Diversity variation and community succession of aquatic macrophytes in Lake Futou.
Due to extensive human activities, habitat loss and segmentation induce destruction and disappearance of aquatic plants in the shallow lakes. These activities cause secondary extinctions of aquatic animals, leading to loss of biodiversity in lakes and animal reproduction. Lake Futou, locates in southeastern Hubei Province, China, has the same functions, such as irrigation and aquaculture, as other shallow lakes in the middle and lower reaches of the Yangtze River. However, in recent 50 years, human disturbances, including reclamation, damming and over-fishing, have caused accelerated loss of diversity of aquatic plants. This worsened the ecosystem fuction and seriously affected the productivity of aquatic resources and the quality of species. Thus, the aims of the this study were to understand the succession of aquatic plants in Lake Futou in recent decades and to comprehend the reasons associated with exploitation and utilization of resources in this lake. In order to investigate the aquatic plant diversity in Lake Futou, the species and community diversity were studied using field investigation in 2009, and the topology were analysed by geographical information system technique with ARC/INFO. Based on the results obtained from field investigation and previous studies, species diversity variations and succession of aquatic macrophytes community in Lake Futou from 1988 to 2009 were investigated and the reasons between the changes and some controlling factors were analyzed. The results showed that there were some variations on the number of species and dominant species of aquatic plants. Some species that were sensitive to disturbances such as Nymphaea stellata disappeared and some dominant species such as Potamogeton maackianus, Vallisneria denseserrulata and Hydrilla verticillata became sub-dominant species or accompanying species from 1988 to 2009. In addition, the introduced species such as Elodea nuttalli occurred in Lake Futou and became dominant species. Before the early 1980s, vegetation coverage was 100%. At the end of 1980s, coverage decresed to 80.5%, and the coverage further decresed significantly to 16.7% in 1999 and increased to 47.9% in 2009. From 1988 to 2009, emergent macrophytes increased the coverage from 24.18% to 56.93%, and Nelumbo nucifera became the dominant species in the summer. In this period, the coverages of submersed and floating-leaved macrophytes declined from 47.25% and 28.57% to 29.21% and 10.35%, respectively. Associations dominated by Nymphoides peltata in floating-leaved plants and dominated by Elodea nuttalli in submersed plants increased in the communities. Associations of Ceratophyllum demersum, Myriophyllum spicatum, and Ceratophyllum demersum also increased. Potamogeton maackianus decreased significantily. Overall, the aquatic macrophyte communities in the lake have changed markedly since the natural succession status in the 1950s changed toward the artificial succession status due to human disturbances observed in this study. Vegetation type, vegetation coverage, biomass and structure of community changed drastically. Our analyses indicated that the main reasons of species replacement of aquatic plant were human disturbances such as aquaculture in enclosures, mowing and introducing species, and natural factors such as water level fluctuation, life span and reproduction strategy. Based on this study, thorough planning of comprehensive exploitation and utilization of Lake Futou are needed in future lake management.