Application of Ecopath model on trophic interactions and energy flows of impounded Manwan reservoir ecosystem in Lancang River, southwest China

The structure and function of aquatic communities in reservoir ecosystems can be strongly affected by dam construction. The Ecopath model is an effective tool that reveals the food web structure and pathways of energy flows. In this study, it was applied to analyze the trophic interactions and energy flows within the Manwan reservoir ecosystem on Lancang River in southwest China. Ecotrophic efficiency (EE) was calculated and the value of EE was 0.073 for the least-exploited piscivorous fishes (top predators) and 0.93 for the most-exploited zoobenthos. Four estimated trophic levels of the groups varied from 1 for detritus and phytoplankton (level I) to 3.69 for piscivorous fishes (level IV) and the remaining groups were mainly at trophic levels II and III. Food web structures and interactions were well represented by a linear food chain that was dominated by a detritus pathway; that is, energy flows from detritus were as important as phytoplankton in the web. The proportion of total energy flow originating from detritus was 46% while the other 54% came from primary producers. The average transfer efficiencies between trophic levels were 16.6% from primary producer and 15.7% from detritus. Total system throughput was found to be 5550 t km−2 yr−1, total primary production/total respiration ratio was 2.46, and the ascendency index was 27.4%. These results showed that Manwan reservoir ecosystem was an immature ecosystem and still at its development stage. These results are helpful for biodiversity preservation and the understanding and monitoring of reservoir ecosystems which are key resources for fish and other aquatic organisms.