Assessing changes of trophic interactions during once anthropogenic water supplement in Baiyangdian Lake

Abstract

Baiyangdian, located in Hebei province, is the biggest freshwater lake in North China. Since the 1960s, due to increasing human activities and climate change, this area has suffered from markedly shrinking and drying up several times. In current situation, anthropogenic water supplement plays a very important role in maintain this wetland's existence and development, and from 1981 to 2003 this approach had been already carried out 15 times. But until now there is few study in the aspect of whole ecosystem level responded to anthropogenic water supplement. In this study we used Ecopath model to analyze the changes of ecosystem's structure and function in connecting with once water supplement event which started in middle September 2009. Based on field experimental data in September and October 2009, two mass-balance models of the Baiyangdian Lake were developed to compare differences in energy flow process, trophic composition and other system character indexes during this two periods. As the results show, from September to October, the biomass proportion of first trophic level distinctively increased but in higher trophic level this proportion declined, meanwhile the total primary productivity/total respiration (TPP/R) increased by 12.07%, the system omnivorous coefficient (SOI), Finn's cycling index (FCI), and the average path length decreased by 4.16%, 20.13%, and 23.4% respectively. Most of the change directions of the indexes are contrary to the natural processes of ecosystem development, which meant that the interactions of organics are weakened, system maturity is degraded further and the ecosystem became more vulnerable to external disturbance after this time of anthropogenic water compensation.