(371h) Sustainable Management for a Salt Lake Basin with a Water-Food-Energy-Carbon Nexus Approach with Dynamic Optimization

In this work, we address the formulation of an agrohydroecological optimization model to manage a salt lake and its basin within a semiarid region, taking into account environmental impact of the proposed activities. The mitigation of the consequences of extreme environmental events, such as floods and droughts, has been addressed as an optimal control problem of an endorheic salt lake in a semiarid region [1]. In the present work, an extension of the optimization model is proposed for the sustainable management of ecohydrological processes, agriculture and livestock of a salt lake basin. Five objectives are set out: (a) to prevent flooding from the salt lake to a nearby village and its touristic areas during wet periods by diverting part of the flow from its tributary into an artificial reservoir (the diversion flowrate is a control variable); (b) to optimize management of the artificial reservoir to keep lake salinity within desired levels for silverside fish during drought periods (the stream flowrates from this artificial reservoir to the salt lake and to irrigation purposes are control variables); (c) to include restoration strategies for native species that comprise a xerophilic woodland currently existing in the salt lake basin, combining plantation of Prosopis flexuosa and P. caldenia with drought resistant crops (Chenopodium quinoa) and pasture, and (d) to provide drinking water and shade to cattle. In this project, a 300 ha semi-arid area that is not being currently used within the basin has been selected for native tree, drought resistant crop and pasture plantation, as well as livestock breeding (100 cattle). An additional objective has been incorporated: (e) to perform life cycle assessment (LCA) for the agricultural and livestock system under study. The objective function is an integral one that aims to keep the salt lake volume (and its associated salinity, as it is an endorheic basin), at a desired value, to avoid flooding of the nearby village and to keep salinity at optimal values for reproduction of a valuable fish species. The resulting optimal control problem is constrained with a DAE system of equations representing the above-mentioned processes. Energy calculations are performed for pumps used in drip irrigation for crop and pasture. Numerical results show that the proposed agroecological system can produce 22.5 t/y of meat (cattle), which would represent a profit of 150,000 US$/y plus 3.6 MMUS$/y incomes from quinoa sales (2 t/ha yield at 9,000 US$/t), within a currently unproductive area. Furthermore, negative environmental impacts due to tree plantations, drought resistant crops and pasture are slightly larger than positive impacts associated to cattle CO2-eq emissions (gases and manure). This fact contributes to achieving the net zero-carbon objectives, while mitigating the consequences of extreme events such as floods and droughts. The model has proven to be an efficient computational tool for the sustainable management in the context of the water-food-energy-carbon nexus of a salt lake and its basin.

References

Siniscalchi, A, Diaz, M.S, Lara, R.J (2022). Sustainable long-term mitigation of floods and droughts in semiarid regions:Integrated optimal management strategies for a salt lake basin.Ecohydrology. 2022;15:e2396