Tile-drained Agricultural Fields Research Articles

Long-term phosphorus removal by Ca and Fe-rich drainage filter materials under variable flow and inlet concentrations

Phosphorus (P) losses from tile-drained agricultural fields may degrade surface water quality by accelerating eutrophication. Among the different edge-of-field technologies, compact filter systems using different filter materials have been identified as potentially effective solutions for removing P from drainage water before discharge downstream.This study investigated the long-term (>696 days) P removal efficiency of 5 different filter materials in a column setup, using artificial drainage water (pH 6). Filter materials included two iron-based granulates (calcinated diatomaceous earth (CDE), ferric hydroxide granules (CFH)), and three calcium-based granulates (seashells, limestone, calcinated silicate/calcium oxide (Filtralite-P)). Experiments were performed under variable flow rates (0.037 and 1.52 L h−1; hydraulic retention time of 26–43 min and 18–30 h) and inlet P concentrations (0.14 and 0.7 mg L−1). An overall analysis revealed that the Fe-based materials achieved higher P retention than Ca-based materials. In particular, CFH was capable of retaining 99 and 98 % of the high and low inlet P concentrations, respectively. Conversely, limestone retained only 25 % of the high P load. CDE performed moderately well, independently of the inlet P concentration. Filtralite-P and Seashells performed well at high inlet P concentration but relatively poorly at low P concentration. The sensitivity of filter material P removal efficiency to variations in P loading was generally lowest for CFH and highest for limestone.

Important Role of Overland Flows and Tile Field Pathways in Nutrient Transport.

Nitrogen and phosphorus pollution is of great concern to aquatic life and human well-being. While most of these nutrients are applied to the landscape, little is known about the complex interplay among nutrient applications, transport attenuation processes, and coastal loads. Here, we enhance and apply the Spatially Explicit Nutrient Source Estimate and Flux model (SENSEflux) to simulate the total annual nitrogen and phosphorus loads from the US Great Lakes Basin to the coastline, identify nutrient delivery hotspots, and estimate the relative contributions of different sources and pathways at a high resolution (120 m). In addition to in-stream uptake, the main novelty of this model is that SENSEflux explicitly describes nutrient attenuation through four distinct pathways that are seldom described jointly in other models: runoff from tile-drained agricultural fields, overland runoff, groundwater flow, and septic plumes within groundwater. Our analysis shows that agricultural sources are dominant for both total nitrogen (TN) (58%) and total phosphorus (TP) (46%) deliveries to the Great Lakes. In addition, this study reveals that the surface pathways (sum of overland flow and tile field drainage) dominate nutrient delivery, transporting 66% of the TN and 76% of the TP loads to the US Great Lakes coastline. Importantly, this study provides the first basin-wide estimates of both nonseptic groundwater (TN: 26%; TP: 5%) and septic-plume groundwater (TN: 4%; TP: 2%) deliveries of nutrients to the lakes. This work provides valuable information for environmental managers to target efforts to reduce nutrient loads to the Great Lakes, which could be transferred to other regions worldwide that are facing similar nutrient management challenges.

Linking water age, nitrate export regime, and nitrate isotope biogeochemistry in a tile-drained agricultural field [Dataset

Linking water age, nitrate export regime, and nitrate isotope biogeochemistry in a tile-drained agricultural field [Dataset

When Chemicals Go to the Dark Side

When Chemicals Go to the Dark Side

NIT-DRAIN model to simulate nitrate concentrations and leaching in a tile-drained agricultural field

Agricultural pollution, due to excessive land fertilization, affects the quality of both surface and ground water. This paper presents a conceptual and reservoir-based model that simulates the time variation of nitrate concentrations [NO3-] at the outlet of a subsurface drainage network, referred to herein as “NIT-DRAIN.” The model is based on a simplified scheme of water and nitrate transfer processes by decomposing the soil profile located between the drain and the mid-drain into three interconnected and conceptual compartments. Hence, the fast transfer throughout the macroporosity located above the pipe is described by the first compartment while the low and residual nitrate transfers are managed by the two other compartments. The model assumes that all seasonal nitrogen transformations at the field scale lead to the remaining pool of nitrate available for leaching at the beginning of the winter season (RNBW). This variable is updated by the model at the beginning of each hydrological year. The NIT-DRAIN model requires two input data: the measured or simulated drainage discharge and the RNBW. Seven parameters were introduced to manage nitrate leaching and water flow through the three soil compartments using two different transfer functions. The calibration and validation step (C/V) was performed to assess the performance of the model in reproducing the nitrate concentration observations acquired at Rampillon (355 ha, data for 6 years), located east of Paris, France. The results showed performance criteria of KGE greater than 0.5 and of RMSE less than 5 mgNO3-/l, which confirm the ability of the model to simulate the observed nitrate concentrations with a good agreement. The annual model calibration framework, implemented to assess the parameter variability, confirms the model stability and consistency. However, the use of simulated drainage discharges as input underlines the need to reproduce with accuracy the earlier low discharge values by the drainage model. The innovative management of nitrate transfer through the conceptual compartments based on the annual update of the RNBW variable enables the simulation of the nitrate concentrations with a high performance using a limited number of input data. In addition, the periods of flushing and dilution are clearly identified by the NIT-DRAIN model thanks to the accurate estimation of the nitrate storage variation inside each model compartment.

