Using structural equation modeling to better understand microcystis biovolume dynamics in a mediterranean hypereutrophic reservoir

Abstract

Cyanobacteria blooms, especially those involving Microcystis, are an increasing problem worldwide. Complex pathways between temperature and nutrient loads are thought to be the major drivers leading to Microcystis dominance in freshwater systems. In this paper, Microcystis dominance in a Mediterranean hypereutrophic reservoir is studied over a period of three years. A Structural Equation Model (SEM) was developed to delineate the main pathways responsible for Microcystis dominance. The model results showed that direct temperature effects appear to be the primary driving force behind Microcystis growth and dominance. Nonetheless, indirect temperature effects, captured through pathways representing water column stratification and internal nutrient release, also influenced Microcystis. While direct nutrient pathways were significant; they were less important than temperature effects, likely due to the eutrophic nature of the reservoir and Microcystis’ high affinity and storage capabilities for phosphorus. Internal nutrient loads were shown to be the main driver sustaining high nutrient concentrations in the reservoir. The model was able to explain 50% of the observed variability in Microcystis biovolume, 81% of the variation in surface TP, and 46% of the variation in stratification magnitude.Overall, the developed SEM proved to be an effective tool towards capturing and quantifying the complex causal relationships leading to the dominance of Microcystis in a hypereutrophic semi-arid Mediterranean reservoir. © 2020 Elsevier B.V.