OBSERVATION OF AN EXTREME SNOWMELT EVENT TO REVEAL FLOW PATH HETEROGENEITY AT A KARST SPRING

Geochemical and hydrologic variations observed at karst springs can be driven by 1) the flow path network which connects the recharge area to the subsurface and 2) the nature of the recharge event. Pathways for water movement in karst operate as a continuum of conduit flow and diffuse flow, and networks can be a combination of the two. Geochemical and hydrologic variations at karst springs are widely investigated during rain events, while snowmelt recharge is investigated less. Hydrochemographs were observed during a 26-day snowmelt period of 88 cm of snow. Chloride from road salt provided a tracer and the snowpack a recharge source during the melt period. Long term (multiple day) upward trends in conductivity and water level were observed when air temperature was mostly above freezing, but became steeper with increased time spent above freezing. The trends switched downward under freezing conditions when snowmelt stopped. Long term upward and downward trends were interrupted by daily pulses of increased conductivity and water level. Timing of these spikes suggests recharge water moved as overland flow across a frozen surface to focused pathways. The daily pulses fingerprint the conduit component and the long term trends the diffuse component. Hydrochemograph patterns were linked to air temperature which controls available recharge from the snowpack. Monitoring at a spring during snowmelt is shown to be quite beneficial, because the assumption can be made that the entire capture area is active. This monitoring can lead to better conceptual models for karst aquifers.