Correlation between Riparian Buffers and Water Quality in North Carolina Watersheds

Abstract

Stream water quality is often impacted by changes in land use such as deforestation or conversion of wetlands to agricultural or developed land use. Since streams, or other surface water such as lakes and reservoirs serve as drinking water sources for millions of people across the U.S., Water Treatment Plants are the most common water resource management option for treating degraded stream water for drinking water purposes. However because treatment plants are capital intensive, land use conservation as both a water resource management option and ecological management option is now widely being adopted. In particular, forest cover in watersheds are recognized as providing unique ecosystem services; the ability of forests to acts as natural water filters could drive down water treatment costs and offer a cost-effective way to provide clean drinking water. The purpose of this study is therefore to test the hypothesis that an increase of forest cover in watersheds and riparian buffers leads to water quality improvement. Land use metrics were generated from geospatial analysis using ArcGIS. Intake points were located for 31 WTPs across North Carolina, and their corresponding watershed boundaries were delineated. The 2006 National Land Cover and Land Use dataset was used to determine percent of forest cover, impervious cover and agricultural cover at three different spatial scales; watershed, 300ft riparian buffer and 100ft riparian buffer. In addition, monthly water quality data of two water quality parameters, Turbidity and Total Organic Content (TOC) were obtained from the NC Division of Environment and Natural Resources. The water quality data were reported as monthly averages between 2009 and 2012 for Turbidity and between 2009 and 2012 for TOC. Simple and multiple regressions were conducted for available explanatory variables, including percent of forest cover, impervious cover, agricultural cover and watershed size. The results of the regression analyses overall indicated that percent of forest cover in all three spatial scales strongly affected mean TOC while agricultural land cover within the 100ft riparian buffer strongly affected mean Turbidity. Impervious cover did not seem to have strong effects on water quality. Therefore it is recommended that the efforts should be directed at minimizing agricultural land cover within riparian buffers or diverting agricultural runoff from streams to reduce Turbidity. Protection of forest cover to reduce TOC concentration in streams should also be prioritized. Across the three different spatial scales, 100ft riparian buffers should continue to be protected as well. These measures will help towards maintaining the quality of drinking water sources.