Robust interpolation of agricultural census data to hydrological units and implications for diffuse pollution modelling
Diffuse pollution from agriculture is often responsible for observed concentrations of
agricultural compounds being in excess of the upper limits prescribed by the WFD in some river catchments, and reductions in these concentrations will require widespread changes in farm practice. One of the aims of the Catchment hydrology, Resources, Economics and Management (ChREAM) study at the University of East Anglia in the UK is to assess likely impacts of WFD implementation on agricultural land use, and consequent implications for water quality and farm incomes. An element of this has involved updating an existing diffuse pollution model to reflect present-day land use profiles and comparing outputs (in terms of nitrate concentrations) from current land use with those modelled from early 1990s land use. Combining agricultural land use data with hydrological spatial units can involve a number of problems arising from the integration of a variety of data formats at a range of spatial and temporal resolutions, and the aggregation of source data over different spatial extents. This work assesses uncertainty arising from areal interpolation of agricultural census data to hydrological units in the River Derwent catchment in north-east England. The study sets out to identify the range of spatial resolutions at which robust estimations of agricultural land use can be made and examines the implications for diffuse pollution modelling.