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

2020 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, data analyses and manuscript preparation were conducted on an experiment describing spatial and temporal variation in denitrification rates in Beasley Lake, Mississippi, the Unit’s Conservation Effects Assessment Program (CEAP) watershed. Additional analyses and manuscript preparation were conducted on transport, breakdown, and effects of benthic nutrient processing in Roundaway Lake (Mississippi). Research on sediment and organic matter traps continued with new testing elements implemented to compare a new trap design that can better handle fluctuating water depth, as well as reestablishment of traps in Roundaway Lake for comparisons between watersheds with and without extensive BMPs. Laboratory algal bioassays on nutrient and temperature gradients for summer and fall mesocosms were completed in November 2019, while selection of physical stressors based on laboratory algal bioassay results were completed in early March 2020. In support of Objective 2, a manuscript describing empirical links between conservation practices and runoff water quality was published in a CEAP special issue of the Journal of Soil and Water Conservation. 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 FY20, three years of runoff and agrochemical transport data and four 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 Fall 2020. Phase 2 of the 21-Gun study with soybean as the focus crop was completed in 2019, and four papers were submitted and accepted for publication. In spring 2020, the experimental area was prepared for a new phase using cotton as the crop of focus and new conservation treatments. 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 FY20 and one for FY21. In support of Objective 4, the Long-Term Agroecosystem Research (LTAR) common experiment sites have been secured and work is underway to install eddy-covariance towers and soil moisture sensors in the aspirational and “business-as-usual” fields at two farms in the late summer and early fall of 2020. 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 2021. In support of Objective 5, we continued development of a novel pilot project for investigating managed aquifer recharge in the Mississippi Valley Alluvial Aquifer. Construction of the project is nearing completion. The monitoring plan is being developed. Observation wells are online. A rigorous routine of sensor calibration and cleaning was establishment to prevent fouling of instruments. Collected data is automatically broadcast to the National Sedimentation Laboratory and archived by WISKI. The 2009 lidar dataset of the Yazoo River Basin was corrected for topographic discontinuities along flight line edges. Lentic surface water bodies have been delineated in the Yazoo River Basin utilizing the 2009 lidar data and these are currently being compared to manually delineated water bodies from three HUC-10 watersheds and to the National Hydrography Dataset Plus High Resolution (NHDPlus HR). A database with these water bodies is under development and includes surface area, precipitation, estimated evaporation, and will include estimated average depth and volume. Centerlines of lotic water bodies in the HUC-12 Roundaway Bayou watershed were delineated showing significant deficiencies in NHDPlus HR for application to the Yazoo River Basin with respect to lotic ecosystems.

Accomplishments
1. Aquatic vegetation removes nitrogen and phosphorus in runoff. A common concern for using wetland vegetation to reduce nitrogen in agricultural ditches is that these plants may release nutrients back into the water during winter plant decay. ARS researchers in Oxford, Mississippi, demonstrated through a summer, fall, and winter experiment, along with a model, that vegetation permanently removes extra nitrogen in runoff using microbial transformations to gaseous nitrogen. These results support efforts to establish ditch vegetation to lessen nutrient impacts downstream. Farmers, landowners, and conservationists can use these results to address issues of hypoxia in the Gulf of Mexico.

2. Conservation Effects Assessment Program demonstrates positive results from Beasley Lake, Mississippi. Runoff, sediment, and nutrient losses from sub-drainage areas were monitored from 2011 to 2017 in areas under row crops with and without edge-of-field buffers and under the Conservation Reserve Program. ARS researchers in Oxford, Mississippi, determined edge-of-field vegetated buffers and conservation reserve effectively reduced topsoil loss and transport of nutrients downstream, reducing water quality impacts on rivers and lakes. Farmers, landowners, and action agencies can use these results from a watershed-scale study to improve water quality in the Lower Mississippi River Basin.

3. A novel revision for modeling denitrification in shallow ditches significantly changes nitrogen reduction estimations in the field. Popular ecological models for denitrification in water bodies, used to estimate nutrient reduction, do not represent what really occurs in shallow agricultural systems, such as drainage ditches. ARS researchers in Oxford, Mississippi, conducted an intensive experiment that included typical sampling parameters, as well as other factors that influence nitrogen gas flux. As a result, an improved model was developed to more accurately estimate nitrogen gas fluxes and denitrification from agricultural drainage ditches which serve as unique conservation management practices. This study will provide conservationists and action agencies more reliable data in their efforts to address hypoxia in the Gulf of Mexico.

4. Subsoiling in conservation tillage has positive environmental and agronomic benefits in soybeans. A factor reducing the adoption of conservation tillage on medium- to coarse-textured soils in the mid-southern USA is reduced yield due to the development of restrictive soil layers. ARS researchers in Oxford, Mississippi, conducted research to determine if the inclusion of subsoiling in conservation tillage systems would maintain crop yield, profitability, and water use efficiency (WUE) relative to that of conventional tillage. Inclusion of subsoiling as a component of a conservation tillage system maintained or improved soybean grain yield, net returns above specified costs, and WUE up to 68% in three of four years relative to conventional tillage or conservation tillage with no subsoiling. Inclusion of subsoiling as a component of conservation tillage systems would maximize soybean grain yield, net returns above specified costs, and WUE on medium- to coarse-textured soils in the mid-southern USA, while addressing resource conservation concerns.

U.S. DEPARTMENT OF AGRICULTURE

Water Quality and Ecology Research: Oxford, MS