Research Project: Assessment of Sediment and Chemical Transport Processes for Developing and Improving Agricultural Conservation Practices

Location: National Soil Erosion Research Laboratory

2025 Annual Report

Objectives
Objective 1: Quantify physical and chemical processes affecting sediment and nutrient transport in surface and subsurface waters. Sub-objective 1.A: Determine the dominant flow pathways for water and nutrient transport in tile-drained headwater watersheds. Sub-objective 1.B: Quantify the effects of landscape, surface, and climate conditions on erosion and related processes. Sub-objective 1.C: Evaluate how flow characteristics impact the ability of soils to behave as nutrient sources and sinks. Objective 2: Evaluate and improve the efficacy of novel soil and water conservation practices. Sub-objective 2.A: Optimize and demonstrate phosphorus removal structures and sorption materials for removing pollutants from water. Sub-objective 2.B: Determine effects of combined management practices on water quality. Objective 3: Enhance soil erosion and water quality models for improved predictions and management of agricultural and forested lands. Sub-objective 3.A: Improve natural resource model functionality and performance. (This is a non-hypothesis research sub-objective.) Sub-objective 3.B: Application of natural resource models and develop modeling techniques. Objective 4: Utilize long-term field and watershed datasets to enhance agricultural production and environmental quality in agroecosystems, and facilitate and support collaborations through the Conservation Effects Assessment Project (CEAP) and Long-Term Agroecosystem Research (LTAR) network. Sub-objective 4.A: Monitor fields and subcatchments in the St. Joseph River Watershed as part of the St. Joseph River CEAP and Eastern Corn Belt LTAR.

Approach
Hydrometric monitoring and conservative tracer analysis will be used to evaluate antecedent conditions on surface runoff and subsurface tile drainage flow generation and quantify surface and subsurface flow contributions to water quantity and quality. Runoff and groundwater within a tile-drained watershed will be analyzed to determine soil physical property effects and management practices on water quality. A lab rill channel and soil box will quantify sediment deposition and transport under different hydrologic conditions, and develop equations for process-based erosion models. Surface topographic techniques will be assessed to quantify spatial distribution of soil erosion and sediment deposition, and morphology of the drainage network. Collect high P soils from Western Lake Erie Basin and characterize for chemical and physical properties, followed by flow-through desorption experiments. Construct a subsurface P removal structure on an agricultural tile drain, using Fe-rich P filter media. Monitor inflow and treated water for P removal. Lab studies to assess different biochars at pollutant removal. Lab and field studies will assess conservation practice impacts on water quality at plot and field scales. Continued efforts on physical-based soil erosion model, including improved channel erosion simulation for ephemeral gullies and grass waterways, water quality routines for pollutant losses, and expanded subsurface tile drainage for better winter simulations and controlled drainage management. Changes to science model have resulted in separate code branches. We will unify these to have a single WEPP version applied by user agencies. Incorporate code from graduate student and other research. Conduct simulations using TauDEM, comparing results to both observed data and simulations using TOPAZ. Assess current code bases for WEPP and WEPS, and determine if common algorithms can be shared. Evaluate data needs of WEPP, WEPS, RHEM and RUSLE2 for common databases. Refactor WEPP code and maintain existing functionality. Use web services locally for desktop WEPP and WEPS, and for web-based applications to separate science and database logic from user interfaces. Expand web service software to fully support WEPP. Develop parallel processing for watershed applications, controlled by software service layer. Use parallelization on CPU and GPU processors. Update P-TRAP software, build mobile research/demo P removal structure, and help with P removal structures across the country. Climate change is resulting in elevated temperatures, more variable rainfall occurrence, and more intense rainfall events. Current conservation practices may be less effective in the future, and other practices may be needed to keep soil and pollutant losses to lower desired levels. Modeling studies will be used to assess impacts of climate change on erosion and off-site water quality, and effectiveness of control practices. Collaborate and support ongoing and future CEAP and LTAR projects and initiatives through sharing historical data from fields and watersheds, continued monitoring of field and watershed sites, and collection of new data and samples for cross-location analyses.

