Determining historic ecological conditions in lowland rivers: applying palaeoecological techniques to river restoration planning

It is widely recognised that anthropogenic activities have resulted in significant changes to the hydromorphology (flow characteristics and fluvial geomorphology) and ecology of riverine ecosystems globally and that to reinstate morphological diversity physical river restoration may be required in many instances. However, significant questions remain regarding the nature and number of riverine flora and fauna that have been lost or disadvantaged by historic channel modifications across much of lowland England. Many of these rivers have been extensively modified for many centuries for a variety of purposes. Some of the most significant modification took place in the decades following World War II, in a drive to increase food security through improved land drainage and associated flood management. Channelisation, involving straightening, deepening, widening and reprofiling resulted in greatly reduced habitat heterogeneity, with serious implications for riverine and floodplain biodiversity. A better understanding of the geomorphological, hydrological and particularly the 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. To generate this understanding in an environment where natural processes have been impacted over large spatial scales, an innovative palaeoecological approach is proposed that will provide a window on past riverine conditions so that the contemporary channel and community inhabiting it can be gauged prior to restoration. This project will combine analysis of contemporary river morphology and ecology with palaeoecological techniques (via examination of instream and floodplain deposits associated with the river) to explore the recent history of selected lowland rivers in England. We hypothesise that natural elements of channel morphology and the instream faunal community have been lost or compromised due to historic management practices. The project will characterise some of the critical habitat features that have suffered from modifications and through the use of palaeoecological techniques characterise the changes in the faunal community through examination of fossil and contemporary Trichoptera (caddis fly larvae) and aquatic Coleoptera (beetles) assemblages. Study sites have been selected from the English network of rivers designated as Sites of Special Scientific Interest (SSSIs). This network includes representative examples of different river types found in England and research will focus on six rivers comprising: the River Beult (Kent), R. Eye (Leicestershire), R. Hull (EastYorkshire) and R. Wensum (Norfolk) all exhibiting straightening and over-widening to varying degrees, and the R. Mease (Staffordshire) with significantly less modification and the R. Blythe (W. Mids.) which has a largely unmodified channel form. Potential palaeochannel localities have been identified dating from the post-war era of channel modification. These include old channel features (including meanders cut off following channel straightening or natural ox-bows) or sediments within largely modified channels that have escaped disturbance. Detailed site identification will involve examination of historical maps, geomorphological appraisals of the rivers, study of aerial photos and consultation with local Natural England and Environment Agency staff. Sediment cores and/or sections will be collected and analysed for sub-fossil macroinvertebrates (Trichoptera and Coleoptera) following the procedures developed at Loughborough University. This data will be compared with the communities recorded in the contemporary modified channel, in order to directly evaluate changes likely to have resulted from the altered geomorphology.