Department of Zoology, University of Otago, Dunedin, New Zealand.
Glob Chang Biol. 2017 Sep;23(9):3882-3894. doi: 10.1111/gcb.13696. Epub 2017 Apr 25.
Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co-occurring stressors result in biological responses that cannot be predicted from single-stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple-stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow-through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (-12% compared to controls) and condition (-8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (-25% compared to controls) and abundance of dominant invertebrate prey (-30% compared to controls), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple-stressor situations. However, in real streams, compensatory mechanisms and behavioural responses, as well as seasonal and spatial variation, may alter the intensity of stressor effects and the sensitivity of trout populations.
农业土地利用导致多种胁迫因子影响溪流生态系统。由于水资源抽取导致的水流减少、营养物和化学污染物水平升高是全球范围内常见的农业胁迫因子。同时，溪流生态系统也越来越受到气候变化的影响。多种共存胁迫因子的相互作用导致生物响应不能仅从单一胁迫因子的影响来预测（即协同作用和拮抗作用）。在生态系统水平上，多种胁迫因子的影响可以通过生物相互作用（如营养相互作用）进一步改变。我们使用 128 个流水式溪流中观模型进行了一项野外实验，以研究水资源抽取、营养物富化和硝化抑制剂双氰胺（DCD）添加对幼体褐鳟的存活率、生存状况和肠道内容物以及其无脊椎猎物底栖生物丰度的单独和联合影响。流速降低降低了鱼类的存活率（与对照组相比降低了 12%）和生存状况（与初始状况相比降低了 8%），而营养物和 DCD 添加的影响以及这些胁迫因子之间的相互作用并不显著。流速降低对鱼类存活率和生存状况的负面影响与对鱼类肠道内容物（与对照组相比降低了 25%）和优势无脊椎猎物丰度（与对照组相比降低了 30%）的影响一致，这表明一种负面的代谢平衡导致鱼类死亡和生存状况下降，这一结果通过结构方程模型得到了证实。在接近鱼类耐受范围上限的最大日水温下，由于流速降低导致的鱼类死亡率增加，反映了这些胁迫因子之间的协同相互作用。我们的研究强调了间接胁迫因子效应的重要性，如通过营养相互作用传递的效应，在评估和管理多种胁迫情况下的鱼类种群和溪流食物网时需要考虑这些效应。然而，在现实溪流中，补偿机制和行为反应以及季节性和空间变化可能会改变胁迫因子效应的强度和鳟鱼种群的敏感性。
