Are zooplankton useful indicators of water quality in subtropical lakes with high human impacts?

摘要

To explore whether zooplankton are useful indicators of water quality in subtropical lakes with large surrounding human populations and aquacultural activities, we conducted a study involving 90 lakes in the Yangtze River plain with total phosphorus (TP) concentrations ranging from 0.022 to 0.437 mg/L. We found inapparent responses of the zooplankton community structure and body size to TP gradients. Additionally, we compared our results with those of previous studies, which showed that lakes in the Yangtze River plain were top-down effect-dominated lakes in which planktivorous fish had more important effects on zooplankton than did TP. Results based on a bias-variance decomposition analysis, structural equation model and linear regression analysis further showed that top-down effects were strong in the relationships between planktivorous fish and zooplankton and that the fish positively influenced zooplankton, especially rotifers. The size distribution and richness of zooplankton were not affected by the trophic status but were affected by planktivorous fish. Bottom-up effects were strong only in the relationship between the TP and phytoplankton, while the relationship between zooplankton and phytoplankton was weak. This study implied that the use of zooplankton as reliable indicators of trophic status may be questionable in subtropical lakes with high human impacts from aquaculture, while top-down effects had a major influence on the zooplankton community composition, size distribution and biodiversity. In addition, top-down control will result in a weak relationship between zooplankton and the water nutrient concentrations in lakes. Community shifts in both taxon-based and size-based indexes and zooplankton biodiversity might be useful indicators of predation pressure from planktivorous fish in subtropical lakes.