Toulouse, Figure 2c) taking into account the influence of the urban area of Toulouse (www.eaufrance.fr). The nitrate concentrations in the LUs were simulated by the model. Studies have found that the further away from the river, the more stable the DOC concentrations [16]. In our study, the DOC concentrations in LU2 and LU3 were assumed to be constant. The input DOC concentrations in the LUs and in the river water were determined based on the measurements at Monbéqui in 2013. The DOC concentrations in LU1 were calculated based on the DOC concentrations in the river water and LU2. As the DOC concentration in the river water significantly increases on flooding days [30][31][32], we used two DOC concentration values to distinguish the difference, one for no flooding days and another higher value for flood ...
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... observed daily discharges at the Portet gauging station ( Figure 2c) were applied as input data to represent the river water discharges from the upstream area. The nitrate concentration in the river water was considered as a constant 1.13 mg·L −1 (N-NO 3 − ), which was given based on the nitrate concentrations measured at the Blagnac station (located downstream of Toulouse, Figure 2c) taking into account the influence of the urban area of Toulouse (www.eaufrance.fr). The nitrate concentrations in the LUs were simulated by the model. Studies have found that the further away from the river, the more stable the DOC concentrations [16]. In our study, the DOC concentrations in LU2 and LU3 were assumed to be constant. The input DOC concentrations in the LUs and in the river water were determined based on the measurements at Monbéqui in 2013. The DOC concentrations in LU1 were calculated based on the DOC concentrations in the river water and LU2. As the DOC concentration in the river water significantly increases on flooding days [30][31][32], we used two DOC concentration values to distinguish the difference, one for no flooding days and another higher value for flood ...
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... calibration was performed automatically for the original SWAT parameters and manually for the newly developed SWAT-LUD parameters. The automatic calibration was performed with SWAT-CUP, which is an external software tool permitting SWAT users to realize automatic calibration with more comfort and efficiency [36]. SWAT-CUP includes several possible algorithms, of which SUFI-2 is known to achieve better calibration performance in a limited number of iterations [37]. The observed discharges from the Larra, Verdun, and Lamagistère gauging stations (see station locations in Figure 2c) were used for calibration. Sensitivity analysis and calibration were performed by SWAT-CUP with the SUFI-2 algorithm [38]. After sensitive parameters were identified, a 1500-run calibration was performed as recommended by Yang et al. ...
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... the SW-GW exchange and shallow aquifer denitrification processes were not included in the SWAT model, the parameters of these functions could not be calibrated by SWAT-CUP. Therefore, manual calibration was carried out to adjust the newly developed parameters. The observed groundwater levels in the four BRGM piezometers, P91, P170, P286, and P3247 (Figure 2), were used to calibrate the river water exchange. The nitrate concentrations in the shallow aquifer, which were measured in 2004-2005 and 2013 at Monbéqui, were used to calibrate the denitrification process. In 2013, nitrate concentrations were measured in six piezometers in LU1, 14 piezometers in LU2, and three piezometers in LU3, andin 2004-2005, nitrate concentrations were measured in two piezometers in LU1, one piezometer in LU2, and one piezometer in LU3. The measured nitrate concentrations were also used to calibrate the model. The nitrate fluxes observed at the St-Aignan station were used to validate the nitrate flux output simulated at the outlet of the simulated area. The evaluation of the quality of the simulation included the percent bias (PBIAS), the root means square error (RMSE), and the coefficient of determination (R 2 ...
Citations
... However, NO 3 -N transport to the stream was lower than Scenario 1 due to NO 3 -N loss to denitrification, resulting in peak concentrations of 50 µg/L in October 2020 and 41 µg/L in August 2021 (Figure 8b). Sun et al. [64] similarly identified decreased NO 3 -N transport in SW due to SGW denitrification while studying a riparian floodplain area, and the reduction of NO 3 -N was in a range of 5 mg/L to 10 mg/L. ...
... However, NO3-N transport to the stream was lower than Scenario 1 due to NO3-N loss to denitrification, resulting in peak concentrations of 50 µg/L in October 2020 and 41 µg/L in August 2021 (Figure 8b). Sun et al. [64] similarly identified decreased NO3-N transport in SW due to SGW denitrification while studying a riparian floodplain area, and the reduction of NO3-N was in a range of 5 mg/L to 10 mg/L. (Figure 8b). ...
