Effect of human development on bacteriological water quality in coastal watersheds

Human development along the land-seawater interface is considered to have s ignificant environmental consequences. Development can also pose an increas ed human health risk. In a rapidly developing coastal region we investigate d this phenomenon throughout a series of five estuarine watersheds, each of which differed in both the amount and type of anthropogenic development. O ver a four-year period we analyzed the abundance and distribution of the en teric pathogen indicator microbes, fecal coliform bacteria and Escherichia coli. We also examined how these indicator microbes were related to physica l and chemical water quality parameters and to demographic and land use fac tors throughout this system of coastal creeks. Within all creeks, there was a spatial pattern of decreasing enteric bacteria away from upstream areas, and both fecal coliform and E. coli abundance were inversely correlated wi th salinity. Turbidity was positively correlated with enteric bacterial abu ndance. Enteric bacterial abundance was strongly correlated with nitrate an d weakly correlated with orthophosphate concentrations. Neither fecal colif orms nor E. coli displayed consistent temporal abundance patterns. Regardle ss of salinity, average estuarine fecal coliform abundance differed greatly among the five systems. An analysis of demographic and land use factors de monstrated that fecal coliform abundance was significantly correlated with watershed population, and even more strongly correlated with the percentage of developed land within the watershed. However, the most important anthro pogenic factor associated with fecal coliform abundance was percentage wate rshed-impervious surface coverage, which consists of roofs, roads, driveway s, sidewalks, and parking lots. These surfaces serve to concentrate and con vey storm-water-borne pollutants to downstream receiving waters. Linear reg ression analysis indicated that percentage watershed-impervious surface are a alone could explain 95% of the variability in average estuarine fecal col iform abundance. Thus, in urbanizing coastal areas waterborne health risks can likely be reduced by environmentally sound land use planning and develo pment that minimizes the use of impervious surface area, while maximizing t he passive water treatment function of natural and constructed wetlands, gr assy swales, and other "green" areas. The watershed approach used in our st udy demonstrates that the land-water interface is not restricted to obvious shoreline areas, but is influenced by and connected with landscape factors throughout the watershed.