Macrozoobenthic community structure in a large shallow lake: Disentangling the effect of eutrophication and wind-wave disturbance

Biological communities in shallow lakes are often subject to the combined effects of eutrophication and wind-wave disturbance. However, their relative importance in regulating macrozoobenthic community assembly has not been well addressed. In the present study, a monthly sampling of macrozoobenthos and environmental parameters was conducted at ten sites from December 2012 to November 2013 in Lake Hongze, the fourth largest freshwater lake in China, which has undergone serious water quality deterioration over the past few decades. A total of 30 taxa were recorded during the 12 sampling occasions, including 6 chironomids, 6 bivalves, 4 gastropods, 4 oligochaetes, 4 polychaetes, 4 crustaceans and 2 other aquatic insects. The mean abundance and biomass of total macrozoobenthos varied greatly among the ten sites and presented distinctive taxonomic composition between the protected bays and the offshore zone. Three eutrophication parameters (including permanganate index (COD_Mn), chlorophyll a, and total phosphorus in surficial sediments) and three wind-wave variables (including Secchi depth, turbidity, and mean effective fetch) were highly related to spatial variation of macrozoobenthic assemblages. When eutrophication variables were controlled, there was a significant correlation between community similarity and wind-wave disturbance condition, and vice versa. Variation partitioning showed that wind wave disturbance explained 15.9% of the variation in benthic community composition, slightly lower than that explained by eutrophication (17.9%). These results indicate that wind-wave disturbance is as important as eutrophication in regulating benthic community structure in this large shallow lake. Wind-wave disturbance imposed opposite effects on benthic community relative to eutrophication, and were more prominent in the offshore zone weakening the role of eutrophication.