AQUEOUS GEOCHEMISTRY OF LAKE TUSCALOOSA, WEST-CENTRAL ALABAMA, USA: POSSIBLE ANTHROPOGENIC IMPACTS

Lake Tuscaloosa was created in 1969 by the impoundment of the North River near Northport and Tuscaloosa, AL. The reservoir is 25 miles long with a capacity of 123,000 acre-feet, a surface area of 5,885 acres, and an estimated safe yield of 200 M gal/d. It is the receiving water body of a 432 square mile drainage basin and supplies water to approximately 200,000 people. Land use changes in the watershed raise questions about possible impacts on lake water chemistry. This project studies the aqueous geochemistry of surface waters using samples representative of different seasonal conditions and land cover. Of the 21 sample locations in this study, three are located on tributaries, four transect the axis of the lake, and the rest are divided among semi-restricted coves representing forested and residential land cover. Sample chemistry is quantified for major, minor, and trace cations, anions, and nutrients, total dissolved nitrogen, DOC, and ALK.

Three main trends are evident from samples collected to-date. First, samples collected from residential coves have elevated concentrations of most ions relative to those collected from forested coves. Second, nutrient trends are evident in samples from the axis of the lake. Nitrate and silica decrease while ammonium increases in concentration, in the down-current direction. Third, seasonally heavy rainfall has a strong dilution effect which mitigates, but does not completely mask some of the distinctions that can be made based on land cover. One notable exception to this observation is an increase in dissolved manganese concentrations during the rainy season, particularly in residential coves.

Historical data is available from the USGS for seven locations sampled since 1986 on a semi-annual basis. These data illustrate a general increase in TDS and nutrients since the lake's creation. Some USGS locations coincide with those of the current study. Recently collected data agrees well with recent USGS data for the same locations. It is likely that trends observed in this study are related to anthropogenic effects along the lake shore, as evidenced by the geochemical differences between residential and forested coves. Long-term trends observed in historical data are likely the result of land use in the watershed related to mining, agriculture, and residential development.