Geospatial Modeling of Impervious Surfaces, Forests, and Water Quality

Water quality of stream and river systems is affected by the land cover compositions that are present within their watersheds and riparian corridors. Research in recent decades has demonstrated that impervious surfaces such as roads, rooftops, and parking lots can exert significant stress on the health of riverine systems. Impervious surfaces prevent groundwater infiltration, reduce aquifer recharge, increase surface runoff and contaminant transport, deprive surrounding vegetation of aeration, and increase the temperature of stormwater runoff. Forests serve to enhance water quality and to ameliorate the negative effects of human altered land covers through mechanisms such as absorption of stormwater runoff, filtration of pollutants and sediments, increasing groundwater infiltration and aquifer recharge, stabilization of streambanks, providing cooling effects through shading of stream ecotones, and promotion of healthy riparian habitats for flora and fauna.This thesis research was undertaken with the goal of examining the effects that impervious surfaces and forests exert on stream system water quality. The research was conducted in the headwaters of the New River in Watauga County, North Carolina in order to provide a study area of origin streams within a nested watershed assemblage which provided a variety of sub-watersheds with varying land cover proportions for comparison. Water quality variables, collected through an ambient water quality monitoring program, of specific conductivity, chloride, nitrate, and sulfate were examined over an eight month study period. The results of this research demonstrated that the effects of impervious surfaces and forests on stream water quality are clearly identifiable. Correlation analysis and linear regression testing provided robust evidence to support the central hypothesis of the research, there is a statistically significant relationship between land cover and water quality in the headwater stream systems of the Upper South Fork watershed of the New River, with impervious surfaces exerting a negative influence and forest land covers exerting a positive influence on water quality. The influences of spatial scale on these effects was examined through investigation of water quality datasets and calculations of the total percentage impervious area (TPIA) and total percentage forest area (TPFA) for the Upper South Fork watershed, in six sub-watersheds within the Upper South Fork, and riparian buffer distances of 25 m, 50 m, 100 m, and 150 m. The TPIA at the 100 m buffer distance was found to exert the strongest negative effects on water quality, and TPFA at the 50 m buffer was found to exert the strongest positive effect. Nearly all spatial arrangements of land cover composition were found to have statistically significant relationships with water quality. Limiting the amount of impervious surfaces that occur within 100 meters of streams and establishing a 50 meter forested stream buffer zone would serve to protect stream water quality from the effects of non-point source pollution. In the context of population growth and increasing urban development continuing into the 21st century, preservation and restoration of forested riparian buffers and the elimination of impervious surfaces within them should be a primary concern for the general public, the scientific community, and public-policy decision makers.