A Field Guide to British Rivers. George Heritage
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Название: A Field Guide to British Rivers

Автор: George Heritage

Издательство: John Wiley & Sons Limited

Жанр: География

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isbn: 9781118488027

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СКАЧАТЬ regimes are also influencing the potential for flooding with heightened levels of gravels accumulating in urban areas because of disconnected storage in the catchment and altered sediment transport efficiencies in upstream rivers. Natural Sediment Management where sediment storage zones are reconnected and channel form naturalised to a more storage friendly configuration can help reduce flood sediment inputs to vulnerable areas whilst restoring natural form and processes to the fluvial system upstream. Finally, the trend amongst owners of large estates to re‐wild the landscape and reintroduce extinct species is also improving larger and larger areas, often with valley bottom land being encouraged to naturalise through light touch interventions that act as the precursor for wider river‐driven landscape change. The recent efforts to reintroduce ecosystem engineers such as beaver also points to greater willingness in UK river managers to turn back the clock and allow greater space for nature.

      The natural environment is now rising in value with an increasing recognition of the role that natural system dynamics can play in climate change, biodiversity, as well as amenity, and there appears to be a growing political will in the United Kingdom to instigate change, with new government stewardship schemes likely to place a very strong emphasis on environmental functionality, helping push the river restoration agenda forward. In all cases, this can only be achieved successfully with the appropriate knowledge. During the time we have been writing this book, Britain has left the European Union, and so it remains to be seen what trajectory environmental protection will take post departure, but initial statements from government indicate a willingness to legislate for more protection, not less. What is key is that any range of protection methods should ensure a place for enhanced dynamism, not less.

      Future sustainable management of our rivers and floodplains therefore requires a fuller understanding of river form and function to ensure that opportunities are fully exploited, and our perception of rivers is changed towards more naturally functioning dynamic systems. We have written this book deliberately as a field guide to maximise the practical examples of river types and to highlight the pressures they experience and their often parlous condition. This book is intended to better inform both river management approaches and policy necessary to achieve this. It will hopefully stimulate a desire to bring back the diversity and dynamism associated with naturally functioning temperate fluvial systems in the United Kingdom. The ethos of the book is to inspire the river scientists in us all, by providing a holistic picture of the variety of temperate river forms in Britain and linking this explicitly to functional controls within the catchment. Fundamentally, we seek to demonstrate and evidence how the hydrological, geomorphological, and ecological functions of rivers integrate to generate and maintain the dynamic whole. If those who have read this book find themselves questioning what they see each time they encounter a river and its floodplain, this volume will have served its purpose.

       George Heritage

       Andy Large

       David Milan

      July 2021

      1.1 Introduction

      Rivers in the United Kingdom are an important component of the natural and social environment. Humans have long influenced valley bottom ecosystems, with impacts recorded consistently across Europe since the Bronze Age (Brown et al. 2018). Through the historic period, there has been a near‐consistent alteration of system character and functionality with ecosystem dynamics suppressed to facilitate human exploitation of watercourses and valley bottoms. Landscape‐scale disturbance across regimes that sustain habitats and biotic communities have resulted in a permanent loss of environmental heterogeneity and biodiversity (Warren and Liss 1980).

      Dynamic landscapes exhibit high spatial and temporal environmental heterogeneity and strong speciosity (Connell 1978) and naturally functioning fluvial systems represent some of the most dynamic landscapes on the planet. This is reflected in their very high conservation value (Ratcliffe 1977). They also display some of the highest biological productivity and ecosystem diversity on Earth (Tockner and Stanford 2002), principally due to their dynamic behaviour and their transitional nature as they form an ecotone, or transitional boundary, between terrestrial and aquatic environments. Mitsch and Gosselink (2000) estimated that, globally, floodplains cover approximately 1.4% of the planet’s land surface (0.8 × 106 km2 to 2 × 106 km2); however, they contribute around 25% of all terrestrial ecosystem services (Tockner and Stanford 2002). When the natural dynamics of river and floodplain systems are subdued or lost; however, the system becomes dysfunctional and the loss of dynamism results in environmental homogeneity and stasis. Diversity is reduced under such conditions with the landscape becoming dominated by a few key species best adapted to the imposed conditions (Stanford et al. 1996). Flood‐controlled disturbances, occurring as part of the natural flow regime, stimulate geomorphic processes and promote vegetative succession (Amoros and Roux 1988; Junk et al. 1989). As a result, natural floodplains display complex dynamic spatial vegetation mosaics controlled by the morphology and the associated surface and subsurface hydrological regime (Thoms 2003). The features and vegetation present are often also a reflection of both present and past geomorphological activity associated with the fluvial system (Nanson and Croke, 1992) with features developing ecologically as connectivity with the main river alters over time.

      The preponderance of a near homogenous fluvial landscape, where natural processes are almost completely suppressed and continue to be suppressed through active management, offers little hope of any return to a more natural, dynamic, and diverse system unless current agricultural practices, not just on floodplains but also across the wider catchment, are fundamentally altered. Small‐scale restoration may partially restore some river and floodplain features and processes, but suppression elsewhere will mean that ecological gains remain highly localised and fundamentally unsustainable into the long term.

      Longitudinal and lateral fragmentation of large river systems, linked principally to human activities, has also contributed to severe and widespread floodplain degradation, and this is fundamentally threatening the integrity of running water ecosystems (Dynesius and Nilsson 1994; Schiemer 1999). This degradation is closely linked to a rapid decline in freshwater biodiversity, principally due to habitat alteration through altered land use and flow patterns, flood control, pollution and to invasive species. Tockner and Stanford (2002) provide the stark statistic that in Europe and North America, up to 90% of floodplains are already “cultivated” and therefore functionally extinct.

      This generally poor state of river system form and function was noted by Seager et al. (2012) who conducted a stratified random sample of 4849 River Habitat Survey sites across England and Wales in 1995–1996 and again in 2007–2008 to assess the general physical character of rivers and streams. From these data, they estimated that only 11% of river length had a “near‐natural” channel form, with a further 14% classed as predominantly unmodified. A single river study СКАЧАТЬ