Location: Southeast Watershed Research
2019 Annual Report
Objectives
1. Quantify and assess the interactions among agroecosystems and landscape components and their impacts on water supply and water quality in agricultural watersheds of the southeastern U.S.
2. Quantify and assess the effects of agricultural conservation practices and managed land-use interfaces at field, landscape, and watershed scales in agricultural watersheds of the southeastern U.S.
3. As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in the Gulf Atlantic Coastal Plain (GACP), use the Little River Experimental Watershed (LREW) 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 Gulf Atlantic Coastal Plain (GACP) 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.
4. Utilize landscape and watershed scale assessment models to evaluate the long-term sustainability of agricultural watersheds.
Approach
The research integrates field, landscape, and watershed observations. As such, research sites are located at multiple scales each supporting watershed observations. The SEWRL operates watershed facilities Little River Experimental Watershed (LREW) that are the basis for our long-term hydrology and natural resources research. In addition to these watersheds, the SEWRL has established long-term research at plot (~0.2 Ha) and field (> 10 Ha) scales. The objectives in this plan contribute to the LTAR Common Experiment over-arching hypothesis that “aspirational treatments will increase overall carbon stocks and in particular, soil carbon…leading to increased ecosystem resiliency”. Individual sub-objectives are focused on providing an improved understanding of spatial and temporal drivers and ecosystem services responses associated with the three Common Experiment sub-hypotheses: 1) The magnitude, direction and rate of change will vary with topographic and soil characteristics of the landscape; 2) Sustainable ecosystem productivity, yield, and yield quality will be significantly improved by the development of specific and adaptive G x E x M x Social x Economic systems; and 3) Biologically-based inputs will drive the rate and magnitude of carbon stock increases (e.g., nutrient cycling, insect comminution, decomposition, etc.). The experiments presented are designed as an integrated systems approach to understanding processes at the plot-to-landscape scale using the LREW as the synthesis scale for testing and verification of the Long Term Agroecosystem Research Common Experiment hypothesis. Each objective and sub-objective is designed to address selected spatial and temporal scale processes, provide information for qualifying extrapolations between scales, and/or explore novel technical approaches for characterizing ecosystems services within the LREW. We will use remote sensing, geospatial modeling, statistical modeling and process modeling to evaluate linkages and identify information gaps across scales. Specific research will: 1) characterize the impacts that agricultural land management and land-cover have on water resources in southern coastal plain watersheds; 2) examine relationships between conservation practices (including winter cover), indicators of productivity (e.g. SOC, NPP), other drivers of land cover change, and water quality; 3) characterize composition of DOM with land-use; 4) quantify differences between watersheds with agricultural livestock impacts to watersheds with minimal agricultural livestock impact; 5) quantify stream flow and chemistry differences between urbanized and agricultural watersheds; 6) quantify the impact of agricultural irrigation ponds on watershed water balance; 7) quantify differences in provisioning and regulating ecosystem services between typical and aspirational agricultural production systems; 8) compare spatial and temporal variations between provisioning and regulating ecosystems services; and 9) use landscape and watershed scale assessment models to evaluate the long-term sustainability of agricultural watersheds.
Progress Report
Flow data and water quality collection and analysis efforts on the Little River
Experimental (LREW), Gibbs Farm, Tifton Urban Watersheds, and Upper Suwannee River in South Georgia continue. Geographical Information System (GIS) databases of soils, hydrography, land-cover, and land-management across the LREW are being updated. Historical land-cover data are being assembled in a geodatabase. Water samples are being collected at all sites in the LREW to relate dissolved organic matter (DOM) quality to land-use. Bi-weekly water samples from the LREW, Dairy Farm, Gibbs Farm and Tifton Urban Watersheds, are being analyzed for DOM optical characteristics (started in November 2016). The resulting optical data is being processed using parallel factor (PARAFAC) analysis. After major rainfall events, water samples from select sites were extracted and the extracts will be analyzed for DOM molecular-level composition using high resolution mass spectrometry (FT- ICR MS).
Existing sites at the Dairy Farm, LREW Watershed O3, and LREW Watershed O, along with new sites at the Wilson Farm will be used to evaluate livestock impacts at the watershed scale. Boundary maps for Watersheds O3 and New River were developed based on newly released 1m resolution digital elevation models for Tift County. Automated flow monitoring and sample collection at existing sites at the Dairy Farm, LREW O3, and LREW O continues. Sample collection has begun at the Wilson Farm and plans are being developed for installation of hydrologic equipment. Data continue to be collected from the meteorological station installed at the Wilson Farm. Dairy Farm soil cores have been processed for analysis of microbial biomass C and N, processing of the Wilson Farm cores is underway.
Re-design of field scale plots at the University of Georgia Gibbs and Ponder Farms was begun in the spring of 2018 for purposes of this project. As part of this project and our participation in the ARS Long Term Agroecosystem Research (LTAR) network, we have implemented studies to complement ongoing research conducted at all participating LTAR locations. Data collection continues at the SEWRL LTAR meteorological and phenology stations. These data are available through the National Agricultural Library (https://ltar.nal.usda.gov/). Eddy covariance data are being collected at two sites for quantifying the exchange rates of trace gases over natural ecosystems. Very high resolution RGB, multispectral imagery and thermal data from a small unmanned aerial system (sUAS) are being gathered throughout the growing season on two private landowner farms for model development to scale yield measurements from field to landscape.
