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

PhD start date: 1 October 2018
Supervisors: Dr Megan Klaar (Leeds), Prof Lee Brown (Leeds), Prof Alexander Milner (Birmingham)

Extreme flood events (≥ 1% in magnitude) 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 and biota, extreme floods can significantly impact river ecosystem biodiversity, ecosystem functioning and instream habitat quality. Understanding these impacts on river ecosystems is a major priority for river managers who are under pressure to balance competing needs of environmental protection policy and the provision of 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 and 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 Water Framework Directive.
Recent advances in river habitat modelling have allowed the extrapolation of habitat modification data throughout England’s river networks. Large-scale habitat quality and 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 and resilience to extreme flow events. Long term data held by the Environment Agency (one of the project partners) provides this project with the opportunity to undertake advanced statistical modelling of the resilience of macroinvertebrate populations (e.g. persistence, extinction, invasion) and community assembly/disassembly responses to floods.
The successful candidate will have the opportunity to collect river ecology data (fish, macroinvertebrates) and river habitat modification data to extend the database held by the Environment Agency to identify flow thresholds (flow magnitudes or durations from long term flow data above which ecological communities may not recover from) and 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 and loss of complexity reduces the resilience of ecological communities to extreme flood events, (2) habitat quality indices can be used to predict ecological 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.
The student will benefit from extensive training and work placements (minimum of 3 months) with project partners JBA Trust (an independent charity that supports research and the development of knowledge and skills in environmental risk management in the water environment) and Environment Agency (environmental regulator for England). The outcomes of the research will aid our understanding of how anthropogenic impacts (physical habitat change) and climate change (increasing magnitude and frequency of flood events) will interact to affect the ecological quality of UK rivers. This information will be useful for environmental regulators and managers and help in informing new river restoration policy by providing evidence of the role of habitat complexity in mitigating the hydrological impacts of extreme events.