Progress Report
Water management is critical to farming operations across the Midwestern United States. Most of the Midwest is characterized by poorly-drained soils, which requires artificial drainage including surface ditches and subsurface (tile) drainage for farming. Artificial drainage lowers seasonally to perennially high groundwater tables allowing farmers to plant and harvest crops. ARS scientists in West Lafayette, Indiana, measured both groundwater and surface water within a long-term (2012-present) tile-drained watershed in northeastern Indiana (Objective 1). Scientists collected data on groundwater depth, surface ponding depth in closed depressions, runoff and groundwater water quality (i.e., nitrogen and phosphorus concentration), and a suite of hydrologic tracers (i.e., electrical conductivity, chloride, and stable water isotopes) from twenty locations throughout the watershed. Combined with discharge and water quality measurements from the watershed outlet, these in-field measurements of groundwater and surface water have resulted in an unprecedented dataset of water quantity and quality within tile-drained landscapes. Data and findings from this research will help farmers better manage water and nutrients leading to improved nutrient use efficiency, water management, and crop productivity, while minimizing negative impacts of off-site nutrient loss such as eutrophication and harmful algal blooms (HAB). In addition to the research described above, ARS scientists monitored stable water isotopes in a large watershed in northeastern Indiana to quantify dominant flow pathways for water and nutrients (Objective 1). It is imperative to understand how, when, and where water and nutrients move through the landscape to provide better recommendations for soil and water conservation strategies. Results of this study showed that most of the watershed discharge occurred during the winter and spring seasons, with hydrologic tracers suggesting that 26% of discharge was derived from rainfall and the remaining water from soil water or groundwater. Nutrient loads during storm events were strongly related to watershed discharge. Findings suggest that decreasing discharge, decreasing the nutrient supply, and enhancing nutrient removal within ditch networks are needed to decrease nutrient loading drained watersheds. The dataset from the ARS watershed in Indiana will be combined with similar datasets being collected in Ohio, Minnesota, and Iowa, as part of the Stable Water Isotope Flowpath Tracing (SWIFT) project led by ARS researchers in West Lafayette, Indiana. To date, 4,000 rainfall and discharge samples from fields and watersheds at these locations have been analyzed for stable water isotopes. The SWIFT project will help farms from across the U.S. Midwest to better manage soil, water, and nutrient resources. Phosphorus loss from agricultural lands is a persistent challenge, as these losses decrease crop nutrient use efficiency and impair downstream surface waters such as rivers and lakes. ARS scientists in West Lafayette, Indiana developed and monitored a phosphorus removal structure located in the St. Joseph River watershed (Objective 2). Phosphorus removal structures are large landscape scale filters, that are can help decrease dissolved phosphorus loss in surface runoff or subsurface tile drainage, especially from fields with high soil test phosphorus values. New potential phosphorus sorption materials were received from private industry and tested for inclusion in the phosphorus removal structures using flow-cell tests in the laboratory. To date, a phosphorus removal structure containing gravel and spent metal shavings has removed 30% of all phosphorus that has flowed into it, which captured 100% of the field drainage (surface and subsurface). Trace metals in the structure outflow have also been test, indicating no hazard with regard to the use of steel turnings as a phosphorus sorption filter media. Research findings highlight the potential of this conservation practice to effectively decrease dissolved phosphorus from agricultural drainage water and provide farmers with an alternative practice to trap nutrients before they leave their field. Results have been incorporated into the P-TRAP software, a free software developed by ARS for designing phosphorus removal structures, that is used by state and government agencies, non-profits, and private industry. To demonstrate the effectiveness of phosphorus removal structures to farmers and other stakeholders, ARS scientists in West Lafayette, Indiana, developed a demonstration-mobile phosphorus removal structure (Objective 2). The mobile phosphorus removal structure was used on three occasions this past year to teach stakeholders, including farmers, about phosphorus removal technology. Training modules were also developed to help farmers, state and federal government