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，英国各地的极端洪水事件发生得越来越频繁，预计其规律性将进一步增加。虽然洪水自然地维持生态系统的多样性，并重新分配能量，营养物质，沉积物和生物群，但极端洪水会严重影响河流生态系统的生物多样性，生态系统功能和栖息地质量。了解这些对河流生态系统的影响是环境署（EA）的主要优先事项，他们面临着平衡环境保护政策相互竞争的需求的压力（例如欧盟WFD、欧盟反卫星指令），政府施加压力，有限的证据表明，河流生态系统对极端洪水的恢复力取决于瞬时地貌的复杂性和洪水的规模，之前高流量事件的时间。然而，在整个英格兰，52%的低地和42%的高地河流受到银行加固和/或重新分割的影响，主要是为了防洪。这种栖息地的改变，导致了广泛的失败，英国河流根据欧盟WFD。河流栖息地建模的最新进展，允许外推的半定量调查数据的栖息地改造整个英格兰的河流网络。大规模的栖息地质量和河流改造数据现在可以与长期流量和生态数据集配对，以测试栖息地的改变如何影响河流生态系统的生态质量和对极端事件的恢复力。环境评估所掌握的数据（同地大型无脊椎动物样本、河流生境调查（RHS）和河流流量数据）包括来自>16000个地点的>12年的连续数据，从而为大型无脊椎动物种群的恢复力（例如持久性、灭绝、入侵）和群落对洪水的组装/拆卸反应提供了先进的统计建模的可能性。对数据集进行的试点数据匹配工作仅在西北地区确定了37个站点，其中洪水，无脊椎动物和RHS数据在时间和空间上都充分paried，以允许在统计模型中使用这些站点，从而证明了该数据集和方法的适用性。增加来自EA测量仪的长期河流流量数据（可通过CEH的NRFA数据库和EA获得），以识别极端流量事件，结合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，这将为识别流量阈值提供独特的机会（流量大小或持续时间从长期流量数据，无脊椎动物群落可能无法恢复），洪水敏感的物种或栖息地监测洪水恢复。这将提供一个预测能力，河流恢复工作如何通过提供流量避难所来减轻高流量的影响。使用这种方法，学生将能够测试以下假设：（1）生境的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力，（2）RHS生境质量指数可用于预测大型底栖动物群落对洪水的恢复和恢复力;（三）生态社区复原力措施和生境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，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.