南水北调中线干渠生态系统结构与功能分析

为分析和掌握南水北调中线干渠生态系统结构与功能的特征参数，根据2015~2019年中线干渠鱼类资源调查数据及实测的鱼类生物学参数数据，应用Ecopath with Ecosim 6.6软件构建了Ecopath食物网模型.模型由18个功能组组成，包括了初级生产者、初级消费者、主要鱼类和有机碎屑等.结果显示：中线干渠生态系统规模总流量、总生产量和总消耗量分别为19186.330，8947.857和1106.002（t/（km²·a）），食物网主要由4个整合营养级（1.00~3.71）构成，最高营养级为大型肉食性鱼类鱤（3.71）.食物网能量传递主要有两条途径，分别为牧食食物链和碎屑食物链，两者传递的能量相当，但牧食食物链传递效率是碎屑食物链的近两倍.交互营养分析结果表明，捕食者对其饵料生物的影响一般为抑制作用，碎屑生物量的增加对大部分功能组的影响为正效应，小型上层鱼类对浮游动物生物量起抑制作用.从各功能组之间的生态位重叠来看，各功能组间捕食者生态位重叠现象不普遍，重叠指数适中，部分肉食性鱼类的捕食者生态位重叠指数达到1.对生态系统总体特征分析发现，中线干渠生态系统的总初级生产量与总呼吸量的比值（P/R）、总初级生产量与总生物量的比值（P/B）、Finn's循环指数（FCI）和Finn's平均路径长度（FML）都表明该生态系统处于发展的幼态期，抵抗外界干扰的能力差.此外，中线干渠生态系统对初级生产力的利用率很低，导致过多的营养物质未进入更高营养级的食物链中进行循环，造成系统能量流动的滞缓.因此，根据生物操纵理论，可通过优化和完善鱼类群落结构，增强对系统初级生产力的利用效率，促进物质循环和能量流动，维持生态系统稳定.

Ecosystem structure and function of the main channel of the middle route of south-north water diversion project

A mass-balance food web model was constructed with Ecopath with Ecosim 6.6according to the field data collected in the main channel of the middle route of south-to-north water diversion project (MSNWDP) from 2015 to 2019. Generally, 18 functional groups were consisted in the Ecopath model which includes primary producers, primary consumers, main species of fishes as well as organic detritus. The results showed that the total system throughput, total production and total consumption of the ecosystem is 19186.330, 8947.857 and 1106.002 (t/(km²·a)) respectively, the food web is mainly composed of four integrated trophic level (1.00~3.71) with the yellowcheek carp (Elopichthys bambusa) occupied the highest trophic level (3.71). Two pathways of energy flow were found including grazing pathway and detrital pathway. Despite the same amount of energy flow through these two pathways, the efficiency of grazing pathway is nearly twice as high as that of detrital pathway. The analysis of mixed trophic impacts (MIT) showed negative effects of predators on prey groups in the ecosystem, positive effects of the increasing detrital biomass on most functional groups, and negative effects of the small pelagic fishes on the biomass of zooplankton. With regard to the niche overlap between functional groups, the niche overlap of predators is not that common with moderate overlap index, the niche overlap index of some carnivorous fishes is approaching 1. The comprehensive analysis of multiple indices, including total primary production/total respiration (P/R), total gross primary production/total biomass (P/B), Finn's cycling index (FCI) and Finn's mean path length (FML), showed that the ecosystem is in its juvenile stage, with poor ability to resist external disturbance. Moreover, the utilization rate of primary productivity of the ecosystem is quite low, and large amount of nutrients do not flow into the higher trophic level for circulation which will slow down the system energy flow. Therefore, based on the theory of bio-manipulation, optimization of the fish community structure was thus suggested to enhance the utilization efficiency of the system's primary productivity, to promote material circulation and energy flow, as well as to maintain the stability of the ecosystem.