Water quality targets and maintenance of valued landscape character – Experience in the Axe catchment, UK
Highlights
► The Soil and Water Assessment Tool (SWAT) model was used. ► Effectiveness of three mitigation scenarios was tested for reducing nutrient loads. ► The measures were found to be effective in reducing nutrients loads. ► WFD targets and current agricultural systems impact on the landscape were compared. ► There may be a fundamental incompatibility between them.
Introduction
The direct economic importance of agriculture to rural communities has diminished over the past fifty years, but the managed landscapes created and maintained by these agriculture systems is valued by both the rural and urban populations, with, in many places, important contributions to the local economy from tourism. As a result, the perception of the existing landscape, and the value that is derived from the cultural (aesthetic, spiritual, educational and recreational) ecosystem services, which it contributes to human well-being, are a result of agricultural activity. There is therefore a need to establish whether achieving ecological standards for water bodies are compatible with maintaining desired landscape value.
The need for clean rivers to support a range of services, such as drinking water, irrigation, recreation, industry and environment, has seen progressive strengthening of water quality legislation in most European countries since the Second World War. Implementation of the Water Framework Directive (WFD) 2000/60/EC (European Union, 2000) represents a paradigm shift in the management of water quality across Europe, with a change from water quality targets based on chemistry (e.g. biological oxygen demand, ammonium and dissolved oxygen) to targets based on the ecological structure of natural systems. The WFD obliges Member States to achieve “Good Ecological Status” in all water bodies by 2015, although there are defined cases where derogations can be sought. Given this change in emphasis on ecological condition, it is unlikely that Good Ecological Status will be achieved in most water bodies through further restrictions on point sources alone. Instead, twin-track approaches of reducing the pressures exerted on the aquatic environment by diffuse (predominantly agricultural) and point sources are needed.
In many United Kingdom (UK) rivers high nutrient concentrations, specifically nitrate and phosphorus, are exceeding water quality targets (Table 1) and causing deterioration in aquatic habitat and water quality. In 2005, 51% of the rivers in England and Wales had high concentrations of phosphorus (>0.1 mg P l−1) and 28% of rivers had high concentrations of nitrate nitrogen (>6.8 mg NO3–N l−1) (Environment Agency, 2007). In addition 11% are judged to be “at risk” from excessive sediment, with an additional 20% “probably at risk”. The need to address diffuse pollution is demonstrated by Environment Agency (2007), which reports that diffuse pollution pressures are observed in 87% of rivers, solely point discharges pressures are observed in 13% of river and both pressures are observed in 26% of the rivers “at risk” of not achieving WFD objectives.
Nutrient models have been developed to describe and quantify nutrients transfer from agriculture to aquatic environments, due to the lower costs of investigating different scenarios in comparison to those of actual implementation (Kronvang et al., 2009a). The EUROHARP project (Kronvang et al., 2009a) aimed to harmonise procedures for the quantification of nutrient losses from diffuse sources, through providing end users with guidance for choosing appropriate tools or models to facilitate WFD implementation (Kronvang et al., 2009a), concluding recommendation of a single nutrient model suitable for all catchments in Europe was not yet possible (Kronvang et al., 2009b). One of the important modelling elements is choice of model time-step (annual, sub-annual), which greatly depends on the temporal availability and variability of measured data for the calibration procedure (Glavan et al., 2011; Hejzlar et al., 2009; Schoumans et al., 2009a). The model output information provides a range of values which indicate the uncertainty in load and yield estimations and can, together with expert knowledge about specific types of catchments, provide required information (Schoumans et al., 2009b). Important findings from EUROHARP are also in agreement with Volk et al. (2009) who suggested that achievement of WFD environment targets is only possible with a consideration of regional land use distinctions between catchments.
This paper uses the Soil and Water Assessment Tool (SWAT) model (Arnold et al., 1998) to investigate whether the application of controls on agricultural diffuse source pollution to meet WFD targets are compatible with farming systems which maintain desired landscape values, using the Axe catchment in south-west England as a case study. Given that much of the landscape of the catchment is covered by national (Areas of Outstanding Natural Beauty) and county (Areas of Great Landscape Value and Special Landscape Areas) protective landscape designations, we consider whether fundamental changes to the farming systems, and associated changes to the landscape character, are likely to be necessary to meet the requirements of the WFD.
Section snippets
Study area
The river Axe catchment is a diverse area of approximately 400 km2 (Fig. 1) in which altitude varies from sea level at the coast to 315 m above sea level in the uplands. The terrain maximum slope inclination is 25° with 50% of slopes below 5°, 38% from 5° to 10°, 10% from 10° to 15°, 2% from 15 to 20 and 0.1% of slopes from 20° to 25°. The area experiences a temperate Atlantic climate. Average annual rainfall ranges from 820 mm in the lowland areas to over 1100 mm in the hills. Average monthly
Calibration and validation
The model was run for a period of 20 years, from the 1st January 1986 until the 31st December 2005. The study period was divided into three periods of time: warm up (1986–1987), calibration (1988–1997) and validation (1998–2005). Many SWAT users use three years warm up period (Gassman et al., 2007), however, comparison of the data trend between measured and simulated data showed stable conditions already after one year. The model calibration for hydrology and nutrients (N, P) was informed
Scenarios
Three different land management scenarios were developed to reduce diffuse water pollution from agriculture, particularly phosphorus, within a context of sustaining a livestock agricultural sector which would still be able to operate at an appropriate intensity to maintain the landscape in its present state. The scenarios were based on interviews with the Environment Agency and local farmers, reports and action plans produced by the Catchment Sensitive Farming Programme (DEFRA, 2002) and by the
Results and discussion
To evaluate the effectiveness of the scenarios in reducing nutrient losses, the study focused on the model outputs for the outlets of the three main sub-catchments (River Yarty; River Coly, Upper Axe) and of the entire catchment, located at the outlet of SWAT sub-catchmnets 21, 12, 4 and 25, respectively (Fig. 1).
Conclusions
The SWAT model has been calibrated and validated on river flow and nutrients for the river Axe catchment in south-west England, which has an attractive and valued landscape typical of this livestock-farming dominated region. SWAT was used to estimate the impacts of different land management scenarios to deliver water quality improvements to the river Axe.
The results of this study suggest that there may be a fundamental incompatibility between the delivery of WFD targets and the maintenance of
Acknowledgements
The data provided by the Joint Research Centre, (CORINE land cover map), EDINA (DEFRA June Agriculture Census), British Atmospheric Data Centre and the UK Meteorological Office (weather data), British Geological Survey (geological data via EDINA), Ordnance Survey (elevation data via EDINA) and the Environment Agency (river flows and water quality data) are acknowledged.
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