agencies, and private industry design and construct phosphorus removal structures. These modules have been made publicly-available and have had significant impact on P removal technology throughout the world. Several phosphorus removal structures in Wisconsin, Ohio, and Canada have been constructed through this educational series and the use of the P-TRAP software. ARS scientists have directly helped several groups deign their first phosphorus removal structure at various locations across the U.S. Private industry has come to rely on the P-TRAP software to provide services related to construction of phosphorus removal structures. The Water Erosion Prediction Project (WEPP) is a computer model designed to help farmers, state and federal agencies, and local soil and water conservation districts predict water-induced soil erosion. ARS scientists in West Lafayette, Indiana, extensively modified and released a new version of the WEPP model to support the simulation of nonpoint source nutrient transport in nonuniform hillslopes based on science developed for the Soil and Water Assessment Tool (SWAT) (Objective 3). This was accomplished utilizing WEPP’s overland flow element in place of SWAT’s hydrologic response unit construct which enabled more physically plausible routing within a hillslope. In addition, several improvements to the WEPP model code were implemented including: free-source format, modern Fortran conventions, and code refactoring. WEPP and WEPP-Water Quality (WEPP-WQ) code bases were compared, and a sensitivity analysis of the final model code was completed, whereby the results indicated that the WEPP-WQ modeling was performing as expected. A follow-up study evaluated uncalibrated and calibrated model performance in two plot-scale, artificial rainfall studies. 179 observations were compared to corresponding WEPP-WQ simulations of runoff, sediment yield, and soluble and particulate nitrogen and phosphorus forms. Uncalibrated validation results were mixed for the different field conditions, model configurations, and prediction variables. However, calibrated results for both uniform and non-uniform conditions were generally ‘satisfactory’ or ‘good’ according to widely accepted model performance criteria. The improved WEPP-WQ model now provides farmers and stakeholders with additional features for predicting and assessing soil and nutrient loss. The Water Erosion Prediction Project (WEPP) model can now also be used within the open-source Quantum GIS (QGIS) software (Objective 3). The so-called QGeoWEPP source code is now available through GitHub with a validation data set. It allows QGeoWEPP to be used for precision agriculture data worldwide with a minimum of data limitations as well as test QGeoWEPP and WEPP for other potential validation data sites. The QGeoWEPP software includes a validation data set for a long-term rangeland watershed. This enables users to make changes while assuring that any model changes do not impact the validity of the software. While QGeoWEPP still uses the 2012 version of WEPP, the newest stand-alone WEPP revision includes the latest science and was released to the public at the end of 2024. ARS scientists in West Lafayette, Indiana, continue to be leaders and major contributors to both the Conservation Effects Assessment Project (CEAP) and the Long-Term Agroecosystem Research (LTAR) Network (Objective 4). Both CEAP and LTAR are networks of sites across the United States conducting cross-site research to assess the impacts of conservation practices on soil, water, and nutrient management. At long-term research sites in northeastern Indiana, ARS scientists have made substantial upgrades to field and watershed monitoring including upgrading solar panels that provide power to our remote sites, replacing soil moisture sensors, and upgrading dataloggers to make data downloads quicker and more efficient. Data collected from these long-term sites are shared with numerous collaborators from the across the country through the CEAP and LTAR initiatives allowing for regional and national scale analyses. For example, data from long-term sites in Indiana are actively participating in projects to quantify water and nutrient budgets, improve/develop tile drainage modeling routines, evaluate UAVs for locating and mapping tile drainage, assessing edge-of-field structural practices (phosphorus removal structures, bioreactors), quantify algal nutrient limitations and eutrophication thresholds, and assess microplastics in agricultural drainage water. Data from our LTAR field-sites were made publicly available through USDA Ag. Data Commons. The dataset includes water quantity and quality data from two field sites in Indiana and four field sites in Ohio. The continued collaboration across these networks underscores their value for improving agricultural production and resource management for American farmers.

