Influence of underwater light climate on periphyton and phytoplankton communities in shallow lakes from the Pampa plain (Argentina) with contrasting steady states

摘要

Shallow lakes from the Pampa plain (Argentina) are subjected to the impact of different human activities, and as a consequence, most of them are in a turbid state. Three types of shallow lakes have been described in this region: clear-vegetated, phytoplanktonturbid and inorganic-turbid. We analysed the periphyton and phytoplankton structure in five selected shallow lakes with contrasting optical characteristics. In the case of periphyton, we studied the variation in depth. Pigment compositions of both algal communities were analysed by means of high-performance liquid chromatography. Additionally, we studied the taxonomic algal composition of both communities and the mass variables of periphyton. We observed a general decreasing pattern in the mean values of periphytic abundance with depth, and stratification in periphyton was generally consistent with the vertical profiles of pigments. Relationships between cell counts and pigments also suggested changes in the intracellular pigment concentration due to photoacclimation. In clear lakes, surface periphytic communities were co-dominated by chlorophytes and diatoms. In turbid lakes the surface assemblages were mainly represented by diatoms and the relative contribution of cyanobacteria increased with depth. The interaction between light and nutrients in different turbid scenarios may explain the patterns observed in the development of the periphytic community. We observed lower periphyton accrual in lakes that presented boundary values in the restrictions of either nutrients or light availability. In phytoplanktonturbid lakes, periphyton exhibited a considerable growth due to the rich nutrient conditions, but the community was dominated by the heterotrophic fraction and we also found algal groups well adapted to light limitation.