Assessment of real and perceived cost-effectiveness to inform agricultural diffuse pollution mitigation policies

Diffuse water pollution is a major problem in many agroecosystems, especially in irrigated areas linked to ecosystems of high ecological value. Pollution abatement policies imply the modification of agricultural measures and are usually rejected by farmers because of their impact on farm profitability. This paper aims to design an assessment procedure for an implementation programme of agricultural measures aimed at mitigating diffuse pollution, by combining relative effectiveness across measures with the perceived and real cost of the measures. Measures proposed by a law intended to mitigate diffuse pollution and thereby the degradation of the Mar Menor lagoon, a unique natural space in the southeast of Spain, have been used as a case study. The real cost was obtained from the market, and the perceived cost of the measures was obtained from a representative sample of the farmers involved. This work has allowed comparative real and perceived evaluations of the cost-effectiveness of the proposed measures to prioritise them and to reduce information bias, aimed to favours measures adoption. Results show that banning crops less than 100 m from the coast is the most cost-effective measure, followed by the adoption of a nitrate reduction system in desalinated effluent. Divergences between real and perceived cost-effectiveness indicates that good agricultural practices code adoption would require specific actions to reduce these subjective gap. Finally, increasing the acceptability of the policy would imply translating to the farmers information required to reduce the gap between real and perceived cost of the specific agricultural measures.