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

2024 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
A manuscript was submitted for publication which evaluates ecological needs of Mississippi lakes and how surface water contributions may reduce the need for groundwater pumping for irrigation needs in the Delta. Additionally, ecological surveys of macroinvertebrates and migratory shorebird presence, as well as soil and water samples were collected and 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. Data is being analyzed for several manuscripts. 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. A series of experiments in limnocorrals led to the publication of a manuscript describing the reaction of zooplankton to various nitrogen and phosphorus ratio enrichments. Small-scale experiments were conducted that examined the use of woodchip-bioreactors in filter sock material (typically used for erosion control in construction) to mitigate nitrogen and phosphorus in simulated storm runoff, and a manuscript was submitted and published, demonstrating the bioreactor’s effectiveness at mitigating nitrogen, but less so, for phosphorus. 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. Within the Conservation Effects Assessment Project (CEAP), long-term monitoring of lake water quality and ecology continued within the Beasley Lake watershed. The non-cropland areas of the watershed were highly modified by the landowners, resulting in shifting of research sites and priorities. Data continues to be centralized for multiple landscape-scale manuscripts, including those with collaborators focusing on modeling aspects. A drainage ditch within the Beasley Lake watershed was prepared in the spring to compare mitigation of runoff water in vegetated versus unvegetated sections. This experiment is on-going for the next calendar year. Long-Term Agroecosystem Research (LTAR) Project samples of soil, biomass, as well as eddy covariance data continued to be collected as part of the common experiment across LTAR sites. We have three collaborative farmers which allow us two comparisons of prevailing (PRV) practices versus two comparisons of alternative (ALT) field practices. Of the three farmers, one is owned and operated by a minority farmer in Mound Bayou, Mississippi. A non-assistance cooperative agreement was established with Ohio State University to gap fill and process backlogged eddy covariance data. Cooperators are providing an algorithm to use for future data collection. A cross-site (national) experiment with seven locations completed the first year of data collection to assess phytoplankton algal nutrient limitation and thresholds in order to determine eutrophication in watersheds with different agricultural land use. The cross-site experiment is currently in its second field season. Several new initiatives within the LTAR Drainage Working Group (microplastics, ecosystem metabolism, and greenhouse gas measurements) were designed and research will be initiated beginning in FY25. One manuscript was submitted and published this FY detailing the common experiment in the Lower Mississippi River Basin LTAR project.

Accomplishments
1. Row crop agriculture in Mississippi uses irrigation to reach optimal production levels. Overuse of groundwater for irrigated agriculture has led to declines in levels of the Mississippi Alluvial Aquifer. Resource managers are searching for alternative strategies and sources of irrigation water to improve the sustainability of the aquifer. Surface waterbodies are plentiful in the Mississippi Alluvial Plain (MAP) region, information is lacking on the ecological impacts of using these water bodies (typically oxbow lakes and sloughs) as surface water for irrigation. ARS researchers at Oxford, Mississippi,irrigation, Roundaway Lake, Mississippi, to demonstrate the impacts of irrigation on water temperature and dissolved oxygen levels, two characteristics that affect ecological health. Using geospatial datasets, 392 waterbodies adequate to support irrigation needs were utilized. Based on case study results, farmers should assess potential surface waterbodies to determine if extraction for irrigation would still provide enough water depth (>2 m) to maintain aquatic ecosystem services and minimize the potential for hypoxia and harmful algal blooms. Waterbodies not meeting water depth criteria for irrigation use can be improved and/or restored through installation of weirs to increase water level elevation and/or dredging of heavily sedimented systems to increase depth and water volume.

2. Phosphorus is a critical nutrient needed for adequate crop production. In excess, phosphorus (P) can cause environmental problems by increasing algal growth in aquatic ecosystems. Successful P management is dependent on knowing P concentrations in soils and understanding potential pathways for transport to waterbodies. In the Lower Mississippi Alluvial Plain, soil P concentrations are higher than expected, considering low P fertilizer application rates. ARS researchers at Oxford, Mississippi, evaluated P concentrations across four dominant soil types in both cropland and forest land across 76 locations. Results showed P concentrations were relatively similar across soil types and land uses, suggesting there is a naturally high level of P in soils of this region—commonly referring to as “legacy P”. Understanding P sources and dynamics will be helpful to guide management decisions and improve watershed modeling simulations in the region.

3. Current agricultural practices can have negative environmental impacts. ARS researchers at Oxford, Mississippi, along with collaborators conducted a field experiment as part of the Long-Term Agroecosystem Research Project (LTAR) to evaluate effects of tillage and Austrian pea cover crop on soil water content in sorghum and cotton cropping systems. Sensors were used to measure soil water content to a 1.2-m soil depth during two cover crop growing seasons (2019-2021). Runoff and crop water use were estimated using a simulation model (RZQM) and soil water balance equation. Results showed that no-till could increase soil water storage and reduce surface runoff by nearly 25% over conventional till, resulting in increased crop water use by 17%. Cover crops reduced runoff from no-till plots, but not from conventional till plots. Cover crops produced substantial biomass with minimal risk of depleting soil water. Results suggested that inclusion of no-till in the current cropping system is an important factor to conserve water and reduce irrigation draft in the Lower Mississippi River Basin.

4. Microplastics are an emerging environmental contaminant that are causing water quality problems as well as the potential to damage wildlife. Biochar is the black carbon and ash resulting from burning material like wood chips and plant residue with extremely high heat. Biochar has been shown to effectively bind with and filter out many environmental contaminants. ARS researchers at Oxford, Mississippi, along with collaborators conducted a laboratory study to determine efficiency of biochar binding with microplastics found in runoff water collected from an agricultural field. Biochar bound up and reduced 87-93% of the microplastics in the water. Additionally, more than 90% of the different size microplastics were bound up in the biochar used in this study. The proof-of-concept research shows that farmers may be able to use biochar filters in their drainage ditches to bind microplastics and filter them out of the runoff water.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS