For the lake eutrophication and the degeneration of ecosystem, it is believed that restoring the lake ecology focusing on the restoring and reconstruction of aquatic vegetation is the important way to manage the lake eutrophication, improve water quality and reconstruct a good ecosystem. In recent years, for the functions of aquatic vegetation in the shallow lake ecosystem, the domestic and foreign scholars have carried out a large number of physiological and ecological experiments and lake ecology restoring practices and have made a lot of achievements. However, the successful cases of large-scale restoring experiments for lake ecology of natural shallow lakes are quite few because our knowledge of the ecological mechanism of the shallow lake eutrophication, aquatic vegetation subsidence and the degeneration of lake ecolsystem. Funded jointly by the programs like the National Science Fund for Distinguished Young Scholars, Zhang Yunling research group  of Nanjing Institute of Geography and Limnology studied the long-term dynamic changes characteristics and effect factors of aquatic vegetation in East Taihu Lake, the typical grass type lake of Taihu Lake, and clarified the action mechanism of the subsidence of aquatic vegetation on the basis of long-term positioning observation data of the water environment parameter from 1998 to 2014 and the remote sensing supervision data of the frequency of the emergence of aquatic vegetation from 2003 to 2004 and through statistics analysis and classification and regression tree models. The research result has been published on the Science Reports recently (Scientific Reports, 2016, 6, 23867; doi: 10.1038/srep23867).

This paper, firstly basing on long-term localization observation data of the water environment parameter from 1998 to 2014 in East Taihu Lake, finds that in East Taihu Lake, the nitrogen and phosphorous nutrient, suspended solids and algae aquatic organisms have increased greatly and transparency has decreased substantially. The lake has operating at a high level for a long time. The lake habitat is becoming decreasingly suitable for the growth of aquatic vegetation. The MODIS image from 2003 to 2004 reveals that the emergence frequency of aquatic vegetation gradually decreases and the water area with low-frequent emergence of aquatic vegetation gradually expands. The aquatic vegetation and ecological system are in the degeneration trend. The classification and regression tree models reveals that among the habitats factors of total nitrogen, total phosphorous, total dissolved nitrogen, total dissolved phosphorous, ammoniac nitrogen, chlorophyll a, suspended solids, transparency and water level, the ratio between the concentration of ammoniac nitrogen (reflecting the eutrophication level), transparency and water level (reflecting the light intensity under the water) has an explanation rate to the emergence frequency of aquatic vegetation up to 60.1%, which is the decisive factor of the subsidence of the aquatic vegetation in East Taihu Lake. Therefore, reducing the input of nutrients, especially ammoniac phosphorous and decreasing the water level in spring when the aquatic vegetation sprouts all can effectively promote the growth and development of aquatic vegetation. The above researches results can be used to instruct the restoring of damaged lake system focusing on the reconstruction of aquatic vegetation.

Link to the full text:

http://www.nature.com/articles/srep23867