... However, NO3-N transport to the stream was lower than Scenario 1 due to NO3-N loss to denitrification, resulting in peak concentrations of 50 µg/L in October 2020 and 41 µg/L in August 2021 (Figure 8b). Sun et al. [64] similarly identified decreased NO3-N transport in SW due to SGW denitrification while studying a riparian floodplain area, and the reduction of NO3-N was in a range of 5 mg/L to 10 mg/L. From Scenario 1, a cumulative nitrate loss of 947 g was observed from the shallow aquifer to the stream between 2020 and 2021. ...
Simulating shallow groundwater (SGW) flow dynamics and stream–SGW interactions using numerical modeling tools is necessary to develop a mechanistic understanding of water flow systems and improve confidence in water resource management practices. A three-dimensional (3D) SGW flow model was developed for a riparian wetland in a mixed forest and agricultural catchment in West Virginia (WV), Appalachia, USA, using a Modular 3D Groundwater Model (MODFLOW). The MODFLOW simulation was calibrated in steady (R2 = 0.98, ME = −0.21, and RMSE = 0.77), transient state (R2 = 0.97, ME = −0.41, and RMSE = 1.28) and validated (R2 = 0.97, ME = −0.28, and RMSE = 1.05) using observed SGW levels from thirteen nested piezometers under steady and transient states. An experimental MT3D transport scenario was developed to show the lateral transport of NO₃-N from the aquifer to stream cells. Relatively stable SGW head distribution was observed. In the downstream reach, SGW discharge varied from 948 m3/day to 907 m3/day in 2020, with creek seepage ranging from 802 m3/day to 790 m3/day. Similarly, SGW input to the stream ranged from 891 m3/day to 978 m3/day, while creek seepage ranged from 796 m3/day to 800 m3/day in 2021. In upstream reaches, losing stream conditions were observed in January, June, and September 2020 and January to April 2021, while gaining stream conditions prevailed during other months. Thus, an approximately monthly alternating gaining–losing stream condition was observed in the upstream area. An experimental MT3D transport scenario resulted in an advection-dispersion scenario, showing a cumulative loss of 947 g of NO3-N from SGW to the stream. Denitrification accounted for the cumulative loss of 1406 g of NO3-N from SGW, surpassing 639 g of nitrate from the SGW to the stream during the study period. Additionally, particle tracking using MODPATH indicated a long residence time for SGW nutrients, affirming the efficiency of nitrogen transformation through denitrification. This study is among the first to simulate hydrologic and nutrient interactions in riparian wetlands of a mixed land-use catchment in the Appalachian region of the northeastern United States. The results better inform water resource management decisions and modeling efforts in the Appalachian region and similar physiographic regions globally.
... The processes of nutrient deposition in the bottom sediments of lakes depend on the physicochemical conditions in the water body. At the same time, the assimilation of nutrients by primary producers occurs in lakes during the growing period, which consequently reduces the content of these elements in surface waters (Saunders and Kalff, 2001;Sun et al., 2018;Uuemaa et al., 2018). Depending on the processes occurring in lakes, different trends of water quality changes were observed in the rivers below them. ...
River-lake systems in Central Europe represent the majority of surface water system forms. In these systems lakes play an important role in river water quality. Published reports on the quality of surface waters in Europe indicate progressive deterioration of their quality, resulting mainly from increasing eutrophication. This study analyzed the content of two biogenic elements—nitrogen and phosphorus—and their mineral forms in the Głuszynka river, representative for the river-lake systems of Central Europe. The research was conducted in the hydrological years 2016–2018. The ecological status of the Głuszynka river, due to the “poor” status of both biological elements and physicochemical elements (content of phosphorus and nitrogen compounds), was classified as “poor.” In the period analyzed an increase in the content of nitrogen compounds was recorded in the hydrological year 2018. However, during the growing period a significant decrease in the content of total and nitrate nitrogen was observed, which was related to the activity of primary producers. For phosphorus compounds a slight increase of their content was observed during this period. This was associated with high tourist and recreational pressure on the analyzed system. Analyzing the spatial variability of biogenic compounds it was observed that along the course of the river the content of nitrite and nitrate nitrogen as well as total nitrogen increased at successive sampling points. An opposite trend of change along the river course was observed for phosphorus compounds (content of P-PO4 and total phosphate decreased by 14 and 15.9%, respectively). Statistical analyses carried out highlighted the relationship between water quality and land use in the direct catchments of lakes included in the river-lake network. Arable land was associated with higher the content of orthophosphorus phosphate, grassland total nitrogen, nitrite and nitrate nitrogen, while urbanization was strongly associated with ammonium nitrogen.
