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

Abstract

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.

Mass balance model of Lake Volta fisheries: The use of Ecopath model

“…Fetahi and Mengistou () and Deng et al. (), working on Lake Awassa, Ethiopia and the Manwan Reservoir in China, respectively, also reported low EE values for primary producers, consistent with the findings of the present Lake Volta study. The EE value (0.13) for the top predator ( Bagrus ) was the lowest of all the fish groups in the lake, indicating their low predation, since most of the Bagrus stocks have been exploited as suggested by their reduced biomass levels.…”

“…In contrast, the catch statistics of Alestes and Synodontis have indicated declining trends over time, mainly attributed to overexploitation (Dankwa et al., ; FAO ), and confirming their diminishing role within the current food web. In terms of biomass, Lake Volta is also dominated by lower trophic organisms, particularly phytoplankton, benthos and zooplankton, with these groups also found to dominate most of the system flows in marine and freshwater ecosystems (Deng et al., ; Piroddi et al., ). Thus, Lake Volta, although described as mesotrophic (Karikari, Akpabey, & Abban, ), exhibits a high biomass of primary producers, and is capable of producing a relatively high fish biomass.…”

“…Construction of dams for hydropower, irrigation, aquaculture and control of flood is a major anthropogenic interference in river ecosystems (Deng et al., ). Such constructions result in alterations in the ecosystem from a riverine to lacustrine state, with the existing ecosystem being exposed to multiple ecological stressors that impact the dynamics and composition of fish species (Feroz Khan & Panikkar, ; Heymans, Shannon, & Jarre, ).…”

Impact of Hydropower Dam Development on River Ecosystems: Ecopath Model Application on the Red River in China as an Example

“…If the system is more mature, the links (food webs) among various functional groups of the system will be more complex, so the values of CI and SOI are positively correlated with the maturity of the system [40][41]. The results indicate that CI and SOI of the ecosystem of NC are 0.301 and 0.043, respectively, and those of CR are 0.308 and 0.140, respectively, while those of CB are 0.290 and 0.086, respectively.…”

“…Cycling flows refers to the total re-entering and recycling trophic flows in the system, and FCI indicates the ratio of the cycling flows to the total flows in the system, while FML denotes the mean length of each cycle flowing through the food chain [40][41]. One of the characteristics of the mature system is the higher proportion of the material recycling and the longer food chain where trophic flows pass.…”