Effects of a wastewater outfall in a rocky intertidal community

The Crescent City wastewater treatment facility services a small community on the northern coast of California, where treated wastewater is discharged into a rocky intertidal community. A biological assessment of the habitat was conducted to determine if the released effluent had a negative impact on the intertidal community. I predicted the community composition at the outfall site would differ when compared to a site not subjected to an outfall. I also expected to detect a gradient in community composition moving away from the outfall. Enderts Beach was selected as a control site because it is in close geographic proximity and is similar to the discharge site in elevation, wave exposure and micro-topography. Three sampling events occurred in August 2002, April 2003, and August 2003, during which, I obtained thirty samples at each site. Descriptive statistics comparisons showed no significant differences between sites. However, differences in community composition were detected between the two sites. A number of confounding factors may have influenced the statistical results of the study. The type of sampling design utilized during this study provided no means of determining why the differences occurred. However, there was no obvious impoverishment of the community composition at the outfall site. Furthermore, there was no detectable gradient in community composition moving away from the outfall. Conditions at the outfall site made it difficult to locate more than one reference site. Therefore, results of the study were statistically inconclusive. In order to provide a less ambiguous conclusion, more control sites would be required.