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

2021 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
In support of Objective 1, a manuscript was published assessing the relationship between sediment nutrient fluxes, including denitrification and water quality (measured as eutrophication) in a shallow, freshwater riverine lake in the journal Water. A second manuscript was accepted in mid-June 2021 that examined the influence of water depth on algal blooms and water quality in shallow, freshwater riverine lakes. The manuscript is to be published in the journal Ecohydrology. A third manuscript investigating the role of nitrogen and phosphorus enrichment on lake metabolism and dissolved oxygen dynamics in experimental ponds was submitted to the journal Limnology & Oceanography. Revisions based on peer review have already been submitted. A fourth manuscript examining 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 is being revised for journal submission. Two additional manuscripts are in preparation, one examining spatial and temporal patterns in sediment nutrient fluxes, including denitrification, in Beasley Lake, Mississippi [a Conservation Effects Assessment Project (CEAP) watershed] will be submitted in late Summer/early Fall 2021. The other manuscript will examine the transport and processing of crop litter in Roundaway Lake and its influence on sediment nutrient fluxes and will also be submitted in late Summer/early Fall 2021. In support of Objective 2, a manuscript describing publicly available water quality and lake data from Beasley Lake, Mississippi, a Conservation Effects Assessment Project (CEAP) watershed, was published in a special issue on Catchment Science in the journal, Hydrological Processes. Another manuscript assessing how best management practices affect long-term eutrophication in the CEAP watershed in Beasley Lake, Mississippi, was published in Water. Additionally, a review paper incorporating ecological responses to conservation practices throughout the world and including Beasley Lake (CEAP) watershed was published in Water. Soil, agronomic, and economic analyses of the effects of conservation management on environmental, agronomic, and economic parameters in Mid-South corn crops proceeded as planned. At the conclusion of FY21, four years of runoff and agrochemical transport data and five years of soil, agronomic, and economic data will have been collected. Additionally, water quality and hydrology data has been analyzed and a manuscript is in preparation describing results of tailwater recovery system’s ability to improve runoff water quality. Expected submission data is Summer 2021. In spring 2020, the 21-Gun experimental area began a new phase using cotton as the crop of focus and new conservation treatments. Data collection continues. A novel conservation practice was evaluated in FY21, examining effects of shallow flooding of post-harvest fields for agronomic benefits and migratory shorebird habitat. Preliminary results indicated positive benefits, and as a result, a $1 million U.S. Environmental Protection Agency Farmer-to-Farmer grant was received by ARS scientists and their University collaborators to continue the study. A manuscript describing the first year results is in preparation. A manuscript was published in the journal Water which experimentally evaluated the role of vegetated ditch habitats on whole ditch metabolism, nutrient update, and denitrification. Data from experimental field trials of within-ditch filter socks are being evaluated in preparation for publication. In support of Objective 3, a long-term simulation of the 21 Gun study at Stoneville, Mississippi is under development to evaluate AnnAGNPS’ ability to simulate differences in management and then to evaluate long-term trends related to these practices. These simulations will be part of two manuscripts, one expected to be submitted in FY21 and one for FY22. In support of Objective 4, the Long-Term Agroecosystem Research (LTAR) common experiment sites have been secured and eddy-covariance towers and soil moisture sensors are collecting data in the aspirational and “business-asusual” fields at two farms. Additionally, historical datasets from both the Goodwin Creek and Beasley Lake watersheds have been uploaded into a common data management platform and the data are currently under quality assurance/quality control checks. Plans for analyzing and submitting manuscripts on these datasets are underway for a special journal issues related to the Lower Mississippi River Basin in 2022. In support of Objective 5, the construction phase was completed for the groundwater transfer and injection point project with the U.S. Army Corps of Engineers. Currently, the extraction well is operating 24 hours per day at approximately 1500 gallons per minute, with both injection wells operating as designed at 750 gallons per minute, each. As of April 15, 2021, the system injected approximately 60 million gallons during the first four weeks of operation. Remote monitoring and system controls are accessible through a web portal for ARS team members. Since April 15, 2021, data collection and archiving of water level and water quality data from the network of 17 observation wells has continued. Water quality data from six observation wells is measured in the field at weekly to biweekly intervals, while monthly samples are collected from all observation and pumping wells, the Tallahatchie River, and three sites in Lake Henry (the receiving water body for backwash water from injection wells). Pumping is expected to continue into the fall and winter, and a decision regarding the continued operation after this period will be based on results of intensive monitoring efforts.

Accomplishments
1. Aquatic vegetation removes nitrogen and phosphorus in runoff. Many farmers remove aquatic plants growing in their drainage ditches because of perceived inhibition of flow and aesthetics reasons. ARS researchers in Oxford, Mississippi, demonstrated that allowing managed vegetation to remain in farm ditches resulted in significant nitrogen and phosphorus removal through biological activity of bacteria, algae, and uptake by the associated aquatic plants. These results support efforts to establish and manage ditch vegetation to lessen nutrient impacts downstream and into the Gulf of Mexico.

2. Manage nitrogen and phosphorus for lake health. Since the 1970s, the dominant scientific thought has been that phosphorus impacts water quality in freshwater systems and nitrogen impacts water quality in marine systems. Using experimental freshwater ponds, ARS researchers in Oxford, Mississippi, determined that the highest concentrations of algae and ecosystem production occurred at the highest levels of nitrogen concentrations. These results demonstrate that water quality problems in nutrient enriched freshwater lakes cannot be solved unless both nitrogen and phosphorus concentrations are managed appropriately.

3. Key water quality indicators for freshwater lake health. Sediments, nutrients, and water withdrawal can negatively impact agricultural watershed lakes in the Lower Mississippi River Basin. ARS researchers in Oxford, Mississippi, examined water and sediment samples from three lakes with varying water depths and determined that deeper water had fewer nutrients and would often be clearer in the summer, as opposed to more shallow water which consistently possessed more algae. Algal blooms in lake water were best predicted by nitrogen concentrations, while dissolved oxygen was the best water quality indicator for phosphorus concentrations. Water temperature controlled algal blooms more than light limitation due to turbidity. These results demonstrate that increasing water storage in agricultural watershed lakes could help reduce algal blooms and hypoxia in the Lower Mississippi River Basin.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS