Simulating management options and scenarios to control nutrient load to Mar Menor, Southeast Spain

Abstract

1 - The Mar Menor, with an area of 135 km2, is the largest coastal lagoon in the Western Mediterranean. The ecological value of the Mar Menor lagoon and associated wetlands has been recognised in a series of rules and resolutions, at regional, national and international level. However, several hydrological and land-use changes in the Mar Menor watershed are threatening the conservation of the Mar Menor as a result of urban and tourist developments and the intensification of agriculture. As a result, an initial eutrophication process is affecting the ecological functioning of the lagoon and the tourist activities. Several BAU (Business As Usual) and PT (policy-target) scenarios have been defined, characterised and simulated using hydrological and integrated watershed models developed for the Mar Menor site. 2 - The load of nutrients into the lagoon constitutes a key issue for all relevant scenarios for Mar Menor. Under the BAU scenario of urban and tourist development, it is expected a high rise in resident and seasonal population, which would lead to a 50% increase in the average annual load of nutrients and would further promote the eutrophication process in the lagoon. The management option of re-use of agricultural drainages would allow around a 10% reduction in nutrient loads into the Mar Menor lagoon. The recovery of wetlands constitutes a better option to reduce DIN load into the lagoon, as compared with the management option of re-use of agricultural drainages, since the achieved reduction in total nutrient loads doubles the one achieved by the re-use of agricultural drainages. As revealed by the cost-effectiveness analysis, the optimisation of wetlands for nutrient removal seems to be also more efficient compared to the re-use of agricultural drainages, with unitary costs around four times lower. 3 - The results obtained confirm the usefulness of the applied methodological approach for the overall understanding of coastal lagoons and the provision of practical inputs for the decision making process.