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Wetland plays an important role in maintaining ecological balance. Water regimes are the most important driving forces for wetland structure and function. Unfortunately, in recent decades, impacts of anthropogenic activities (e.g. dam construction, agricultural irrigation, industry, settlements) compounded with climate change have altered natural flow regimes profoundly and led to severe degradation of wetlands worldwide. Baiyangdian Wetland, the largest freshwater lake wetland in North China, has dried up on several occasions due to increasing human activities since the 1960s. To alleviate the ecosystem degradation trends, flow regulation was introduced to recharge the drying wetland on 19 occasions from 1997 to 2009. However, the impacts of these actions on ecosystem structure and function remain poorly understood. In this study the Ecopath software was employed to establish two mass-balance ecosystem models before and after the flow regulation in September 2009. The changes in trophic composition, flow processes, and other ecosystem indices were compared. The results show that following the flow regulation process the biomass in the first trophic level increased, while a decrease was recorded for the higher trophic levels. Furthermore, total primary productivity/total respiration (TPP/R) increased by 12.07%, while the system omnivorous index (SOI), Finn's cycling index (FCI), and average path length (APL) decreased by 4.16, 20.13, and 23.40%, respectively. Overall, the shift in indices indicates that ecosystem process during flow regulation was contrary to natural wetland succession. The weakened interactions among organisms in different trophic level will result in degrading ecosystem maturity. Hence flow regulation in September 2009 increased the vulnerability of Baiyangdian Wetland to external disturbance. This study indicates that ecosystem trophic interactions should be modelled before flow regulation to prevent ecosystem degradation and key ecosystem indices should be monitored and regulated toward natural ecosystems during and after flow regulation.
Keywords: wetland, Ecopath, food web, trophic level, flow regulation