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to control SS and P loads from agricultural land must therefore be targeted within
catchments to those areas where combinations of landscape and land management
generate the highest pollution risk. To facilitate the cost-effective targeting of a
range of land management options to mitigate SS and P export in catchments, a
prototype decision support tool called PSYCHIC (Phosphorus and Sediment Yield
Characterization In Catchments) has been developed within two catchments in
England and Wales (Hampshire Avon and Wye) with siltation and eutrophications
problems (Withers and Sharpley, 2006). This paper describes the further application
and testing of the PSYCHIC prototype (Tier 1 screening tool) to four catchments with
varied landscapes and land management. Its potential for use as part of river basin
management planning is discussed.
MODELLING APPROACH USED IN PSYCHIC
PSYCHIC is used to quantify the export of sediment, particulate P and dissolved P in
surface and sub-surface run-off from agricultural land and assess their contribution
relative to other ‘point’ sources of P in the catchment. PSYCHIC involves a processbased
modelling approach that is sensitive to those land management practices
which have a large influence on the mobilisation and delivery of sediment and P.
The model takes account of climate, landscape and land management factors and
utilises current knowledge on the processes of sediment and P export. Predictions
of the spatial and temporal distribution of flow, and SS and P loads, are provided on
a monthly time step and at both 1 km 2 and field scales within a GIS environment. The
decision support tool integrates model predictions of catchment areas with a high
risk of export or ‘hotspots’ (Tier 1 screening tool) with field scale risk assessment of
contributing areas on farms (Tier 2) to help identify appropriate best management
practices (BMPs) to improve nutrient and land management. PSYCHIC then
assesses the impact of the selected BMPs on sediment and P export at the field
and catchment scale. Further description of the PSYCHIC model structure and its
parameters is given by Davison et al. (2006).
APPLICATION OF THE TIER 1 SCREENING TOOL TO PILOT CATCHMENTS
The Tier 1 screening tool within PSYCHIC was applied to the four pilot catchments
(Hampshire Avon near Salisbury, Teme in Shropshire/Worcestershire, Wensum in
Norfolk and Bassenthwaite Lake in Cumbria) selected as part of the governments
Catchment Sensitive Farming Initiative (Defra, 2004). These are all priority
catchments suffering from sediment and/or P pollution and catchment officers
have been designated to encourage farmers to adopt Good Agricultural Practice
and additional targeted measures chosen from a range of options under Defra’s
countryside stewardship schemes. PSYCHIC is used to inform which measures
would be most cost-effective to tackle local water quality issues and where they
need to be targeted within the catchment area. PSYCHIC input data (derived from
the MAGPIE system, Lord and Anthony, 2000) and results were mapped, and risk
factors and resulting mapped estimates of sediment and P transfer presented to
catchment stakeholders.
The catchments differ widely in their climate, topography, land use and farming
practices (Table 1). The Hampshire Avon is a chalkland catchment with mixed farming,
variable relief and very low river drainage density; the Wensum catchment is largely
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