Location: Southeast Watershed Research
2020 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 by ARS reseachers at Tifton, Georgia, on the Little River Experimental (LREW), Gibbs Farm, and Tifton Urban Watersheds continue (Obj. 1-4). 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 were collected by ARS researchers from Tifton, Gerogia, at all sites in the LREW to relate dissolved organic matter (DOM) to land-use (Obj. 1). Bi-weekly water samples from the LREW, Dairy Farm, Gibbs Farm and Tifton Urban Watersheds, were analyzed by ARS researchers at Tifton, Gerogia, for DOM optical characteristics (began in November 2016). The resulting optical data were processed by ARS researchers at Tifton, Gerogia, using parallel factor (PARAFAC) analysis. After major rainfall events, water samples from select sites were extracted and the extracts will be analyzed by ARS researchers at Tifton, Georgia, 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 (Obj. 1). Boundary maps for Watersheds O3 and New River have been developed and are being refined using newly acquired data. Automated flow monitoring, sample collection, and water quality analysis by ARS researchers at Tifton, Gerogia, at existing sites at the Dairy Farm, LREW O3, and LREW O continues. Plans are being developed by ARS researchers at Tifton, Gerogia, for installation of hydrologic measurement and sampling equipment at the Wilson farm. 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 (Obj. 2, 3). As part of this project and ARS researchers at Tifton, Gerogia, participation in the ARS Long Term Agroecosystem Research (LTAR) network, we have implemented studies to complement ongoing research conducted at all participating LTAR locations (Obj. 3). Sampling from surface runoff collectors has begun and ARS researchers at Tifton, Gerogia, are in the final stages of making the University of Ponder Farm plots fully operational. Completion of the University of Georgia Gibbs Farm plots is anticipated by the end of 2020. 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/) (Obj. 3). Eddy covariance data are being collected at two sites by ARS researchers at Tifton, Gerogia, for quantifying the exchange rates of trace gases over natural ecosystems (Obj. 3). Very high resolution Red Green Blue (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 (Obj. 3, 4).
ARS researchers at Tifton, Georgia, are utilizing landscape and watershed scale assessment models to evaluate the long-term sustainability of agricultural watersheds (Obj. 4). 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 will be 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 LREW 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. Tremendous improvements have been made by ARS researchers at Tifton, Gerogia, in accuracy and resolution of these remotely sensed data, documented through 34 scientific publications utilizing data collected at the LREW and other locations within the core validation network. The credibility of the remotely sensed data has been greatly enhanced by the testing provided by this nation-wide 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. ARS scientists at Tifton, Georgia, collected streamflow samples and measured stream nutrient concentrations from the Little River Experimental Watershed over a 36-year period. Stream nutrient concentrations are unresponsive to change 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 for critical land-use planning and regulatory decision-making across the Coastal Plain.
3. Crop classification. Observations of crops from satellite borne sensors are critical for international crop monitoring activities, but cloudy conditions reduce the utility of optical imagery by obscuring surface reflectance. ARS scientists at Tifton, Georgia partnered with the Joint Experiment for Crop Assessment and Monitoring (JECAM) to include the LREW as one of ten international validation sites to evaluate Synthetic Aperture Radar (SAR). Overall crop type classification accuracies were above 80%. Classification results were influenced by the mix and number of agriculture classes present at each site. These results have important operational implications for regions of the world dominated by cloudy conditions and the lack of adequate amounts of optical imagery to support satellite-based crop monitoring.
Review Publications
Endale, D.M., Schomberg, H.H., Truman, C., Franklin, D., Tazisong, I., Jenkins, M., Fisher, D. 2019. Runoff and nutrient losses from conventional and conservation tillage systems during fixed and variable rate rainfall. Journal of Soil and Water Conservation Society. 74(6):594-612. doi:10.2489/jswc.74.6.594.
Colliander, A., Jackson, T., Berg, A., Bosch, D.D., Caldwell, T., Chan, S., Cosh, M.H., Holifield Collins, C.D., Martinez-Fernandez, J., Mcnairn, H., Prueger, J.H., Starks, P.J., Walker, J., Yueh, S. 2020. Effect of rainfall events on SMAP radiometer-based soil moisture accuracy using core validation sites. Journal of Hydrometeorology. 21:255-264.
