Research has demonstrated that landscape or watershed scale processes
can influence instream aquatic ecosystems, in terms of the impacts of
delivery of fine sediment, solutes and organic matter. Testing such
impacts upon populations of organisms (i.e. at the catchment scale) has
not proven straightforward and differences have emerged in the
conclusions reached. This is: (1) partly because different studies have
focused upon different scales of enquiry; but also (2) because the
emphasis upon upstream land cover has rarely addressed the extent to
which such land covers are hydrologically connected, and hence able to
deliver diffuse pollution, to the drainage network However, there is a
third issue. In order to develop suitable hydrological models, we need
to conceptualise the process cascade. To do this, we need to know what
matters to the organism being impacted by the hydrological system, such
that we can identify which processes need to be modelled. Acquiring such
knowledge is not easy, especially for organisms like fish that might
occupy very different locations in the river over relatively short
periods of time. However, and inevitably, hydrological modellers have
started by building up piecemeal the aspects of the problem that we
think matter to fish. Herein, we report two developments: (a) for the
case of sediment associated diffuse pollution from agriculture, a
risk-based modelling framework, SCIMAP, has been developed, which is
distinct because it has an explicit focus upon hydrological
connectivity; and (b) we use spatially distributed ecological data to
infer the processes and the associated process parameters that matter to
salmonid fry. We apply the model to spatially distributed salmon and fry
data from the River Eden, Cumbria, England. The analysis shows, quite
surprisingly, that arable land covers are relatively unimportant as
drivers of fry abundance. What matters most is intensive pasture, a land
cover that could be associated with a number of stressors on salmonid
fry (e.g. pesticides, fine sediment) and which allows us to identify a
series of risky field locations, where this land cover is readily
connected to the river system by overland flow. (C) 2010 Elsevier B.V.
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