Land-Use Practices and Fecal Coliform Pollution of Coastal Waters
Michael A. Mallin
Center for Marine Science Research
The University of North Carolina at Wilmington, Wilmington, NC 28403
phone 910-256-3721 ext 275
Human development along the land-sea interface can have significant environmental consequences. Likewise, this development can pose a increased hum health risk as well. In a rapidly-developing coastal region (New Hanover County, North Carolina) we investigated this phenomenon through a series of five estuarine watersheds, each of which differed in both the amount and type of anthropogenic development. Over a four-year period we investigated the abundance and distribution of the enteric pathogen indicator microbe, fecal coliform bacteria and Escherichia coli. We also examined how these indicator microbes were related to physical and chemical water quality parameters and demographic and land-use factor throughout this system of coastal creeks. within all creeks there was a spatial patter of decreasing enteric bacteria away from upstream areas, and both fecal coliform and E. coli abundance was inversely correlated with salinity. Turbidity was positively correlated with enteric bacterial abundance. Enteric bacterial abundance was strongly correlated with nitrate and weakly correlated with orthophosphate concentrations. Neither fecal coliform nor E. coli displayed consistent emparl abundance patterns. Regardless of salinity, average estuarine fecal coliform abundance differed greatly among the five systems. An analysis of demographic and land-use factors demonstrated that fecal coliform abundance was significantly correlated with watershed population, and even more strongly correlated with the percent of developed land within the watershed (Table 1). However, the most important anthropogenic factor associated with fecal coliform abundance was percent watershed impervious surface coverage, which consists of roof, roads, driveways, sidewalks, and parking lots. Percent watershed impervious surface area alone could explain 95% of variability in average estuarine fecal coliform abundance (Table 1; Fig. 1). In New Hanover County, highly developed watershed such as Bradley and Hewletts Creeks maintained large estuarine areas which were not only unfit for shellfish harvesting but unfit for human contact as well (Table 2).
In urbanized watersheds non-point source runoff is considered to be a major general source of many pollutants (Klein 1979; Bannerman et al. 1993; Weiskel et al. 1996). Standard drainage designs commonly channel untreated runoff from impervious surfaces into storm drains, some of which feed wet detention ponds, while many drains lead directly into streams, lakes, or estuaries, including those containing shellfish beds. In contrast, vegetated pervious surfaces serve as passive runoff treatment systems in several ways. Lateral flow through vegetation settles out solids and associated bacteria, vegetation utilizes nitrogen and phosphorus through uptake, downward percolation achieves further nitrogen removal through denitrification by soil bacteria, and soil particles adsorb phosphate, ammonium, enteric bacteria, and other pollutants. Stormwater runoff which passes through vegetated buffers or through shallow groundwater reaches sensitive surface water bodies more slowly and in a much less impaired state than runoff from impervious surfaces.
Increases in impervious surface area can also lead to increases in runoff and flooding. By removal of the natural filtering and groundwater recharge capability, stormwater runoff is channeled into much smaller pervious areas and overwhelms their natural carrying capacity leading to extensive standing water and flooding (New Hanover County has had a number of examples of this in recent years). Additionally, tree removal leads to increased flooding potential as well. Trees, especially mature trees, are natural pumps which draw in water from the roots and transpire excess moisture into the atmosphere. Leaving large green spaces and natural mature vegetation will both help protect water quality and decrease flooding risks in developing areas. Thus, in urbanizing coastal areas waterborne health risks and other environmental problems can be minimized by utilizing sound land use planning and development.
REFERENCES AND RELATED READING
Arnold, C.L. and C.J. Gibbons. 1996. Impervious surface coverage – the emergence of a key environmental indicator. Journal of the American Planning Association 62:243-258.
Bannerman, R.T., D.W. Ownes, R.B. Dodds, and N.J. Hornewer. 1993. Sources of pollutants in Wisconsin stormwater. Water Science and Technology 28:241-259.
Klein, R.D. 1979. Urbanization and stream quality impairment. Water Resources Bulletin 15:948-963.
Kocasoy, G. 1995. Effects of tourist population pressure on pollution of coastal areas. Environmental Management 19:75- 79.
Maiolo, J.R. and P. Tschetter. 1981. Relating population growth to shellfish bed closures: a case study from North Carolina. Coastal Zone Management Journal 9:1-18.
Mallin, M.A., L.B. Cahoon, J.J. Manock, J.F. Merritt, M.H. Posey, R.K. Sizemore, W.D. Webster and T.D. Alphin. 1998. A four-year environmental analysis of New Hanover County tidal creeks. CMSR Report No. 98-01. University of North Carolina at Wilmington, Wilmington, NC.
May, C.W., R.R. Horner,J.R. Karr, B.W. Mar and E.B. Welch. 1997. Effects of urbanization on small streams in the Puget Sound lowland ecoregion. Watershed Protection Techniques 2:483-494.
Schueler, T. 1994. The importance of imperviousness. Watershed Protection Techniques 1:100-111.
USEPA. 1996. Ambient water quality criteria for bacteria – 1986. EPA440/5-84-002, United Stated Environmental Protection Agency, Washington, D.C.
Weiskel, P.K., B.L. Howes, and G.R. Heufelder. 1996. Coliform contamination of a coastal embayment: Sources and transport pathways. Environmental Science and Technology 30:1872-1881.
Young, K.D. and E.L. Thackston. 1998. The influence of septic tank leachate on urban streams in Nashville. Environmental and Water Resource Engineering, Vanderbilt University, Nashville, TN.