Accomplishments
1. Quantified the interaction between soil hydrology and soil chemistry during phosphorus leaching. Water movement through the soil can carry nutrients from the soil surface to subsurface tile drains. Understanding how water and nutrients move through the soil in agricultural fields is important for retaining nutrients for crop use, as well as helping prevent nutrient loss to nearby waterbodies. ARS scientists in West Lafayette, Indiana, led a series of experiments to assess the relationship between water flow through the soil and the ability of the soil to adsorb or desorb phosphorus (P). Results showed that the soil’s ability to retain or release P depends on the rate of water movement through the soil. Water traveling through the soil too fast or too slow resulted in low dissolved P concentrations in leachate. When the flow rate was “just right”, high dissolved P concentrations were observed. These findings improve the ability to predict P losses, and can be used to better understand how conservation practices can improve P use efficiency.

2. Assessed herbicide loss following long-term implementation of conservation practices. Pre-emergent herbicides such as atrazine and simazine are used to manage weeds in agricultural settings. Understanding the impact of farming practices and herbicide application on water quality is essential because herbicides can negatively impact in-stream biota and increase costs for treating drinking water. Researchers from ARS in West Lafayette, Indiana, and Columbus, Ohio, collected data on herbicides from agricultural drainage water for ten years in the Cedar Creek watershed. The watershed covers 48,000 acres of cropland in northeastern Indiana. Results showed that atrazine levels have not significantly changed following implementation of conservation practices and continue to be greater than safe drinking water limits at several monitoring locations throughout the watershed. No-till, a farming practices that keeps soil undisturbed, may lead to more atrazine loss from fields due to wash-off during rainfall events after herbicide application. Simazine levels have decreased over time because farmers are using it less and are planting cover crops in the fall. Findings show that farming practices can affect herbicide loss to streams. Elevated atrazine levels in streams present challenges to Midwest communities since these waterbodies are used as a drinking water source. Findings highlight conservation approaches that can result in decrease herbicide loss from agricultural watersheds.

3. Determined how drainage water management improves farm profitability and water quality. Drainage water management is the practice of adjusting the outlet elevation of a tile drainage network. By doing so, water and nutrients can be kept in the field. It is also known as controlled drainage. In collaboration with university researchers, ARS scientists in West Lafayette, Indiana, reviewed the cost-effectiveness of this practice. Data collected between 1979 and 2022 from across the world were reviewed. Findings showed that drainage water management can improve corn and soybean yield by up to 3%. It can also decrease the amount of nutrients lost from fields by 40%. Through increases in crop yield and nutrient retention, drainage water management can increase farm income by $125 per acre per year. There are 25 million acres of cropland in the Midwest where this practice can be used. This practice could provide a $3 billion increase in revenue for American farmers.

4. Released updated computer model to help farmers predict water-induced erosion. The Water Erosion Prediction Project (WEPP) is a processed-based model designed to help farmers and decision makers such as state and federal agencies and local soil and water conservation districts predict soil loss. In 2024, ARS scientists in West Lafayette, Indiana, released an updated version of the WEPP model (WEPP2024) that includes improved science in channel erodibility and shear stress functions. These changes significantly enhance hillslope simulations with revised rill erodibility parameters (soils susceptibility to detachment and transport). Users can now expect more reliable modeling results between adjacent fields along with in-stream processes. Specifically, soil erosion functions in WEPP2024 were confirmed to have better performance to properly address actual field/watershed behavior in practice. Multiple case scenarios of conservation practices were applied using data of the Upper Cedar Creek, Indiana. The latest version of WEPP provides significant updates over the previous version allowing better prediction of water-induced soil erosion, which will facilitate increased productivity of agricultural land across the United States.

5. Released WEPP-COMPARE: a user-friendly tool to assess soil and water conservation practices. Comparing various management options for crop production and efficient resources use is essential for farmers. The Water Erosion Prediction Project (WEPP) is a model that simulates plant, water, and soil budgets (tracking flow of water and nutrients in soil) along hillslope flowpath in fields and small watersheds. The new WEPP-COMPARE interface stands for WEPP- Comprehensive Operation Management Practice Assessment and Rotation Engine. This new customized interface was tested by a group of invited stakeholders. WEPP-COMPARE can be used by farmers and decision makers such as state and federal governments and local soil and water conservation districts with only minimal input data. The WEPP-COMPARE platform is ready to use with all relevant modeling data available such as weather, land use, and soil information. In addition, users only need to have access to the internet without the need to install any professional programs on computers. The second annual workshop for stakeholders in February 2025 resulted in feedback ARS scientists were able to use to further improve the interface and user experience. This new platform will allow farmers to compare different management scenarios quickly and easily for their farm allowing them to save both time and money.

