Location: Southeast Watershed Research2021 Annual Report
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.
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.
ARS scientists at Tifton, Georgia, continue flow data and water quality collection and analysis efforts 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 have been updated. Historical land cover data are being assembled by ARS scientists at Tifton, Georgia in a geodatabase. Dissolved organic matter (DOM) optical characteristics are still being measured by as part of our routine water quality analyses (2016-present). Existing sites at the Dairy Farm, LREW Watershed O3, and LREW Watershed O, along with new sites near Sumner, Georgia are being used to evaluate livestock impacts at the watershed scale (Obj. 1). The University of Georgia Dairy Farm transitioned to beef cattle operation only in 2021. ARS scientists at Tifton, Georgia will continue to monitor changes in hydrology and water quality at the farm. Boundary maps for Watersheds O3 and New River have been developed and refined using newly acquired data. ARS scientists at Tifton, Georgia continues automated flow monitoring, sample collection, and water quality analysis at the Dairy Farm, LREW O3, and LREW O. Plans are being developed for installation of hydrologic measurement and sampling equipment at the Sumner Farm. Data continue to be collected from the meteorological station installed at the Sumner Farm. Dairy Farm soil cores have been processed for analysis of microbial biomass C and N, and processing of the Sumner Farm cores is underway. Re-design of field scale plots at the University of Georgia Gibbs and Ponder Farms began in the spring of 2018 for purposes of this project (Obj. 2, 3). As part of this project and ARS scientists at Tifton, Georgia participation in the ARS Long Term Agroecosystem Research (LTAR) network, ARS scientists at Tifton, Georgia have implemented studies to complement ongoing research conducted at all participating LTAR locations (Obj. 3). The University of Ponder Farm plots are fully operational. Collection of runoff and drain tile samples started in Fall 2020. Samples have been processed by ARS scientists at Tifton, Georgia for DOM optical characteristics. Other water quality analyses are pending. Completion of the University of Georgia Gibbs Farm plots is anticipated by the end of 2021. Data collection continues at the SEWRL LTAR meteorological and phenology stations (Obj. 3). Eddy covariance data are being collected by ARS scientists at Tifton, Georgia at two sites for quantifying the exchange rates of trace gases over natural ecosystems (Obj. 3). 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 (Obj. 3, 4). ARS scientists 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 by ARS scientists at Tifton, Georgia 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. 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. ARS scientists at Tifton, Georgia, began collaborating with an ARS scientist at Beltsville, Maryland to examine the transport and fate of enteric pathogens in irrigation water. The Beltsville team has selected three irrigation ponds at two of SEWRL’s LTAR farm sites (Sumner and Ty Ty), and biweekly sample was initiated in July. Sites were selected based on presence of enteric bacteria and the capacity to leverage ARS Tifton, Georgia current research quantifying groundwater pumping rates, irrigation pumping rates, pond water residence time, nutrient and dissolved organic matter loads, and extensive sUAS data collection program.
1. Validation of remotely sensed soil-water. ARS scientists at Tifton, Georgia suggest estimates of soil moisture across the globe are critical for prediction of climate, water balance, and crop production. The Little River Experimental Watershed (LREW) managed by ARS researchers at Tifton, Georgia provides a unique dataset for the diverse Coastal Plain landscape as part of a nation-wide network of core validation sites collecting continuous soil-water measurements across large spatial areas. The national network has played a crucial role in improving the accuracy, resolution, and credibility of satellite based remotely sensed data as documented through 34 scientific publications.
2. Importance of long-term data in understanding soil moisture. ARS scientists at Tifton, Georgia, found validation of soil moisture utilizing data collected from satellites and simulated by numerical models use ground based measurements for verification purposes. The ground-based measurements are often assumed to be stable, but there has been little research showing the consistency of a data and their variability over time. A nationwide study including researchers from several ARS watersheds showed that ground-based measurements effectively measure soil moisture conditions during the year, which increased confidence in management and assessment decision-making tools that rely on soil water content data.
3. Hydrologic and water quality effects from biofuel crops. ARS scientists at Tifton, Georgia, suggest bioenergy crop production has been introduced globally as an alternative fuel source aiming to reduce greenhouse gas emissions. Using the Soil and Water Assessment Tool (SWAT), ARS researchers from Tifton, Georgia along with researchers from the University of Georgia showed that adding carinata as a winter crop in rotation with wheat in the Atlantic Coastal Plain may reduce surface runoff and sediment and phosphorus loads to downstream water bodies.
4. Conservation Effects Assessment Project - Watershed Assessment Studies Network. The U.S. Department of Agriculture created the Conservation Effects Assessment Project (CEAP) in 2003 to measure the effects of agricultural conservation practices and develop the science-base for managing agricultural landscapes. Results from 23 watershed studies at 18 locations,including Tifton, Georgia, showed CEAP efforts improved simulation models and developed new and effective conservation practices and assessment tools that address goals and document outcomes for the USDA Mississippi River Basin Healthy Watersheds Initiative, the Great Lakes Restoration Initiative, the Chesapeake Bay Watershed Initiative, the Lake Champlain Basin Initiative, and local source water protection efforts.
5. Groundwater analysis with the Soil and Water Assessment Tool (SWAT+). USDA and the US EPA use the Soil and Water Assessment Tool (SWAT+) watershed model to evaluate impacts of national conservation policy in the United States. A new physically based, spatially distributed groundwater flow module for the SWAT+ watershed model was developed by ARS scientists at Tifton, Georgia that accounts for aquifer recharge and evapotranspiration, groundwater pumping, and surface-groundwater interactions through the stream. Application of the model on the 327 km2 ARS Little River Experimental Watershed in southern Georgia, showed reasonable agreement with measured streamflow. The new model provides improved representations of the interaction between surface and subsurface processes in agricultural landscapes.
6. Understanding spatial variability of crop pests. Precision agriculture (PA) is the application of management solutions only when and where needed instead of on whole fields. However, knowledge on why crop pests aggregate in different parts of a field during different times is limited. ARS researchers at Tifton, Georgia, along with researchers from the University of Georgia found that numbers of pest insects and their natural enemies shifted in relation to environmental conditions across 81 locations within a field of the perennial biofuel feedstock grass, Miscanthus. Results showed that pest numbers increased at higher wind speeds but decreased in parts of the field having higher elevation, higher soil silt and sand content, and greater field greenness. Documenting patterns of pest responses to environmental factors at fine space and time scales has the potential to inform and improve PA decisions that reduce damage to beneficial insects.
7. Complexity of Dissolved organic matter (DOM) dynamics in agricultural watersheds. The chemical composition and reactivity of stream DOM are dependent on landscape source, rainfall, and in-stream processes. ARS researchers from Tifton, Georgia, showed that DOM composition in the Little River Experimental Watershed (LREW) is influenced by both land cover and hydrology. During average and low streamflow conditions, DOM is primarily autochthonous (recently produced, less complex material believed to arise from in-stream production or transformation). However, during periods where streamflow changes from average to high, DOM from watersheds having greater riparian area in residential or woodland land cover shifts to older, more complex material typically associated with allochthonous (non-stream) production and then back to autochthonous during low flow. Developing an improved understanding of DOM sources, transport and reactivity will improve our ability to predict downstream water quality in agriculturally impacted watersheds.
8. Tradeoffs and synergies of ecosystem services in working lands. Working lands are highly valued for their provisioning services, and, to some degree cultural services, while regulating, and supporting services are harder to quantify and less appreciated. Researchers from ARS at Tifton, Georgia, and from the USDA Long-Term Agroecosystem Research (LTAR) network documented some of the complexities in assessing tradeoffs among indicators of net primary production (provisioning), agricultural Nitrogen runoff (regulating), and habitat for biodiversity (supporting). Synergies were found among supporting and regulating services, while tradeoffs exist among provisioning and supporting services. For example, natural lands embedded in agricultural landscapes of the Southeastern U.S. score lower in regional production values but mitigate N loading in some areas (Georgia) while supplying critical habitat for biodiversity in others (Florida). Thus, even simplistic comparisons can result in conflicting outcomes depending on the perspective of the user, and assessments at multiple scales can be critical to finding the sweet spot conducive to compromise among sometimes conflicting perspectives.
9. Nitrous oxide emission from agricultural soils may be much lower than assumed. Although much attention has been given to the potential for agricultural soils to store carbon, the 100-year global warming potential (GWP) of nitrous oxide (N2O) is 265-298 times higher than carbon dioxide. Scientists at the City University of New York working in collaboration with ARS scientists at the Columbia, Missouri; Tifton, Georgia; and University Park, Pennsylvania long term agroecosystem research (LTAR) network sites measured potential soil denitrification rates (grams per hectare per day) that ranged from 46-783 at the PA site, 227-763 at the MO site, and 1246-1448 at the GA site. Of these totals, conversion to nitrogen gas (N2), which has no GWP, was consistently greater than 90% of the denitrification product. Topographic position, deep soil layers that trap water, and soil rewetting after dry periods affected N2 and N2O production. These observations suggest that areas of high denitrification can be predicted and thus improve our ability to manage N for soil fertility, water quality, and reduced N2O emissions.
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