Wetlands provide essential ecological functions and services for human, animal, and plant life, including carbon storage, water supplies, fisheries, biodiversity, and recreation, but are under increased threat from human activities and climate change. Since 1990, at least 64–71% of wetlands worldwide have suffered degradation, which includes changes to their physical states, and these changes may result in losses of biodiversity and jeopardize the functions and stability of their ecosystems.
The lack of long-term biological indicators (e.g., macroinvertebrates) in China limits the understanding of historical changes in biodiversity in response to environmental factors, complicating the identification of major drivers of wetland declines. The freshwater biomonitoring systems in China has not been well established prior to 2010, making it challenging to capture longer-term freshwater community dynamics.
In this study, we combined a continuous 30-year-long biomonitoring dataset from Dongting Lake with satellite imagery to investigate the drivers of local ecosystem change. We hypothesize that human-induced changes, including changes in land-use, climate, and hydrology, led to a decline in the integrity of the aquatic community in Dongting Lake. We further hypothesize that these changes occurred along three paths, namely, "land-water connection", "climate change" and "river-lake connection" paths.
From 1988 to 2017, the region around the Dongting Lake wetland experienced comprehensive environmental changes, such as an increase in land-use intensity, warming of the climate, fluctuations in its connectivity with the Yangtze River, and increasing frequency of algal blooms. The results revealed declining macroinvertebrate alpha diversity (species richness and functional redundancy) but increased beta diversity (taxonomic and functional dissimilarity).
We applied path analysis based on piecewise fitting of component hierarchical linear-mixed-effects models to test the three hypotheses in Figure 1 for the dynamic changes of the macroinvertebrate communities in Dongting Lake. An increase in nutrients due to changes in land-use intensity in the surrounding terrestrial ecosystem was the primary mechanism for the losses of species and functional groups.
To explore the best spatial extent of the associations between human land-use intensity at the surrounding terrestrial ecosystem and parameters in the lake, we tested the associations with increasing terrestrial extent from the sample locations. Alpha diversity changes were most influenced by land-use changes in adjacent land areas 1.5 kilometers from the sampling sites, while beta diversity was affected within 50 meters.
Our analysis filled a gap in our understanding of the historical dynamics of wetland ecosystems in China while also providing a valuable case study for comparisons worldwide. The results suggest that the land adjacent to the lake is critical for maintaining wetlands and lake biodiversity. Consequently, establishing protected land buffer areas around these wetlands and lakes may be the most suitable strategy for wetland/lake conservation, particularly in the developing world.