Rainfall-runoff models compared for tile-drained agricultural fields in the Western Lake Erie Basin, Ohio

Simple models like the curve number method are commonly used to predict runoff volumes from agricultural fields, playing a key role in nutrient transport modeling and watershed management; however, the curve number method has not been evaluated for use in tile-drained fields and it may therefore produce erroneous runoff predictions if applied in these settings. In this study, we evaluate the curve number method at 12 tile-drained research sites in the Western Lake Erie Basin of Ohio. Rainfall and runoff observations at each of these sites were used to calculate curve numbers using six published variations of the curve number method. These were compared to published curve numbers, selected from NRCS tables to correspond to land use in the study sites. In addition to the curve number methods, the complacent-violent method was also used to develop runoff model parameters for the research sites. Methods were compared to one another using Nash-Sutcliffe efficiency, bias, and R-squared. The curve number methods often performed poorly, and sometimes altogether failed to produce a real solution. Of the rainfall-runoff models evaluated, the complacent-violent method produced the most accurate results and should be used in place of the curve number method to make runoff predictions from tile-drained fields.

Nit-Drain Model to Simulate Nitrate Concentrations and Leaching in a Tile-Drained Agricultural Field

Nit-Drain Model to Simulate Nitrate Concentrations and Leaching in a Tile-Drained Agricultural Field

Important factors when simulating the water and nitrogen balance in a tile-drained agricultural field under long-term monitoring

Despite the effectiveness of tile drain systems as a water management practice in naturally poorly drained soils, they facilitate the transport of NO3−-N to surface water bodies. In order to improve the risk assessment of this significant transport under increased applications of N fertilisers in agriculture, it is imperative to delineate the controlling factors and processes. The aim of this study was to acquire such knowledge using the 1D Daisy model to simulate water and N balance based on comprehensive data from a ten-year monitoring study of a tile-drained loamy field in Denmark under the actual crop rotation of winter wheat, sugar beet, spring barley, winter rape and maize. The model simulated the cumulative drainage and NO3−-N leaching over the ten-year period satisfactorily with NSE of 1.00 and 0.87 respectively. While the annual N input to the model was 181 kg N ha−1, an average of 139 kg N ha−1 was harvested in the crop, 22 kg N ha−1 was leached through deep percolation, 17 kg N ha−1 was leached to the tile drains, and 14 kg N ha−1 was lost due to denitrification. Although the model satisfactorily captured the monitored data, the results of this study highlight: (i) the requirement for improved parameterisation of winter crops, (ii) the need to give further consideration in the model to soil surface and macropore processes that govern water infiltration and (iii) that measured and simulated NO3−-N concentrations in the drainage exceeded the limit defined by the European Drinking Water Directive and Nitrates Directive for drinking water and hence improved N management strategies are essential for tile-drained agricultural fields in temperate regions under conventional crop rotations.

Water storage, mixing, and fluxes in tile-drained agricultural fields inferred from stable water isotopes

