基于营养通道模型的淀山湖生态系统结构与能量流动特征

Structure and energy flow of Dianshan Lake ecosystem based on the Ecopath model

根据2008-2009年间对淀山湖湖区水生生物资源调查的结果,运用Ecopath with Ecosim 6.1软件构建了淀山湖生态系统的营养通道模型,初步分析了淀山湖水域生态系统的结构和能量流动特征。模型中涉及水鸟、鱼类、虾类、软体动物、底栖动物、浮游动物、浮游植物、碎屑等21个功能组分,基本涵盖了淀山湖生态系统的主要能量流动过程,分析结果表明,淀山湖生态系统总流量为4 098.50 t·km-2.a-1。从混合营养效应分析来看,渔业捕捞会对该生态系统的鱼类功能组产生负效应。生态网络分析显示,淀山湖生态系统各功能组的营养级范围为1～3.92,水鸟占据了营养层的最高层。系统的能量流动主要有5级,各营养级之间平均能量转换效率为11.7%。淀山湖生态系统的整体再循环率较低,能量利用效率有待改善和提高。生态系统参数:系统初级生产力/总呼吸量(TPP/TR)、连接指数CI和能量循环指数FCI分别为2.80、0.19和0.0189,表明淀山湖生态系统目前仍然处于幼态化生态系统状态。

Dianshan Lake,the largest freshwater lake in Shanghai,covers an area of 62 km2 with mean depth of 2.0 m and provides drinking water for more than 10 million people.With the rapid development of industry and agri-culture in recent years,Dianshan Lake has become polluted by run-off and sewage,leading to blooms of blue-green algae in some parts of the lake.The self-cleaning ability of Dianshan Lake has been degraded,and city authorities have funded several research projects to explore the reasons for its ecological deterioration.Based on data from a bio-resources survey carried out between September 2008 and September 2009,a mass-balance model of trophic interactions was constructed using Ecopath with Ecosim（EwE,an ecological/ecosystem modeling software suite） to represent energy transfer through the trophic levels of the Dianshan Lake ecosystem.This is the first Ecopath model of Dianshan Lake and consisted of 21 functional groups,including birds,commercial fish species,phytoplankton,zooplankton,benthos,shrimp,mollusks,macrophytes and detritus.Each group repre-sented organisms with similar roles in the food web and covered the main trophic flow in Dianshan Lake.The re-sults show that total throughput was 4 098.50 tonne？km？2？a？1.The trophic levels of different groups ranged from 1 for detritus and phytoplankton to 3.92 for large predators,with water birds occupying the top level.Mixed trophic impact analysis indicated that both trawling and gillnet fishing were impacting components and the negative tro-phic impact of fishing on different groups was relatively high.Top-down or bottom-up control in several preda-tor–prey relationships demonstrated that some species can be used to control blue-green algal blooms can be con-trolled by some species in some areas.For example,Hypophthalmichthys molitrix had a negative trophic impact on algae due to their predatory relationship in the food web,while submerged and other macrophytes had little influ-ence on algae due to their competitive relationship in the food web and low biomass within the niche.The system network was mapped via network analysis into a linear food chain with five main trophic levels.Mean transfer efficiency was 11.3% from detritus and 12.3% from primary producers within the ecosystem,which was higher than nearby lakes.Transfer efficiency is only 7.0% from level I to level II and 3.3% from level V to VI,which indicated that the transfer efficiency of the Dianshan Lake ecosystem is imbalanced.The importance of discarded food and system re-cycling rate in the ecosystem was low;energy utilization rate could be increased.Most unused detritus was deposited on the bottom of lake and affected water transparency via wind and wave agitation.