A coupled 3D hydrodynamic and ecosystemic model of lake Titicaca

Details

Supervisors

Hanert, Emmanuel

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement

Abstract

Mathematical models are essential in the quest to better understand the human impact on the world’s ecosystems. In this thesis, we have provided a new tool that can be used to study Lake Titicaca's hydrodynamics and water quality. This was achieved by coupling NPZD (for Nitrogen-based nutrients, Phytoplankton, Zooplankton and Detritus) ecosystem-type model to an underlying three dimensional hydrodynamic model: the 3D version of the Second-generation Louvain-la-Neuve Ice-Ocean Model. SLIM3D leverages the finite elements method to solve the three-dimensional hydrodynamic equations on each element of an unstructured 3D mesh. Our study focused on the entire Lake Titicaca, and we developed a case study on the smaller section of this lake: Lago Menor. Indeed, in the Cohana bay, eastern part of Lago Menor, a significant nitrogen discharge is caused by anthropogenic activities of the upstream Katari watershed. This discharge is most likely responsible for the algal bloom event occurred in March-April 2015. We thus applied a nitrogen forcing to our NPZD ecosystem-type model in order to replicate the proliferation of phytoplankton. Our model covered the period of January 2014 to May 2015 and required the following inputs: the bathymetry, surface temperatures, and the horizontal wind speeds. Winds and surface temperatures are the major forcings that affect the hydrodynamics of the lake. The results generated by the coupled SLIM3D-NPZD model we chose to exploit were: lake temperatures, the u and v components of water velocity, and the NPZD components. Overall, the validation of our coupled SLIM3D-NPZD model suggests that the task of simulating Lake Titicaca's hydrodynamics was achieved but that our model lacks a more site-specific calibration in order to correctly simulate water quality. We managed to simulate the bloom of 2015 but observed some erroneous simulations in other parts of the lake. Nevertheless, we were able to foresee a few promising applications for this coupled model. These range from the use of the model for research purposes to the forecasting and analysis of different contamination scenarios. We have thus manged to implement a fairly simple ecosystemic model that could be used as a predictive tool in the planification for the environmental protection of Lake Titicaca. Offering new opportunities for research and expanding the potential uses of the SLIM hydrodynamic model.