Zooplankton-based trophic state indices assessment of reservoirs and lakes in Central Mexico

Abstract

Eutrophication presents a significant challenge for water quality management, as it threatens both the availability of freshwater and the integrity of aquatic ecosystems. Here, we integrally assessed the trophic state of ten reservoirs and lakes in Central Mexico that differ in trophic level. Environmental variables, Carlson Trophic State Index (TSI), trophic state indices for zooplankton abundances (TSI_ROT and TSI_CR), and modified guild ratio (GR′) were analyzed. We also compared these indices with diversity indices (species richness, abundance, Hill numbers, and Shannon index). Sites with low Carlson TSI values exhibit reduced species richness, abundance, and diversity, while highly eutrophic and macrophyte-influenced sites display elevated diversity indicators. The modified guild ratio indicates a dominance of raptorial rotifers in reservoirs and lakes with low trophic levels, whereas microphagous species primarily dominate eutrophic ecosystems. The zooplankton indices (TSI_ROT and TSI_CR) overestimate the trophic status when it is low and underestimate it when trophic conditions are high compared with Carlson’s trophic indices. Canonical correspondence analysis shows that Asplanchna priodonta, Synchaeta spp., and Daphnia spp. are associated with more transparent, less nutrient-rich waters, while brachionids, Filinia longiseta, and Diaphanosoma spp. thrive in eutrophic conditions like those in Xochimilco and La Estanzuela wetlands. This study confirms that zooplankton can be a good indicator of the trophic conditions of water bodies in high-altitude tropical regions, but the indices need to be adjusted to improve their accuracy.