Nitrate transport in Chalk catchments : monitoring, modelling and policy implications

Rising nitrate levels have been observed in UK Chalk catchments in recent decades, with
concentrations now approaching or exceeding legislated maximum values in many areas. In
response, strategies seeking to contain concentrations through appropriate land management
are now in place. However, there is an increasing consensus that Chalk systems, a
predominant landscape type over England and indeed northwest Europe, can retard decades
of prior nitrate loading within their deep unsaturated zones. Current levels may not fully
reflect the long-term impact of present-day practices, and stringent land management
controls may not be enough to avert further medium-term rises. This paper discusses these
issues in the context of the EU Water Framework Directive, drawing on data from recent
experimental work and a new model (INCA-Chalk) that allows the impacts of different land
use management practices to be explored. Results strongly imply that timelines for water
quality improvement demanded by the Water Framework directive are not realistic for the
Chalk, and give an indication of time-scales over which improvements might be achieved.
However, important unresolved scientific issues remain, and further monitoring and
targeted data collection is recommended to reduce prediction uncertainties and allow cost
effective strategies for mitigation to be designed and implemented.