... Critical Zone science also focuses on nutrient cycling (e.g Graba et al., 2012;Boithias et al., 2014;Epelde et al., 2016;Cakir et al., 2020), the movement of elements (Garneau et al., 2015), and quantifying erosion rates and carbon fluxes (Cias et al., 2008;Ouerng et al., 2011;Wei et al., 2021). In addition, hydrological studies are conducted to study human effects on water budget (Martin et al., 2016;Volk et al., 2016;Cakir et al.,2019), and various ecological services rendered by individual units of the critical zone (Sànchez-Pérez et al., 2009Sauvage et al., 2012Sauvage et al., , 2018Sun et al., 2018;Cakir et al., 2021). ...
... Wetlands can also transform nutrients and contaminants, for example nitrate to N2 when soil bacteria use nitrate for their respiration instead of oxygen. These transformed compounds can be released as more complex or new ones to downstream ecosystems (Weng et al., 2003;Sun et al., 2018). ...
... Some of the negative impacts that have been reported include; increased runoff, increased peak flow following rainfall events. Others are, increase in nitrogen and phosphorus load from watershed and increased sediment loading (Carpenter et al., 1998;Kirwan et al., 2016;Sun et al., 2018). ...
The Congo River basin (CRB) is the second largest drainage basin on Earth after the Amazon in terms of discharge and basin area. It also contains the second largest area of rainforest (1.8 million km2) that also hosts the single largest peatland deposit found (145,500 km2) in the Tropics. The Cuvette Centrale is the quarternary "sag" basin found at the center of this basin that receives flows from all the principal tributaries located in the right bank, left bank and the upper Congo River. While a few studies of the hydrology, sediments and organic matter biogeochemistry of the CRB have been made, there is a need to better constrain the lateral fluxes of material that pass through the Cuvette in order to best understand its role in the basin biogeochemistry at a daily time step. With the aid of the Soil and Water Assessment Tool (SWAT) hydrological model calibrated using scarce data, and validated with remote sensing products, biogeochemical and hydrological models, we have established the role of the Cuvette Centrale as a source of water to the main River during low flow periods for the 2000-2012 simulation period. Furthermore, an analysis of the sediment dynamics in the 2000-2012 period revealed that the Cuvette Centrale is capable of retaining over 23 megatons of material annually produced within the Cuvette Centrale and from upland sources. The models for DOC and POC revealed that hydrology and slope are primary controls on these fluxes. The results revealed that between 1.2 to 1.5 megatons of DOC is produced in the Cuvette Centrale with 0.9 megatons of POC retained in the Cuvette Centrale. At the basin outlet, a flux of 13.4 Mt yr-1 for DOC and 2.2 Mt yr-1 of POC was estimated, consistent with previous estimates.
... Future improvements to the model will focus on the spatial representativeness of the sedimentation processes as well as the use of high-resolution input data. Incorporation of a wetland module will also aid in a proper understanding of the processes in the central ungauged basin (e.g., [97][98][99] This study is a follow-up to [50] Datok et al., (2021), where a water balance of the Cuvette Centrale was made. They found that as much water passed through the Cuvette Centrale from the upper Congo as efficient precipitation falling over the area. ...
