HR: 0830h
AN: H51C-1078    [PDF]
TI: Stream Water Quality Modeling in the Great Smoky Mountains National Park
AU: * Barnett, T W
EM: tbarnet1@utk.edu
AF: University of Tennessee, 223 Perkins Hall, Knoxville, TN 37996
AU: Robinson, R B
EM: rbr@utk.edu
AF: University of Tennessee, 223 Perkins Hall, Knoxville, TN 37996
AB: The purpose of this study was to examine water quality in the acid-impacted Great Smoky Mountains National Park (GRSM). Water samples have been collected roughly quarterly at ninety sampling sites throughout the Park from October, 1993 to November, 2002.. These samples were analyzed for pH, acid neutralizing capacity (ANC), conductivity, major cations, and major anions. The trout fisheries of the GRSM are considered some of the best in the eastern United States. However, fisheries biologists at the GRSM believe that some of the streams that once supported trout populations twenty or thirty years ago, no longer do. This study outlines and quantifies surface water quality conditions that might be harmful to trout populations through a literature review. This study identifies 71 sites (79 percent of total sampling sites) that currently have a median pH of greater than 6.0, above which, is unlikely to be harmful to trout species unless a high runoff of acid, Al-rich water creates a mixing zone where Al(OH)3 precipitates. The precipitate can accumulate on the gills and impede normal diffusion of O2, CO2, and nutrients. There are 17 sites (18 percent) that have median pH values in the 5.0 to 6.0 range. This range of pH values is likely to be harmful to trout species when aluminum concentrations exceed about 0.2 mg/l. The lower end of this range is probably harmful to the eggs and fry of trout and also to non-acclimated trout especially when calcium, sodium, and chloride concentrations are low. Only two sampling sites have median pH values in the 4.5 to 5.0 range. This pH range is likely harmful to eggs, fry and adult trout, particularly in the soft water conditions prevalent in the GRSM. The mechanisms adversely affecting trout in these ranges are ionoregulatory dysfunction, respiratory stress, and circulatory stress. Currently, there are no sampling sites with median pH values less than 4.5, although pH values could be lowered by more than one pH unit during high-flow episodic events depending on the ANC in the stream. Stepwise multiple linear regression was used to model pH, ANC, nitrate and sulfate. This study incorporates basin characteristics, time, acid deposition data, USGS stream flow data as surrogate hydrologic data, and precipitation data, e.g., inches of rain on preceding days, to determine whether these variables are associated with water quality. Acid deposition data came from biweekly wet only and throughfall monitoring at the Noland Divide, which is a high elevation acid deposition monitoring site within the Park. Precipitation data is collected at five National Weather Service monitoring sites within the Park. Each of the above variables were found to be statistically significant (p$<$0.05) influencing factors to water quality, particularly pH. Water quality conditions were adversely (decreasing pH and ANC and increasing sulfate and nitrate) affected by increased stream flows, acid deposition and precipitation. Models for pH and ANC produced R-square values around 0.71 and 0.86, respectively. Nitrate and sulfate modeling produced R-square values around 0.30. This study also analyzes temporal trends in pH. Modeling reveals statistically significant decreasing trends in pH with time. If conditions remain the same and past trends continue, models suggest that 30.0 percent of the sampling sites will reach pH values less than 6.0 in less than 10 years, 63.3 percent of the sites will reach pH values less than 6.0 in less than 25 years, and 96.7 percent of the sites will reach pH values less than 6.0 in less than 50 years. The models used to predict future pH values explain around 70 percent of the variability in the data.
DE: 1806 Chemistry of fresh water
DE: 1854 Precipitation (3354)
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting