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Within the Teme catchment, largest sediment and P transfer was predicted to be
via surface pathways in the central area, where soils have a substantial silt content
and the proportion of arable land is increasing relative to the uplands (Figure 2).
The stream is important as a fishery, and again siltation is of major concern. Here
measures which impinge on both grassland and arable management including
erosion control measures such as early sowing will be relevant.
In the grass dominated Bassenthwaite catchment, most diffuse P export occurs in
the western part of the catchment, with hotspots associated with more intensive
management (P inputs) on underdrained soils. Lack of opportunity to incorporate P
inputs on the steeper slopes and under the high rainfall in the area means incidental P
transfers are high (Table 1) and need to be controlled by careful fertiliser and manure
management.
DISCUSSION
The PSYCHIC decision support tool is only a prototype at this stage and requires
further modification and refinement as our knowledge of sediment and P mobilisation
and delivery in catchments improves. However, its application is already proving very
useful in helping to (a) rapidly assess the relative contribution of diffuse P sources
relative to point P sources; (b) characterize the land use and farming activities in
catchments in a consistent and spatially distributed manner and (c) quantify the
associated risks of sediment and P transfer in surface run-off and sub-surface runoff
across catchments. The separate delineation in P mobilisation between fertilizers/
manures, the soil and farmyards, and in P delivery between surface and sub-surface
pathways, provides a means of identifying what measures might be most appropriate
and where they need to be targeted. Application of the Tier 2 PSYCHIC model within
the hotspots identified by Tier 1 is now required to further predict the impact of
more specific measures identified through river walks, wet weather surveys and farm
visits by the respective catchment officers. We have found that the presentations,
and especially the maps, promote stakeholder discussion and are appreciated as
a contribution to the development of mitigation strategies. As with the example of
incineration of poultry manure, local factors frequently come to light which require
further consideration. It is planned to apply PSYCHIC to other catchments and to
adapt the approach to maximise its usefulness to stakeholders.
ACKNOWLEDGEMENTS
PSYCHIC was developed by a research consortium including ADAS UK Ltd, National
Soil Resources Institute, Centre for Ecology and Hydrology, Exeter University, Reading
University and Lancaster University with funding from Defra, the Environment Agency
and English Nature.
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