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

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-year 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 the light extinction coefficient (Kd_PAR) and the mean irradiance of the mixing layer (I_m). Our modeling approach using Bayesian inference and a continuous nonmonotonic function successfully predicted changes in Pcy vertical distribution. The model was successful in fitting data for different minerogenic particles (volcanic ash and glacial clay) and in predicting changes under sharp increases in turbidity (volcanic eruptions), as well as in more gradual changes (glacial recession). Pcy maximum abundance increased with transparency (lower Kd_PAR values), and the amplitude of the vertical profile increased with higher I_m values. Using our model, we achieved a full prediction of Pcy vertical distribution under different scenarios of lake transparency and lake thermal structures.