Abstract:
The Water Framework Directive (WFD) (Directive 2000/60/EC) requires new
ecological standards for rivers, lakes and coastal waters by 2015. In the United
Kingdom the English Catchment Sensitive Farming Initiative has identified 40
catchments which are at risk of failing the European Commission WFD targets for good
ecological status of water bodies because of a range of issues. The river Axe catchment
situated in south-west part of the UK, with a mixture of diffuse and point sources of
pollution, is one of these priority sites, as intensive dairy farming and cultivation of high
risk crops (maize), cause problems with enhanced suspended sediment, nitrate and
phosphorus levels in the river. For the purpose of this research the Soil and Water
Assessment Tool (SWAT-2005) and ArcView GIS 3.2 interface AVSWAT-X were
used. SWAT has been found to be a useful tool in numerous EU and UK studies
addressing the objectives of the EU WFD, which requires identification of pollution
sources, their influences and solutions for the studied catchment. The base scenario was
based on field observation and interviews with the Environment Agency and farmers; it
was run with and without point sources. Model was performing well; achieving
hydrological calibration for Nash-Sutcliffe efficiency coefficient (ENS) of 0.62. Three
different scenarios, field buffer strips (FBS), extensive land use management (ELUM)
and sheep land use management (SLUM), were used to evaluate the ability of SWAT to
represent the proposed mitigation methods and assess the effectiveness of the measures
in reducing nutrient loads in the Axe. SWAT was found to be able to represent the
proposed mitigation methods which were included in these three management scenarios.
Management scenarios reduced the average annual loads at the main catchment outlet
by 21.21% (FBS), 37.32% (ELUM) and 45.02% (SLUM), for total nitrogen; 47.72%
(FBS), 60.58% (ELUM) and 62.41% (SLUM) for total phosphorus; and 3.49% (FBS),
7.34% (ELUM) and 5.58% (SLUM) for annual average sediment yield. To deliver the
necessary water quality improvements for the river Axe both diffuse and point sources
of pollution will have to be addressed as results show that reduction only in one type of
source does not achieve the Environment Agency’s Environmental Quality Standard
target values which were set to meet the objectives of the EU WFD.
