Tile-drained Agricultural Watershed Research Articles

Modeling and assessing water and nutrient balances in a tile-drained agricultural watershed in the U.S. Corn Belt

Identifying the key processes and primary sources of water and nutrient losses is essential for water quantity and quality management in watersheds. This is especially true in the U.S. Corn Belt, which has been recognized as the primary region contributing nutrient loads to the Great Lakes and the Gulf of Mexico. A SWAT (Soil and Water Assessment Tool) model simulation was set up in an agricultural watershed with about 50% tile drainage area in the U.S. Corn Belt to study the water and nutrient balance components for the whole watershed and the corn-soybean rotation system. The SWAT model was improved to consider additional nitrogen and phosphorus loss paths from the soil. The model was comprehensively calibrated and validated for simulating monthly stream flow, total suspended solids (TSS), nutrient loads (including total Kjeldahl nitrogen (TKN), nitrate and nitrite nitrogen (NOx-N), total phosphorus (TP) and orthophosphate phosphorus (orthoP)), actual evapotranspiration (ETa), leaf area index (LAI) and annual crop yields in the watershed from 2011 to 2019. Results showed the model performance was very good for simulating the stream flow, TSS and ETa, and acceptable for nutrient loads, LAI and crop yields. ETa, surface runoff, lateral soil flow, tile drainage and percolation respectively accounted for 65%, 15%, 2%, 8% and 9% of the precipitation. Fertilizer was the main source of nitrogen and phosphorus input to the watershed, and harvested crops were the main paths removing nutrients. Surface runoff, tile drainage and percolation each contributed about 30% of total nitrogen losses to water, with surface runoff being dominated by organic nitrogen while tile drainage and percolation were dominated by nitrate nitrogen. Phosphorus losses were mainly through surface runoff, which resulted in 66% of the total losses and was dominated by organic phosphorus and soluble phosphorus. Representing about 49% of the watershed area, the corn-soybean rotation system contributed 83% and 88% of the total nitrogen and phosphorus inputs, respectively, to the watershed, as well as 64% and 46% of the nitrogen and phosphorus losses to the water system, respectively. The non-growing season (October to the next April) was identified as the critical period resulting in water and nutrient losses due to low evapotranspiration and plant uptake. Targeted management strategies for reducing nutrient loads in key hydrological paths were suggested.

Potential for saturated riparian buffers to treat tile drainage among 32 watersheds representing Iowa landscapes

The saturated riparian buffer (SRB) is a new and cost-effective conservation practice that diverts agricultural tile drainage toward subsurface discharge within riparian buffers to achieve nitrate (NO3-N) removal. Conservation planners want to understand the potential role of the SRB practice for reducing NO3-N loads from tile-drained agricultural watersheds. The Agricultural Conservation Planning Framework (ACPF) includes a tool for identifying riparian zones where the SRB practice can be installed with minimal risks of unintended consequences (i.e., crop inundation and streambank failure). Watershed assessment of the potential role for SRBs, however, must identify where SRB-suited sites can actually receive drainage from tile-drained fields. This study compared the extent of SRB-suited riparian sites among 32 Iowa watersheds, and estimated the proportion of each watershed that was tile drained and located above SRB-suited riparian zones. Results showed the extent of sites suited for SRBs did not significantly differ among three Major Land Resource Areas (MLRAs) in Iowa, from which the selected watersheds were randomly chosen. Most watersheds had suitable sites along 30% to 70% of streambank lengths, where tile drainage from 15% to 40% of the watershed areas could be diverted, based on estimated extents of tile drainage above suitable sites. Therefore, the SRB has an important potential role for water quality improvement in many tile-drained watersheds in Iowa. However, the SRB practice is not readily designed for treating drainage from headwater catchments, which frequently comprised more than 30% of watershed areas in headwater streams of north central Iowa (MLRA 103), where tile drainage is extensive.

Development of a distributed hydrological model to facilitate watershed management

ABSTRACTTo facilitate precise and cost-effective watershed management, a simple yet spatially and temporally distributed hydrological model (DHM-WM) was developed. The DHM-WM is based on the Mishra-Singh version of the curve number method, with several modifications: The spatial distribution of soil moisture was considered in moisture updating; the travel time of surface runoff was calculated on a grid cell basis for routing; a simple tile flow module was included as an option. The DHM-WM was tested on a tile-drained agricultural watershed in Indiana, USA. The model with the tile flow module performed well in the study area, providing a balanced water budget and reasonable flow partitioning. The daily coefficient of determination and Nash-Sutcliffe coefficient were 0.58 and 0.56, for the calibration period, and 0.63 and 0.62 for the validation period. The DHM-WM also provides detailed information about the source areas of flow components, the travel time and pathways of surface runoff.EDITOR A. Castellarin; ASSOCIATE EDITOR F.-J. Chang

An Integrated Landscape Designed for Commodity and Bioenergy Crops for a Tile-Drained Agricultural Watershed.

Locating bioenergy crops on strategically selected subfield areas of marginal interest for commodity agriculture can increase environmental sustainability. Location and choice of bioenergy crops should improve environmental benefits with minimal disruption of current food production systems. We identified subfield soils of a tile-drained agricultural watershed as marginal if they had areas of low crop productivity index (CPI), were susceptible to nitrate-nitrogen (NO-N) leaching, or were susceptible to at least two other forms of environmental degradation (marginal areas). In the test watershed (Indian Creek watershed, IL) with annual precipitation of 852 mm, 3% of soils were CPI areas and 22% were marginal areas. The Soil and Water Assessment Tool was used to forecast the impact of growing switchgrass ( L.), willow ( spp.), and big bluestem ( Vitman) in these subfield areas on annual grain yields, NO-N and sediment exports, and water yield. Simulated conversion of CPI areas from current land use to bioenergy crops had no significant ( 0.05) impact on grain production and reduced NO-N and sediment exports by 5.0 to 6.0% and 3.0%, respectively. Conversion of marginal areas from current land use to switchgrass forecasted the production of 34,000 t of biomass and reductions in NO-N (26.0%) and sediment (33.0%) exports. Alternatively, conversion of marginal areas from current land use to willow forecasted similar reductions as switchgrass for sediment but significantly ( 0.01) lower reductions in annual NO-N export (18.0 vs. 26.0%).

Using climate change scenarios to evaluate future effectiveness of potential wetlands in mitigating high flows in a Midwestern U.S. watershed

The Midwestern United States have seen increased flooding and droughts from climate change, urban development, deforestation, and wetlands removal. Adding new wetlands in the landscape have been proposed as a conservation strategy, especially in tile-drained agricultural watersheds, to increase upland storage of runoff and reduce peak flows. The goal of this study was to evaluate the long-term performance of a set of potential wetlands identified in the Eagle Creek Watershed in central Indiana, U.S., to reduce a range of high flows estimated from future climate scenarios. The Soil and Water Assessment Tool model was forced with bias-corrected climate projections from the North American Regional Climate Change Assessment Program to evaluate the impacts of climate change on watershed hydrology and peak flows. The ensemble of climate projections predicted both increase and decrease in magnitudes of the 5% exceedance flow from the past (1971–2000) to the future (2041–2070) time period. However, the model predicted that if the potential wetlands existed in these time periods then the magnitude of the 5% exceedance flow would be reduced by approximately 0.5–1.5m3/s across all climate projections and for both the past and future periods. These identified potential wetlands, which occupied only approximately 1.5% of the watershed area but received runoff from approximately 29% of the watershed area, were also found to reduce peak flows by up to 20–60m3/s (i.e., 15–20% of the reference peak flows for a watershed without these wetlands). The wetlands were also found to decrease the frequency of high peak flows. Wetlands proved to be a robust solution for peak flow reduction, producing consistent reductions from the past to future time periods and across all climate projections. The methodology used in this study to incorporate climate change into hydrologic models to evaluate conservation practices could also be applied to other watersheds and other conservation practices for better long-term watershed management decisions.

Chloride Sources and Losses in Two Tile-Drained Agricultural Watersheds.

