Examining the role of habitat quality in determining river ecosystem resilience to extreme flood events

近年来，由于天气模式的变化，极端洪水事件在英国各地发生得更加频繁，预计还会进一步增加规律性。尽管洪水自然地维持了生态系统的多样性，并重新分配了能量、养分、沉积物和生物群，但极端洪水会对河流生态系统的生物多样性、生态系统功能和河流栖息地质量产生重大影响。了解这些对河流生态系统的影响是环境局(EA)的主要优先事项，他们面临着平衡环境保护政策(如欧盟WFD、欧盟生境指令)与政府、企业和公众要求充分洪水保护的压力之间的相互冲突的需求。有限的证据表明，河流生态系统对极端洪水的弹性取决于河流地貌的复杂性以及以前的高流量事件的规模和时间。然而，内河栖息地的改变在整个英格兰都很广泛，52%的低地和42%的高地河流受到堤岸加固和/或重新分割的影响，主要是为了防洪。这种栖息地的改变导致了欧盟WFD下英国河流的广泛失败。河流栖息地建模的最新进展使人们能够外推整个英格兰河流网络的栖息地改变的半定量调查数据。大规模的栖息地质量和河流修改数据现在可以与长期的流量和生态数据集配对，以测试栖息地变化如何影响河流生态系统的生态质量和对极端事件的弹性。EA(共同定位的大型无脊椎动物样本、河流栖息地调查和河流流量数据)持有的数据由16000个地点12年的连续数据组成，从而为大型无脊椎动物种群的弹性(例如持续、灭绝、入侵)和群落对洪水的组装/分解反应进行高级统计建模提供了可能性。对数据集的试点数据匹配工作仅在西北地区就确定了37个地点，其中洪水、无脊椎动物和RHS数据在时间和空间上都得到了充分的匹配，以便在统计模型中使用这些地点，从而证明了该数据集和方法的适用性。通过EA量表(可通过CEH的NRFA数据库和EA获得)的长期河流流量数据来识别极端流量事件，再加上学生额外收集的大型无脊椎动物和RHS数据以验证和扩展数据库记录，将允许独特的机会来识别流量阈值(从长期流量数据中获得的流量或持续时间，超过这些流量数据，无脊椎动物群落可能无法恢复)、对洪水敏感的物种或栖息地，以监测洪水恢复。使用这种方法，学生将能够检验以下假设：(1)生境改变和复杂性的丧失降低了大型无脊椎动物群落对极端洪水事件的恢复能力；(2)RHS栖息地质量指数可以用来预测大型无脊椎动物群落对洪水事件的恢复和恢复能力；(3)生态群落恢复能力措施和栖息地改变指数之间的关系可以为适当的管理和恢复方法提供指导，以减轻洪水影响。

Extreme flood events have occurred more frequently in recent years throughout the UK due to changing weather patterns, and are predicted to further increase in regularity. Although floods naturally maintain ecosystem diversity and redistribute energy, nutrients, sediments & biota, extreme floods can significantly impact river ecosystem biodiversity, ecosystem functioning & instream habitat quality. Understanding these impacts on river ecosystems is a major priority for the Environment Agency (EA) who are under pressure to balance competing needs of environmental protection policy (e.g. EU WFD, EU Habitats Directive) with pressures from government, businesses and the public for adequate flood protection.Limited evidence suggests that river ecosystem resilience to extreme floods is dependent on instream geomorphic complexity and to the magnitude and timing of previous high flow events. However, instream habitat modifications are extensive throughout England, with 52% of lowland & 42% of upland rivers affected by bank reinforcement and/or re-sectioning largely for flood protection. This habitat alteration has contributed to widespread failures of UK rivers under the EU WFD.Recent advances in river habitat modelling have allowed the extrapolation of semi-quantitative survey data of habitat modification throughout England's river networks. Large-scale habitat quality & river modification data can now be paired with long-term flow and ecology datasets, to test how habitat alteration may influence the ecological quality of the river ecosystem & resilience to extreme events. Data held by the EA (co-located macroinvertebrate samples, river habitat survey (RHS) & river flow data) consists of >12 years of continuous data from >16000 sites thereby affording possibilities for advanced statistical modelling of the resilience of macroinvertebrate populations (e.g. persistence, extinction, invasion) and community assembly/disassembly responses to floods. A pilot data-matching exercise on the dataset identified 37 sites in the North West area alone where flood, invertebrate and RHS data were sufficiently temporally and spatially paried to allow the use of these sites in a statistical model, thus proving the applicability of this dataset & approach. The addition of long-term river flow data from EA gauges (available via CEH's NRFA database and via the EA) to identify extreme flow events, in combination with additional collection of macroinvertebrate and RHS data by the student to validate & extend database records will allow the unique opportunity to identify flow thresholds (flow magnitudes or durations from long term flow data above which invertebrate communities may not recover from), flood-sensitive species or habitats for monitoring flood recovery. This would provide a predictive capacity of how river restoration efforts could mitigate high flow impacts through the provision of flow refugia.Using this approach, the student will be able to test the following hypotheses; (1) habitat alteration & loss of complexity reduces the resilience of macroinvertebrate communities to extreme flood events, (2) RHS habitat quality indices can be used to predict macroinvertebrate community recovery and resilience to flooding events; (3) relationships between ecological community resilience measures and habitat alteration indices can inform guidelines for appropriate management and restoration approaches to mitigate flood effects.