Quantifying hydrological processes that control the upper critical zone water balance and contaminant transport in drained landscapes is needed, especially as precipitation patterns driving water balance dynamics continue to shift due to climate change. Here, hydrometric data are integrated with stable isotope signatures to quantify water storage, mixing, and fluxes to subsurface tile drainage at an agricultural field located in Indiana, USA. Over a 2-yr period, precipitation, soil water sampled with suction lysimeters (10–80 cm depth), groundwater (below tile depth; >1 m), and subsurface tile discharge were sampled 97 times. Results showed that isotopic variability in near-surface soil water (10–20 cm) reflected the seasonality of the precipitation input signal, while groundwater values were relatively consistent indicating that water stored below tile drain depth was recharged during winter. Soil water between 20 and 80 cm depth was a mixture of near-surface water and groundwater that varied seasonally depending upon groundwater hydrodynamics. Mean transit time of water ranged from 12 to 20 d for 10-cm soil water to 225–334 d for groundwater, with tile drainage exhibiting a mean transit time of 245 d. Both two- and three-component hydrograph separation indicated that groundwater was the primary source of water to the tile drain followed by soil water. Tile drain hydrograph response (i.e., celerity) was largely controlled by antecedent wetness. Comparison of tile drain celerities and velocities revealed however varying mechanisms controlling hydrograph response across a range of environmental conditions. Data sets of both water and tracer flux were, thus, useful to track the spatiotemporal variability of water fluxes within and from the critical zone. Such data provide valuable information to improve the representation of critical zone processes in these landscapes within spatially distributed hydrological models.

Effects of three types of amendments in woodchip-denitrifying bioreactors for tile drainage water treatment

Excess nutrient inflow from tile-drained agricultural fields significantly contributes to the pollution of surface waters in Lithuania. Therefore, two parallel experiments, each using three pilot-scale woodchip-denitrifying bioreactors, were conducted for 2.5- and 1.5-year periods to test whether activated carbon (C) and flaxseed cake (both 10% v/v) and biochar (10% v/v and 20% v/v made of deciduous wood) additives, respectively, can enhance the removal of nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P) from tile drainage water and reduce C losses from bioreactors.Higher NO3-N removal efficiencies and rates were achieved in bioreactors amended with activated C (10% v/v) and biochar (20% v/v) than in those amended with woodchips alone. Bioreactors amended with 10% v/v flaxseed cake and 10% v/v biochar showed no significant differences from those amended with woodchips alone. The ability to enhance NO3-N removal by the addition of activated C and biochar was particularly evident at lower temperatures (≤10.0 °C). Moreover, activated C has proven to be an effective additive capable of substantially reducing C losses and supporting the lowest C/N (i.e., carbon loss to N removal) ratios. To a lesser extent, these capabilities were also characteristic of biochar-amended woodchips, whereas the addition of flaxseed cake resulted in the highest C/N removal ratios. These experiments also revealed that woodchips, alone or amended with flaxseed cake or activated C, are a suitable media that can allow PO4-P removal. However, the addition of biochar demonstrated large releases of PO4-P and other inorganic elements. Biochar itself was found to be a potential PO4-P source that poses a risk of large startup and over time releases.Although the addition of activated C under non-N-limiting conditions resulted in undesirable sulfate-sulfur (SO4-S) reduction (this occurred in all study bioreactors), the experiments demonstrated that the addition of activated C can be used to design a more efficient bioreactor with prolonged longevity and higher NO3-N and PO4-P removal capacities. Owing to the risk of adverse environmental effects (i.e., decreased pH, large exports of inorganic elements or organic C), the application of biochar or flaxseed cake additives in woodchip-denitrifying bioreactors proved to be limited for tile water treatment.

Where did the soil go? Quantifying one year of soil erosion on a steep tile-drained agricultural field

Distributed measurements of agricultural erosion at the farm-scale are needed to evaluate both the on and off-site impacts of sediment redistribution. While best management practices have been shown to reduce surface erosion rates and improve water quality, their farm-scale effects can be difficult to quantify. In this study we use imagery from an unmanned aerial vehicle (UAV) and structure-from-motion multi-view stereo (SfM-MVS) to quantify erosion rates and their effects on crop yield across a 15.9-ha agricultural field. Our results highlight that the installation of catch basins were able to stop 159.52 t of sediment and associated nutrients from entering the waterway adjacent to the study site over the course of one year, corresponding to an erosion rate of 18.83 t ha−1 yr−1 across six study basins. Poor soil structure resulting from downslope tillage reduced crop yields on topographic shoulders of the study site, while accelerated water erosion processes were responsible for large areas of washout that caused highly variable crop growth in footslopes. The highest crop yields were associated with backslopes and topographically flat regions of the field which experienced minimal erosion. Change-detection results showed that UAV imagery was able to reliably quantify depositional plumes and was comparable to that of a terrestrial laser scanner (TLS) using a ± 0.04 m confidence interval.

Formation and dissolution of salt crusts as a rapid way of nitrate mobilization in a tile-drained agricultural field under a temperate climate

Agriculture is widely recognized as one of the human activities that have a major impact on the pollution of water resources. In agricultural fields, the formation of salt crusts during dry periods and their fast dissolution due to irrigation or rainfall events can induce the leaching of water with an elevated content of dissolved species towards surface and ground waters. This process is rather common in arid environments but it also occurs in coastal plains in temperate environments. The formation of salt crusts was studied in a 6.3-ha experimental site located in the Po River Delta (Northern Italy). The soil, consisting of interfluvial silty-clay deposits recently reclaimed and equipped with tile drains to avoid water-logging conditions, was investigated for vertical spatial heterogeneity via depth profiles and for horizontal spatial heterogeneity collecting numerous surface soil samples. Extreme drought conditions were recorded over the monitoring period (summer–autumn 2012), leading to soil fracturing and then to fast water percolation during the first rainfall events in autumn. Major ion concentration, measured in pore-water, showed nitrate peaks of several grams per litre, suggesting the dissolution of nitrate salts. Results from this study highlighted the following: (i) that the fertilizers applied to the filed site were evapoconcentrated in the top soil; (ii) a marked spatial heterogeneity in the salt crust formation, which was unevenly distributed over the field with a preferential appearance in the hollows; and (iii) a rapid mobilization of nitrate towards tile drains after the first rainfall events, due to preferential flow through soil cracks developed during the summer season.

Modeling water outflow from tile-drained agricultural fields

The estimation of the pollution risk of surface and ground water with plant protection products applied on fields depends highly on the reliable prediction of the water outflows over (surface runoff) and through (discharge through sub-surface drainage systems) the soil. In previous studies, water movement through the soil has been simulated mainly using physically-based models. The most frequently used models for predicting soil water movement are MACRO, HYDRUS-1D/2D and Root Zone Water Quality Model. However, these models are difficult to apply to a small portion of land due to the information required about the soil and climate, which are difficult to obtain for each plot separately.In this paper, we focus on improving the performance and applicability of water outflow modeling by using a modeling approach based on machine learning techniques. It allows us to overcome the major drawbacks of physically-based models e.g., the complexity and difficulty of obtaining the information necessary for the calibration and the validation, by learning models from data collected from experimental fields that are representative for a wider area (region).We evaluate the proposed approach on data obtained from the La Jaillière experimental site, located in Western France. This experimental site represents one of the ten scenarios contained in the MACRO system. Our study focuses on two types of water outflows: discharge through sub-surface drainage systems and surface runoff.The results show that the proposed modeling approach successfully extracts knowledge from the collected data, avoiding the need to provide the information for calibration and validation of physically-based models. In addition, we compare the overall performance of the learned models with the performance of existing models MACRO and RZWQM. The comparison shows overall improvement in the prediction of discharge through sub-surface drainage systems, and partial improvement in the prediction of the surface runoff, in years with intensive rainfall.

Characterizing phosphorus dynamics in tile-drained agricultural fields of eastern Wisconsin

Summary Artificial subsurface drainage provides an avenue for the rapid transfer of phosphorus (P) from agricultural fields to surface waters. This is of particular interest in eastern Wisconsin, where there is a concentrated population of dairy farms and high clay content soils prone to macropore development. Through collaboration with private landowners, surface and tile drainage was measured and analyzed for dissolved reactive P (DRP) and total P (TP) losses at four field sites in eastern Wisconsin between 2005 and 2009. These sites, which received frequent manure applications, represent a range of crop management practices which include: two chisel plowed corn fields (CP1, CP2), a no-till corn–soybean field (NT), and a grazed pasture (GP). Subsurface drainage was the dominant pathway of water loss at each site accounting for 66–96% of total water discharge. Average annual flow-weighted (FW) TP concentrations were 0.88, 0.57, 0.21, and 1.32 mg L −1 for sites CP1, CP2, NT, and GP, respectively. Low TP concentrations at the NT site were due to tile drain interception of groundwater flow where large volumes of tile drainage water diluted the FW-TP concentrations. Subsurface pathways contributed between 17% and 41% of the TP loss across sites. On a drainage event basis, total drainage explained between 36% and 72% of the event DRP loads across CP1, CP2, and GP; there was no relationship between event drainflow and event DRP load at the NT site. Manure applications did not consistently increase P concentrations in drainflow, but annual FW-P concentrations were greater in years receiving manure applications compared to years without manure application. Based on these field measures, P losses from tile drainage must be integrated into field level P budgets and P loss calculations on heavily manured soils, while also acknowledging the unique drainage patterns observed in eastern Wisconsin.

Estimation of Nonpoint Source Nitrate Concentrations in Indiana Rivers Based on Agricultural Drainage in the Watershed

AbstractSubsurface tile‐drained agricultural fields are known to be important contributors to nitrate in surface water in the Midwest, but the effect of these fields on nitrate at the watershed scale is difficult to quantify. Data for 25 watersheds monitored by the Indiana Department of Environmental Management and located near a U.S. Geological Survey stream gage were used to investigate the relationship between flow‐weighted mean concentration (FWMC) of nitrate‐N and the subsurface tile‐drained area (DA) of the watershed. The tile DA was estimated from soil drainage class, land use, and slope. Nitrate loads from point sources were estimated based on reported flows of major permitted facilities with mean nitrate‐N concentrations from published sources. Linear regression models exhibited a statistically significant relationship between annual/monthly nonpoint source (NPS) nitrate‐N and DA percentage. The annual model explained 71% of the variation in FWMC of nitrate‐N. The annual and monthly models were tested in 10 additional watersheds, most with absolute errors within 1 mg/l in the predicted FWMC. These models can be used to estimate NPS nitrate for unmonitored watersheds in similar areas, especially for drained agricultural areas where model performance was strongest, and to predict the nitrate reduction when various tile drainage management techniques are employed.

Occurrence of Tylosin-Resistant Enterococci in Swine Manure and Tile Drainage Systems under No-Till Management

The sub-therapeutic use of tylosin in commercial swine operations can produce selective pressure for the development of antibiotic resistant bacteria. When swine manure from such operations is applied on drained agricultural fields, it can lead to transport and dissemination of resistant microorganisms through soils, into tile drainage lines, and ultimately into surface waters. The objective of this study was to investigate the occurrence and transport of tylosin-resistant enterococci from two different tile-drained agricultural fields receiving biennial swine-waste applications during different seasons. Resistance to tylosin in manure, soil, and tile water was investigated by a phenotype-based method and polymerase chain reaction. All enterococci in manure samples obtained from the spring application were resistant to tylosin, whereas 68 % of the total enterococci from the fall application were resistant to tylosin. Average concentrations of total and tylosin-resistant enterococci in soil samples over the two sampling periods were 9.8 × 103 and 7.5 × 103 cfu/g of soil, respectively. Total and tylosin-resistant enterococci concentrations in tile water collected from the two plots were significantly different (P < 0.05) during the spring and fall experiments. In drainage water, the total enterococci peaked at 2.6 × 103 and 5.0 × 103 cfu/100 mL for the fall and spring experiments, respectively, while tylosin-resistant enterococci peaked at 1.4 × 103 and 1.2 × 103 cfu/100 mL for the fall and spring experiments, respectively. Total suspended solid concentrations in tile water were correlated with enterococci concentrations when base flow was present. Seven out of eight macrolide-resistance genes tested were detected (ermA, ermB, ermC, ermF, ermT, ermX, and msrA, but not mefA). Five of these genes (ermB, ermC, ermF, ermT, and msrA) were detected in at least 9 % of the samples. On average, most of the phenotypically resistant isolates (97 %) harbored msrA, while only 10 % contained ermT and 9 % contained ermC. Genes containing ermF and ermB were detected in 78 % and 69 % of resistant isolates, respectively. Only 2 % of the total isolates (n = 4) harbored all five genes. Of the isolates collected from manure, soil, and water samples, 12 % were confirmed as Enterococcus faecalis with 96 % of the confirmed E. faecalis isolates containing multiple resistance genes. The findings from this study are useful to provide baseline information on the export of total and tylosin-resistant enterococci during rainfall events from manured, tile-drained agricultural fields of the Upper Midwestern USA.

Modeling the influence of tile drainage flow and tile spacing on phosphorus losses from two agricultural fields in southern Québec

Tile drainage is a widely adopted water management practice in the eastern Canadian provinces of Québec and Ontario. It aims to improve the productivity of poorly drained agricultural fields. Nevertheless, studies have also shown that subsurface drainage is a significant pollution pathway to surface water. This study was undertaken to evaluate the effect of tile drain spacing on surface runoff, subsurface drainage flows, and phosphorus (P) loss from two tile-drained agricultural fields located near Bedford, Québec. Field data were used with the DRAINMOD model, and in developed regression models in order to perform the analysis. Both DRAINMOD and the regression models showed good performance. Simulation results indicated that when lateral tile drain spacing is increased, the volume of subsurface drain flow decreases, and the volume of surface runoff increases, at sites with sandy and clay loam soils. For every 5 m increase in drain spacing, total phosphorus (TP) loads in subsurface drainage decreased by 6% at a site with sandy loam soil, and increased by 20% at a site with clay loam soil. TP loads in surface runoff increased as a result of increased drain spacing.

