Variations in species diversity with the gradients of depths and quality in groundwater at the middle reaches of Tarim River

Based on the data of depths and quality of groundwater as well as species diversity collected from 2006 to 2008,the eco-logical effects of dam construction at the middle reaches of the Tarim River were studied.It is found that the longitude variations in groundwater depths were increase first and decrease then.The temporal variations in groundwater depths were increase gradually.The spatial variations in the chemical type of groundwater varied from Cl--SO42--Na +-Mg2 upwards to Cl--Na + downwards.Like the annual changes of groundwater,the total dissolved solids(TDS) in groundwater increased step by step.Unlike the declining of groundwater depths or the deteriorating of groundwater quality,the species diversity increased generally.Variations in species diver-sity have close relations to both the depths and the quality of groundwater,the species diversity is optimum with the groundwater depths varying from 2.8 m to 3.7 m and TDS in groundwater varying from 1.8 g.L-1to 2.4 g.L-1.