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The chalkstream ecosystem



The chalk-stream ecosystem is the result of a particular combination of geology, organ­isms and management. The physical and chemical features of the environment and the effects of human management are described. Accounts are given of the composition , biomass and production of the communities of higher plants, algae, invertebrates and fish, and of the throughput and deposition of fine detritus, although most of these. are incomp!Cte in·some' respects. The most important factors affecting production are physical and biotic, for few · chemicals vary seasonally and mos.t are present i n excess. The apparent resistance of much of the detritus to biological exploitation is also important.
... Amongst the early investigations on the invertebrate fauna of chalk streams there are only a few detailed studies (Percival & Whitehead 1926,1929Whitehead 1935). More recently, attempts have been made to acquire the data necessary to describe the production ecology of species and species groups, particularly those which are normally abundant (Ladle & Baron 1969;Ladle 1971;Ladle et al. 1972;Bass 1976;Welton 1979). More extensive syntheses of the structure of faunal communities in chalk streams have been made by Westlake et al. (1972), Ladle & Bass (1981), Wright et al. (1983) and Wright et al. (1984). ...
... More recently, attempts have been made to acquire the data necessary to describe the production ecology of species and species groups, particularly those which are normally abundant (Ladle & Baron 1969;Ladle 1971;Ladle et al. 1972;Bass 1976;Welton 1979). More extensive syntheses of the structure of faunal communities in chalk streams have been made by Westlake et al. (1972), Ladle & Bass (1981), Wright et al. (1983) and Wright et al. (1984). ...
... The characteristic gravel beds provide ideal habitat for a rich benthic macroinvertebrate community and spawning conditions for lithophilous fish species. The stable flow, temperature and nutrient regimes, and clear water create conditions for extensive in-stream macrophyte communities (Westlake et al., 1972;Berrie, 1992). A number of chalk stream species are protected under national and international (European) laws and are notifiable features in the designation of many UK chalk stream Sites of Special Scientific Interest (SSSI) and Special Areas of Conservation (SAC) ( Table 1). ...
Fine sediment has a critical role in river ecosystems and is essential for habitat heterogeneity, ecosystem structure and function. Expansion and intensification of specific land uses, including agriculture, have increased fine sediment inputs into river networks. The detrimental impacts of excessive fine sediment on river ecosystems have been well documented and numerous sediment targets have been proposed or adopted to assess the gap between target and current levels of fine sediment. Where sediment targets exist, these are often over-simplified and applied across a wide range of river environments irrespective of the processes of fine sediment deposition and the tolerance or sensitivity of river biota to fine sediment. Thus, targets often fail to provide a reliable basis for identifying the need for management interventions to restore ecosystem health. This review adopts a system-based approach to the impacts of fine sediment after reviewing the suitability of existing targets for guiding management in chalk stream catchments specifically. Chalk streams are groundwater-dominated systems characterised by stable hydrological, ecological and thermal regimes and thus respond differently to excessive fine sediment compared with other fluvial systems. Chalk streams are often subject to high levels of sedimentation and siltation despite their low suspended sediment loads. In this paper, we review the characteristic processes and dynamics of chalk streams and how these influence fine sediment accumulation. The impacts of excessive fine sediment on chalk stream habitats and biota and the role ecosystem engineers play in the processes of fine sediment dynamics are discussed. Finally, we discuss the application of fine sediment targets for chalk streams in relation to the implementation of both source and process-based techniques for meeting the requirement for improved ecosystem management.
... Approximately one third (29% in 2008 and 35% in 2009) of the mobilised sediment flux at WQ3 was composed of volatile organic matter. This is comparable to the 40% organic content of suspended sediment in the Bere stream, Dorset (UK) reported by Westlake et al. (1972). Sediments accumulating in summer may have high organic contents and thus high Biological Oxygen Demand as they are likely to be largely produced in the channel (Mainstone, 1999) through biogenic processes . ...
