利用Ecopath模型评价鲢鳙放养对千岛湖生态系统的影响

Evaluation of the effect of stocking silver carp and bighead carp on the ecosystem of Qiandao Lake using Ecopath model

“保水渔业”是中国控制“水华”暴发等生态灾变的措施之一,其结果存在较大的不确定性。在浙江省的新安江水库(千岛湖),“保水渔业”的实施带来了水质改善和渔业增产的双重效果。但在生态系统自组织层面,这种人工干预手段引起的生态系统结构化效应的研究,尚未真正展开。基于2008—2010年千岛湖的生态和渔业资源调查数据,应用EwE(V6.6)构建了2010年千岛湖生态系统的Ecopath模型,并将其与2004和2016年的模型进行对照,分析了千岛湖生态系统在鲢、鳙鱼放养下的变化。千岛湖生态系统在3个年份均为4个整合营养级,营养能流分布成典型的金字塔型,且营养流总量中流向碎屑的占比很大,营养级Ⅰ、Ⅱ的能量被利用得不够充分;除鲢、鳙鱼外大部分鱼类的生物量逐渐下降,浮游植物和碎屑的生物量增多;系统的初级生产力和规模得到了一定提升,但总体的能量转换效率有所降低。在一些和系统成熟度、复原力和稳定性密切相关的参数方面,总初级生产量/总呼吸量增加,Finn氏循环指数和Finn氏平均路径长度逐渐降低,3个年份的连接指数(CI)分别为0.223、0.219、0.263,系统杂食指数(SOI)分别为0.087、0.102和0.131。研究分析表明,长期的鲢、鳙鱼放养使千岛湖的食物网结构发生了较大的变动,生态系统的营养交互关系不够复杂,成熟度和稳定性有所下降。千岛湖作为一个由水库发展而来的淡水水体,食物网关系本身就较为简单。因此,未来需要避免过多的人为干扰,并基于生态学原理更系统地进行修复工作。

Water quality oriented fishery is one of the measures to control ecological disasters such as water bloom outbreak in China, but the subsequent results are quite uncertain. In Xin′anjiang Reservoir(Qiandao Lake) of Zhejiang Province, the implementation of water quality oriented fishery has brought certain positive effects on the water quality improvement and fishery production. However, the structural effects of such anthropogenic interventions on ecosystem self-organization has remained a significant challenge. In this study, we collected the ecological and fishery resources data of Qiandao Lake from 2008 to 2010 to construct the Ecopath model, dividing the ecosystem of 2010 into 17 functional groups. The ecosystem structure and functional status of Qiandao Lake in 2010 was compared with those in 2004 and 2016 based on our analysis of the Ecopath model, in order to explore the effects of stocking silver and bighead carp. The results showed that the ecosystem of Qiandao Lake in three typical years all mainly consisted of four integrated trophic levels with a typical pyramidal-shape energy flow, and the flow to detritus accounts for a large proportion in the total nutrient flow, thus it can be seen that the energy of trophic levels Ⅰ and Ⅱ was not fully utilized. Except for silver carp and bighead carp, the overall fish stock decreased gradually, while the biomass of phytoplankton and detritus increased simultaneously. The primary production and scale of the system improved to some extent, but the total energy transfer efficiency of the system was not high compared to other reservoirs. In terms of some parameters closely related to system maturity, resilience and stability, the total primary production/total respiration(TPP/TR) increased, and Finn′s cycling index and Finn′s mean path length decreased gradually, accompanied with relatively low connectance index and system omnivory index in all three typical years(CI=0.223, 0.219, 0.263, respectively;SOI=0.087, 0.102, 0.131, respectively). The results indicated that long term stocking of silver carp and bighead carp had resulted in a significant change in the food web of Qiandao Lake, and the overall decline of fish resources might lead to over nutrition in the lake. The ecosystem trophic interactions were not complex enough, and the maturity and stability were reduced. As a fresh water body developed from the reservoir, the relationship between food webs in Qiandao Lake is relatively simple. Therefore, it is necessary to carry out restoration work to avoid too much human interference, and a more systematic restoration measure based on ecological principles is needed in the future.