(371a) Integrated Mathematical Models for Freshwater Bodies and Constructed Wetlands as Tools for Restoration Planning Through an Optimal Control Approach

Authors: 
Diaz, M. S., Planta Piloto de Ingeniería Química, PLAPIQUI (CONICET-UNS), Universidad Nacional del Sur
Siniscalchi, A., Planta Piloto de Ingeniería Química, PLAPIQUI (CONICET-UNS), Universidad Nacional del Sur
Di Maggio, J. A., PLAPIQUI (CONICET-UNS)
Estrada, V., PLAPIQUI (CONICET-UNS)
During the last decades there has been an important increase in the frequency and intensity of harmful cyanobacteria blooms (CyanoHAB) in water bodies in a global scale with documented CyanoHABs in at least 108 countries. This fact is associated to the increased loading of nutrients in freshwater and marine ecosystems from industrial and domestic wastewater, as well as agricultural and livestock activities. Cyanobacteria generate problems that affect public health, commercial and sports fishing, etc. The most severe problem is the potential production of cyanotoxins. Annual cost estimations associated to eutrophication in US and UK freshwater systems are around US$ 2.2 billion (Doods et al., 2009) and US$ 105-160 million (Pretty et al., 2003), respectively.

The first step in the remediation of eutrophication is nutrient loading reduction into lakes, by means of constructed wetlands. These artificial ecosystems are portions of land covered with macrophytes, which assimilate nutrients, plankton and other microorganims. Estrada et al. (2011) and Di Maggio et al. (2016) formulated water quality models as dynamic optimization problems for the determination of restoration strategies in eutrophic water bodies.

In this work we propose the integration of lake models to artificial wetland models within a dynamic optimization framework to address the optimal design of constructed wetlands as well as determination of optimal restoration policies. Mechanistic wetland models are integrated to lake models to obtain wetland sizing and nutrient dynamics, together with phytoplankton, zooplankton, piscivorous and herbivorous fish abundance profiles. The resulting model is an optimal control problem subject to a differential algebraic equation system. Numerical results provide optimal areas of constructed wetlands and temporal profiles of control and state variables for both lake and wetlands, before and after remediation.