Factors controlling phytoplankton community structure in an alkaline versus a softwater lake


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Paraules clau:

Phytoplankton, Lake Sanabria, Lake Banyoles, nutrient lirnitation.


The objective of this paper is to compare nutrient resources that might control phytoplankton species composition and succession in two Spanish lakes located in very different geological areas but at the same latitude. The lakes, Banyoles and Sanabria, are respectively located on Eocene gypsum carbonate rocks and in a Pre-Cambrian regio n dorninated by granitic rock. Their species compositions are quite different: the frrst lake is dominated by diatoms, the second by chroococcal cyanobacteria. Our hypothesis is that the lirniting nutrient in soft-water Lake Sanabria will be nitrogen, and in the alkaline Lake Banyoles, phosphorus (because of its strong precipitation with calcium or coprecipitation with CaC03). In order to test this hypothesis we used principal component analyses with physico-chemical and biological variables on the one hand and species composition on the other. The results show nitrogen to be the more important nutrient, controlling species succession in both lakes. This element is relatively low in both ecosystems during the summer.