Chloride is a relatively unreactive plant nutrient that has long been used as a biogeochemical tracer but also can be a pollutant causing aquatic biology impacts when concentrations are high, typically from rock salt applications used for deicing roads. Chloride inputs to watersheds are most often from atmospheric deposition, road salt, or agricultural fertilizer, although studies on agricultural watersheds with large fertilizer inputs are few. We used long-term (21 and 17 yr) chloride water quality data in two rivers of east-central Illinois to better understand chloride biogeochemistry in two agricultural watersheds (Embarras and Kaskaskia), the former with a larger urban land use and both with extensive tile drainage. During our sampling period, the average chloride concentration was 23.7 and 20.9 mg L in the Embarras and Kaskaskia Rivers, respectively. Annual fluxes of chloride were 72.5 and 61.2 kg ha yr in the Embarras and Kaskaskia watersheds, respectively. In both watersheds, fertilizer chloride was the dominant input (∼49 kg ha yr), with road salt likely the other major source (23.2 and 7.2 kg ha yr for the Embarras and Kaskaskia watersheds, respectively). Combining our monitoring data with earlier published data on the Embarras River showed an increase in chloride concentrations as potash use increased in Illinois during the 1960s and 1970s with a lag of about 2 to 6 yr to changes in potash inputs based on a multiple-regression model. In these agricultural watersheds, riverine chloride responds relatively quickly to potash fertilization as a result of tile-drainage.

SWATDRAIN, a new model to simulate the hydrology of agricultural Lands, model development and evaluation

In this study, a new model was developed by fully incorporating the DRAINMOD model into the Soil and Water Assessment Tool (SWAT). In this modeling approach, surface flow is simulated using SWAT model and subsurface flow is estimated using the DRAINMOD model. The newly developed model, referred to as SWATDRAIN, has the potential to perform simulations of multiple scenarios such as controlled drainage, subsurface irrigation and wastewater treatment to determine cost-effective water management at the watershed scale. The model was evaluated for Green Belt Watershed, located in southern Ontario. Measured tile drainage and water table depth data from this watershed were used to evaluate the capability of the new model to simulate water balance components for this tile-drained agricultural watershed. Simulations were carried out over the period 1991–1993; 1991 and 1992 data were used for model calibration and 1993 data were used for validation. During both calibration and validation periods, SWATDRAIN simulated the watershed hydrologic response, the water table depth, and tile flow very well. Model accuracy statistics for monthly and daily water table depth over the validation period were, respectively, 0.86 and 0.70 for Coefficient of Determination, 0.11 and 2.90 for Percent Bias, and 0.80 and 0.67 for the Nash Sutcliffe Efficiency. Model accuracy statistics for events, monthly and daily tile drainage over the validation period were, respectively, 0.86, 0.88 and 0.70 for R2, 11.7, 13.26 and 13.26 for Percent Bias, and 0.82, 0.86 and 0.69 for Nash Sutcliffe Efficiency. This clearly demonstrates that integrated DRAINMOD approach in SWAT provides an effective water management tool for tile-drained watersheds.

Contribution of tile drains to basin discharge and nitrogen export in a headwater agricultural watershed

Nitrogen (N) fluxes from tile-drained agricultural watersheds have been implicated in water quality studies of the Mississippi River Basin, but the contribution of tile drains to N export in headwater watersheds is not well understood. The objective of this study was to ascertain seasonal and annual contributions of tile drainage to watershed discharge and N loading. Discharge and N concentration were measured at the outlet of an Ohio, USA agricultural headwater watershed and all tile drain outlets in the watershed from 2005 through 2012. Results showed that tile discharge accounted for 56% of annual watershed discharge over the 8-year study. Nitrate–N was the dominant form of N exported in both watershed and tile discharge with concentrations ranging from 0.1 to 70.5mgL−1. Watershed NO3–N concentration increased with increasing discharge up to the 75th percentile of flow where NO3–N concentrations reached an asymptote. This pattern indicates that tile contributions to stream NO3–N concentration were increasingly important as discharge increased, but other sources of water (e.g., precipitation, surface runoff) likely decreased stream NO3–N concentrations at the highest discharge rates. Annual watershed NO3–N load ranged from 12.4 to 39.6kgha−1, with tile drainage contributing between 44 and 82% (mean: 62%) of annual watershed NO3–N export. Study results indicate that tile drainage is the primary factor controlling watershed discharge and N, especially NO3–N, export in systematically tile-drained agricultural headwater watersheds. Thus, in these landscapes, management practices that decrease NO3–N leaching to tile drains (e.g., reduced N application rates, cover crops) and reduce NO3–N loads (e.g., drainage water management) have the potential to improve downstream water quality.

