Quantifying and testing for effects of outfalls on biological communities

The authors discuss some methods for quantifying spatial and temporal changes in biological communities in the vicinity of outfalls. Ordination techniques are particularly useful for this purpose since they can separately quantify the different independent community gradients in outfall area. Often this allows for isolation and quantification of community gradients caused by the effluent discharge. When this is the case, they can graphically display the temporal and spatial patterns of the discharge-related community gradient. They show examples using the monitoring data from two Southern California outfalls to illustrate spatial and temporal patterns of outfall effects. It is often also of interest to statistically test the null hypothesis that an outfall has no effect on the biological communities at one or more test locations. They discuss a statistical approach that compares test locations to a population of reference locations. This approach can avoid the pseudoreplication problems often associated with ANOVA techniques contrasting individual stations separated in space.