Preliminary investigation on the changes in trophic structure and energy flow in the Yangtze estuary and adjacent coastal ecosystem due to the Three Gorges Reservoir

Water projects in the Yangtze River basin, especially the Three Gorges Reservoir (TGR), have strongly affected the biological and ecological integrity of the Yangtze estuary and adjacent coastal ecosystems. The Ecopath with Ecosim model was applied to study trophic structure and energy flow after the impoundment of TGR based on field surveys in 2006. The model results showed that the trophic levels ranged from 1.000 to 4.058; and 44% of the energy flows originated from the detritus food chain, while 56% originated from the grazing food chain in the trophic transfer process; the transfer efficiency of the ecosystem was 10.0%, and TPP/TR (Total Primary Production/Total Respiration) was 1.899. Compared with model results in 2000 (before impoundment of TGR), the trophic structure of the ecosystem did not exhibit substantial changes; however, the mean trophic level and catch amount decreased remarkably after impoundment. The estuary and adjacent coastal ecosystems were found to be more sensitive to external perturbations after impoundment.