Project : USDA ARS

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Research Project: Enhancing Long-Term Agroecosystem Sustainability of Water and Soil Resources Through Science and Technology

Location: Water Quality and Ecology Research

2025 Annual Report

Objectives
1. Assess and quantify impacts of soil and water management strategies in agroecosystems of the Lower Mississippi River Basin (LMRB). 1.A. Examine water management strategies to assess tradeoffs between groundwater sustainability benefits and ecological costs. 1.B. Quantify the influence of soil and water management strategies on water availability and quality, soil health, and wildlife habitat. 2. Evaluate and measure how management practices influence processes to improve water quality, ecosystem services, and ecological integrity. 2.A. Evaluate novel ecological indicators and stressor-response relationships to measure success of best management practices in agricultural watersheds. 2.B. Evaluate how management practices influence processes related to soil health and water quality in agricultural watersheds. 3. Analyze, synthesize, and forecast impacts of implementing conservation practices within agricultural landscapes. 3.A. Forecast and analyze impacts of climate change on the effectiveness of conservation practices. 3.B. Quantify the impacts of conservation practices on aquatic and terrestrial resources in the LMRB. 4. Enhance long-term sustainability of agroecosystems through regional and national (LTAR network) studies that quantify agronomic and environment responses to aspirational management strategies and changing climate. 4.A. Develop the LMRB LTAR site through contributions in monitoring and experimentation to meet network goals. 4.B. Establish a network of LTAR sites distributed regionally and nationally to quantify changes in soil health, water quality and aquatic ecology in LTAR watersheds.

Approach
Many experiments described in the following involve collection and analysis of water quality samples from field sites within the Lower Mississippi River Basin. Data acquisition (sample collection, preservation, handling, analysis, quality control), except where otherwise noted, follows standard procedures (APHA, 2005). Base flow samples are collected manually, while storm event or runoff samples are collected using automated pumping samplers (ISCO GLS Compact Composite Samplers) activated by acoustic Doppler water level and area velocity water flow sensors (ISCO 2100). All samples are placed on ice for transport to the laboratory for analysis and held in cold storage (4o C). Storm samples are retrieved within 24 h of collection. All water samples are analyzed for total and dissolved solids (drying at 105o C), total P and total Kjeldahl N (block digestion and flow injection analysis using a Lachat QuikChem® 8500 Series 2 Flow Injection Analysis System). Additional analyses conducted for certain experiments include hardness (EDTA titrimetric method), alkalinity (titration method), turbidity (calibrated Hach electronic turbidimeter); NH4-N, NO3-N, NO2-N, and soluble (filterable) P (all with the Lachat system), and chlorophyll a (pigment extraction with spectrophotometric determination). Pesticide analyses are conducted using solvent (hexane) and KCl extraction prior to analysis on a gas chromatograph. Soil gas flux is measured using a LiCOR 870 soil gas flux system.

Progress Report
In support of Objective 1, a manuscript was published that uses machine learning models and satellite data to understand groundwater-land use relationships in order to supplement monitoring well logs. Additionally, data from ecological surveys of macroinvertebrates and migratory shorebird presence, as well as soil and water samples has been analyzed as part of a larger research project examining the possibility of using shallow flooded, post-harvest corn and soybean fields for migratory shorebird habitat. Several manuscripts have been published. Soil, water, and crop data continued to be collected from the 21-Gun long-term research plot to support investigation into conservation and irrigation technology management for improved soil health in cotton systems. In support of Objective 2, data from field and stream mesocosm studies have been analyzed and a manuscript published describing how tolerant and intolerant stream taxa respond to excess nutrients using a subsidy-stress gradient. A series of experiments in limnocorrals led to the publication of a manuscript describing how nitrogen fixation may not alleviate imbalances that limit primary production in eutrophic lake ecosystems. Additionally, field soil and water samples were collected and analyzed for pesticide concentrations to determine whether shallow flooding of post-harvest fields for shorebird habitat influences pesticide degradation throughout the fall and winter seasons. A stream mesocosm experiment was conducted to evaluate how CDOM may shift nutrient limitations for algae and bacteria. Data from this experiment will be combined with laboratory assays and watershed monitoring data. In support of Objective 3, within the Conservation Effects Assessment Project (CEAP), long-term monitoring of lake water quality and ecology continued within the Beasley Lake watershed and data have been published supporting this work. The non-cropland areas of the watershed were highly modified by the landowners, resulting in shifting of research sites and priorities. Data continue to be centralized for multiple landscape-scale manuscripts, including those with collaborators focusing on modeling aspects. Samples describing phosphorus in soil and sediments along a landscape gradient within Beasley Lake watershed have been analyzed and data are being developed into several manuscripts. Challenges due to beaver habitat modifications within Beasley Lake watershed have redirected flows and altered the drainage basin, limiting feasibility to move forward with the proposed drainage ditch experiment. Algal nutrient limitation experiments continue to progress, and data are being analyzed. In support of Objective 4, Long-Term Agroecosystem Research (LTAR) project samples of soil, biomass, runoff water as well as eddy covariance data continued to be collected as part of the common experiment across LTAR sites. This year, soil moisture sensors were installed at two farms. We have three collaborative farmers which allow us two comparisons of prevailing (PRV) practices versus two comparisons of alternative (ALT) field practices. Through a non-assistance cooperative agreement with Ohio State University eddy covariance data have been gap filled and processed up to 2024. Cooperators are providing an algorithm to use for future data collection. A cross-site (national) experiment with seven locations completed the second year of data collection to assess phytoplankton algal nutrient limitation and thresholds in order to determine eutrophication in watersheds with different agricultural land use. Cross-site data compilation and analysis is underway for this project. Within the LTAR Drainage Working Group, grab samples for microplastics analysis were collected and are currently being analyzed by collaborators at the University of Mississippi.

