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Universidade do Algarve (2015)

Assessing soil erosion due to land use change at the Alqueva reservoir surrounding area

Ferreira, Vera Lúcia Matias

Titre : Assessing soil erosion due to land use change at the Alqueva reservoir surrounding area

Avaliação da erosão resultante das alterações de uso do solo na área envolvente à albufeira do Alqueva

Auteur : Ferreira, Vera Lúcia Matias

Université de soutenance : Universidade do Algarve

Grade : Doutoramento, Ciências do Mar, da Terra e do Ambiente 2015

Résumé partiel
Soil erosion is one of the most dynamic environmental and economic threats in Mediterranean regions. As a consequence of water availability in the surrounding area of the Alqueva reservoir, new challenges were created. The conversion from native Montado grassland to intensive and irrigated agriculture, the development of golf resorts and the ongoing climate change were insufficiently considered for the erosion problem during the environmental impact study of the Alqueva project, and consequently there is an urgent need to delineate a sustainable land management for the region. The main objective of this investigation was to assess current and future soil erosions in the surrounding area of the Alqueva reservoir using the Revised Universal Soil Loss Equation (RUSLE) in combination with Geographic Information Systems (GIS). Different soil erosion factors, the main causes and consequences, and also spatial variability and seasonality were investigated, and a simulation model was developed to support decision based on the acquired scientific knowledge. On the first part of the study, the RUSLE equation was applied at field scale, and different land uses were selected for erosion assessment (Montado grassland, lucerne cultivation, olive orchard and vineyard). The spatial variability analysis (with geostatistics and HJ-Biplot) indicates that the intensification of land use, with tillage practices and vegetation removal, is likely to increase the susceptibility to soil erosion (soil erodibility). The effect of seasonality on soil erosion was confirmed, with the autumn season contributing the most to annual soil erosion (around 65%). Future soil erosion scenarios were investigated for the entire study area, according to the expected land use changes (which affect vegetation cover) and climate changes (which affect rainfall-runoff erosivity). The forecasting scenarios of land use changes indicated that the intensive agriculture area is likely to increase, as well as sparse and xerophytic vegetation and rainfall-runoff erosivity. As a consequence, soil erosion in the study area is forecasted to increase from 1.78 t/ha to 3.65 t/ha by 2100. A backcasting scenario was investigated by considering the application of soil conservation practices, that will decrease soil erosion considerably to an average of 2.27 t/ha. For each scenario studied, the sediment delivery was assessed, and for the worst case scenario in 2100, an annual sedimentation value of 182 000 tonnes is predicted for the study area. Finally it was developed a dynamic simulation model for soil erosion performed on Stella, and a graphic user interface as a decision support tool allowing the user (e.g. decision maker) to create, modify, save, and select site specific data.

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