ANALYZING THE THERMAL BEHAVIOR AT KARST UNDERFLOW-OVERFLOW SPRINGS FED BY A SINKING STREAM: RELATIONSHIPS AMONG RECHARGE, FLOW PATH PROPERTIES AND TEMPERATURE DYNAMICS

Analysis of temperature variation at karst springs, particularly in combination with conservative tracers, provides important information about the dynamics of groundwater recharge to karst systems and the geometries of karst conduits feeding the springs. Here we study a relatively simple karst system featuring a sinking stream that discharges to a pair of underflow-overflow springs at the Savoy Experimental Watershed (SEW), Arkansas (USA). We study patterns of temperature, conductivity, and discharge variation at the sinking stream and the two springs from individual storm events to seasonal timescales. During individual storm events, the springs exhibit three different patterns of temperature responses: 1, offset; 2, long-lag; and 3, mirrored. Offset spring responses are thermal peaks at the springs where timing of the variations at the two springs significantly differ (>9 hours). These events occur during large precipitation events and under dry antecedent conditions (i.e. low stage at the sinking stream). Long-lag responses exhibit a stair-step-shaped response at the underflow spring with a noticeable peak at the overflow spring. These events occur during smaller precipitation events and under wet antecedent conditions (i.e. high stage at the sinking stream). Mirrored responses are the most common with synchronous peaks at both springs, occurring at a range of flow and precipitation conditions. The springs exhibit a seasonal temperature variability that lags behind sinking stream temperatures by about 3 weeks. This observation indicates substantial thermal inertia within the recharge zone of the conduit system, where sinking stream discharge is captured at sink points buried beneath a cover of gravel and clay. This research provides new insight into the thermal behavior of mantled karst systems, such as the Springfield Plateau aquifer, where thermal dynamics may be strongly damped within the karst cover.