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Using GIS to Examine the Role of Land Cover in the Bacterial Contamination of Swashes 1 Abstract Bacterial contamination of surface waters from non-point sources is an issue of increasing concern. Critically important riparian and estaurine environments are often the receiving body for stormwater as it accumulates and picks up contaminants while moving through a drainage basin. As a result substantial research has been conducted with the goal of better understanding the role of stormwater as a means of pollutant transport. This study examines land cover characteristics within a watershed, a commonly cited contributing factor to water quality degradation. By characterizing landcover in the subwatersheds and comparing it to E. coli densities, correlations between increased development and poor water quality are examined. Coastal Carolina University Department of Coastal Marine and Wetland Studies Methods The influence of upstream development and increased impervious cover within a watershed are examined by comparing land cover data generated within a GIS and water quality data collected in the summer of 2012. Comparisons between the two swashes are also made using a 3 year data set, ranging from 2010 to the present, collected by Coastal Carolina University's Environmental Quality Lab. Watershed Landuse Dogwood Swash Withers Swash Background Nonpoint sources of pollution (NPS), such as those transported via stormwater, are of increasing concern for receiving waters worldwide. The Clean Water Act of 1972 has largely been effective in regulating point source pollutant discharges in the US but has only come to consider the aggregate effects of many, smaller, nonpoint sources since a 1987 addition to the legislation. The Municipal Separate Storm Sewer (MS4) program is a key portion of this act, requiring cities and construction sites to account their runoff (US EPA 2000). As a result there has also been considerable research into the factors affecting NPS pollution of receiving waters. Two of the major factors identified consitently in the literature as having a negative affect on water quality are an increasing population and the associate increase in impervious surface due to development (Mallin et al 2000). These factors are investigated both within a single watershed and between two watersheds in coastal South Carolina. Study Area 1 Kyle Curtis Results Regression analysis comparing percent developed/commercial land cover and E. coli concentrations shows that increasing impervious surface does correlate with higher bacteria values in the Withers Swash watershed. Percent residential land use was also compared but did not significantly correlate with E. coli levels. Population was also examined as a possible predictor of increased bacterial contamination. While increasing population within a watershed did correlate with higher bacteria levels the relationship was also relatively weak. Results for these analyses can be found in the Results Table. Results Table 3,200,000 Withers Swash Land Class Land Use 3,161,781.567 2,599,109.068 813,158.666 65,537.138 5,952.889 68,635.932 3,000,000 2,800,000 2,600,000 2,400,000 2,200,000 2,000,000 1,800,000 Area (m^2) 1,600,000 1,400,000 1,200,000 1,000,000 800,000 600,000 400,000 200,000 0 Residential Undeveloped Class Pond Stream Swash Populations within each subwatershed of the Withers Swash drainage area are determined by summarizing US Census block population units. Blockpop units represent the smallest geographic unit used by the US Census Bureau for calculating the total population of an area, rather than sampling households. Residential Developed Undeveloped Pond Stream Swash 2,000,000 1,900,000 1,800,000 1,700,000 1,600,000 1,500,000 1,400,000 1,300,000 1,200,000 1,100,000 Area (m^2) 1,000,000 900,000 800,000 700,000 600,000 500,000 400,000 300,000 200,000 100,000 Dogwood Swash Land Cover Land Use 1,958,827.114 704,050.561 1,052,243.279 132,019.105 11,393.755 84,392.681 Residential Developed Undeveloped Pond Stream Swash Withers Swash Land Use/Bacteria Comparison Between Swash Comparisons Fecal Indicator Bacteria (cfu/100ml) Fecal Indicator Bacteria (cfu/100ml) r2 P % Developed 0.42 0.046 % Residental 0.129 0.383 Subwatershed Populaton 0.38 0.047 * Bacteria data collected Summer 2012 Dogwood Swash Withers Swash Populaton % Developed % Residental Median FIB 3429 17.86 49.68 33 8414 41.80 46.28 1646 * Bacteria data generated by the CCU Environmental Quality Lab and Volunteer Monitoring Program Conclusions Residential Undeveloped Class Pond Stream Swash Withers Swash Subwatershed Boundaries and Blockpop Units Ü 0 0.5 Kilometers 1 2 Subwatershed Boundaries Block Population Units Subwatershed Boundaries Understanding those factors that contribute to bacterial contamination of surface waters has importance from an economic as well as environmental standpoint. Receiving waters for polluted runoff are often areas of recreation, fisheries, or drinking water sources, all of significant economic importance. These waterbodies also serve as critical habitat in many cases and warrant effective managment regardless of the reason. Results of this study support those found in the body of literature which suggests that bacterial impairment will coincided with increased population and development in an area. While the results presented here do support that, their correlation coefficients are not as strong as those found in previous studies. It is possible this results from the comparatively smaller sample size for both bacteria (n=98 across 14 sites) and that subwatershed comparisons could only be made within a single swash drainage basin (Withers Swash). Despite these limitations it does seem that the relationship is exhibited using regression analyses as well as qualitatively comparing percent impervious cover and population with bacteria values over a longer data set between swashes. Acknowledgements Data for this project has been provided by the following sources: Horry Co., ESRI, Coastal Carolina University Environmental Quality Lab, and Waccamaw Watershed Academy Volunteer Water Quality Monitoring Program. Cited References: U.S. Environmental Protection Agency (2000) NPDES Stormwater Guidance Document. EPA-821/R-97/004 Mallin MA, Williams KE, Esham EC, Lowe RP (2000) Effect of human development on bacteriological water quality in coastal watersheds. Ecol App 10:1047-1058 A big thanks to Dr. Wright and the 612 class for all their help.