Project : USDA ARS

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Research Project: Strategic Investigations to Improve Water Quality and Ecosystem Sustainability in Agricultural Landscapes

Location: Water Quality and Ecology Research

2022 Annual Report

Objectives
1. Assess and quantify ecological processes that influence water resources in agricultural ecosystems. 1a. Identify and quantify environmental factors that drive processes that are related to retention or removal of agricultural contaminants. 1b. Examine relationships between physical, chemical, and biological factors and ecological responses impacted by agriculture in the Lower Mississippi River Basin. 2. Assess and quantify the benefits of water resource management practices to enhance agricultural ecosystems. 2a. Quantify the long-term effects of conservation practices on aquatic and terrestrial resources in the Lower Mississippi River Basin. 2b. Assess the benefits and risks of management strategies and practices on soil and water resources at multiple scales. 3. Develop a watershed-scale integrated assessment of ecosystem services in agricultural landscapes of the Lower Mississippi River Basin. 3a. Develop technologies and tools to assess water and conservation management strategies in agricultural watersheds. 3b. Evaluate how ecosystem services derived from conservation practices improve water quality and ecology in agricultural watersheds. 4. As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in the Mid-South region, use the Lower Mississippi River Basin LTAR site to improve the observational capabilities and data accessibility of the LTAR network and support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the Mid-South region. Research and data collection are planned and implemented based on the LTAR site application and in accordance with the responsibilities outlined in the LTAR Shared Research Strategy, a living document that serves as a roadmap for LTAR implementation. Participation in the LTAR network includes research and data management in support of the ARS GRACEnet and/or Livestock GRACEnet projects. 4a. Develop the Lower Mississippi River Basin LTAR location addressing issues of long-term agroecosystem sustainability specific to the region, participating in the Shared Research Strategy, and contributing to network-wide monitoring and experimentation goals. 4b. Enhance the Lower Mississippi River Basin CEAP watershed longterm data sets and integrate with other long-term data sets in the Lower Mississippi River Basin to address agroecosystem sustainability at the basin scale. 5. Increase knowledge and understanding of the processes governing movement, storage, and quality of water in the Mississippi River Valley Alluvial Aquifer, and develop technologies to enhance the sustainability of water resources for agriculture. 5a: Develop technologies to increase the provision of abundant, sustainable water resources and associated ecosystem services for irrigated agriculture in the LMRB. 5b: Increase knowledge and understanding of the movement, storage, and quality of water along hydrologic pathways between surface and subsurface units of the LMRB.

Approach
Many experiments described in the following involve collection and analysis of water quality samples from field sites within the Lower Mississippi River Basin (LMRB). 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).

