A coupled ecohydrodynamic model to predict algal blooms in Lake Titicaca

Duquesne, François [UCL] Vallaeys, Valentin [UCL] Vidaurre, Prem Jai [Univesidad Mayor de San Andrés, Instituto de Ecología (IE), La Paz, Bolivia] Hanert, Emmanuel [UCL]

Lake Titicaca is home to a unique high-altitude ecosystem that is suffering from increasing anthropogenic pressures. It experienced its first major algal bloom in March–April 2015 that had devastating consequences in the southern shallow lake basin. Such events are expected to intensify in the future and call for a more active and quantitative management of the lake and its watershed. In this paper we describe a coupled ecohydrodynamic model to predict the lake’s water quality and, more particularly, the risk of harmful algal blooms. We have coupled a nitrogen-phytoplankton-zooplankton-detritus (NPZD) ecosystem model to the unstructured-mesh 3D hydrodynamic model SLIM. Our high-resolution multi-scale model explicitly represents the exchanges between the two basins composing the lake, through the narrow Strait of Tiquina. This allowed us to study the biophysical processes driving the entire lake over the period of January 2014 to May 2015. The model has been validated against temperature profiles at several locations throughout the lake. It correctly reproduces the seasonal temperature variations that drive the lake stratification and impact the vertical distributions of phytoplankton. Our model was able to replicate the space–time dynamics of the March–April 2015 algal bloom similarly to what was observed on satellite imagery. We believe that our multiscale ecohydrodynamic model is a promising tool to complement field observations and hence support water management in the lake and its watershed.