Thermal mediation in a natural littoral wetland: Measurements and modeling

As a river flows through shallow littoral regions such as wetlands, forebay s, and side arms, the temperature of the water is modified through atmosphe ric heat exchange. This process, which we call thermal mediation, can contr ol the initial fate of river-borne nutrient and contaminant fluxes within a lake or reservoir. This paper presents temperature observations that demon strate the occurrence of thermal mediation and directly support the theoret ical results derived by Andradottir and Nepf [2000]. The measurements show that the wetland warms the river inflow by approximately 1-3 degrees C duri ng summer and fall nonstorm conditions. Less thermal mediation occurs durin g storms, both because the residence time is significantly reduced and beca use the wetland circulation shifts from laterally well mixed (low flows) to short-circuiting (storms). The dead-zone model can simulate both these reg imes and the transition between the regimes and is therefore a good choice for wetland modeling.