洞庭湖区外洲环境变化对钉螺分布的影响

Impact of environmental changes on Oncomelania snail distribution in Dongting Lake beach

目的探索三峡工程运行后洞庭湖区环境变化对钉螺分布及消长的影响。方法选择紧靠大堤人为影响因素较大和较小的君山区丁字堤和东口外洲为研究现场。测量外洲地面高程,采用GPS定位并设置固定标志。定期调查植被高度,测定洲土含水量和不同高程微环境温度、湿度;调查钉螺、螺卵分布。进行纵向回顾性分析比较。结果丁字堤现场1993年在高程25 m取洲土固堤形成完整的隔离沟,钉螺密度逐年降低,1998年后未发现钉螺,植被高度显著低于东口现场,无高杆植物生长。东口现场高程23.5～26.5 m有钉螺分布;优势植被为莎草科的苔属,退水30 d后草植被生长高度为16.0～54.0 cm,60 d后草植被密度达最高水平;24.5～25.5 m为密螺带,钉螺和螺卵分布高程显著低于20世纪80年代。枯水季节,东口现场密螺带洲土含水量为46.80%～52.20%,显著高于丁字堤,26.0 m高程以上洲土含水量为21.36%～29.77%,与丁字堤相当。结论三峡工程运行后不影响洞庭湖湖洲钉螺种群的繁殖或密螺带形成。

Objective To study the impact of environmental changes on the distribution and the growth and decline of Oncomelania snails in Dongting Lake beaches after the implementation of Three Gorges Project.Methods T-embankment of Junshan District where there was a greater human factor related to the snail spread and a lake beach named Dongkou of Junshan District where there was a less human factor related to the snail spread were selected as study areas.The various ground elevations were measured and the high points were marked with GPS.The height of vegetation was surveyed regularly,soil moisture content and micro-environment temperature and humidity at different elevations in the lake beaches were detected,and the snail distribution was investigated.Both the longitudinal and retrospective studies were conducted.Results In 1993,the soil was taken from the lake beach at the elevation of 25 m to build an isolated canal,and this made snail density decline year by year,and no snails have been found since 1998.The elevation of the vegetation in the T-embankment was significantly lower than that in Dongkou,and there was no high rod plant growth.The snails were found in the elevation from 23.5 to 26.5 m where the vegetation was mainly Cyperus spp.The growth of the vegetation was 16.0 to 54.0 cm 30 days after flood withdrew,and the vegetation reached the highest density 60 days after flood withdrew.The snail density was highest at the elevation from 24.5 to 25.5 m,and the elevation of snails and their eggs was lower than that in 1980s.In the dry season,the water content of the soil in Dongkou was from 46.80% to 52.20%,which was more than that in T-embankment,while at the elevation over 26.0 m,the water content was from 21.36% to 29.77%,which was equal to that in T-embankment.Conclusion Three Gorges Project plays an important role in the control of water level of Dongting Lake,but there is no impact on the snail reproduction and density.