Zonation and its influencing factors of a large subtropical reservoir (danjiangkou reservoir in central china), based on macroinvertebrates

Danjiangkou Reservoir is the water source area of the Middle Route of South to North Water Transfer Project of China. The study on the aquatic ecosystem status and the reservoir zonation pattern are of great importance to the comprehensive management of the water source area. In this study, the ecological zonation based on the macroinvertebrate community, and the influencing factors to the macroinvertebrates were studied between July 2007 and May 2008. The results showed that Tubificidae, Naididae, and Chironomidae were dominating groups of the macroinvertebrate community in Danjiangkou Reservoir. The entire reservoir was divided into 4 zones based on the macroinvertebrate community type: the riverine zone (tributary zone), Hanjiang transitional zone, lacustrine zone and Danjiang transitional zone. The lacustrine zone appeared as the most stable zone with Tubifex community type. Hanjiang transitional zone and Danjiang transitional zone had the same community type, the mixed type of Tubificidae sp.l and Tubifex. The community structure was least stable in the riverine zone. Relative water column stability was the most important factor to the macroinvertebrates composition in the reservoir scale. But in the local scale, macroinvertebrates in the lacustrine zone was mainly influenced by the sediment organic matter; and the transitional zone was significantly affected by both sediment organic matter and water temperature. Water depth was a main factor affecting the seasonal changes of the macroinvertebrate community, significantly correlating with the standard deviation of Shannon-Wiener diversity index (r = -0.768, p = 0.001). It was also the main reason leading to the difference between the length of the lacustrine zone in Hanjiang and Danjiang River (35.5 km and 10 km, respectively). Therefore, due to the dissimilar properties in different zones, they should be treated separately as different sub-systems in the reservoir management.