Long-term succession of aquatic plants reconstructed from palynological records in a shallow freshwater lake

Highlights: • First attempt to reveal long-term aquatic plant succession in the MLYB based on palynology. • There was a low biomass of aquatic plants in Changdang Lake in the first half 20th century. • Changdang Lake is currently in a macrophyte-algae transition. • Hydrological condition and nutrient input are the main factors for succession of aquatic plants. • The 1970–1980s state of aquatic plants in Changdang Lake would be a realistic restoration target. Aquatic plants in shallow freshwater lakes play a key role in stabilizing ecological function and providing valuable ecosystem services, yet they are severely degraded worldwide. An improved understanding of long-term aquatic plant succession is critical to investigate the potential driving mechanisms and to facilitate ecological restoration. In this paper, we reconstructed changes in the aquatic plant community over the past century based on palynological records from Changdang Lake, Middle and Lower Yangtze River Basin (MLYB), China. Our results reveal that aquatic plants in Changdang Lake have undergone three clear phases: emergent macrophytes dominated the aquatic vegetation in the 1900s–1970s, submerged macrophytes in the 1970s–1990s, and floating macrophytes increasingly after the 1990s. Significant changes in the aquatic plant communities were caused by increasing anthropogenic pressures, such as damming and nutrient loading from agriculture, aquaculture, and urbanization after the Chinese economic reform. We argue that Changdang Lake is currently in a transition phase between a macrophyte-dominated state and an algae-dominated state. Our palynological record is different from many contemporary studies, which suggest submerged plants dominated most lakes in this region before the 1950s. We suggest that the return of the aquatic plants to their 1970s–1980s state would be a realistic target for lake restoration. Our results show that palynological records can reveal long-term dynamics of macrophytes in shallow lakes for sustainable lake restoration and management.