Spatio-temporal variations of benthic macroinvertebrates and the driving environmental variables in a shallow lake

Shallow lakes widely distributed in middle and lower reaches of watershed are easily multi-stressed by natural forces and human activities. Here, spatio-temporal variations of macroinvertebrate community and their influential variables in a typical large macrophyte-dominated shallow lake-Baiyangdian Lake were studied, using three-year in-situ observational data of spring, summer, and autumn. In total, ten environmental variables and five biological indices were measured for the six sites from each of the two habitat types, semi-natural habitat and disturbed habitat divided by their different exposures to human activities. Disturbed habitat had deeper mean water depth, lower mean transparency, and higher mean concentrations of DO, TN, NH4-N, NO3-N, and COD than that of semi-natural habitat regardless of seasons. Biological metrics indicate lower family-level richness but higher community tolerance level in disturbed habitat in spring and summer, but the results were close in autumn. The present of Lestidae and Gammaridae was a significant determination of semi-natural habitat. Redundancy analyses showed community temporal distribution was mainly driven by temperature, water depth, and pH that greatly influenced by natural forces, while spatial distribution was mainly driven by TN and transparency that greatly influenced by human activity. Regarding averaged data over the same year, season, and habitat, richness and Shannon-Weiner index had significant Pearson linear correlation with transparency (r = 0.521 and r = 0.541, p < 0.05, respectively), family biotic index significantly correlated with TP (r = 0.495, p < 0.05), and NO3-N (r = 0.592, p < 0.01), and percentage of tolerant individuals significantly correlated with pH (r = 0.667, p < 0.01), temperature (r = - 0.640, p < 0.01) and NO3-N (r = 0.522, p < 0.05). Those variables are likely responsible for the major variations of community characteristics. High concentrations of nitrogen and phosphorus nutrients probably encourage the thriving of tolerate assemblage in the lake. Our results reveal that the macroinvertebrate community can shift to be more monotonous and pollution-tolerant under the stress of eutrophication and organic pollution. Disturbance and pollution, in general, can diminish the benefit of habitat-scale protection in certain location.