Influence of chlorophyll a quantification methods in ecological quality indices

Abstract

ABSTRACT Chlorophyll a concentration in aquatic ecosystems is strongly related to the phytoplankton community biomass, the growth of which depends on nutrient availability. Thus, chlorophyll a concentration provides information about the system status and is the variable most used in limnology for index calculations related to trophic status. Problems may arise when the index does not specify which method is being used to calculate the chlorophyll a concentration. Several researchers have emphasized that chlorophyll a concentration depends on the method used (spectrophotometry, fluorometry, or chromatography). Therefore, we compared the chlorophyll a in 25 samples from 25 reservoirs to test whether differences in methods influence the result of various ecologic quality indices: the Carlson trophic state index (TSI; Carlson 1977), the ecological potential for the Spanish Water Framework Directive (WFD) implementation (obligatory for State Members), and the trophic status adapted to the limnological characteristics of reservoirs. Our results showed that the differences among the methods were not statistically significant, and consequently the method of chlorophyll a quantification does not affect the index results when applying a robust trophic state index, such as the TSI and the ecological potential for the Spanish WFD implementation.