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Title: An Investigation of Ecological Change in the Rivers Kennet and Lambourn
Author: J F Wright
Author: R J M Gunn
Author: N T Kneebone
Author: J H Blackburn
Author: R T Clarke
Author: J Davy-Bowker
Author: H M Vincent
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1039, Representation ID: 311, Object ID: 2316
The Kennet and Lambourn catchments are important regionally for water supply, fisheries and conservation. Reliable long-term data on the ecology of these chalk streams is essential to ensure effective management and to fulfil the UK Biodiversity Action Plan. Between 1971 and 1979, a major study of the macrophytes, macroinvertebrates and fish took place on the River Lambourn at Bagnor, resulting in a unique dataset and numerous publications. Between 1974 and 1976, further studies were undertaken at two sites on the River Kennet downstream of Marlborough (Upper and Lower Savernake) and at Littlecote, just upstream of Hungerford. In 1997, the Environment Agency (Thames Region) commissioned the Institute of Freshwater Ecology (IFE) to re-examine these four sites in summer (June/July) and winter (December) using the 1970s protocols in order to obtain information on longterm ecological change and to examine the impact of the 1996-97 drought. Winter 1997/98 marked the end of the drought and phosphate stripping commenced at Marlborough STW in autumn 1997. Hence, there was a need to document any longterm consequences of the drought and/or changes in water quality. In addition, because management practices had changed on some sites between the 1970s and 1990s, a longterm study could shed light on this important topic. The Environment Agency drew up a contract for a 5-year collaborative project (April 1998 a March 2003) between the Agency and the IFE (now the Centre for Ecology and Hydrology, Dorset). This provided for repeat macrophyte mapping and macroinvertebrate sampling at the four study sites in summer 1999 - 2001. The basic results of the annual macrophyte mapping and macroinvertebrate sampling were to be reported to the Agency each year without any detailed analysis. In this collaborative project, CEH Dorset, would produce one scientific paper on a different aspect of the results in each of the five years. The final year of the contract (April 2002 a March 2003) was devoted to the production of this final report, which summarises the project, and includes synopses of the major findings from the scientific papers, some of which include analyses which incorporate data from the studies in the 1970s. The first four chapters of the report provide an introduction, information on the flow regimes for both rivers, a detailed description of the four sites and the field and laboratory methods used in mapping and macroinvertebrate sampling. Chapter five presents information in tables plus a brief commentary on the percentage cover of the major habitats at each site during the 5-year study, with additional summary data for the 1970s sampling period. Spreadsheets containing the detailed maps for each site in 19972001 have been made available to the Environment Agency. Chapter six gives summary data on the macroinvertebrate sampling programme. This includes family richness (derived from 5 sampling units combined) on each habitat of each site between 1997 and 2001, and further information for the 1970s, accompanied by brief comments. Additional tables give family composition and abundances expressed as numbers per 0.05 m2 for each habitat, site and sampling occasion. Raw data on family composition and abundance in each of the five sampling units for each habitat, site and sampling occasion has been made available to the Agency as an Access Database. Chapter seven presents synopses of the five scientific papers written as the CEH Dorset contribution to this collaborative project. The first two papers deal with the impact of R and D TECHNICAL REPORT W6-104/TR iii drought conditions on the habitats and macroinvertebrate assemblages of the R. Lambourn at Bagnor. In the first of these, it was shown that important families of chalk stream macroinvertebrates such as Baetidae (mayflies) and Simuliidae (blackflies) show a positive relationship to discharge regime, with available habitat as another relevant factor. Thus, their numbers were very low in June 1997 due to the drought conditions, and this was compounded by the poor growth of macrophytes due to heavy shading on the site. A further analysis of the macroinvertebrate assemblages in the drought years of 1976 and 1997, based on quantitative family data, revealed an extreme response to the drought itself, mainly in terms of changes in faunal abundance, but rapid recovery after each drought, whether the site was managed as a trout fishery (1976) or left unmanaged (1997). Another study at Bagnor examined the impact on the flora and macroinvertebrate fauna of changes in management between 1975-79, when the river was managed as a trout fishery and 1997-2001 when the river was unmanaged. Throughout the 1970s, the river keeper undertook selective weedcutting, mowed the north riverbank and controlled the growth of overhanging trees on the south bank. After fishing and the associated management ceased in the 1980s, the river slowly reverted to an unmanaged state with encroaching marginal vegetation on the north bank and shading by trees on the south bank, thus limiting the light reaching the river surface. Between the two study periods the area of instream macrophytes decreased by 50% but overall macroinvertebrate family richness increased slightly, possibly due to the appearance of marginal vegetation. Because the heavy shading impacted on instream habitats and food resources, there were substantial changes in the abundance of many families. Mayflies such as Ephemerellidae and Baetidae, whose subimagos and imagos are mimicked by dry fly fishermen, became less abundant under the no management regime. It appears that management for trout fishing promoted both primary production and secondary production, including the fly life taken by trout and mimicked by fishermen. The next study involved three sites on the R. Kennet which had been sampled in the mid-1970s and resampled from 1997 onwards. The lowest site (Littlecote), near Hungerford had changed little between sampling periods but two other sites (Savernake Upper and Lower), just downstream of Marlborough, suffered progressive loss of macrophytes during the 1990s and attempts at promoting re-growth failed. In autumn 1997 the drought came to an end, phosphate stripping commenced at Marlborough STW, and there was heavy rainfall the following spring. Regrowth of Ranunculus on both Savernake sites was spectacular and it became and remained the dominant macrophyte. Although there were minor changes in macroinvertebrate family composition on the three sites between the 1970s and 1990s, there was no evidence of loss of family richness. Further analyses highlighted important differences in family abundance at Savernake between 1997 and 1998/99, whereas only minor differences were apparent at Littlecote. The relative importance of low flows, poor weed growth, siltation and enrichment from Marlborough STW as contributory factors to changes in faunal abundance at Savernake requires further study. The final paper examines faunal response at all four study sites to the low and high flow events which occurred during the 1997 to 2001 study. In these perennial sections of high quality chalk streams drought events do affect the abundances of many macroinvertebrates, but recovery in the aftermath of the drought is rapid. The unusually high discharge event of winter/spring 2000/2001 had no immediate adverse effects on R and D TECHNICAL REPORT W6-104/TR iv the fauna. In fact, family richness peaked on each of the three Kennet sites in summer 2001 and overall family abundances on the major habitats of all four sites reached their highest or second highest values in 2001. The report ends with a series of conclusions and recommendations before providing an appendix with a full listing of all scientific papers published on the R. Lambourn and R. Kennet within this project as a result of the studies in the 1970s and in 1997-2001. R and D TECHNICAL REPORT W6-104/TR v CONTENTS ACKNOWLEDGEMENTS i EXECUTIVE SUMMARY iii LIST OF FIGURES viii LIST OF TABLE ix 1. 1.1 1.2
Publisher: Environment Agency
Subject Keywords: Chalk streams; Discharge; Drought; Macroinvertebrates; Flood; Ecological change; Macrophytes; Management.
Extent: 66
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