We are utilizing landscape and watershed scale assessment models to evaluate the long-term sustainability of agricultural watersheds. Toward this goal, a framework for simulation utilizing the landscape version of the Soil and Water Assessment Tool (SWAT+) on the LREW has been established. The model has been used to quantify the impacts of conservation practices and winter covers in the LREW. A geodatabase has been designed and geophysical characterization of the watershed is being incorporated into the database.
NASA Synthetic Aperture Radar (SAR) Validation: Crop fields in the southern part of the Little River Experimental Watershed at Tifton, Georgia were selected among a handful of sites flown in the 2019 NASA Uninhabited Aerial Vehicle SAR AM/PM campaign. This NASA effort is in anticipation of future soil moisture and agricultural cover data products by the upcoming NASA-Indian Space Research Organization (ISRO) SAR (NISAR) mission. Synthetic aperture radar data is being compiled with locally collected soil moisture and crop attribute data provided by the LREW.
Accomplishments
1. Validation of remotely sensed soil-water. Estimates of soil moisture across the globe are critical with regard to prediction of climate, water balance, and crop production. The Little River Experimental Watershed (LREW) at Tifton, Georgia, is part of a nation-wide network of core validation sites collecting continuous in-situ soil-water across large spatial areas. This network has played a crucial role in the calibration and validation of satellite based remotely sensed soil-water. ARS researchers in Tifton, Georgia have made tremendous improvements in both the temporal and spatial resolution of these remotely sensed data, largely due to data provided by the LREW and other locations within the core validation network. These improvements have stabilized and increased the accuracy of remotely sensed soil moisture estimates. The credibility of the remotely sensed data has been greatly enhanced by the testing provided by this nation-wide in-situ network. The LREW provides a unique data set for the diverse Coastal Plain landscape.
2. Long-term water quality characteristics of a Coastal Plain Watershed. Long-term hydrologic and water quality observations which integrate the impacts of climate and land-use at the watershed scale are critical for long-range regional planning. A forty-one-year dataset containing hydrologic and water quality assessments of conditions within the Little River Experimental Watershed was assembled by ARS researchers in Tifton, Georgia. Stream nutrient concentrations appear to be unresponsive to changes in cropping and management practices due to removal by the dense riparian forest buffers within the watershed. Thus, nutrient loading is closely tied to streamflow volume which is largely a function of precipitation and climatic season. This information is a critical component for land-use planning and regulatory decision-making across the Coastal Plain.
3. Impacts of conservation tillage. Conservation tillage is a management tool that can reduce runoff, erosion, and agrichemical loss from agricultural fields. ARS researchers in Tifton, Georgia used fourteen-years of crop yield, surface runoff, subsurface flow, and sediment transport data from long-term plots to compare the hydrologic and water quality impacts of conservation tillage (strip tillage, ST) versus conventional tillage (CT) in the Georgia Coastal Plain using the Agricultural Policy/Environmental eXtender (APEX). No treatment differences were found for either cotton or peanut yields, and total water loss (surface and subsurface) was nearly equivalent for the two systems at 30% of annual rainfall. However, surface runoff from CT was found to be 1.7 times that of ST, while subsurface runoff from the ST was found to be 1.7 times that of CT. This research provides critical quantitative data which can be used to improve decision-making regarding risk related to mode of agricultural contaminant export (i.e., water soluble in subsurface flow under ST versus sediment-sorbed in surface runoff under CT) and to quantify the long-term benefits of USDA conservation programs.
4. Carbon Sequestration for two Coastal Plain crops. Potential global climate changes make understanding net carbon accumulation a critical component of future land-use planning. ARS researchers in Tifton, Georgia used biofuel productivity for dryland miscanthus and irrigated corn to quantified using an eddy covariance system that measures crop water use and net carbon gain or loss. Carbon budgets indicated that both the miscanthus and corn systems had a net carbon loss to the atmosphere over the study period. The net carbon loss from both crops appeared to be driven by very high carbon respiration resulting from soil organic matter decomposition and crop energy requirements. Relatively low biomass production, low water use efficiency and high respiration for miscanthus in this experiment suggest that the strain tested (Miscanthus × giganteus IL Clone) may not be well-suited for dryland production under the hot and periodically dry conditions found in South Georgia USA.
Review Publications
Moriasi, D.N., Teet, S.B., Guzman, J.A., King, K.W., Bosch, D.D., Bjorneberg, D.L., Williams, M.R. 2016. Framework to parameterize and validate APEX to support deployment of the nutrient tracking tool. Agricultural Water Management. 177:146-164.
Olson, D.M., Zeilinger, A., Prescott, K., Coffin, A.W., Ruberson, J., Andow, D. 2018. Landscape effects on Solinopsis invicta (Hymenoptera: Formicidae) and Geocoris spp. (Hemiptera: Geocoridae), two important omnivorous arthropod taxa in field crops. Environmental Entomology. 47:1057-1063. https://doi.org/10.1093/ee/nvy104.
Pisani, O., Boyer, J., Podgorski, D., Thomas, C., Coley, T., Jaffe, R. 2017. Molecular composition and bioavailability of dissolved organic nitrogen in a lake flow-influenced river in south Florida, USA. Aquatic Sciences - Research Across Boundaries. 79(4):891-908. https://doi.org/10.1007/s00027-017-0540-5.
Maleski, J.J., Bosch, D.D., Anderson, R.G., Coffin, A.W., Anderson, W.F., Strickland, T.C. 2019. Evaluation of miscanthus productivity and water use efficiency in southeastern United States. Science of the Total Environment. 692:1125-1134. https://doi.org/10.1016/j.scitotenv.2019.07.128.
