Shallow Groundwater Thermal Response to Land Surface Energy Dissipation and Potential Implications on the Use of Heat as a Tracer

This paper investigated and demonstrated the fundamental role of riparian and terrestrial zone heat balances on the use of thermal gradients to characterize and parameterize groundwater systems. The riparian area aquifer (RAA) includes vegetative cover, comprising a forest of lush Acacia karroo together with some reed, sedges, and forbs. On the other hand, terrestrial area aquifer (TAA) is non-forested. The result illustrated the riparian area suppresses groundwater temperature by an average of 2 degrees C compared to TAA during summer. These signals were found to uniformly dampen temperature anomalies resulting from lateral groundwater inflow from TAA in summer. The impact of lateral groundwater flow from the TAA was only observed in winter, where the effect of latent heat was cancelled out because plants had undergone dormancy. Consequently, the study concluded that the riparian groundwater temperature is more sensitive to the riparian energy balance. To this effect, riparian vegetative cover can considerably complicate the interpretation of the shallow groundwater thermal regime across hydrologic landscapes with varying surface vegetative architecture. Therefore, analyzing thermals signals may require correcting the "false" groundwater geothermal signals due to vegetative cover. The recommendation is that isolating the contributions of these signals should be independently constrained (e.g., introducing thermal data offset) to strengthen the plausibility of heat in parameterizing groundwater systems.