Mathematical modelling for ecohydrological management of an endangered endorheic salt lake in the semiarid Pampean region, Argentina

Abstract

In this work, we propose a mathematical model within a dynamic optimization framework to address the management of a salt lake in a semiarid region in Argentina (Chasicó Lake). The main objective is to elaborate strategies to control recurrent floods and keep salinity values around the physiological optimum for the high-commercial value fish silverside. The model comprises dynamic mass balances for water and salt, as well as evaporation calculation based on energy and momentum balances on a daily basis. A collection of meteorological and hydraulic data in the basin for several decades and bathymetric information is included. The simulation of different scenarios with historical data provide a deeper insight into the ecohydrological dynamics of Chasicó Lake basin. Model predictions under moderate drought conditions, with rainfall about 70% of the historic average, show a large increase in salinity after three years under that setting. This would induce drastic changes in ecological conditions producing fish mass mortality, what likely occurred repeatedly throughout the lake’s history, since such dry periods occurred repeatedly during the analyzed 1911‐2016 period. The comparison between drought and wet scenarios indicates a differential vulnerability dynamics in which the system shows less resistance to the effects of drought than to those due to floods. The proposed model allows the determination of optimal lake tributary diversion flowrate to prevent flooding of croplands, keeping lake salinity within optimal values for silverside, and providing water for the creation of wetlands for wildlife and an artificial reservoir for alleviation of wet period effects.