Divergent sensitivity of primary producers and benthic invertebrates to hydrological alteration in floodplain lakes

Floodplain lake ecosystems are hydrologically dynamic and biologically important. Their ecosystem functioning is complex due to the concurrent influence of multiple anthropogenic stressors. Paleolimnological studies focused on a single biotic proxy might lead to biased results, as multiple trophic levels may show different responses to the same driver. In this study, multiple proxies including chlorophyll and carotenoid pigments (indicators of phytoplankton) and chironomids (indicators of invertebrates) were analyzed in a ²¹⁰Pb dated sediment core from Luhu Lake (Yangtze floodplain, China). Using these indicators, we investigated how different trophic levels respond to external driving forces (i.e., hydrological alteration represented by K/Al ratios and nutrient influxes indicated by TP) in floodplain lakes. Sedimentary pigments showed that algal production increased in Luhu Lake after the 2000s. The chironomid community shifted from a fauna dominated by Microchironomus tener-type to an assemblage characterized by macrophyte-dwelling taxa (e.g., Tanytarsus, Paratanytarsus, Paratanytarsus penicillatus-type) after the 1970s. Finally, nutrient-tolerant taxa (e.g., Microchironomus tabarui-type) increased in abundance after the 1990s. Redundancy analysis and hierarchical partitioning analysis showed that the increases in algal production were mainly correlated with anthropogenic nutrient influxes, followed by hydrological alteration. In contrast, the transition in the chironomid communities were mainly associated with hydrological alteration, followed by food sources. Our study revealed asynchronous responses of phototrophs and benthic invertebrates to hydrological alteration, highlighting the necessity of analyzing multiple trophic levels to obtain a sophisticate understanding of long-term ecosystem evolution in lotic floodplain lakes which are influenced by multiple stressors. These findings will provide valuable information for the sustainable development, as well as the conservation and restoration of floodplain lakes.