6. Free, open-source software estimates water and sediment transport for precision agriculture. Soil and water conservation is not only important for both increasing farm profitability and efficiency, but also for minimizing negative environmental impacts. Estimating the infiltration and flow of water, moving sediments within and off a managed field, is critical for soil and water conservation. ARS researchers developed a prediction tool in a freely available, open-source Geographic Information System (GIS) for fields or small managed watershed. The Water Erosion Prediction Project (WEPP) model can now be used within the open-source Quantum GIS (QGIS) software. It allows QGeoWEPP to be used for precision agriculture data worldwide with a minimum of data limitations. The software includes a validation data set for a long-term rangeland watershed. This enables users to make changes while assuring that any model changes do not impact the validity of the software. The users are invited to test the software and submit potential validation datasets for other land management such as croplands and forests. The software allows the user to use remote sensing derived land cover changes and select from a menu of soils, management practices, and historic weather patterns for the United States and similar conditions around the world. This new software will allow farmers to better visualize areas on their farm that they can increase productivity through implementation of soil and water conservation practices.

Review Publications
Penn, C.J., Williams, M.R., Askar, M., Stinner, J.H., King, K.W. 2024. Stack ‘em up: Field-scale performance of a stacked woodchip bioreactor and phosphorus removal structure. Journal of the ASABE. https://doi.org/10.13031/aea.16145.
Flanagan, D.C., Mankin, K.R., Thompson, A.M. 2024. Soil erosion research studies in the age of changing climate. Journal of the ASABE. https://doi.org/10.13031/ja.16096.
Williams, M.R., Penn, C.J., King, K.W. 2025. Hydrologic pathways and nutrient loading in the headwaters of the Western Lake Erie Basin. Journal of Hydrology: Regional Studies. https://doi.org/10.1016/j.ejrh.2025.102275.
Ford, W.I., Williams, M.R., Mumbi, R.C. 2024. Subsurface sediment transport in the shallow vadose zone of fine-textured soils with heterogenous preferential flows. Hydrological Processes. https://doi.org/10.1002/hyp.15327.
Gonzalez, J.M., Smiley, P.C. 2025. Temporal trends of atrazine, simazine, and metolachlor in a U.S. Midwest agricultural watershed: A 10-year study. Environmental Processes. https://doi.org/10.1007/s40710-025-00753-7.
Elliot, W. J., and Flanagan, D. C. 2024. Corrigendum to “Estimating WEPP cropland erodibility values from soil properties”. Journal of the ASABE. 67(5): 1241-1244. https://doi.org/10.13031/ja.16069.
Tabatabaeefar, A., Penn, C.J., Comeau, Y., Claveau-Mallet, D. 2025. Clogging of reactive filters for phosphorus removal – a review. Journal of Environmental Management. https://doi.org/10.1016/j.jenvman.2025.124386.
Ampong, K., Penn, C.J., Camberato, J.J. 2024. The timing of phosphorus availability to corn: what growth stages are most critical for maximizing yield. Agronomy. https://doi.org/10.3390/agronomy14112731.
Osterholz, W.R., Simpson, Z.P., Williams, M.R., Shedekar, V., Penn, C.J., King, K.W. 2024. New phosphorus losses via tile drainage depend on fertilizer form, placement, and timing. Journal of Environmental Quality. 53:241-252. https://DOI.org/10.1002/jeq2.20549.
