Ecological Effects of Dam Impoundment on Closed and Half-Closed Wetlands in China

Whether dam impoundment for water resource purposes improves wetland ecosystems is heavily disputed. In this study, we investigated the effects of dam impoundment from 2006 to 2011 on wetland plant communities and wintering water birds in Lashi Lake, a typical closed wetland in Northwest Yunnan, China. The surface area of the water body increased from 933 hm(2) before impoundment to 1262 hm(2) after impoundment; the area of meadows and emergent, submerged and floating vegetation increased from 1006 to 1149 hm(2). After the dam impoundment and with the rising water level, formerly dominant plant communities, such as Com. Phragmites australis, Com. Potamogeton pectinatus and Com. Nymphoides peltatum, disappeared. New communities, such as Com. Polygonum hydropiper, Com. Acorus calamus and Com. Leersia hexandra, rapidly expanded into the newly formed lakeside. During these changes, the species and number of wintering water birds slightly increased, but the populations and distributions of birds were altered. Some birds chose the newly formed lakeside as habitat, while others disappeared or decreased greatly. Notably, the major protected birds, such as species of Ciconia nigra, did not appear in the new area, and the species number of Grus grus decreased. The results showed that damming impacted wetland ecosystems. Given the importance and complexity of dam impoundment in alpine wetlands, the effects of food-chain modifications on plants, water birds, aquatic organisms, and humans could be extensive.