Distribution patterns and changes of aquatic communities in Lashihai Plateau Wetland after impoundment by damming
筑坝扩容下高原湿地拉市海植物群落分布格局及其变化

Damming could alter hydrological cycle in a region rapidly and produce profound influences on ecosystem structures and functions of wetlands. Plants are the essential composition of the wetland ecosystem and the alteration of hydrological conditions caused by damming can directly affect spatial distribution, ecosystem structures and functions of wetlands. The impacts of impoundment by damming on wetland ecosystems have become a worldwide concern. Lashihai, a typical closed and semi-closed wetland in the northwestern Yunnan Plateau, belongs to the Jinsha River catchment and is also one of the 12 wetlands of international importance in the plateau region. Since 1994, Lashihai has changed from a seasonal flooding wetland to a lake with relatively stable water level after a dam establishment. To study the distribution patterns and changes of aquatic communities in Lashihai after impoundment by damming can provide a sound basis for scientific assessment of impacts of dam establishment on wetland ecosystems. By using the RS and GIS technologies combined with field surveys, the plant communities, species composition and their distribution patterns in the plateau wetlands of Lashihai were studied over 13 years following impoundment by damming. The results of a comparative analysis of changes in plant communities from 1994a to 2006a showed that 13 years after dam establishment, there were two emergent communities (Scirpus tabernaemontani and Polygonum amphibium), two floating-leaved communities (Potamogeton tepperi and Trapa bispinosa), five submerged communities (Myriophyllum spicatum, Potamogeton pectinatus, Potamogeton crispus, Potamogeton perfoliatus and Potamogeton pusillns) and lakeside meadow community in Lashihai. The number of species was 61, belonging to 25 families and 48 genera. Plant species richness was the lowest in the submerged communities and increased gradually in the floating-leaved communities and emergent communities, and reached the highest in the lakeside meadows. The current distribution area of the submerged communities amounted to 615.08 hm2, the meadows and floating-leaved communities covered 214.60 hm2 and 140.01 hm2, respectively, and the emergent communities was only 9.34 hm2. In the past 13 years after impoundment, the plant communities in Lashihai changed from a simple submerged community to a diverse system of submerged, floating-leaved and emergent communities, where the submerged plant communities of Myriophyllum spicatum, Potamogeton pectinatus and Potamogeton pusillns remained, and Butrachium bungei, Potamogeton malaianus and Chara spp. communities had disappeared. Damming altered the natural hydrological conditions and changed greatly species composition, community structure and spatial patterns of wetland vegetation in Lashiha. The key driving force for the changes in wetland vegetation was dam construction, as the wetland plants with different strategies of renewal and spreading responded to hydrologic changes by d