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(P391) Delisting 303(d) streams for pH impairment: North Mississippi experiences.
Moore, Matthew*,1, Testa, Sam1, Cooper, Charles1, Knight, Scott1, Welch, Terry1, 1 USDA Agricultural Research Service National Sedimentation Laboratory, Oxford, MS, USA
ABSTRACT- As part of Mississippi,s 1998 303(d) list, 52 state water bodies (roughly 962 river and stream miles) were identified as being impaired by pH. Approximately 38% of those water bodies are located in the loess hill lands and delta of the Yazoo River Basin (YRB), north Mississippi. The YRB encompasses 3.46 million hectares of land and is the largest of Mississippi,s nine river basins. With the exception of soils recently derived from Mississippi River alluvium, most soils in the YRB are historically acidic in nature. Extensive and almost exclusive pine planting throughout the YRB over the last half century, for both erosion control and economic reasons, along with scattered naturally occurring pine and cedar stands, contribute to the acidity of water bodies in the YRB. In addition to soil pH values, the Water Quality and Ecological Processes Unit of the USDA-ARS National Sedimentation Laboratory collected extensive water quality data, including over 7,000 pH values alone, on approximately 19 different waterbodies throughout the YRB since the Demonstration Erosion Control (DEC) Project,s inception in 1984. Approximately 40% of all pH values collected in the DEC Project fall below the current water quality criteria of 6.5 standard units. In one particular listed stream, Otoucalofa Creek, 72% of recorded pH values were below the 6.5 s.u. criteria. Utilizing this expansive database, a suggestion for delisting 26 waterbodies was formulated and delivered to the Mississippi Department of Environmental Quality. Based on this same database, it was suggested that the minimum water quality criteria be lowered from 6.5 to 6.0 standard units to allow for natural variations observed specifically in the YRB of Mississippi. Data based observations allow states to vary from EPA regional default criteria which do not, within themselves, allow for special exceptions.
Key words: TMDL, pH, criteria
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