A Chlorophyll a Trophic Status Classification System for South African Impoundments

Chlorophyll a data from 24 South African impoundments were examined with the objective of developing a trophic status classification system. For the combined data set, standard deviation of the mean annual chlorophyll a concentration displayed an almost 1:1 linear relationship to the mean, indicating a wide annual variation in chlorophyll a for most impoundments. There appeared to be no common seasonal pattern to the occurrence of chlorophyll a maxima and minima, leading to the conclusion that trophic status was best described by a statistical parameter based on annual data (notably the mean value). Statistically significant empirical formulae that relate both the maximum value and the frequency of occurrence of specific chlorophyll a ranges to the mean annual value were established, and their potential use in the assessment of trophic status and impoundment management is described.