Vertical distribution of picocyanobacteria in deep lakes: the influence of inorganic turbidity

Abstract

Picocyanobacteria (Pcy) represent the dominant photosynthetic fraction in aquatic systems, contributing significantly to global primary production and playing a key role in global biogeochemical cycles. Based on a 20-years dataset of in situ observations in four deep Andean North-Patagonian lakes, we analyzed and presented a simple model to understand how the input of inorganic particles affects light penetration and influences the vertical distribution of freshwater Pcy during summer stratification. The analyzed temporal series includes two important events (volcanic eruption and glacial recession) that substantially affected lake turbidity. Thus, our mechanistic model was constructed as a function of changes in light extinction coefficient (KdPAR) and mean irradiance of the mixing layer (Im). Our modeling approach using Bayesian inference and a continuous non-monotonic function successfully predicted changes in Pcy vertical distribution. The obtained model was successful in fitting data of different minerogenic particles (volcanic ashes and glacial clay) and in predicting changes under sharp increases in turbidity (volcanic eruptions) as well as in more steady changes (glacial recession). Pcy maximum abundance increased with transparency (lower KdPAR values) and the amplitude of the vertical profile increased with higher Im values. Using our model, we achieved a full prediction of Pcy vertical distribution under different scenarios of lake transparency and lake thermal structures.