Reinhart, K.O., Vermeire, L.T., Penn, C.J., Lekberg, Y. 2024. Experimental evidence that poor soil phosphorus (P) solubility typical of drylands due to calcium co-precipitation favors autonomous plant P acquisition over collaboration with mycorrhizal fungi. Soil Biology and Biochemistry. 199. Article 109605. https://doi.org/10.1016/j.soilbio.2024.109605.
Simpson, Z.P., Mott, J.D., Elkin, K.R., Buda, A.R., Faulkner, J., Hapeman, C.J., Mccarty, G.W., Foroughi, M., Hively, W., King, K.W., Osterholz, W.R., Penn, C.J., Williams, M.R., Witthaus, L.M., Locke, M.A., Pawlowski, E., Dalzell, B.J., Feyereisen, G.W., Dolph, C., Bjorneberg, D.L., Nouwakpo, S.K., Rogers, C.W., Scott, I., Bolster, C.H., Duriancik, L., Kleinman, P.J. 2024. Phosphorus lability across diverse agricultural contexts with legacy sources. Environmental Quality. 1-19. https://doi.org/10.1002/jeq2.20632.
Scott, I.S., Penn, C.J. 2024. Effects of redox on the phosphorus removal ability of iron-rich phosphorus sorption materials. Chemosphere. https://doi.org/10.1016/j.chemosphere.2024.141416.
Tabatabaeefar, A., Penn, C.J., Clauveau-Mallet, D. 2024. Nitrogen and phosphorus removal by reactive filter as a tertiary treatment unit for isolated houses with high alkalinity groundwater source. Journal of Water Process Engineering. https://doi.org/10.1016/j.jwpe.2024.105319.
Ampong, K., Penn, C.J., Camberato, J., Williams, M.R. 2024. An efficient subsampling method for estimating corn root characteristics with scanner-based image analysis. Agronomy Journal. https://doi.org/10.1002/agj2.21645.
King, K.W., Williams, M.R., Bos, J.H., Rumora, K.R., Stinner, J.H. 2025. ECB-WQ: A Long-Term Agroecosystem Research (LTAR) - Eastern Corn Belt node field-scale water quality dataset. Journal of Environmental Quality. Pg 1-12. https://doi.org/10.1002/jeq2.20675.
King, K.W., Williams, M.R., Stinner, J.H., Rumora, K.R. 2024. The LTAR common cropland experiment at eastern corn belt. Journal of Environmental Quality. 1-10. https://doi.org/10.1002/jeq2.20611.
Lekberg, Y., Jansa, J., Johnson, D., Milham, P., Penn, C.J., Colman, B. 2024. Tracing phosphorus from soil through mycorrhizal fungi to plants: Reply to Spohn and Wanek. New Phytologist. https://doi.org/10.1111/nph.20217.
Liebig, M.A., Abendroth, L.J., Robertson, G., Augustine, D.J., Boughton, E.H., Bagley, G.A., Busch, D.L., Clark, P., Coffin, A.W., Dalzell, B.J., Dell, C.J., Fortuna, A., Freidenreich, A.S., Heilman, P., Helseth, C.M., Huggins, D.R., Johnson, J.M., Khorchani, M., King, K.W., Kovar, J.L., Locke, M.A., Mirsky, S.B., Schantz, M.C., Schmer, M.R., Silveira, M.L., Smith, D.R., Soder, K.J., Spiegal, S.A., Stinner, J.H., Toledo, D.N., Williams, M.R., Krecker-Yost, J.L. 2024. The LTAR Common Experiment: Facilitating improved agricultural sustainability through coordinated cross-site research. Journal of Environmental Quality. 53(6):787-801. https://doi.org/10.1002/jeq2.20636.
Mumbi, R., Williams, M.R., Ford, W.I., Camberato, J.J., Penn, C.J. 2024. Identifying dissolved reactive phosphorus sources in agricultural runoff and leachate using phosphate oxygen isotopes. Journal of Contaminant Hydrology. https://doi.org/10.1016/j.jconhyd.2025.104501.
Mumbi, R.C., Williams, M.R., King, K.W., Penn, C.J., Camberato, J.J. 2025. Drought to inundation: Precipitation extremes exacerbate phosphorus loss in artificially drained watersheds. Agricultural Water Management. https://doi.org/10.1016/j.agwat.2025.109606.