(1) Pairs of Gammarus pulex were kept in laboratory incubators at 5, 10, 15 and 20 degrees C to study brood development time and growth. (2) The most satisfactory description of the relationship between brood development time (D days) and temperature (T degrees C) was the power law, loge D = a + b loge T where a = 5.752 and b = 0.962 within the temperature range 5-20 degrees C. The specific growth rate in length (mm) of young individuals increased with increasing temperature from 0.28 to 0.96% day-1 at 5 and 20 degrees C respectively. (3) Laboratory data were extrapolated to the field situation to predict the longevity of the species. This was 17-23 months for females, which produced 6 broods throughout the summer and up to 2.5 years for males.
Technical Report
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see - RoughnessReviewFinal_July07 .pdf UMMARY Under their joint R&D programme for Flood and Coastal Defence, DEFRA/Environment Agency are funding a Targeted Programme of research aimed at obtaining better predictions of flood water levels. In order to achieve this, advances in knowledge and understanding made over the past three or four decades in the estimation of river conveyance will need to be introduced into engineering practice. The project relates particularly to water level estimation, leading to a reduction in the uncertainty in the prediction of flood levels and hence in the flood risk, and consequently facilitating better targeting of expenditure. The project will equally benefit the targeting of maintenance by providing better estimates of the effects of vegetation and its management. It is expected that the application of this knowledge from UK engineering research will have an international impact through improving the methods available to consultants. The above objectives will be achieved through two core components of the new Conveyance Estimation System (CES) that will be developed: the Conveyance Generator and the Roughness Advisor. The CES is to be designed so that new knowledge from a parallel Strategic Programme of research can be integrated into the CES in due course. This report is the designated output for Task T4 of the Targeted Programme of research. The Task objective is to gather, validate and catalogue knowledge on the boundary roughness of UK rivers. The information obtained will then be incorporated in the CES, comprising the Roughness Advisor component. The techniques and underlying assumptions used by the Roughness Advisor in determining the boundary roughness of UK rivers are described in this report. A review of the information identified in the expert paper in the Scoping Study of this project is provided. In addition a wider range of papers are reviewed including papers that have been published or sourced since the expert paper was completed. There are a number of key references where the hydraulic data available is extensive. These papers have been identified and the data within the papers forms the basis of the roughness review. Some of the data sets also have associated vegetation data and this is used alongside the hydraulic data to determine the roughness of vegetated and non- vegetated channels. The report also incorporates a large body of knowledge related to vegetation in and around UK waterways and the effect of this vegetation on water flow. The various river types and vegetation morpho-types have been identified along with any information provided on substrate characteristics. This roughness review document reviews the various methods and techniques of estimating roughness. The approach selected for use within the roughness advisor is based on Manning’s n roughness. A unit roughness is applied for different types across the channel and floodplain and combines them in a suitable manner within a type. The combined roughness value is then fed in to the conveyance generator. The processes and justifications for selection of this technique and the data used in the roughness advisor are given. Data gaps and further research needs are suggested. In addition to the review of channel and vegetative roughness, information is also incorporated on river maintenance procedures. This includes the basic principles of plant biology and management; traditional and alternative techniques of plant control, along with advice on weed cutting. Overall this roughness review report provides the technical background information for the Roughness Advisor.
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Four significant areas of thought, (1) the holistic approach, (2) the linkage between streams and their terrestrial setting, (3) material cycling in open systems, and (4) biotic interactions and integration of community ecology principles, have provided a basis for the further development of stream ecosystem theory. The River Continuum Concept (RCC) represents a synthesis of these ideas. Suggestions are made for clarifying, expanding, and refining the RCC to encompass broader spatial and temporal scales. Factors important in this regard include climate and geology, tributaries, location-specific lithology and geomorphology, and long-term changes imposed by man. It appears that most riverine ecosystems can be accommodated within this expanded conceptual framework and that the RCC continues to represent a useful paradigm for understanding and comparing the ecology of streams and rivers.
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