Pesticide contamination interception strategy and removal efficiency in forest buffer and artificial wetland in a tile-drained agricultural watershed

Pesticide pollution is a major threat to aquatic ecosystems that can be mitigated through complementary actions including buffer zones (BZs). This paper discusses the results of 3yr of field-scale monitoring of the concentration and load transfer of 16 pesticides out of a tile-drained catchment (Bray, France) and their reduction through two BZ: an artificial wetland (AW) and a forest buffer (FB). Typically, the highest concentrations were measured in the first flows following pesticide applications or resuming after periods of low or no flow. An open/close water management strategy was implemented to operate the parallel BZ based on pesticide applications by the farmer. The strategy was efficient in intercepting molecules whose highest concentrations occurred during the first flows following application. Inlet vs. outlet pesticide load reductions ranged from 45% to 96% (AW) and from −32% to 100% (FB) depending on the pesticide molecule and the hydrological year. Partly reversible adsorption was a dominant process explaining pesticide removal; whereas, degradation occurred for sufficiently long water retention time. Apart from the least sorbing molecules (e.g., isoproturon), BZ can partially remove pesticide pollution.

Impact of Climate Change on the Hydrology and Nitrogen Pollution in a Tile-Drained Agricultural Watershed in Eastern Canada

The potential effects of climate change on the hydrology and nitrogen pollution of an agricultural watershed are predicted using the DRAIN-WARMF model. This newly developed, physically based hydrological model is applied on the St. Esprit watershed in southwestern Quebec, Canada. Under the assumption of no changes in land cover and land management, the model is applied in order to simulate annual, seasonal, and monthly changes in surface and subsurface flows and NO3-N loads at the outlet of the watershed under current and future climate conditions. The climate scenario under consideration in this study for 1961 to 2100 is based on projections from the Canadian Regional Climate Model (CRCM). The simulation results from the CRCM model suggest an increase in temperature and precipitation in the region being studied. These changes result in a significant increase in simulated mean annual and seasonal flow in the watershed. Moreover, water quality simulations under future climatic conditions show a significant increase in annual and seasonal NO3-N losses.

Evaluating Agricultural Best Management Practices in Tile-Drained Subwatersheds of the Mackinaw River, Illinois

Best management practices (BMPs) are widely promoted in agricultural watersheds as a means of improving water quality and ameliorating altered hydrology. We used a paired watershed approach to evaluate whether focused outreach could increase BMP implementation rates and whether BMPs could induce watershed-scale (4000 ha) changes in nutrients, suspended sediment concentrations, or hydrology in an agricultural watershed in central Illinois. Land use was >90% row crop agriculture with extensive subsurface tile drainage. Outreach successfully increased BMP implementation rates for grassed waterways, stream buffers, and strip-tillage within the treatment watershed, which are designed to reduce surface runoff and soil erosion. No significant changes in nitrate-nitrogen (NO-N), total phosphorus (TP), dissolved reactive phosphorus, total suspended sediment (TSS), or hydrology were observed after implementation of these BMPs over 7 yr of monitoring. Annual NO-N export (39-299 Mg) in the two watersheds was equally exported during baseflow and stormflow. Mean annual TP export was similar between the watersheds (3.8 Mg) and was greater for TSS in the treatment (1626 ± 497 Mg) than in the reference (940 ± 327 Mg) watershed. Export of TP and TSS was primarily due to stormflow (>85%). Results suggest that the BMPs established during this study were not adequate to override nutrient export from subsurface drainage tiles. Conservation planning in tile-drained agricultural watersheds will require a combination of surface-water BMPs and conservation practices that intercept and retain subsurface agricultural runoff. Our study emphasizes the need to measure conservation outcomes and not just implementation rates of conservation practices.

Development of DRAIN–WARMF model to simulate flow and nitrogen transport in a tile-drained agricultural watershed in Eastern Canada

