Water quality improvement in the firth of forth: A discriminant functional analysis

Abstract

Extensive water sampling in the intertidal zone at eight sites on the south shore of the Firth of Forth during the period 1973–75, before major changes in the Edinburgh sewage disposal system, and subsequently during the period 1978–80 after these changes, has made it possible to assess improvement in water quality as measured on a set of seven variables. Mean sample values before and after were compared for these variables and the method of discriminant functional analysis was applied to assess the extent of change. Mahalanobis distance measures were used for this purpose. On this measure at only two of the sites has there been a statistically significant change in the global measure of pollution employed, though at two others the difference was almost statistically significant. However, all statistically significant differences between sites before the change ceased to be statistically significant after the change. At the originally most grossly polluted sites the reduction in faecal coli numbers has been substantial. Measurements of suspended solids (organic and inorganic) turned out to be the most heavily weighted variables in the discriminant functions for the majority of sites.