The influence of hydromorphology on instream ecology in lowland rivers

With the formal adoption of the Water Framework Directive in 2000, into European legislation it committed all member states to ensure that all inland waterbodies should reach good ecological status by 2015. As a result examination of the influence of hydromorphology on the ecological health of riverine ecosystems has become an increasingly important priority for statutory monitoring agencies such as the Environment Agency of England and Wales and equivalents in other parts of the UK. It is anticipated that by increasing our understanding of the role that hydromorphological processes play in shaping river habitats and the ecosystems that they support, river management strategies can be developed that will help lead to waterbodies achieving good ecological status. In this thesis, the influence of river hydromorphology and instream channel management activities on instream macroinvertebrate communities is explored. A two-scale approach was used at a regional macro-scale and local / catchment micro-scale. The macro-scale study examines the ecological, hydrological and geomorphological data for 88 river reaches located within the Environment Agency , Anglian Central and Anglian Northern regions, over a twenty year period (1986-2005). At the micro-scale two sub-catchments were selected, the River Bain and River Lymn, both located in Lincolnshire, England for detailed investigation. The micro-scale study was undertaken using ecological, hydrological and geomorphological data collected over three successive seasons (Autumn 2008, Spring 2009 and Summer 2009) enabling the seasonal variations and the influence of both stream size and habitat biotope on macroinvertebrate community composition and structure to be explored. The hydromorphological characteristics and condition of the rivers were quantified using ecologically relevant hydrological indices, calculated from flow discharge paired with geomorphological indices from River Habitat Survey data. The response of the instream macroinvertebrate communities was examined using a range of ecological indices including the Lotic-invertebrate Index for Flow Evaluation (LIFE). The results of the macro-scale investigation demonstrate that the macroinvertebrate community is directly influenced by instream hydromorphology and the level of anthropogenic modification. The micro-scale study highlights important differences in macroinvertebrate communities associated with instream habitat / biotope composition. The quantification of river hydromorphology, with the use of ecologically relevant hydrological indices and geomorphological indices, derived from River Habitat Survey data, is discussed with regards its ability to help explain the structure and composition of macroinvertebrate communities within highly managed /regulated riverine ecosystems. The implications of this research for river managers and for implementing river restoration and rehabilitation schemes are explored.