Start Date: Dec 21, 2011
End Date: May 21, 2012
The underlying approach to the research is the acquisition, analysis, and interpretation of data from the LRW as a means for assessing the effectiveness of conservation practices and the impacts of agricultural production on watershed processes in general. The USDA-ARS SEWRL has collected hydrologic and climatic data on the 334 km2 LRW near Tifton, Georgia since 1968. The LRW is currently instrumented to measure streamflow for the 334 km2 primary drainage area (Watershed B) and seven subwatersheds that range from approximately 3 km2 to 115 km2 (Fig. 1). The experimental watersheds are located in a paired and nested arrangement to facilitate scientific research and testing of analytical formulas and modeling concepts. Construction of the original eight streamflow measurement devices began in 1967 and was completed in 1972. The watershed is typical of the heavily vegetated, slow-moving stream systems in the Coastal Plain Region of the U.S. Land use within the watershed is approximately 50% woodland, 31% row crops (primarily peanuts and cotton), 10% pasture, and 2% water. The LRW is located in the Southern Coastal Plain physiographic province, the Tifton Upland subprovince. The watershed is located on sands, silts, and clays underlain by limestones that form the Floridian aquifers. The major soil series within the watershed are loamy sands with infiltration rates of approximately 5 cm/hr. Upland slopes within the watershed are 2 to 5% while channel slopes are on the order of 0.1 to 0.5%. Precipitation occurs almost exlusively as rainfall, with an annual mean at Tifton, Georgia of 1200 mm. Distribution of rainfall within the year is highly variable, although the fall months are typically dry. Water balance studies on the watershed indicate streamflow is around 27% of annual rainfall, evapotranspiration is 73%, and percolation to deep groundwater is negligable. Streamflow is composed of direct surface runoff (5% of annual rainfall) and return flow from the shallow aquifer (22% of annual rainfall). Deep seepage and recharge to regional groundwater systems is impeded by the Hawthorn geologic material 0 to 6 m below the land surface, promoting lateral movement of excess water from uplands downslope as shallow return flow to surface drainage systems. Environmental concerns in the LRW include: low dissolved oxygen; high fecal coliform and other bacterial indicators; nutrient enrichment; pesticides and sediment in field runoff; drought impacts on irrigation water supplies; and erosion. While sediment and agrochemical losses from upland cultivated fields can be high, filtering within the dense riparian buffers which surround the watershed streams reduces the loading to streams substantially. Based upon GA-EPD monitoring, many streams within the Coastal Plain are impaired by low dissolved oxygen. Preliminary assessments indicate that on the average, a 40% reduction in nitrogen and phosphorous loading must be achieved in the impaired watersheds to attain dissolved oxygen standards. Because of their widespread use within the region, pesticides in streamflow are also a concern.