Growth factors controlling periphyton production in a temperate reservoir in Patagonia used for fish farming

Abstract

Abstract In the early stages of pollution it is not always possible to detect contamination by chemical parameters as some components of the biota react more rapidly to inputs of pollutants. The purpose of this work is to determine the importance of nutrient inputs as a control of growth of the periphyton community and to evaluate the feasibility of using changes in the periphyton community to monitor the effects of contamination from fish farms. Wastes derived from fish farming in the Alicura Reservoir changed the nutrient concentrations of the sediment just below the fish cages and decreased the nitrogen: phosphorus (N:P) ratio to below 1. This situation stimulated the development of cyanophytes and increased the total algal biomass as a consequence of higher nutrient availability. In laboratory bioassays, diatoms dominated the periphyton community at high N:P (>4) and Si:P (> 1000) ratios, while cyanophytes were dominants at low N:P and Si:P (< 10) ratios. These results suggested that not only the N:P ratio controls periphyton composition, because in the reservoir (where N:P ratio was always low) the periphyton was dominated by diatoms as a result of the presence of extremely high Si:P ratios (3000‐5000). These results suggest that periphyton is a powerful tool for detecting the first signs of contamination.