| The impacts of afforestation at Plynlimon in the Severn catchment, mid-Wales,
and in the Bedford Ouse catchment in south-east England are evaluated using the INCA model
to simulate Nitrogen (N) fluxes and concentrations. The INCA model represents the key
hydrological and N processes operating in catchments and simulates the daily dynamic
behaviour as well as the annual fluxes. INCA has been applied to five years of data from
the Hafren and Hore headwater sub-catchments (6.8 km2 area in total) of the
River Severn at Plynlimon and the model was calibrated and validated against field data.
Simulation of afforestation is achieved by altering the uptake rate parameters in the
model. INCA simulates the daily N behaviour in the catchments with good accuracy as well
as reconstructing the annual budgets for N release following clearfelling; a four-fold
increase in N fluxes was followed by a slow recovery after re-afforestation. For
comparison, INCA has been applied to the large (8380 km2) Bedford Ouse catchment
to investigate the impact of replacing 20% arable land with forestry. The reduction in
fertiliser inputs from arable farming and the N uptake by the forest are predicted to
reduce the N flux reaching the main river system, leading to a 33% reduction in N-Nitrate
concentrations in the river water.
Keywords: afforestation, water quality, nitrogen, modelling, land-use change, Wales,
Plynlimon, Hore, Hafren, Bedford Ouse, Severn |