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The impacts of recycled water on Great Western vineyard soils
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... Depending on the composition and pH of the specific wastewater used, irrigation with municipal wastewater may have variable effects on soil pH. Irrigation using municipal wastewater has been shown to (i) increase soil pH (Qian & Mecham, 2005;Gwenzi & Munondo, 2008;Hermon, 2011;Lado et al., 2012), (ii) decrease soil pH (Shahalam et al., 1998;Rattan et al., 2005;Keser, 2013;Abunada & Nassar, 2015) or (iii) have no significant effect at all (Stevens et al., 2003;Duan et al., 2010;El-Nahhal et al., 2013). This agrees with inconsistent trends in soil pH where soils were irrigated with treated municipal wastewater for different periods (Rusan et al., 2007). ...
Sustainable viticulture is important for socio-economic prosperity in the Western and Northern Cape provinces of South Africa. Limited natural water resources, as well as periodic droughts in these regions necessitate the need to find alternative sources of irrigation water to sustain yield and quality. The large volumes of treated municipal wastewater generated annually holds promise as an alternative water source. Despite various treatment procedures, municipal wastewater may contain high levels of Na+, B3+, Cl- and SO42-, as well as trace elements and heavy metals. However, it often contains essential plant nutrients, e.g. N, P and K+. If treated properly, municipal wastewater may be beneficial when reused for irrigating agricultural crops. Possible benefits include recycling of nutrients, fertiliser savings, the addition of organic material, a reduced pressure on fresh water sources and reduced environmental contamination. However, high salt loads, in particular Na+, can have detrimental effects on soil physical and chemical properties, as well as crop sustainability. Therefore, it is essential to implement measures that will limit damage caused by salinity and/or sodicity. The attenuation and accumulation of toxic substances should also be managed to a minimum. Most of the information regarding treated municipal wastewater has been generated through laboratory studies using simulated wastewater, or in some cases actual wastewater. No studies have yet investigated the impact of irrigation with treated municipal wastewater under the conditions that prevail in South African grape growing regions.
Subsurface drip irrigation was compared to sprinkler irrigation of bermudagrass turf in a multi-year experiment using reclaimed water. The experimental plots were established with sprinkler irrigation. During the following three irrigation seasons, plots were irrigated when the average soil water content in the upper 30 cm of soil decreased below 20% by volume, which corresponded to a management-allowed depletion value of 50%. The amount of irrigation water, the visual appearance of the turf, shoot biomass production, soil salinity, and health risks due to reclaimed water reuse were examined. Management problems such as emitter clogging were identified. No emitters were completely clogged, and emitter clogging was not serious enough to impact visual quality. Statistical uniformity of emitters was reduced from 91.8% (for new emitters) to 85.3% after the first year and 86.2% after the third year, while flow rates remained at 3.75, 3.78, and 3.89 L/h, respectively. The amount of water applied in the subsurface drip irrigated plots to maintain acceptable visual quality was similar to that applied in the sprinkler irrigated plots. Increases in the electrical conductivity of the soil surface of the subsurface drip irrigated plots were noted after the first and second seasons. However, these increases were not high enough to negatively affect turf appearance. Inspection of the emitters at the end of the irrigation seasons found signs of root intrusion into the emitters, which may pose a threat to the long-term use of subsurface drip irrigation.
In recent years, worldwide attention has shifted from point source to non-point source (NPS) pollutants, particularly with regard to the pollution of surface and subsurface sources of drinking water. This is due to the widespread occurrence and potential chronic health effects of NPS pollutants. The ubiquitous nature of NPS pollutants poses a complex technical problem. The area1 extent of their contamination increases the complexity and sheer volume of data required for assessment far beyond that of typical point source pol- lutants. The spatial nature of the NPS pollution problem necessitates the use of a geo- graphic information system (GIS) to manipulate, retrieve, and display the large volumes of spatial data. This chapter provides an overview of the components (i.e., spatial vari- ability, scale dependency, parameter-data estimation and measurement, uncertainty analy- sis, and others) required to successfully model NPS pollutants with GIS and a review of recent applications of GIS to the modeling of non-point source pollutants in the vadose zone with deterministic solute transport models. The compatibility, strengths, and weak- nesses of coupling a GIS to deterministic one-dimensional transport models are discussed.
Measurement of dispersible clay is important for the diagnosis of structural stability problems in soil. However, clay dispersibility is known to change with water content and time. The purpose of the present study was to determine how incubation of sodic soil under different water content regimes influences clay dispersibility. Two topsoils (depth 0-0.1m), one sodic [exchangeable sodium percentage (ESP) 9.7] and the other non-sodic (ESP 3.8), were collected from an experimental pasture at Kyabram, Victoria, and 2 soils, a sodic topsoil (depth 0-0.1 m, ESP 6.9) and the corresponding subsoil (depth 0.2-0.3 m, ESP 25.7), Mere collected from a cropped field at Two Wells, South Australia. The soils were incubated for 264 days in a split-plot design. The main treatments were soil type and incubation water content: continuously air-dry, continuously wet (50 kPa), or with wet/dry cycles. The subtreatment was water content at analysis: air dry or wet (-50 kPa). Clay dispersion was greater when measured on wet soils than dry soils, irrespective of water contents during the prior incubation. Electrical conductivity increased, and sodium adsorption ratio (SAR), pH, and organic carbon content decreased as a function of the time for which the soils were wet. In the Kyabram soils that were wet when analysed, easily dispersible clay content increased with SAR. Decreases in moderately dispersible clay under the wetting/drying regime were not related to electrolyte composition, and were attributed to particle rearrangement and cementation. The decreases in clay dispersibility with time occurred despite net losses of carbohydrate and aliphatic materials. An implication of the work is that the decomposition of soil organic matter, even in the absence of fresh additions, may reduce clay dispersion in sodic soils by altering electrolyte concentration and composition.
Elevated Cd concentrations have been observed in potato (Solanum tuberosum L.) tubers from commercial crops in certain regions of southern Australia. Reasons for enhanced Cd uptake by tubers were investigated by a survey of commercial crops and associated soils. Eighty-nine sites were selected and paired tuber and soil samples taken. Concentration of Cd in tubers was compared to potato variety, tuber elemental composition, and chemical-physical characteristics of topsoil (0-150) and subsoil (150-300 mm). Tuber Cd concentrations were positively related to soil electrical conductivity (EC) and extractable Cl (R² = 0.62, P < 0.001) in the topsoil, with extractable Cl accounting for more variation than EC. Tuber Cd concentrations were not strongly related (R² = 0.23, P < 0.05) to potato variety alone. However, inclusion of variety and EDTA-extractable Zn with water-extractable Cl in a multivariate model resulted in a small but significant improvement in the variance accounted for by the model (R² = 0.73, p < 0.001). Tuber Cd was unrelated to tuber concentrations of P or tuber but was positively related to concentrations of major cations in the tuber particularly Na. Soil pH, total C, EDTA-extractable Cd, or particle-size distribution were not correlated to tuber Cd concentrations, either singly or after inclusion in a multivariate model with soil Cl concentrations. As Cl is known to mobilize soil Cd and increase its phytoavailability, elevated Cd concentrations in potato tubers in southern Australia appear to be largely a result of the use of saline irrigation waters. 41 refs., 5 figs., 4 tabs.
In order to statistically evaluate the differences between intact and packed columns of soil, two tracers were applied to four intact and four packed columns of a Woodbridge soil. Bromide (Br-) was used as a conservative tracer and Blue dye as a moderately adsorbed tracer (which mimics herbicides such as atrazine) to develop breakthrough curves (BTC) at four different water potentials (heads) of -100 mm, -50 mm, +10 mm, and +50 mm at the top of the soil. Variables used in the statistical comparisons included volumetric flow rate (Q), Br- and Blue dye peak relative concentrations (C/C0), and time-to-peak concentrations (Tp) for the two tracers. Intact columns exhibited a significantly (p = 0.05) higher Q than packed columns. The Qs increased significantly with water potential for both intact and packed soil columns. Peak C/C0 of Blue dye exhibited a negative linear relationship with water potential for packed columns. The Tp of Br- exhibited a negative linear relationship with water potential for intact columns. The overall shapes of the BTCs were also compared statistically in order to explore objective methods of BTC comparisons. The non-parametric Kolmogorov-Smirnov Two-Sample Test was determined as the best method of BTC shape comparison. The differences for intact vs. packed columns were attributed to greater preferential flow due to soil structure and macropores in the intact soil columns.
The concepts of preferential flow are reviewed. Five types of preferential flow are recognized and defined. These include macropore flow, gravity-driven unstable flow, heterogeneity-driven flow, oscillatory flow, and depression-focused recharge. Spatial scales at which each of these preferential flow processes occurs are suggested. An overview is presented of the relationship between preferential flow and water quality, both for surface water sources and ground water sources. Much of the direct knowledge about the impact of preferential flow on water quality has been derived within the last two decades. The evidence for the impact of preferential flow on surface water quality is much more plentiful, probably because it is easier to measure chemical breakthroughs to surface water sources. Some of the newer methods for experimentally quantifying preferential flow are outlined. These methods include the tension infiltrometer, time domain reflectometry, chemical tracing, and geophysical methods such as ground penetrating radar and electrical resistance tomography. Theoretical analyses of preferential flows are based on conservation of mass and momentum. It is explained that the use of Darcy's law (and therefore Richards' equation) may not be valid for some preferential flows.
Preferential flow in soils is thought to be dominated by the dissipation of momentum. The strict application of momentum dissipation to flow in macroporous soils leads to a kinematic wave approach. The basics are summarized and calibration procedures are introduced. The approach represents well drainage flow and soil moisture variations, measured with either horizontally or vertically installed TDR-wave guides. Rates of preferential flow can be estimated from soil moisture readings. The approach yields mobile soil moisture, its total contact length with the parts at rest and its average film thickness, thus providing for information on the geometry of flow and the flow paths. The depth range to which the approach applies, to either drainage flow or soil moisture data, is viewed as measure for the vertical extent of hydraulically functional macropores. The effects of soil compaction on structural pores can thus be demonstrated.
Wastewater was applied to three soils to determine the sealing effect or change in hydraulic properties. Saturated conductivities of disturbed soils were measured weekly under laboratory conditions over a 40-wk period. For the Lester clay loam and Waukegan silt loam, saturated conductivities of the wastewater seal. In Hubbard loamy sand, an immediate seal was formed due to the application of wastewater.
Since many of the practical applications of solute modeling are to situations where crop roots are present, it is necessary to investigate the effect of roots and void root channels on the transport of solutes through soils. In an attempt to do this chloride breakthrough experiments were conducted over a two year period in soil columns packed uniformly with sandy loam or loamy sand. A series of experiments were conducted in bare soil, followed by repeated experiments with wheat plants in the columns, and finally in bare soil again after the wheat crop had died.-from Authors