[Studies on impact of Water Conservancy Project of Poyang Lake on schistosomiasis transmission I: impact of water level regulation schemes of project on Oncomelania hupensis snail habitats].

Objective: To investigate the impact of the Water Conservancy Project of Poyang Lake after operation on Oncomelania hupensis snail habitats in 10 counties (cities or districts) around Poyang Lake.

Methods: The data of the distribution, numbers, areas, elevation and slope, etc. of snail infested marshlands on upstream of the project site in Poyang Lake were investigated and collected. Accordingly, the status of the submerged and flooding areas of the marshlands were analyzed and calculated respectively in the case that the project ran by different water regulation schemes at 14, 13, 12 m and 11 m levels.

Results: In accordance with the regulation and storage preset programs at 14, 13, 12 and 11 m water levels, the number and its areas of submerged marshlands, from downstream to upstream in Poyang Lake, in turn decreased. Under the condition of the regulation at the 14 m water level, the numbers of completely submerged and partially submerged marshlands as well as the submerged areas were accounted for 32.9%, 51.4% and 60.3% of the whole marshlands, respectively. At the 13 m water level regulation, they were 9.8%, 46.8% and 1.9% respectively. At the 11 m level, only part of 4 marshlands were flooded, which were accounted for only 0.5% of the total number of marshlands and 0.2% of whole areas of the marshlands.

Conclusions: The Water Conservancy Project of Poyang Lake may create a condition for eliminating snails through water flooding. If implementing regulation at the 14 m level for two or three consecutive years, 60.3% of snail habits could realize the snail-free objective. However, if implementing the 11 m or 10 m water level regulation, there will be little impact on areas of snail habitats and the snail distribution in the Poyang Lake region from the point of view of "marshlands flooding". The impacts on marshlands in different counties might differ due to the location and elevation.