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United States Department of Agriculture

Agricultural Research Service


Location: Southeast Watershed Research

2009 Annual Report

1a. Objectives (from AD-416)
1. Use remote sensing tools to develop rapid assessment procedures for soil and water resources in Coastal Plain agricultural systems. a. Evaluate tillage and residue management effects on soil carbon accretion, soil water content and associated changes in crop response. b. Remotely quantify variability in crop residue cover to better develop indices that may be used to rapidly assess conservation tillage adoption at the watershed scale. 2. Modify, test, and apply the Riparian Ecosystem Management Model (REMM) to evaluate and guide restoration and management of riparian buffers and wetlands. 3. Develop an improved GIS modeling framework for accurately quantifying soil moisture, evapotranspiration (ET), and infiltration in Coastal Plain watersheds. a. Evaluate techniques for assimilating estimates of soil-moisture at the soil surface into field and watershed scale hydrologic models. b. Improve methods for estimating evapotranspiration and infiltration within Coastal Plain watersheds. 4. Evaluate the effects of land use and surface water features on nutrient and dissolved oxygen levels in Coastal Plain watersheds.

1b. Approach (from AD-416)
OBJ.1: Direct measurements of soil and plant attributes will be related to crop yield and measurable changes in soil organic carbon accretion, soil water content, plant available water content, microbial community size, soil nitrogen, and nitrate leaching. Remotely sensed data will allow us to 1) integrate the combined effects of soil organic carbon accretion and nitrogen management via real-time, non-destructive assessments of crop response, 2) monitor crop response as a function of plant available water and nitrogen contents, and 3) refine crop coefficients for improved irrigation management and water use efficiency. OBJ.2: The Riparian Ecosystem Management Model will be modified to facilitate use for specific applications such as pesticide transport, P retention estimates, and watershed scale buffer scenario testing. Procedures will be tested for integrating modifications of REMM with watershed scale models. REMM integrations with watershed and channel process models will be tested using watershed data collected at ARS and cooperator watersheds in Georgia, Delaware, Mississippi, Maryland, and elsewhere. OBJ.3: A GIS based modeling system will be developed to simulate soil moisture conditions across the region. Based upon existing soil, climate, and vegetation data, the system will allow point, field, and watershed scale estimates of evapotranspiration, runoff, and soil moisture. It is anticipated that the system will be capable of estimating soil moisture across spatially variable fields for purposes of irrigation scheduling, as well as watersheds equivalent in size to the Little River Experimental Watershed for purposes of long term water resource planning. OBJ.4: Levels of dissolved oxygen will be correlated with other measured water quality parameters for 18 sites in the Suwannee River Basin to determine if relationships exist between dissolved oxygen and stream chemistry.

3. Progress Report
Measurement of processes affecting dissolved oxygen in coastal plain streams were continued, focusing on the role of leaf litter and dissolved organic carbon in consuming dissolved oxygen. Measurements of water quality in the Suwannee River Basin continued including sampling stations on streams draining an urban area. These sampling stations will allow comparison of water quality and hydrology in agricultural and urban watersheds of the Suwannee River Basin. Output from REMM using pesticide components were compared to field data. Began work on modifications to REMM to a) simulate conditions in tropical environments such as Puerto Rico; b) more accurately simulate conditions in permanently flooded wetlands; and c) estimate outputs of greenhouse gases from simulated riparian ecosystems. Measurement of soil quality, water content, and crop residue spectra was continued for the second year. Twenty-five farms in the Little River Watershed were surveyed for soil texture, soil C&N content, soil microbial biomass C&N and plant biomass and biomass C&N content. Satellite data are being processed for NDVI determinations. These data will be used to evaluate spatial patterns in winter and summer biomass production in association with soil quality attributes at the landscape level.

4. Accomplishments
1. Natural stream features rather than anthropogenic pollution causes low dissolved oxygen in Coastal Plain blackwater streams. Blackwater streams are found throughout the Coastal Plain of the southeastern United States and are characterized by low gradients, high summertime temperatures, and extensive inundation of surrounding floodplains during high flows. Typically lasting from winter to early spring, the long inundation period creates a multitude of instream floodplain swamps that play a vital role in overall water quality. Over 90% of the blackwater streams listed as impaired on the Coastal Plain of Georgia are listed as being in violation of the state’s dissolved oxygen (DO) standard. A key influence on the DO levels within these floodplain swamps is sediment oxygen demand (SOD), a critical and dominant sink for oxygen in many river systems that is often poorly investigated or roughly estimated in oxygen budgets. New results show SOD rates up to 18 times higher than values reported for other southeastern sandy-bottomed streams and suggest that in-stream swamps are repositories of large amounts of organic matter and are thus areas of intense oxygen demand and a major factor in determining the oxygen balance of the stream as a whole. These areas of intense oxygen demand in relatively unimpacted areas indicate that low DO concentrations may be a natural phenomenon. SOD rates were significantly correlated with a number of sediment parameters with organic carbon and total organic carbon being the best predictors of SOD rate. The estimated SOD was adequate to reduce DO levels from saturation levels to below the water quality standard during flow through a swamp on the Little River Experimental Watershed.

Review Publications
Choi, M., Jacobs, J.M., Bosch, D.D. 2008. Remote Sensing Observatory Validation of Surface Soil Moisture Using Advanced Microwave Scanning Radiometer E, Common Land Model, and Ground Based Data: Case Study in SMEX03 Little River Region, Georgia, U.S.. Water Resources Research. 44:WO8421, doi:10,1029/2006WR005578.

Sullivan, D.G., Nuti, R.C., Truman, C.C. 2009. Evaluating a Nonionic Surfactant as a Tool to Improve Water Availability in Irrigated Cotton. Hydrological Processes. 23:2326-2334.

Last Modified: 2/23/2016
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