Long-term stream chemistry trends in the South Georgia Little River Experimental Watershed

Authors: Feyereisen, Gary; Lowrance, Robert; Strickland, Timothy; Bosch, David; Sheridan, Joseph

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2008
Publication Date: 11/1/2008
Citation: Feyereisen, G.W., Lowrance, R., Strickland, T.C., Bosch, D.D., Sheridan, J.M. 2008. Long-term stream chemistry trends in the South Georgia Little River Experimental Watershed. Journal of Soil and Water Conservation. 63(6):475-486.

Interpretive Summary: Access to long-term, high quality watershed data records is invaluable for gaining an understanding of how watersheds work, researching techniques to preserve soil and water, and observing the effects of changes in climate, land use, agricultural systems, and land management on water resources. The USDA-Agricultural Research Service, Southeast Watershed Research Laboratory initiated flow measurement of the Little River in a 334 km**2 area near Tifton, Georgia in the late 1960's. Stream nutrient concentrations for nitrogen, phosphorus, and chloride were measured from 1974 through 2003 for five nested subwatersheds in the Little River Experimental Watershed. Data for three other nested watersheds are also available, but for shorter periods of time. The objective of this paper is to analyze nutrient concentration and load data to see if there have been increases or decreases over the years. The analysis was performed on five nested watersheds, which exhibit some variability in cropped versus forested areas and presence of animal agriculture. There was a statistically significant downward trend for annual mean total phosphorus concentration in six of eight subwatersheds and an upward trend for chloride in three of the watersheds. The decrease in total phosphorus concentration occurred primarily in winter. The increase in chloride concentration was during winter among the smaller subwatersheds and in the summer among the larger watersheds. The nutrient loads and concentrations from these watersheds were very low compared to other agricultural watersheds. Earlier short term studies attributed the low values to buffering provided by forests both along the streams and interspersed among the fields in the watersheds.

Technical Abstract: Concentrations and loads of chloride, ammonium-N, nitrate plus nitrite-N, total Kjeldahl N, total P, and dissolved molybdate reactive phosphorus were determined from 1974 through 2003 for eight nested subwatersheds in the Little River Experimental Watershed. There was a statistically significant downward trend for annual mean total phosphorus concentration in six subwatersheds and an upward trend for chloride in three subwatersheds. The decrease in total phosphorus concentration occurred primarily in winter. There were no differences in flows or nutrient loads among the nested watersheds. Annual and seasonal flow-weighted mean concentrations were different among the watersheds for nitrate and chloride. The larger watersheds had significantly higher nitrate in winter and spring. The nutrient loads and concentrations from these watersheds were very low compared to other agricultural watersheds. Earlier short term studies attributed the low levels of nutrient transport to the presence of extensive riparian forests and the general prevalence of forest in these mixed land use watersheds.