Long-term seasonal water quality trends categorized by watershed impervious area in AL, 1974 – 1998.
Elias, Emile*,1, Dougherty, Mark1, 1 Auburn University, Auburn, AL
ABSTRACT- In 1974, the State of Alabama launched the ambient monitoring program designed for the detection of long-term trends in chemical water quality constituents. Between 1974 and 1998, monthly samples were collected at multiple sampling locations throughout the state to evaluate changes in surface water quality due to point and nonpoint source pollution. The percentage of impervious area within the sampling watersheds varies. The goals of this study are to determine monotonic water quality trends in selected constituents between 1974 and 1998 as a function of watershed impervious area (IA). Chemical water quality trends, trend direction and the rate of the change are estimated for monitoring stations within four impervious area classifications. A total of 47 sampling locations are separated into the following four impervious area categories; low (n=12; 1.5 – 2.8 percent IA), medium (n=12; 2.9 – 5.2 percent IA), medium-high (n=11; 5.4 – 12.6 percent IA), and high (n=12; 12.7 – 33.3 percent IA) . Geographic information system analysis is used to determine sampling location watershed and impervious area. Trends in chemical water quality data are determined using seasonal Kendall trend analysis on a monthly basis with software developed for use by the Virginia Department of Environmental Quality. Preliminary results indicate a statistically significant increase in nitrate nitrogen (mg/l) (p=0.0008) in watersheds of medium-high impervious land cover. No trends were detected for nitrate in low, medium or high impervious area watersheds.
Key words: impervious watershed water quality, seasonal kendall trend analysis, AL surface water
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