In this study, the SWAT hydrological model was used to estimate the sediment yields in the principal drainage basins of the Congo River Basin. The model was run for the 2000–2012 period and calibrated using measured values obtained at the basins principal gauging station that controls 98% of the basin area. Sediment yield rates of 4.01, 5.91, 7.88 and 8.68 t km−2 yr−1 were estimated for the areas upstream of the Ubangi at Bangui, Sangha at Ouesso, Lualaba at Kisangani, and Kasai at Kuto-Moke, respectively—the first three of which supply the Cuvette Centrale. The loads contributed into the Cuvette Centrale by eight tributaries were estimated to be worth 0.04, 0.07, 0.09, 0.18, 0.94, 1.50, 1.60, and 26.98 × 106 t yr−1 from the Likouala Mossaka at Makoua, Likouala aux Herbes at Botouali, Kouyou at Linnegue, Alima at Tchikapika, Sangha at Ouesso, Ubangi at Mongoumba, Ruki at Bokuma and Congo at Mbandaka, respectively. The upper Congo supplies up to 85% of the fluxes in the Cuvette Centrale, with the Ubangi and the Ruki contributing approximately 5% each. The Cuvette Centrale acts like a big sink trapping up to 23 megatons of sediment produced upstream (75%) annually.
... While POC mostly comes from soil erosion, DOC is a result of soil leaching (Meybeck 1993;Raymond and Bauer 2001). DOC is the most consumed OC form in denitrification (Peyrard et al. 2011;Zarnetske et al. 2011;Sun et al. 2018). ...
... Modelling tools that focus on the exchanges between rivers and floodplains were usually used for hydrology interactions (Yamazaki et al. 2011;Jung et al. 2012). Regarding floodplains biogeochemistry, previous models showed their ability to simulate denitrification (Hattermann et al. 2006;Sun et al. 2018). They can be used to identify nitrate sources and sinks (Boano et al. 2010;Peyrard et al. 2011;Zarnetske et al. 2012) as well as hot spots and hot moments of nutrients cycling (Groffman et al. 2009;Bernard-Jannin et al. 2017). ...
... Two options are commonly used to estimate denitrification at large scale: coupling a hydrological with biogeochemical models (Peyrard et al. 2011) or implementing biogeochemical modules in a hydrological model . Sun et al. (2018) was the first study to show models capacity to simulate daily denitrification variations at the scale of a reach by considering the river-aquifers exchanges of water, nitrate and OC. Denitrification is usually modelled as a nitrate retention rate (Boyer et al. 2006;Ruelland et al. 2007;Peyrard et al. 2011;Sun et al. 2018). ...
Floodplains play a crucial role in water quality regulation via denitrification. This biogeochemical process reduces nitrate (NO3−), with aquifer saturation, organic carbon (OC) and N availability as the main drivers. To accurately describe the denitrification in the floodplain, it is necessary to better understand nitrate fluxes that reach these natural bioreactors and the transformation that occurs in these surface areas at the watershed scale. At this scale, several approaches tried to simulate denitrification contribution to nitrogen dynamics in study sites. However, these studies did not consider OC fluxes influences, hydrological dynamics and temperature variations at a daily time step. This paper focuses on a new model that allows insights on nitrate, OC, discharge and temperature influences on daily denitrification for each water body. We used a process-based deterministic model to estimate daily alluvial denitrification in different watersheds showing various pedo-climatic conditions. To better understand global alluvial denitrification variability, we applied the method to three contrasting catchments: The Amazon for tropical zones, the Garonne as representative of the temperate climate and the Yenisei for cold rivers. The Amazon with a high discharge, frequent flooding and warm temperature, leads to aquifers saturation, and stable OC concentrations. Those conditions favour a significant loss of N by denitrification. In the Garonne River, the low OC delivery limits the denitrification process. While Arctic rivers have high OC exports, the low nitrate concentrations and cold temperature in the Yenisei River hinder denitrification. We found daily alluvial denitrification rates of 73.0 ± 6.2, 4.5 ± 1.4 and 0.7 ± 0.2 kgN ha−1 y−1 during the 2000–2010 period for the Amazon, the Garonne and the Yenisei respectively. This study quantifies the floodplains influence in the water quality regulation service, their contribution to rivers geochemical processes facing global changes and their role on nitrate and OC fluxes to the oceans.
... DOC in the shallow aquifer can be lost due to biological and chemical reactions. A first-order kinetic is used to represent the net effects of all reactions occurring in the shallow aquifer (Sun et al., 2018). The amount after the reaction processes is calculated as: ...
Dissolved organic carbon (DOC) is not only a critical component of global and regional carbon budgets, but also an important precursor for carcinogenic disinfection byproducts (DBP) generated during drinking water disinfection process. The lack of process based watershed scale model for carbon cycling has been a limiting factor impeding effective watershed management to control DOC fluxes to source waters. Here, we integrated terrestrial and aquatic carbon processes into the widely tested Soil and Water Assessment Tool (SWAT) watershed model to enable watershed-scale DOC modeling (referred to as SWAT-DOC hereafter). The modifications to SWAT mainly fall into two groups: (1) DOC production in soils and its transport to aquatic environment by different hydrologic processes, and (2) riverine transformation of DOC and their interactions with particular organic carbon (POC), inorganic carbon and algae (floating and bottom). We tested the new SWAT-DOC model in the Cannonsville watershed, which is part of the New York City (NYC) water supply system, using long-term DOC load data (from 1998 to 2012) derived from 1399 DOC samplings. The calibration and verification results indicate that SWAT-DOC achieved satisfactory performance for both streamflow and DOC at daily and monthly temporal scales. The parameter sensitivity analysis indicates that DOC loads in the Cannonsville watershed are controlled by the DOC production in soils and its transport in both terrestrial and aquatic environments. Further model uncertainty analysis indicates high uncertainties associated with peak DOC loads, which are attributed to underestimation of high streamflows. Therefore, future efforts to enhance SWAT-DOC to better represent runoff generation processes hold promise to further improve DOC load simulation. Overall, the wide use of SWAT and the satisfactory performance of SWAT-DOC make it a useful tool for DOC modeling and mitigation at the watershed scale.
... Depending on the prevailing conditions, numerous processes occur in water which affect the transformation of nitrogen and its deposition on the bottom. The main processes of nitrogen transformation in surface waters include nitrification and denitrification processes [7]. Anaerobic bacteria are involved in denitrification by producing a gas in the form of nitrogen oxide or nitrogen dioxide by converting nitrate nitrogen into nitrite nitrogen. ...
Generally, in water ecosystems, it is assumed that rivers play a transport role. In turn, lakes have accumulation properties. However, in fluvio-lacustrine systems, each water body located on a river track can disrupt naturally occurring processes. One such process is the nitrogen cycle. An analysis of the nitrogen cycle, at both the global and local levels, is of extreme significance in view of the progressive degradation of aquatic ecosystems. In this study, we attempted to show that the specific properties of reservoirs located in river–lake systems contribute to an adequate reaction of these reservoirs to situations involving an excessive pollution load. Despite the intensive exchange of water in lakes, they were mainly shown to have an accumulation function. In particular, in those located in the lower part of the system, the total nitrogen load transported outside the example reservoir decreased by 4.3%. The role of these reservoirs depends on the morphometric, hydrologic, and meteorological conditions. The actual loading of the water body was shown to be more than double the permitted critical loading. The creation of conditions similar to those occurring in river–lake systems by, for example, delaying the outflow of water, may favor the protection of surface water from the last element of the system, because this limits the transport of pollutants. This study of the functioning and evolution of lakes’ fluvio-lacustrine systems, including the balance of the nutrient load, enables the prediction of the aquatic ecosystem’s responses in the future and their changes.
Riparian zones can effectively reduce excess nitrogen loading to streams. Modeling nitrogen retention in riparian zones is useful, especially at larger scales. We evaluated select riparian nitrogen models for their robustness in representing hydrology, vegetation, soils, nutrients, and channel morphodynamics. We used global, time-varying sensitivity analyses of REMM (Riparian Ecosystem Management Model) and SWAT+ (Soil and Water Assessment Tool+) to identify the most influential parameters for calculating water table depth and nitrogen processes. Both REMM and SWAT+ were sensitive to topographic and soil parameters such as slope and soil layer thickness, although spatial and temporal scale and hydroclimatic conditions affected parameter sensitivity. Neither model was sensitive to stream channel depth, which is known to affect riparian hydrology and nitrogen cycling. It is necessary to incorporate stream morphodynamics like channel change into both riparian-scale and watershed-scale nitrogen models to provide useful management tools for addressing excessive nitrogen loading in stream networks.
