EVALUATION OF LIMITING NUTRIENT OF ALGAL PRODUCTION IN RESERVOIRS OF THE BRAZILIAN SEMIARID

Abstract

Nutrient overload in artificial reservoirs can pose a risk to human health and aquatic biodiversity. Thus, the trophic state of a reservoir is an important characteristic for understanding its environmental conditions and possible uses. Its description can be made from the concentration of nutrients, mainly phosphorus. Thus, this study tested the hypothesis that total phosphorus is the limiting nutrient of phytoplankton growth in Brazilian semiarid reservoirs. Three empirical models were used to infer the status of limiting nutrient. In addition, a multiple linear regression analysis was used to establish the causality relationship between nutrients (total nitrogen — TN and total phosphorus — TP) and algal production. The results did not confirm the hypothesis. According to two models used, the TN was the preponderant factor for algal production in about 60% of the reservoirs. This was also observed in the linear regression analysis. According to Carlson’s model, herbivory can be an important factor in algal development. Thus, our results showed that eutrophication by both nutrients, especially the TN, and zooplankton grazing deserve to be considered.