As one of the primary consumers in freshwater lake ecosystems, it is extremely sensitive to changes in the living environment. After the death of the branch horns, its chitin remnants fell to the bottom of the lake and were preserved in sediments, becoming an important carrier for lake environmental research. As a part of Taihu Lake, the ecological environment of East Taihu Lake is different from the western, northern and central lake areas of Taihu Lake with algae-type ecology as the main environmental characteristics, and East Taihu Lake is characterized by a more obvious grass-type ecological environment. In recent decades, due to the interference of human activities, East Taihu Lake has faced a series of environmental problems such as swamping and eutrophication, and its ecological environment has undergone great changes, which have had a dramatic impact on the composition of zooplankton in the lake. Shengjin Lake is not only a typical Tongjiang lake in the middle and lower reaches of the Yangtze River, but also a wetland ecology and a national key waterfowl nature reserve in Anhui Province. Over the past few hundred years, due to the joint influence of rivers and human activities, the ecological environment of Shengjin Lake has also undergone significant changes.
Based on the sensitive response of zooplankton phylum to changes in the ecological environment, therefore, with the support of the National Key Research and Development Project, the National Natural Science Foundation of China and the Special Project of the Basic Work of the Ministry of Science and Technology, Cheng Longjuan, a researcher at the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, analyzed the composition characteristics of the branches and horns of East Taihu Lake and Shengjin Lake over the past few hundred years, supplemented by geochemical indicators and chronological data. The evolution of the ecological environment of two shallow freshwater lakes and the response characteristics of branch group community composition to the evolution of lake ecological environment are revealed.
Specifically, the analysis and study of the fossils of branches in the sediments of East Taihu Lake in the past 100 years revealed that since the 1960s, the composition of branch horns in East Taihu Lake has shown a significant decrease in the concentration of planktonic species (mainly represented by elephant trunks), and the number and concentration of coastal species (mainly represented by round disc intestines and Western pen stripes) have increased significantly (Figure 1). RDA and Pearson correlation analysis together revealed a significant correlation between TP content and total number of weevils, long-pronged weevils, and round disc intestines (correlation coefficients -0.720, -0.646, and 0.667, respectively) (Figure 2). The study found that the change of the composition of the branches and horns of East Taihu Lake responded to a series of changes in the water environment of East Taihu Lake since the 1960s due to the influence of human activities such as large-scale reclamation and fish and crab farming, resulting in intensified eutrophication of the lake, gradual reduction of lake water area, shallow water depth, increased biomass of submerged plants, and enhanced marshing trend (Figure 3).
The results of the Shengjin Lake study showed that before the 1980s, the total concentration and number of species of branches in Shengjin Lake were low, but the number of coastal species was relatively large, the concentrations of LOI, TOC and nitrogen and phosphorus were low, and the concentration of δ13Corg was heavy; after the 1980s, the total concentration of branches and the proportion of weevils gradually increased, and the abundance of coastal species such as round disc intestine and Western stroker was decreased (Figure 4), the concentrations of LOI, TOC and nitrogen and phosphorus increased, and the concentration of δ13Corg tended to be negative. The study found that the change in the composition of branches and horns of Shengjin Lake responded to the gradual increase in the concentration of nutrient salts and organic matter in Shengjin Lake and the gradual increase in ecological and environmental pressure due to human reasons (reclamation, establishment of sluice dams, extensive use of pesticides and fertilizers, etc.) and natural causes (accumulation of a large number of migratory bird droppings).
These results further expand the understanding of the relationship between the composition of zooplankton species and the ecological environment in the ecological environment of freshwater lakes, and deepen the understanding of the evolution of the ecological environment of lakes along the middle and lower reaches of the Yangtze River. The research was recently published in the international journals Catena and Quadernary International.
Figure 1 Characteristics of fossils of branches and horns in East Taihu Lake in the past 100 years
Figure 2 Relationship between geochemical indicators and community composition of clades
Figure 3 Evolution of the water environment of East Taihu Lake
Figure 4 Characteristics of the composition of fossils of branches and horns in Lijin Lake over the centuries
Source: Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences