Nutrient patterns in a mainstem reservoir, Kentucky Lake, USA, over a 10-year period

Nutrient patterns were examined spatially and temporally from 1989 to 1998 in Kentucky Lake U.S.A., the largest mainstem reservoir on the Tennessee River system. Nutrients included NO3-N, NH4+4-N, PO4, SiO2, SO4-2, and Cl. Seasonal patterns in most nutrient concentrations were described well by cosine functions. Seasonal descriptions had less variance than discharge related descriptions of nutrient concentrations, possibly due to regulation of reservoir discharge. Differing land-use practices on either side of the reservoir were associated with significantly different nutrient concentrations in their related embayments. The agriculturally dominated western side embayments had lower nutrient concentrations than either the forested eastern side of the reservoir or mainstem sites. Annual average nutrient concentrations did not vary greatly over the 10-year period, indicating no change in eutrophication potential during the sampling period. An exception was a significant decline in SO4-2 levels from 23 mg(.)L(-1) in 1992 to 12.8 mg(.)L(-1) in 1998. Annual export of nutrients was computed from yearly regressions on seasonal concentrations and daily discharge rates.