International Journal of Sustainable Development & World Ecology 14 (2007) 192–200
Watershed integrated management: A decision-support model on Sete Cidades Lake (Azores) João Porteiro1, Helena Calado1, Margarida Pereira2, Adriano Quintela1 and Tomáz Dentinho3 1
Universidade dos Açores, Departamento de Biologia Universidade Nova de Lisboa, Departamento de Geografia e Planeamento Regional 3 Universidade dos Açores, Departamento de Ciências Agrárias
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Key words: Eutrophication, models, generate and evaluate scenarios, multicriteria decision-support system
SUMMARY The Sete Cidades Lake (437 ha) is located in a volcanic crater of São Miguel Island (Azores). The watershed is 1923 ha, and 25% of it is covered with water. Extreme logging and the use of fertilizers in the cattle grazing areas have caused sedimentation and eutrophication of the main water body (Carlson Trophic State Index TSI = 40–50 mesoeutrophy). To deal with the issue, a linear programming model was created to generate efficient land-use scenarios for different amounts of phosphorus release. The model was calibrated for the present situation and then simulated to obtain 29 scenarios. It allowed us to derive parameters for each scenario. Then a multiobjective program was used to derive an acceptable weight for each indicator. The dominant solutions were discovered and discussed with different stakeholders.
INTRODUCTION The Sete Cidades Lake in the Island of Saint Michael (Azores) is located in a volcanic crater that forms the catchment of the lake. The size of the catchment is 1923 ha, of which 25% is water. The dry areas (1448 ha) are occupied by pasture 32% (458 ha), wild forest 31% (454 ha), timber forest 26% (379 ha) and other uses 11% (157 ha). Intensified dairy production and unsustainable farming and logging practices have resulted in degradation of the lakes. The increased frequency of logging and use of fertilizers on pastures and forages have already destroyed several small lakes through eutrophication and sedimentation. The issue
became a public concern when two of the major lakes in Saint Michael Island became degraded by eutrophication and sedimentation (Calado 2000). Figure 1 presents the current situation of the Sete Cidades catchment. The land is currently used for intensive farming/dairy production, which results in deforestation, soil erosion and sedimentation of the lake. The soil erosion increases the flow of nutrients and fertilizers into the lake, which contributes directly to eutrophication. Until now, the increased sedimentation has resulted in a decrease of the depth of the lake by 10 m. Continued sedimentation and eutrophication will have two major
Correspondence: João Porteiro , Universidade dos Açores, Departamento de Biologia – Secção de Geografia, Rua da Mãe de Deus, 52, 9500 Ponta Delgada. Email:
[email protected]
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