COMPARING HYDRAULIC MECHANISMS CONTROLLING SALINITY OF CLOSED LAKES IN SEMIARID CLIMATES

Lakes of varying salinity are ubiquitous in regions with semi-arid climates. Frequently, lake-aquifer hydrodynamics leads to purely gaining regimes, and lakes become solute traps. Such lake systems host rich ecosystems. Therefore, salinity trends are of great interest in predicting consequences of climate changes. Over geological periods of time after emergence of such lakes, the advection and solute accumulation in these lakes should result in mineral deposition. However, this is not so in general. In fact, solute concentrations in gaining lakes are far from reaching a precipitation level in some areas of the world. We explore the potency of hydrodynamic factors constraining the lake salinity by counter-flow, namely dispersion and convection. A new coupled lake-aquifer model yields salinity concentrations and gradients beneath the lake. Results show that dispersion is too weak and salinity gradients near the interface may be insufficient to induce free convection that reduces the lake salinization. Thus, the common view that hydraulic factors mainly control the lake salinity must be re-considered to be consistent with observations.