Spatial Variation in Fine Sediment Transfer and the Impact on Biodiversity: The River Esk, North Yorkshire UK.

Land use change, including the resulting changes in fine sediment supply, is seen as the most significant threat to global biodiversity (Sala et al. 2000). Silt is important for three reasons; firstly, it can act as a pollutant itself in silting up gravel spawning beds of fishes such as salmonids (Walling et al. 2003). Secondly it can have detrimental effects on conservation species such as freshwater pearl mussels through direct and indirect effects (pearl mussels rely on juvenile salmonids for lifecycle completion). Thirdly, sediment associated transport of nutrients and pollutants can result in long-term pollution problems detrimental to most species (Walling et al. 2001). However, some key conservation species such as lampreys require abundant silt for the larval lifecycle stage, as well as gravel for adult spawners. Hence, a plentiful silt supply and transport in river systems is not necessarily detrimental to some key biodiversity elements, but may be more damaging for others. This debate is compounded by a lack of data on silt in river systems. This paper; i) introduces Time Integrated Mass Flux Samples (TIMS) as a cheap, effective and efficient method of collecting data on spatial variations in fine sediment transfer; ii) presents data for variations in loads and specific yields of fine sediment in the River Esk (North Yorkshire, UK) and; iii) links these patterns of silt transfer to potential impacts of biodiversity and salmonids.