Accomplishments
1. Fall field flooding helps ecosystem. Fall flooding on fields for migratory waterbirds can enhance ecosystem services without impacting agricultural production. This study is focused on a best management practice where farmers hold water on fields with pipe and pad structures to create temporary habitat for migrating birds during the fallow season. ARS research at Oxford, Mississippi shows this practice can provide other environmental and agronomic benefits including: reduction in soil and nutrient losses during storm runoff events, increased crop residue decomposition, and weed suppression in flooded areas. There were no negative yield impacts and, in some cases, slight yield bumps for soybean crops following flooding. This research demonstrates that wildlife and environmental benefits can be integrated into traditional agricultural production systems.

2. Nitrogen reduction rapidly reverses algal blooms in shallow lakes. Nitrogen mitigation can improve water quality in shallow phosphorus-rich lakes. The general rule of thumb is that excess phosphorus causes algal blooms in lakes, but scientists found that the role of nitrogen is more complicated in shallow lakes with high phosphorus. In a 5-year replicated pond experiment, ARS scientists at Oxford, Mississippi and collaborators tested the influence of different nitrogen fertilization rates on algal productivity in shallow phosphorus-rich lakes. Results demonstrated strong algal bloom events in response to excess nitrogen and a rapid reversal of algal growth when nitrogen inputs ceased. Approximately 1.4 million (40%) of the nation’s lakes are shallow with high phosphorus conditions, highlighting the potential for nitrogen mitigation to improve water quality in a significant portion of our nation’s waters.

3. Using AI to understand groundwater-land use relationships. AI models and satellite data can be used to understand groundwater-land use relationships. Groundwater is essential for irrigated agriculture in the Mississippi Delta. Managers rely on monitoring wells for planning purposes, but these wells are only assessed twice a year which may not be often enough for regional planning. Monitoring can also be accomplished using remote sensing data from the GRACE satellite. Scientists used AI methods to quantify differences in groundwater levels between¿monitoring well logs and satellite data. AI models had an 88% correlation to well log models, which resulted in no significant difference in estimated groundwater withdrawal from 2008 – 2020, suggesting they could be used to supplement monitoring well data for regional water management planning.

4. Woodchip filters are more than just construction tools. Woodchip filter socks are commonly used for erosion control at construction sites, but ARS researchers at Oxford, Mississippi found they are also useful to help clean up runoff water from agricultural fields. In a series of small-scale experiments, woodchip filter socks decreased the amount of nitrate in runoff water. Filter socks that remained constantly wet reduced more nitrate than socks that would dry out and rewet from flood events. Placing woodchip filter socks at strategic locations in and around farms can be a cost-effective way to help farmers reduce the amount of nutrients making their way to rivers, lakes, and streams.

5. Improving soil water storage with no-tillage cover cropping. Mitigating runoff and erosion are important for the long-term sustainability of row crop systems in the mid-southern United States. A long-term plot study in Stoneville, Mississippi demonstrated that conservation management systems that increase plant residue can mitigate runoff and sediment losses in non-irrigated cotton. Reductions in sediment losses also correlated with reductions in total Kjeldahl nitrogen and total phosphorus associated with coarse sediments. Dissolved nutrient losses associated with runoff increased up to 29%. No tillage was the most effective at reducing sediment loss, followed by reduced tillage with rye cover crop, and reduced tillage with no cover crop. Edge-of-field buffers were also effective at reducing sediment and nutrients associated with coarse solids but were not effective at reducing dissolved nutrients.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS