Land use contributions to phosphorus loading in an impaired stream, Mill Creek, Tennessee

Abstract

EARTH AND ENVIRONMENTAL SCIENCE

LAND USE CONTRIBUTIONS TO PHOSPHORUS LOADING IN AN IMPAIRED STREAM, MILL CREEK, TENNESSEE

VENA JONES

Thesis under the direction of Professor Kaye Sawyer Savage Located in Middle Tennessee’s Central Basin, Mill Creek is listed with EPA for water quality impairment [303(d)] from high phosphorus concentrations that affect its biogeochemical properties. Mill Creek was sampled at three locations according to land use during dry and wet weather. Imperviousness associated with land use increases downstream. Agricultural regions, MCW-A, are in the headwaters, suburban portions, MCW-B, are downstream and the lower reaches are highly urbanized and industrial, MCW-C. Water samples were filtered successively to fractions >0.65µm, 0.65>0.45µm, 0.45>0.1µm, and <0.1µm using tangential flow filtration and analyzed for total phosphorus, soluble reactive phosphate, and trace metals.

Phosphate loads increased downstream. Total phosphorus and Pb increased during wet weather; other trace metals were diluted. Phosphorus was associated with fractions <0.1µm and >0.65µm. Phosphorus contributed to the stream from bedrock and soils was minor. Most contaminants associated with industry were diluted with increasing discharge; this suggests that non-point sources are inducing impairment.

Increased impervious surfaces increased frequent flood peak discharge values and runoff. Urban runoff in MCW-B and MCW-C most likely increased soluble reactive phosphate concentrations in Mill Creek. Continued development will most likely contribute to higher P loads through increased runoff from impervious surfaces where overland flow has the opportunity to suspend and redistribute pollutants. The source of this P is most likely domestic during wet weather. Increased particulate phosphorus will likely increase with increased development where erosion from disturbed land surfaces is a common problem.