Progress Report
This project has been replaced by project number 6060-13660-009-00D “Enhancing Long-Term Agroecosystem Sustainability of Water and Soil Resources Through Science and Technology.” Within the life of the five-year plan, 23 peer-reviewed journal articles were published in support of the research described in Objective 1, with an additional four peer-reviewed articles currently in review. These products were a result of laboratory-based biological assays, stream mesocosm experiments, and field experiments which manipulated certain physical and chemical components that influenced nutrient and carbon processes in aquatic ecosystems. As a result of this project plan, a significant denitrification research program was established, seeking to address research problems facing the Gulf of Mexico hypoxic zone and other nutrient-related issues. This new research program has led to multiple national collaborations, with interest also building from the international community. As a result of this project plan, an improved organic matter trap was designed for variable water depths typically encountered in ephemeral streams in the Mississippi Alluvial Plain. Other notable findings from research in Objective 1 include the role of nitrogen and phosphorus enrichment on lake metabolism and dissolved oxygen dynamics, the role of carbon and nitrogen availability, as well as temperature, on nutrient fluxes, denitrification, and the relative proportion of nitrogen gas to nitrous oxide end products of the denitrification process. In support of Objective 2, 22 peer-reviewed journal articles were published, with an additional eight peer-reviewed articles currently in review. Lake and runoff water quality assessments of Beasley Lake watershed, part of the Conservation Effects Assessment Program (CEAP) continued throughout the duration of the five-year plan. Highlighted results from the last five years include demonstration that vegetated buffers, vegetated drainage ditches, and a vegetated sediment retention pond, as well as acreage in the Conservation Reserve Program (CRP) that were best management practices in place in and around Beasley Lake, were effective in reducing suspended solids loads and moderately effective at reducing nutrient loads in runoff while simultaneously improving lake water quality. Effects of cover crops (Austrian pea, crimson clover, cereal rye, and tillage radish) and tillage (no-tillage and reduced tillage) on soil quality, crop yield, irrigation application efficiency (furrow and sprinkler), runoff erosion, and off-site nitrogen (N) and phosphorus (P) transport were examined as part of a long-term study initiated prior to the five-year project plan. Sealing in the surface of silt loam soils contributes to low permeability and low irrigation application efficiency in Mississippi corn production systems, but utilization of cover crops may improve irrigation application efficiency. Initial yield data for the first growing season showed a negative cover crop effect on grain yield, with both cereal rye and Austrian pea reducing yield up to 45% compared to the reduced tillage, no cover control. Irrigation application efficiency was evaluated using an overhead sprinkler and furrow irrigation by conducting a simulation of each during the growing season and a rainfall simulation immediately after tillage operations in the fall. Under overhead sprinkler irrigation during the first year, some cover crops increased infiltration up to 24% while cereal rye resulted in greater amounts of some nutrients in runoff. Under furrow irrigation, there were no differences in infiltration between treatments; however, cover crops slowed the furrow advance time. Also in support of Objective 2, a tailwater recovery system (reservoir and tail ditch) in Sunflower County, Mississippi, was assessed for its ability to improve water quality and reduce dependence on groundwater resources for crop irrigation. Four years of continuous monitoring and flow-triggered sampling runoff events were collected, while five years of bi-monthly water quality samples were collected. Seasonal trends, as well as recommendations and cautions for tailwater recovery system use were reported. Several studies were conducted to determine the impact of tillage and cover crops on contaminant loss and soil properties. Results indicate a minimum tillage system with a cereal rye cover crop may be implemented without reductions in soybean grain yield; however, additional costs of planting the cover crop will decrease net returns above costs. After two years, zone tillage and rye cover crop systems reduced off-site transport of solids and nutrients compared to a minimum tillage system with no cover crop. Another study examined effects of Austrian winter pea, cereal rye, crimson clover, and tillage radish in a corn field. Mesocosm and plot-scale studies examined the ability of manufactured filter socks filled with a woodchip blend to mitigate N and P in agricultural runoff. Mesocosm study results are currently being analyzed by a university collaborative partner, while plot-scale study results provided development of a new model for measuring metabolism. Creation and release of a new R package for metabolism modeling in shallow, stagnant systems were performed during the five-year project plan. Toward the end of the five-year plan, an opportunity to assess a novel conservation practice was initiated. ARS researchers examined effects of shallow flooding of post-harvest fields for agronomic benefits and migratory shorebird habitat. Results indicated positive benefits in yield and habitat, and as a result, a $1 million U.S. Environmental Protection Agency Farmer-to-Farmer grant was received by ARS researchers and their university collaborators to continue the study into a new five-year plan. In support of Objective 3, 10 peer-reviewed journal articles were published. The USDA Annualized Agricultural Non-Point Source (AnnAGNPS) pollutant loading model was enhanced to utilize remotely sensed data to improve the characterization of associated topography, soil properties, and management associated with riparian buffers and constructed wetlands within national and international watersheds. Databases associated with the AnnAGNPS model were developed in a tailwater recovery system project in the Mississippi Delta for enhancement of the model and evaluation of the impacts of tail water systems on agricultural ecosystem services. Databases in the Sunflower River Watershed system in the Mississippi Delta were assembled and evaluated for their use in simulating the effects of long-term conservation practices on agricultural ecosystems. The databases included a description of topography, climate, soil properties, agronomic and irrigation practices for characterization within the AnnAGNPS model. This provided a better understanding of the link between irrigation water management practices and downstream water quality. Additionally, a long-term simulation of the 21 Gun study at Stoneville, Mississippi, is evaluated AnnAGNPS’ ability to simulate differences in management and then to evaluate long-term trends related to these practices. In support of Objective 4, 13 peer-reviewed journal articles were published. Long-Term Agroecosystem Research (LTAR) common experiment sites were secured, and eddy-covariance towers and soil moisture sensors were installed in the aspirational and “business-as-usual” fields at two farms in the late summer and early fall of 2020. Historical datasets from both the Goodwin Creek and Beasley Lake watersheds were uploaded into a common data management platform and the data are currently under quality assurance/quality control checks. We are currently in the second year of field biomass collection, and this project will continue into the next five-year project plan. Objective 5 was a late addition to the project plan, resulting from new funding and direction. Objective 5 focused on a pilot project testing managed aquifer recharge technology utilizing riverbank filtration and groundwater transfer and injection. The construction phase was completed for the groundwater transfer and injection point project with the U.S. Army Corps of Engineers. Protocols for pre-operation water level and water quality data were established; monthly water sample collection for laboratory analyses were completed; a three-month pumping/injection experiment was completed in July 2021. Collaboration with faculty and graduate students from a university partner has led to 12 presentations (four regional/national conferences; four local interest groups; and four stakeholder groups) being given on the project. This project will continue into the next five-year project plan.

