How cost-effective are diffuse pollution measures in real agricultural landscapes?

Published on 12 July 2010 in Ecosystems and biodiversity , Food, health and wellbeing

Introduction

The European Water Framework Directive (EC, 2000) requires Member States to set water quality objectives and identify cost-effective mitigation measures to achieve good ecological status (GES) for all waters in Europe. Diffuse agricultural pollution is a key contributor affecting water quality (Fezzi, et al., 2008), and 24% of Scottish river water bodies and 18% of loch water bodies are considered at risk. The WFD stipulates that a cost-effectiveness analysis (CEA) of water pollution mitigation measures be conducted, to identify the least cost options for meeting water quality objectives, as a pre-requisite to formulating programmes of measures (WATECO, 2003). However, depending on the attributes of land (topography, hydrology, cover, connectivity to water etc) and its economic productivity, the costs and effectiveness of agri-environmental measures vary significantly across the landscape.

Landscape based CEA enables a more catchment specific assessment and ranking of alternative measures on the basis of their costs and effectiveness. Selective targeting of ‘hot spot’ locations across the landscape could result in maximum environmental benefits subject to fixed funds or minimum economic costs for achieving specific environmental objectives. This note examines how spatial targeting of measures could help achieve water quality targets cost-effectively, illustrated by a case study on optimizing the size and placement of edge-of-field buffer strips for phosphorus (P) mitigation in Rescobie Loch, Angus,Scotland.

Key Points

A review of CEA studies of agri-environmental measures related to WFD in UK indicates that most were based on ‘representative’ farm types. This may lead to biased cost and effectiveness estimates of measures, due to the inherent variability in effectiveness and abatement costs among ‘real-world’ farms.

An integrated economic, hydrologic, and GIS modelling framework was developed to examine the cost-effective targeting of land retirement for establishing buffers in agricultural land.

This is being used to explore cost-effective targeting of buffer strips for mitigation of P loading into Rescobie Loch, Lunan Water, Angus, and results suggest that use of buffer strips alone will not allow cost-effective mitigation of water quality to the extent needed to achieve Good Ecological Status.

Research Undertaken

The aim was to investigate optimal buffer widths and spatial distribution across the landscape to achieve water quality targets at minimum economic costs, taking the case study of Rescobie Loch, part of the Lunan Water Monitored Diffusion Pollution project .

An excel spreadsheet model linking landscape and land use based P export to water, as a function of edge-of-field buffer strip width, with economic impacts of buffer strips, is being developed. P export coefficient, delivery ratio, and buffer P trapping efficiency estimates were based on expert judgements and literature data. The model makes use of catchment scale simulations of field by field land use and crop cover, using the LANDSFACTS modelling tool to create scenarios of crops or land uses within the landscape. Average gross margins were estimated for various cropping activities based on four rotation cycles on the basis of RERAD’s agricultural census (1995-2007). Preliminary modelling results (Table 1) show that:

Modest (ca. 20%) P reduction targets can be achieved cost-effectively by establishing 2 m width buffers on selected fields;
For higher P reduction targets (up to 70% reduction), cost-effectiveness increases by targeting both the spatial configuration of fields and buffer width variability;
For higher P reduction targets the marginal abatement cost increases at an increasing rate.

Table 1. P mitigation cost estimates using buffer strips (for Rescobie Loch catchment)

P reduction goal (%)	P reduced (kg/yr)	land area in buffers (ha)	Abatement costs (£)
P reduction goal (%)	P reduced (kg/yr)	land area in buffers (ha)	total abatement cost(£k/yr)	average abatement cost (£/kg P/yr)	marginal abatement cost (£/kg P/yr)
10	34	5	1.5	44	44
20	68	13	4.0	59	73
30	102	24	7.9	77	115
40	136	49	15.4	113	222
50	170	107	33.4	197	529
60	204	209	66.5	326	972
70	238	395	129.0	542	1838

Policy Implications

Landscape based CEA is needed to achieve realistic assessment of diffuse pollution measures.
Based on the single benefit of P mitigation, the case study demonstrated that it is unlikely that a single measure, such as buffer strips, will be sufficient to achieve environmental targets for Rescobie Loch. So other measures need to be considered.
Additional positive and negative impacts, not related to the targeted objective must also be considered. Implementing a mitigation measure for reducing a particular pollutant may generate co-benefits (e.g., enhance biodiversity) or unintended impacts (e.g., pollution swapping). Ranking and choice of measures based on CEA findings should be further supplemented by qualitative assessment of wider co-benefits and external costs.
Since the P export coefficient, delivery ratio, and buffer P trapping efficiency estimates were based on expert judgements, the results reported in this study are only indicative.

References

Defra, 2004. Cost curve of nitrate mitigation options. Defra report No. NT2511. Produced by Institute of Grassland and Environmental Research (IGER), Devon, UK.

European Commission (EC), 2000. Directive 2000/60/EC (Water Framework Directive). Official of the European communities, 22 December 2000.

Fezzi, C., Rigbay, D., Bateman, I.J., Hadley, D., Posen, P., 2008. Estimating the economic impacts of nutrient leaching reduction policies. Agricultural Economics 39: 197-205.

WATECO, 2003. Common implementation strategy for the Water Framework Directive (2000/60/EC). Economics and environment – the implementation challenge of the WFD European Commission, Luxembourg.

Author

Bedru B. Balana , Andy Vinten, Manuel Lago, Marie Castellazzi and Bill Slee b.balana@macaulay.ac.uk

Topics

Ecosystems and biodiversity , Food, health and wellbeing