Abstract: Dam enlargement can lead to the increasing distribution area of flooded wetlands. In the present study, soil samples along a flooding gradient in Lashihai Plateau wetland were collected and analyzed in order to understand the distribution patterns of soil organic matter and total nitrogen, and the differences in their contents before and after the dam impoundment were compared. The results showed that compared to the unflooded area, the contents of soil organic matter and total nitrogen in the flooded area were higher. Also, as the flood intensity increased, the contents of organic matter and total nitrogen first increased and then decreased. As far as the same flood intensity was concerned, the soils severely affected by human activities (e.g., abandoned cropland soils) had lower levels of organic matter and total nitrogen than the undisturbed soils
(e.g., meadow soil). The analysis of variance (ANOVA) showed that the contents of organic matter and total nitrogen were significantly changed in the perennial waterlogging area (P<0.05) but not in the seasonal flooding area with the alternation of wet and dry seasons (P>0.05). Correlation analysis showed that flood intensity was positively correlated with soil organic matter and total nitrogen contents (P<0.01). Also, soil organic matter was positively correlated with total N (P<0.01). The results could provide basic data to evaluate the impacts of dam impoundment on wetland ecosystems and also a theoretical basis for protection and management of plateau wetland ecosystems.

Key words: community structure, driving factors, Tangshan Bay, zooplankton, pollution effects