Saline lakes or “Salares”, are found in the central depression of the closed catchments in the Andean Altiplano region of Chile, Bolivia, Peru, and Argentina. Salares are formed by the upwelling of groundwater, which evaporates at the ground surface to form salt-rich flat lakes. Located at approximately 4 km above sea level, Salares are subjected to severe environmental conditions including low humidity and extreme temperature/wind patterns. Due to their geospatial positioning, salares have a great mineralogical wealth, where some metallic oxides stand out. Recent observations at the Salar del Huasco (Chile) suggest there are CO2 consumption processes related to solar irradiance that were not explained by previously modeled transport processes (i.e., Model 1, includes air-water interface (AWI) and water-sediment interface (WSI) fluxes). Thus, a photocatalytic process was considered as a potential sink in the overall CO2 mass balance of the system. In the presence of a photocatalyst (i.e., metallic oxides), CO2 is reduced to organic molecules and even methane, thus being a sink of atmospheric carbon. This study uses field observations of CO2 and O2 fluxes across the AWI, water quality parameters (e.g., TDS, water temperature, and DOSat), measured soil mineralogy data, and phenomenological models to characterize and quantify the transport and reactivity of CO2, and its relation to the photocatalytic process. In particular, this study focuses on the importance of metal oxides present on the ground of the salar and its potential catalytic activity under solar irradiation. Preliminary results suggest that exponential kinetic expressions for the rate of the photochemical reaction, alongside phenomenological models for oxygen demand due to organic matter degradation, respiration, photosynthesis, AWI and WSI (water-sediment interface) transport fluxes, can describe the CO2 dynamic in the Salar del Huasco (Figure 1). The proposed model (Model 2) was validated using statistical analysis over calibrated parameters and results were compared with the literature for further discussion.

Characterization of photocatalytic processes as part of the mechanisms governing transport and reactivity of CO2 in the Huasco saline lake (Chile)

ACS Spring 2022

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