Eutrophication in the Azores islands

Abstract

Introduction Phosphorus, well known as an essential nutrient for plant and animal growth, has been recognized as one of the major elements affecting surface waters by leading to eutrophication. The eutrophication of fresh waters affects its quality for most of human uses (drinking, fisheries or recreation), because of the excessive growth of algae and aquatic weeds and the subsequent anoxia phenomena caused by their decomposition. Also, periodic blooms of cyanobacteria in drinking waters may pose serious health hazard to livestock and humans. Nonpoint source pollution, especially from fertilizer and manure applications in agricultural lands, has in many parts of the world been identified as the major source of nutrients responsible for accelerating the rate of eutrophication. Over the last two decades the intensification of pasture production and cattle grazing in the Azores archipelago have brought excess nutrient loads to the soils and as a consequence several lakes are currently under eutrophic conditions. The lake has been reported as being under a mesoeutrophic condition (22-29 mg P L-1) (INOVA 1999). The Lagoa das Sete Cidades-a typical picture postcard of the S. Miguel Island-is a volcanic caldera which forms a large watershed approximately circular in shape, with an average diameter of 5 km and delimited by a ridge of almost vertical slopes, with a maximum height of 500 m. Two interconnecting lakes occupy a central position in the watershed. In this chapter, we take Sete Cidades as a case example for the Azores, presenting some results discussed in the context of the global issue of eutrophication. © Springer-Verlag Berlin Heidelberg 2007.