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

2019 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
Two mesocosm experiments were conducted evaluating nutrient mitigation capabilities of three emergent aquatic plants in monocultures and mixtures. Samples have recently been processed, and data evaluation is underway. This complements two previous years of experiments conducted to examine plant mitigation ability over multiple exposures and years. Diel denitrification studies were conducted utilizing stream mesocosm systems. Nutrient gradients were amended into the aquatic systems and response of water quality parameters was measured. Additional denitrification measurements were also conducted in oxbow lakes within the lower Mississippi River Valley. Physical stressors (temperature, nutrients, and suspended solids) were determined at field sites currently under investigation. Laboratory experiments (bioassays) were conducted with natural algal populations. Long-term (1996-present) assessments in the Conservation Effects Assessment Program (CEAP) Beasley Lake watershed continue. Lake and runoff water quality assessments are ongoing. Two manuscripts have been recently submitted and are currently in revision/review. Select study results demonstrated that vegetated buffers, vegetated drainage ditches, vegetated sediment pond and conservation reserve program best management practices (BMPs) in place were effective in reducing suspended solids loads, moderately effective at reducing nutrient loads in runoff, and improving lake water quality. Long-term studies as well as studies established from 2017-2019 to determine the effect of cover crop (Austrian pea, crimson clover, cereal rye, tillage radish) and tillage (no-tillage and reduced tillage) on soil quality, yield, economic analysis, irrigation application efficiency (furrow and sprinkler), runoff erosion, and off-site N and P transport continued. Sealing in the surface of silt loam soils contributes to low permeability and low irrigation application efficiency in Mississippi corn production systems. Cover crops may improve irrigation application efficiency and interest in incorporating cover crops into Mississippi production systems has risen in recent years. Yield data for the 2017 growing season shows 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. Yield data for 2018 is under analysis. 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 in 2017, 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. In 2019 a separate study was established to determine yield effects of nitrogen by irrigation level in a leguminous cover crop (Austrian pea). An experimental plot was established in Fall 2018 in support of the LTAR Common Experiment Project to assess tillage, cover crop, and crop rotation in sorghum and cotton systems. The 2019 growing season was the first year of assessment. Assessment of a tailwater recovery system (reservoir and tail ditches) continues in Sunflower County, Mississippi, for its ability to improve water quality and reduce dependence on groundwater resources for crop irrigation. Continuous monitoring and flow-triggered sampling runoff events have four years of storm sampling, while five years of bi-monthly water quality sampling have been completed. Data analyses is ongoing. Denitrification studies using manufactured filter socks were conducted in July 2018 in a plot-size, replicated field setting. Collected data are being analyzed to narrow down possible research questions for future studies. One manuscript was published, with a second manuscript in the final stages of production by the journal regarding this research. Integrated capabilities of the AnnAGNPS (Annualized Agricultural Non-Point Source pollution) model to characterize and evaluate ephemeral gullies, riparian buffers, and constructed wetlands, as well as sheet and rill erosion was successfully performed on an experimental watershed in Mississippi. This provides critical management tools to evaluate the most efficient combination of conservation practices applied within watershed systems needed in conservation management planning. Additionally, the Little Sunflower River watershed in Mississippi was evaluated for the impact of management practices on runoff and erosion using AnnAGNPS, providing a better understanding of the link between irrigation water management practices and downstream water quality.

Accomplishments
1. Mulch and gypsum help reduce nutrient export into rivers. Runoff containing excess nitrogen and phosphorus fertilizer from agricultural fields can be transported into water bodies and cause algal blooms and dead zones impacting fisheries and tourism. Denitrification is a natural process that transforms nitrogen, like that from fertilizer, into an unreactive gas. ARS researchers at Oxford, Mississippi, examined the ability of additions such as hardwood mulch and mulch mixed with gypsum in order to determine whether denitrification could be enhanced in sediment cores taken from edge-of-field systems. Mulch and mulch-gypsum amendments were able to remove 65-69% of the nitrogen load in the system. When gypsum was included with the mulch, release of phosphorus from the system significantly decreased. Adding organic carbon sources to the sediment cores significantly increased denitrification rates. By adding inexpensive organic sources, such as hardwood mulch, to edge-of-field systems such as ditches, farmers can reduce the impact of nitrogen pollution while maintaining agricultural production.

2. Management practices battle nature for long-term water quality improvements. In theory, when fewer agricultural nutrients are transported to water bodies, the likelihood of eutrophication, or nutrient enrichment of the water body, is lessened. Eutrophication of waters leads to environmental problems such as hypoxia and other water quality issues. ARS researchers in Oxford, Mississippi, examined 19 years of nutrient-related water quality data from an oxbow lake in the lower Mississippi River Valley. With the implementation of vegetated buffers, a sediment retention pond, and conservation tillage within the watershed, lake water clarity improved, and phosphorus concentrations decreased. Algal concentrations increased with conservation tillage and vegetative buffers, indicating that while summer eutrophication effects can be improved, these changes can be off-set by other natural factors which may negatively affect water quality.

3. Changing cropland production over the last several decades in the Mississippi Delta has resulted in increased irrigated agriculture and runoff during the irrigation season. The Mississippi River alluvial floodplain is one of the most productive agricultural regions in the United States, and the Upper Sunflower River watershed is an important part of this region. Over the past decade, land-use patterns in the Upper Sunflower River watershed have shifted to include more corn and soybean cropland and less cotton. In addition, irrigation adoption has increased from approximately 26% of the watershed in 2001 to 43% in 2015. This study by ARS scientists in Oxford, Mississippi, uses watershed modeling technology, specifically the Annualized Agriculture Non-Point Source (AnnAGNPS) watershed pollution model, to assess the impacts of these land-use and irrigation changes on runoff and sediment loads in the Upper Sunflower River watershed. Modeling simulations demonstrated that the increase in irrigation adoption increased runoff during the irrigation season, while conversion of cotton to corn and soybean cropland reduced average annual suspended sediment loads. These results provide a starting point for understanding watershed sensitivity to changes in crop type and irrigation applications.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS