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United States Department of Agriculture

Agricultural Research Service

Title: Water quality and hydrology in farm-scale coastal plain watersheds: Effects of agriculture, impoundments, and riparian zones

Authors
item Lowrance, Robert
item Sheridan, Joseph
item Williams, Randall
item Bosch, David
item Sullivan, Dana
item Blanchett, Donald

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2006
Publication Date: March 1, 2007
Citation: Lowrance, R.R., Sheridan, J.M., Williams, R.G., Bosch, D.D., Sullivan, D.G., Blanchett, D.R. 2007. Water quality and hydrology in farm-scale coastal plain watersheds: Effects of agriculture, impoundments, and riparian zones. Journal of Soil and Water Conservation Society. 62(2):65-76.

Interpretive Summary: Farms are economic units but a farm also occupies a particular portion of a rural landscape. In the Tifton Upland region of the southeastern coastal plain, average farm size is typically at a scale where one or two small streams will drain the land and deliver water to downstream areas. There is increasing interest in how farm practices affect both the quantity and quality of water delivered from a farm scale watershed. Farm scale watersheds in the southeastern coastal plain were studied to determine the effects of land use differences on water quality and hydrology. Two adjacent basins, both of which were 120 to 150 acres in size were compared for 7 years to determine the effects of upstream agricultural land uses, downstream riparian zones, and small ponds on stream water quality and watershed hydrology. Five sampling points were used to define hydrology on the two basins and a downstream site that was the outlet pipe for a farm pond. The North Basin had more cropland than the South Basin and had much more area in plastic covered beds for vegetable production. The South Basin had more of the total watershed area in farm ponds used to supply irrigation water. The North Basin had more surface runoff and higher loads of all nutrients and sediment. The South Basin had only 55% of the total runoff of the North Basin, probably due to the presence of about 6% of the total watershed area in farm ponds. In the last two years of the study, up to 26% of the North Basin (38% of total cropland) was occupied by wide plastic covered beds (plasticulture). Large quantities of sediment transported in surface runoff from these fields on the North Basin lead to increases in sediment concentrations and loads of over 100 times compared to both the South Basin and to earlier years of the study for the North Basin. Although both streams were bordered by riparian forests between the upstream and downstream sampling sites, there was limited potential to reduce nutrients and sediment once these materials are in stream flow. A downstream pond that received inputs from both the North and South Basins had significantly lower concentrations of nutrients and sediments than either of the upstream basins.

Technical Abstract: Dense dendritic stream networks in the Tifton Upland (southeastern U.S. coastal plain) provide an opportunity to determine the effects of land management practices on individual farms on downstream hydrology and water quality. Two or three small streams will drain a typical farm. The streams may be bordered by riparian forests or impounded into farm ponds. Two adjacent farm-scale watersheds, both of which were 50-60 ha in size were compared for 7 years to determine the effects of upstream agricultural land uses, downstream riparian zones, and small impoundments on stream water quality and watershed hydrology. Five sampling points were used to define hydrology on the two watersheds and a downstream outlet where the two streams came together in a farm pond. The North Basin had more cropland than the South Basin and had much more area in plastic covered beds for vegetable production. The South Basin had less land in crop production and much more of the total watershed area in farm ponds used to supply irrigation water. The North Basin had more surface runoff and higher loads of all nutrients and sediment. The South Basin had only 55% of the total runoff of the North Basin, probably due to the presence of about 6% of the total watershed area in farm ponds. Up to 26% of the North Basin (38% of total cropland) was occupied by wide plastic covered beds in the last two years of the study. Large quantities of sediment transported in surface runoff from these fields on the North Basin lead to increases in sediment concentrations and loads of over 100 times compared to both the South Basin and to earlier years of the study. Based on reductions in differences in loads and concentrations between upstream and downstream sites, there is less potential to reduce nutrients and sediment once these materials are in stream flow than when water is moving to streams through a riparian buffer. A downstream pond that received inputs from both the North and South Basins had significantly lower concentrations of nutrients and sediments than either of the upstream sampling sites.

Last Modified: 10/23/2014
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