Hydrologic and anthropogenic influences on aquatic macrophyte development in a large, shallow lake in China

Macrophyte composition and abundance affect the overall ecological structure and function of lakes, and information on the nature and timing of changes in macrophyte assemblages is therefore crucial for understanding their impact on the lake ecosystem. We examined plant macrofossils, diatoms, cladocerans, and physical and geochemical proxies in two sediment cores from Lake Liangzi, a large shallow lake located on the Yangtze floodplain in south‐east China, in order to assess recent and historical trajectories of ecological and environmental change. We also used archival records of environmental changes (i.e. hydrological, climatic, fishery, and social factors) in the lake and its catchment. Lake Liangzi is of particular interest as it, unlike most other lakes in the region, has maintained a macrophyte‐dominated state. The results revealed a shift in the lake during the past ca. 160 years from a clear water, low‐growing submerged macrophyte community (e.g. Najas minor, charophyte species), dominated by planktonic diatoms and planktonic cladocerans, towards a more pollutant‐resistant, tall‐growing macrophyte community (Potamogeton spp., Ceratophyllum demersum and Myriophyllum spicatum) and dominance by benthic and epiphytic diatoms and littoral cladocerans. However, a pronounced increase in the abundance of planktonic Bosmina spp. at the expense of true littoral cladoceran species and a decline in plant macrofossil assemblages in the surface samples suggest that the lake recently entered into a new unprecedented state. Redundancy analysis indicated major changes in hydrology and moderate inputs of anthropogenic pollutants as well as climate warming as the main drivers of ecological and environmental changes in the lake. Our study demonstrated that plant macrofossils from radionuclide‐dated short sediment cores provide reliable information on the nature and timing of changes in the macrophyte community in Lake Liangzi. Furthermore, our study provided information on the composition of the plant community before recent strong perturbations and also showed the trajectories and suggested the drivers of ecological and environmental change, thereby offering valuable information for lake managers in the Yangtze region and elsewhere. Our study identifies a relatively resistant community of submerged macrophytes, which may be an initial restoration target for managers when restoring the many lakes in the region where submerged vegetation coverage has declined during the last few decades.