氨氮胁迫下鲢幼鱼下行洄游通道质量研究

Research on the quality of downward migration passage of juvenile silver carp stressed by ammonia nitrogen

为定量揭示氨氮浓度对鱼类栖息地质量的影响,以淮河干流鲁台子至窑河闸段为研究区域,选择典型土著洄游鱼类鲢作为目标物种,耦合研究区域内平面二维水动力水质模型构建了含有氨氮指标的鲢幼鱼下行洄游通道栖息地模型。假定入流边界氨氮浓度满足地表水Ⅲ类水质标准(1.0 mg·L^(-1)),选取栖息地面积、栖息地斑块数和栖息地连通性指数三个景观生态学特征指标,定量评估了高、中、低三组代表性流量下氨氮对鲢幼鱼下行洄游通道质量的影响。结果表明:与不考虑氨氮指标情况下的洄游通道质量相比,(1)鲢幼鱼下行洄游通道适宜生境面积分别下降1.6%、6.7%和3.4%,氨氮对洄游通道适宜生境面积的影响较小。(2)鲢幼鱼下行洄游通道斑块数分别增加4.5%、28.7%和3.6%,在原本具有较高破碎度的情况下氨氮影响最大,二者存在一定程度的正相关和协同效应。(3)鲢幼鱼下洄游通道连通性分别降低54.3%、34.6%和24.8%,连通性下降幅度与入流边界流量成反比。研究结果可为鱼类栖息地指标体系构建和基于水质需求的生态流量调度提供依据。

In order to quantify the impact of ammonia nitrogen stress on fish habitat quality,a two-dimensional hydrodynamic and water quality model was set up in the main stream of Huaihe River from Lutaizi to the Yaohe sluice through three landscape ecological characteristic indices,namely:suitable habitat area,patch number and habitat connectivity.Typical indigenous migratory fish juvenile silver carp was used as the target species.Under the assumption of Class Ⅲ water quality standard for the inflow boundary with the ammonia nitrogen concentration of 1.0 mg·L^(-1),the impacts were evaluated for low,medium and high flow rates in the study site,respectively.In comparison with the benchmark case where no ammonia nitrogen index was considered,the results showed that:(1)the suitable habitat area of the downstream migration passage was decreased by 1.6%,6.7% and 3.4% respectively;(2)the fragmentation was increased by 4.5%,28.7% and 3.6% respectively;(3)the connectivity was decreased by 54.3%,34.6% and 24.8% respectively.It is clear that the impact of ammonia nitrogen stress on the suitable habitat area is insignificant,but considerable on the patch number for the medium flow rate which boasts the highest fragmentation,indicating that there is a certain degree of positive correlation and synergy between the impacts of ammonia nitrogen and fragmentation.Finally,the decline range of connectivity is negatively proportional to the flow rate of inflow boundary.The qualification of the different impacts of ammonia nitrogen stress on different landscape ecological characteristic indices can improve the construction of fish habitat indicator system and help to manage the required flow rate in the natural rivers for the water quality demand of juvenile silver carp.