Influence of Seasonal Water Level Fluctuations on Food Web Structure of a Large Floodplain Lake in China

Abstract

Seasonal shifts in hydrology are known to alter the abundance and diversity of basal production resources and habitats and hence strongly influence the structure and function of river ecosystems. However, equivalent knowledge of natural lake ecosystems in floodplain regions is lacking. Here, we used stable isotope ratios of carbon and nitrogen to assess available primary production sources and consumer taxa during the dry and wet seasons in a large floodplain lake connected to the Yangtze River. Fish species showed distinct δ13C values between two hydrological periods but only small changes in δ15N values. Most of the fish species had higher estimated trophic levels in the dry season, likely indicating greater carnivory. Results of Bayesian mixing models revealed that benthic algae and benthic organic matter (BOM), combined with C3 vegetation, were the principal food sources supporting the biomass of most fish species during the low-water period, whereas benthic algae and seston were the most important carbon sources during the flood period. Overall, these findings demonstrate that seasonal hydrological changes, such as water-level fluctuations, can affect the trophic structure and ecosystem functioning of floodplain lake food webs in the subtropical zone.

Effects of Summer and Autumn Drought on Eutrophication and the Phytoplankton Community in Dongting Lake in 2022

“…The water level of the mainstream of the Yangtze River continues to be low, which in turn caused the cut-off of the Yangtze River entering the Dongting Lake in September, resulting in a rapid shrinkage of the watershed area, dry bottom, and narrowed living space for aquatic organisms. At present, investigations of the extreme drought events in Dongting Lake mainly focuses on the hydrometeorological analysis of the causes of drought [32][33][34] and the impact on fishery farming and wetlands [35,36]. However, there is no study on the impacts of extreme hydrometeorological drought on the aquatic ecosystem of the lake area.…”