Human population growth and land cover change in coastal areas increase the sources of anthropogenic-induced pollution, microbial pathogens and potential transport of these contaminants to important nearshore habitat, shoreline public use and access areas. Impervious surface is a well-documented indicator of the consequences land development has on the ecological integrity of aquatic ecosystems (Alberti et al., 2004; Arnold and Gibbons 1996). While most existing studies have focused on the relationship between watershed urbanization and the associated biotic conditions in streams (Booth et al., 2002), there have been some recent investigations that consider impervious surface and development impacts to coastal areas (Holland et al., 2003; Lerberg et al., 2000; Fulton et al., 1993). This project was motivated by the need to better integrate the results of landscape-scale drainage basin analysis into comprehensive zoning, land use regulations, and storm water and shoreline planning.
The overall goal of this project was to test apply a GIS landscape metric methodology to complete spatially-explicit characterizations of select marine drainage basins in Washington’s Puget Sound. Specific objectives included: 1) hydrogeomorphologic delineation of marine drainage basins, including shoreline surface flows and ground water seeps (Alberti and Bidwell 2005); 2) assessment of drainage and drift cell system functions; 3) a prioritized list of natural resource sites for preservation and restoration; and 4) identification of the most appropriate areas to implement storm water retrofitting and low impact development (including clustering and storm water Best Management Practices) to most effectively accommodate flood and geologic hazard conditions, protect water quality and preserve and restore habitat.
A GIS landscape metric methodology was developed to characterize a marine drainage basin in Washington’s Puget Sound. The results of the analysis were then evaluated with respect to land use, storm water and shoreline planning. Recommendations for restoration and retrofitting emerged from the analysis.
The approach involved first creating a matrix based on the most recent scientific literature on non-point source pollution and land use impacts to marine systems that defined the landscape parameters that would be evaluated. The characterization relies on measures of land use change that are indicative of ecological stressors such as alterations in physical habitat, modification of upland vegetation and release of contaminants. The land cover metrics evaluated (such as deciduous vegetation patch size, aggregated impervious patches per unit length of shoreline) and their relationships to ecosystem function (e.g. transport of storm water runoff) have been defined or estimated through empirically based studies and process model results available in the scientific literature. These metrics were used to establish the baseline conditions for a marine drainage; indicate potential adverse impacts; and indicate existing impacts. The matrix provides information on sources of data, GIS processing requirements and a narrative description of how each parameter is evaluated.
A study site Woodard/Chapman embayment in Thurston County was chosen to test apply the approach. This site was selected because it is on public lands, within the State Natural Area Program, there are numerous listed species or species of interest inhabiting the area, the larger watershed area is rapidly developing and there are opportunities for restoration and enhancement projects.
A series of GIS process steps were applied to identify the freshwater drainage points that linked the terrestrial drainage to the marine waters. Changes in land use and shoreline development were analyzed together with changes in the physical and biological features of the site to assess the current status of the marine ecosystem function. Priority sites for restoration and stormwater retrofitting were identified and mapped.
A Powerpoint-based web module was developed providing step-by-step directions for the GIS analyses. The project was also presented at a public workshop hosted by Washington Department of Natural Resources attended by state agency, local government and tribal natural resource managers.