Temporal and Spatial Features of the Thermohydrodynamics of Shallow Salty Lagoons in Northern Chile

Salares in the altiplanic region of Chile, Bolivia, and Argentina sustain important ecosystems in small, shallow wetlands, with inflows provided by groundwater and outflows consisting mainly of evaporation. The temporal and spatial thermohydrodynamics of one of these extremely shallow, saline, endorheic wetlands in northern Chile is analyzed on the basis of field observations of water temperature and salinity, and low-dimensionality models accounting for conservation of heat, mass, and volume. Temperature in the studied system is spatially homogeneous but with strong daily oscillations. Salinity, on the other hand, exhibits longitudinal gradients from the zone of (salty) groundwater upwelling to the final evaporation lagoon. Heat balance in the system is largely controlled by wind, as the evaporative heat flux balances out the net solar radiation. Heat exchange with the bottom sediments damps the daily temperature oscillations by retaining (releasing) heat from (to) the water column. Simulated longitudinal profiles of salinity and flow discharge agree reasonably well with field observations but salinity effects on the rates of both evaporation and salt precipitation need to be taken into account. Laboratory experiments were conducted to develop a simple model for the former effect while the latter effect was accounted for by using existing information. Field measurements provided calibration of the model parameters. The observed longitudinal salinity gradients are correlated with the biological structure of the associated ecosystem to explain, for instance, the existence of specific flamingos' feeding areas in the system.