| Dongping Lake, the second largest freshwater lake in Shandong Province, China, serves not only as a vital fishery water body but also as the sole flood detention area in the lower reaches of the Yellow River. Additionally, it plays a crucial role as the final regulating reservoir in the Eastern Route of the South-to-North Water Diversion Project. Benthic animals, as an essential component of the lake ecosystem, are indispensable in material cycling and energy flow. They also act as indicators of environmental monitoring, providing significant value in assessing water quality and predicting ecological changes.
In recent years, with the official commencement of water diversion operations in the Eastern Route Project and the implementation of ecological regulation measures such as wetland construction and aquaculture withdrawal by the local government, the hydrological conditions, and aquatic environment of Dongping Lake have undergone remarkable changes. These changes have undoubtedly impacted the benthic animal community structure, potentially affecting the stability and function of the entire lake ecosystem. Therefore, this study aims to investigate the macrobenthic animal community and its aquatic environmental conditions in Dongping Lake after the formal water diversion operations and the complete withdrawal of aquaculture activities. The findings will provide scientific evidence and foundational data for the conservation and utilization of fisheries resources and the maintenance of aquatic ecosystems in Dongping Lake.
In this study, a total of 16 sampling points were set up in different areas of Dongping Lake, and four surveys and samplings were conducted in March (winter), May (spring), August (summer), and November (autumn) of 2017 respectively. Benthic animal samples were collected and preserved on site, and then brought back to the laboratory for species identification and biomass measurement. Meanwhile, environmental samples from each sampling point were collected on site for measurement, including key indicators such as dissolved oxygen, pH, ammonia nitrogen, total nitrogen, and total phosphorus. Ecological statistical analysis was performed on the benthic animal community structure to calculate biodiversity indices, richness indices, evenness indices, and dominant species, and to explore the relationships between species diversity, dominant species, and environmental factors. RDA was used to screen out the most influential environmental factors. Furthermore, the study also compared the differences between historical data and current survey results to assess the changing trends of the ecological environment in Dongping Lake in recent years.
The survey identified a total of 22 benthic animal species, representing an increase from the species numbers during the trial water diversion periods (16 species in 2013 and 19 species in 2015). However, this number is still significantly lower than the 29 species recorded in the 1979-1980s (mollusks were counted separately). The biomass of benthic animals has shown a continuous declining trend, with a decrease in mollusks and a succession of dominant species to arthropods (chironomid larvae) and oligochaetes (Limnodrilus hoffmeisteri). Seasonal dynamics revealed that the highest biomass (peaking at 23.16 g/m2) and density (252.18 ind/m2) occurred in March, while the lowest biomass (9.83 g/m2) was observed in August. This seasonal variation is closely related to changes in fish predation pressure and water physicochemical indicators.
The water diversion project has also exerted certain influences on the benthic animal community in Dongping Lake, including increased nutrient influx and changes in water depth. The biomass of benthic animals showed a highly significant positive correlation with chemical oxygen demand (COD) (P<0.01), and the Shannon index was significantly negatively correlated with chlorophyll-a (Chl-a) (P<0.05). In May, community indicators exhibited significant negative correlations with nutrient salts such as total nitrogen (TN) and nitrate nitrogen (NO3-N), indicating that eutrophication leads to reduced biodiversity. The biodiversity at the outlet D16 was significantly higher than that at the inlet D5, reflecting the impact of external inputs brought by water diversion.
The survey results demonstrate that, although the species richness of benthic animals in Dongping Lake has increased after water diversion, their dominant populations have shifted from large mollusks to aquatic insects, oligochaetes, and small snails. This shift is influenced by multiple factors, including water quality conditions, water diversion changes, and human disturbances. The impacts of the water diversion project require further tracking and verification, and the protection of the lake aquatic ecosystem needs to be comprehensively considered from more influencing factors and continuously strengthened.
This study delineates the cascading impacts of large-scale water diversion on benthic ecosystems in Dongping Lake, revealing a transition from mollusk-dominated to insect-oligochaete communities under nutrient enrichment. While short-term species recovery is evident, long-term ecological risks persist, particularly regarding functional diversity loss and eutrophication acceleration. To mitigate these challenges, adaptive management strategies must reconcile hydrological regulation with nutrient control, incorporating benthic community dynamics as sentinel indicators. Future research should prioritize long-term monitoring across hydraulic gradients and experimental studies on species-specific stressor responses. |