Rainwater lens dynamics and mixing between infiltrating rainwater and upward saline groundwater seepage beneath a tile-drained agricultural field

Thin rainwater lenses (RW-lenses) near the land surface are often the only source of freshwater in agricultural areas with regionally-extensive brackish to saline groundwater. The seasonal and inter-annual dynamics of these lenses are poorly known. Here this knowledge gap is addressed by investigating the transient flow and mixing processes in RW-lenses beneath two tile-drained agricultural fields in the Netherlands. Evidence of RW-lens dynamics was systematically collected by monthly ground- and soil water sampling, in combination with daily observations of water table elevation, drain tile discharge and drain water salinity. Based on these data, and numerical modeling of the key lens characteristics, a conceptual model of seasonal lens dynamics is presented. It is found that variations in the position of the mixing zone and mixing zone salinities are small and vary on a seasonal timescale, which is attributed to the slow transient oscillatory flow regime in the deepest part of the lens. The flow and mixing processes are faster near the water table, which responds to recharge and evapotranspiration at a timescale less than a day. Variations of drain tile discharge and drain water salinity are also very dynamic as they respond to individual rain events. Salinities of soil water can become significantly higher than in the groundwater. This is attributed to the combined effect of capillary rise of saline groundwater during dry periods and incomplete flushing by infiltrating freshwater due to preferential flow through cracks in the soil. The results of this study are the key to understanding the potential impact of future climate change and to designing effective mitigating measures such as adapting tile-drainage systems to ensure the future availability of freshwater for agriculture.

Hormone loads exported by a tile-drained agroecosystem receiving animal wastes

Little is known regarding hormone export from tile-drained agricultural fields despite the widespread presence of tile drains in the Midwestern United States. By intensively measuring water flow rates and hormone concentrations in four subsurface tile drains and three receiving ditches at a working Midwest farm, hormone fluxes and loads from the tile-drained fields were quantified. Before and during the 17-month study period (January 2009 – May 2010), the associated farm fields received various animal waste applications (beef, dairy, poultry, sheep, and swine). Hormones monitored included the estrogens17β- and 17α-estradiol, estrone, and estriol; the natural androgens testosterone, and androstenedione; and the synthetic androgens 17β- and 17α-trenbolone, and trendione. Hormone loads measured in the ditches for three drainage areas during the entire 17-month study period were in ranges of 16–58 mg/ha for total estrogens, 6.8–19 mg/ha for natural androgens, and 4.2–44 mg/ha for synthetic androgens. Because higher hormone concentrations generally occurred during discrete periods of increased flow, high flow rates often were associated with a disproportionately high hormone flux. For example, 80% of total estrogens and natural androgens exported into the ditches occurred during only 9–26% of the study period, coinciding with the most significant storm events. In addition, hormone fluxes were highest during storm events that occurred shortly after animal waste applications. Therefore, to effectively reduce hormone loads exported to downstream aquatic ecosystems in the absence of any application reduction, the short periods during which high-flow events occur must be targeted. Copyright © 2012 John Wiley & Sons, Ltd.

Water Quality Modeling of Two Agricultural Fields in Southern Quebec Using SWAT

To study the dynamics of nutrient transport at the field scale, we collected data from two tile-drained agricultural fields in the Pike River watershed of southern Quebec. A two-year data set was used to calibrate and validate the Soil and Water Assessment Tool (SWAT) for sediment, nitrate, and phosphorus loads exiting the field through surface runoff and tile drainage. We found that SWAT output on water quality required an accurate estimation of the timing and form of field management practices employed. After calibration, the monthly coefficients of performance (Cp) over four site-years varied from 0.23 to 0.89 for sediment loads, from 0.48 to 1.35 for nitrate loads, and from 0.38 to 0.67 for total phosphorus loads. Subsurface nitrate loads accounted for 97.7% and 86.7% of the total nitrate yield, while particulate phosphorus accounted for 61.2% and 87.7% of total phosphorus load on sites 1 and 2, respectively. SWAT underestimated nitrate loads in subsurface drainage during spring snowmelt and large storms. Sediments and particulate phosphorus predictions were most accurate of all simulated parameters, whereas dissolved phosphorus was marginally overestimated year-round. Overall, SWAT satisfactorily reproduced field observations for sediment and nutrient transport and could be used to compare the impacts of implementing different best management practices (BMP) on individual fields for the study site.