Characterising historic ecological conditions in lowland rivers: applying palaeoecological techniques to river restoration planning
2014-06-06T11:05:25Z (GMT) by
It is widely recognized that anthropogenic activities have resulted in significant changes to the ecology and hydromorphology of riverine ecosystems globally. Across much of lowland England a number of riverine habitats and the flora and fauna inhabiting them, have been lost or disadvantaged by historic channel modifications. Many of the most significant modifications took place in the decades following World War II, in a drive to increase food security through improved land drainage and associated flood management. A better understanding of the geomorphological, hydrological and biodiversity elements that have been compromised or lost is required in order to characterise the benefits of planned measures to restore and reinstate channel form and function for EU WFD, Habitats Directive and other conservation designations (e.g. SSSI condition assessments). To generate this understanding in an environment where natural processes have been impacted over large spatial scales, an innovative palaeoecological approach is employed in this thesis that provides a window on historic riverine ecology and habitat conditions so that the contemporary channel and community inhabiting it can be gauged prior to the implementation of river restoration programmes. The analysis of historic archival material (maps, photographs, local authority and management records), and the detailed investigation of sedimentary records and sub-fossil insect remains (Trichoptera, Coleoptera and Gastropoda) associated with in-channel bars, weirs, bridges and palaeochannels is used in this thesis in order to achieve this. These records will provide data regarding changes to the aquatic macroinvertebrate community and instream hydromorphology within specific reaches/biotopes/habitats subjected to historical physical modification. The historic data (documents and palaeoenvironmental data) is analysed in parallel with contemporary data on instream habitats and faunal community composition to define benchmark conditions on three Site of Special Scientific Interest rivers. This approach enables a comparison between past and present channel hydromorphology and the instream faunal communities. The characterisation of benchmarks provides a baseline for future conservation and restoration policies within riverine ecosystems that can be used to help define pre-impacted or reference conditions. The research presented in this thesis has relevance to the conservation objectives of rivers with special designations (e.g. SSSI and Habitats Directive) for wildlife and to meeting the wider requirements of the Water Framework Directive.