Accomplishments
1. Oxbow Lakes May Contribute to Nutrient Problems. Shallow oxbow lakes are a common feature of the Mississippi Alluvial Plain draining nearby agricultural fields. Best management practices are implemented to decrease nutrient loads that enter the oxbow lakes and improve their water quality. ARS researchers in Oxford, Mississippi, conducted a series of experiments over the course of a year to examine patterns of nutrient flux and denitrification (a permanent nitrogen removal mechanism) across three different habitats in Beasley Lake, Mississippi. Computer modelling showed dentrification was affected by temperature, dissolved inorganic nitrogen, sediment oxygen demand, and sediment carbon-to-nitrogen ratios. Beasley Lake was a source of nitrogen and phosphorus annually based on estimated loads coming in and out. Research efforts should continue to focus on implementing management practices that further reduce nutrient loads coming into oxbow lakes located in intensively cultivated areas. Otherwise, goals of improved water quality cannot be attained.

2. Farmers Split on Use of Efficient Irrigation Technologies. Water withdrawals for irrigation in the Mississippi River Valley Alluvial Aquifer have occurred at an unsustainable rate, resulting in a decline in groundwater levels which threatens regional agricultural production. ARS researchers in Oxford, Mississippi, along with ARS researchers in Jonesboro, Arkansas, and collaborators at Mississippi State University evaluated results of an irrigation survey sent to 580 Mississippi Delta farmers. Of the 460 respondents, over 50% believed there is sufficient water in the Delta region, but it is not properly managed. At least 25% or more farmers believed on-farm storage and center pivot were not efficient water conservation practices. It was also noted that the longer the farmer has operated their business, the less likely they were to use groundwater conserving practices. Results point to the need for targeted, improved extension outreach and training related to the value of irrigation conservation practices in order to address dangerous groundwater depletion in the Mississippi River Valley Alluvial Aquifer.

3. Understanding Phosphorus Flux Provides Long-Term Management Strategies. Phosphorus, an essential nutrient for crop growth, is routinely applied to agricultural lands; however, small amounts of phosphorus entering surface waters can cause eutrophication and harmful algal blooms. ARS researchers in Oxford, Mississippi, joined other ARS researchers and university collaborators to examine data collected from 24 research locations across the U.S. and Canada to better understand phosphorus inputs and outputs to 61 diverse agricultural production systems including cropland, forage, rangeland, and bioenergy systems. Phosphorus Inputs, outputs, and budgets were highly variable across the production systems. Results indicate areas where improved data collection could improve understanding of phosphorus cycling and transport. Findings also highlight important steps such as efficient use of fertilizers, adoption of P-based manure management, and consideration of crop rotation for improved phosphorus management.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS