Ecohydrological Management and Valuation Insights of Ecosystem Services in Salt Lakes through Advanced Dynamic Optimisation Strategies

SINISCALCHI A.G; RANIOLO A; GARCIA PRIETO C; LARA R.J; GOMEZ E; DIAZ M, S

Pittsburgh

Congreso; AICHE; 2018

In this work, we propose a mathematical model within a dynamic optimization framework to address the management and enhancement of ecosystem services of a salt lake in a semiarid region in Argentina (Chasicó Lake). Further, useful criteria for valuation of ecosystem services in continental salt water environments are provided. Ecosystem services are the direct and indirect contributions of ecosystems to human well-being (TEEB, 2010, Jorda-Capdevila et al., 2016). They support directly or indirectly the survival and quality of life. The salt lake basin under study provides multiple ecosystem services that include production of silverside (Odonthestes bonariensis), a fish species of regional importance and high commercial value; recreational space for boating; sports fishing; the appreciation of the wilderness; natural wetlands; birds sanctuary; etc.We formulate dynamic mass balances for water and salt; evaporation is calculated based on energy and momentum balances on a daily basis. The model has been validated with collected data for the period 2008-2016 (Siniscalchi et al., 2018a). Based on two bathymetric studies, we include rigorous calculations for lake volume, as composed of several geometric forms. We formulate an optimal control problem to manage the water resource during wet and dry periods. In wet periods the water body is managed to prevent flooding of the nearby fields. In dry periods, management actions are carried out to address an important ecological and economic issue, the maintenance of optimal environmental conditions for silverside.The objective is to keep lake salinity around a desired value considered as optimal for silverside reproduction, while fulfilling the differential algebraic equations system describing the hydrological model. Therefore, the objective function is integral of the square difference between a set point value and current salinity value at each time instant. There are two control variables: the diverted flowrate to a nearby artificial reservoir in a wet scenario and the required inflow from the artificial reservoir in dry periods. We consider a four-year wet period (mean annual rainfall 800 mm), followed by a two-year dry period (annual rainfall 408 mm). Numerical results show diverted river flowrate profiles in the wet period, which are between 0 and 85% of the river discharge. During the four-year wet period, a new artificial reservoir of 80 hm3 volume (area: 11 km2) could be constructed fed with the diverted water flowrate. This reservoir, for which mass balances and evaporation calculation are performed, can later provide an input stream to Chasicó Lake throughout the two-year dry period. Stream profiles are obtained. In this way, salinity can be kept within desired values, as well as lake volume. The model is implemented within a control vector parameterization environment in gPROMS (PSEnterprise, 2017). The driving forces of the ecosystem services provided by the salt lake, identified through the proposed integrated model, represent useful tools towards their valuation.