▶ Development of a new distributed watershed hydrologic/water quality model for simulating the hydrologic processes and the nitrogen fate and transport in tile-drained watersheds. ▶ The model is capable of simulating flow in watersheds which experience periodic freezing and thawing conditions. ▶ The new model uses a distributed parameter approach by subdividing the watershed into cells to calculate tile-flow at each cell. ▶ The new model provides a method for simulating the hydrology of tile-drained watersheds where subsurface drainage systems are the main mechanisms for removing excess water from the root zone . A new watershed model, DRAIN–WARMF, was developed to simulate the hydrologic processes and the nitrogen fate and transport that occur in small, predominantly subsurface-drained, agricultural watersheds that experience periodic freezing and thawing conditions. In this modeling approach, surface flow is simulated using a watershed scale model, WARMF, and subsurface flow is estimated using a field-scale model for subsurface-drained shallow water table fields, DRAINMOD 5.1. For subsurface flow calculations, the watershed is subdivided into uniform cells, and DRAINMOD is run on each cell with inputs based on the individual hydrologic characteristics of the cell. The coupling results in a distributed parameter model that calculates the total flow at the outlet of a watershed as well as the nitrogen losses. The model was evaluated for the St. Esprit watershed, located approximately 50 km northeast of Montreal. Simulations were carried out from 1994 to 1996; data from 1994 and 1995 was used for model calibration and data from 1996 was used for model validation. The new model was able to adequately simulate the hydrologic response and nitrate losses at the outlet of the watershed. Comparing the observed daily flow/monthly nitrogen with the model's outputs over the validation period returned an R 2 value of 0.74/0.86 and modeling efficiency of 0.72/0.83. This clearly demonstrates the model's ability to simulate hydrology and nitrogen losses occurring in small agricultural watersheds in cold climates.

Nitrogen Mass Balance of a Tile‐drained Agricultural Watershed in East‐Central Illinois

Simple nitrogen (N) input/output balance calculations in agricultural systems are used to evaluate performance of nutrient management; however, they generally rely on extensive assumptions that do not consider leaching, denitrification, or annual depletion of soil N. We constructed a relatively complete N mass balance for the Big Ditch watershed, an extensively tile-drained agricultural watershed in east-central Illinois. We conducted direct measurements of a wide range of N pools and fluxes for a 2-yr period, including soil N mineralization, soybean N(2) fixation, tile and river N loads, and ground water and in-stream denitrification. Fertilizer N inputs were from a survey of the watershed and yield data from county estimates that were combined with estimated protein contents to obtain grain N. By using maize fertilizer recovery and soybean N(2) fixation to estimate total grain N derived from soil, we calculated the explicit change in soil N storage each year. Overall, fertilizer N and soybean N(2) fixation dominated inputs, and total grain export dominated outputs. Precipitation during 2001 was below average (78 cm), whereas precipitation in 2002 exceeded the 30-yr average of 97 cm; monthly rainfall was above average in April, May, and June of 2002, which flooded fields and produced large tile and riverine N loads. In 2001, watershed inputs were greater than outputs, suggesting that carryover of N to the subsequent year may occur. In 2002, total inputs were less than outputs due to large leaching losses and likely substantial field denitrification. The explicit change in soil storage (67 kg N ha(-1)) offsets this balance shortfall. Although 2002 was climatically unusual, with current production trends of greater maize grain yields with less fertilizer N, soil N depletion is likely to occur in maize/soybean rotations, especially in years with above-average precipitation or extremely wet spring periods.

Phosphorus Transport Pathways to Streams in Tile‐Drained Agricultural Watersheds

Agriculture is a major nonpoint source of phosphorus (P) in the Midwest, but how surface runoff and tile drainage interact to affect temporal concentrations and fluxes of both dissolved and particulate P remains unclear. Our objective was to determine the dominant form of P in streams (dissolved or particulate) and identify the mode of transport of this P from fields to streams in tile-drained agricultural watersheds. We measured dissolved reactive P (DRP) and total P (TP) concentrations and loads in stream and tile water in the upper reaches of three watersheds in east-central Illinois (Embarras River, Lake Fork of the Kaskaskia River, and Big Ditch of the Sangamon River). For all 16 water year by watershed combinations examined, annual flow-weighted mean TP concentrations were >0.1 mg L(-1), and seven water year by watershed combinations exceeded 0.2 mg L(-1). Concentrations of DRP and particulate P (PP) increased with stream discharge; however, particulate P was the dominant form during overland runoff events, which greatly affected annual TP loads. Concentrations of DRP and PP in tiles increased with discharge, indicating tiles were a source of P to streams. Across watersheds, the greatest DRP concentrations (as high as 1.25 mg L(-1)) were associated with a precipitation event that followed widespread application of P fertilizer on frozen soils. Although eliminating this practice would reduce the potential for overland runoff of P, soil erosion and tile drainage would continue to be important transport pathways of P to streams in east-central Illinois.