Relative Importance of Karst-Conduit Hyporheic Zones Co-occuring at Different Spatial Scales

Abstract:

Hyporheic zones at the margin of karst conduits occur at different spatial scales, from those associated with the smallest scales (cm) of conduit-wall topography (e.g., scallops) to large-scale (100 m) conduit sinuosity, and to even larger conduit network patterns. Hyporheic flows are believed to influence the processing of nutrients and dissolved organic carbon from the conduit flow, the evolution of karst-water chemistry, the reaction and sequestration of contaminants, and speleogenesis. Multiple spatial scales of hyporheic interaction lead to a wide distribution of hyporheic flow path lengths, residence times, and opportunities for both abiotic and microbially-mediated reactions of various kinetics.

Using mathematical modeling we examine hyporheic flows for a single karst conduit with two different scales of flow disturbance: wall topography at the sub-meter scale and sinuosity at the scale of 10’s of meters. By varying the amplitude of each disturbance we examine changes in hyporheic flow magnitude, paths, residence times, and other metrics. We test the hypothesis that while sinuosity-driven hyporheic flow occupies the greatest volume of karst matrix rock, with the longest residence times, the much smaller volume of topographically-driven hyporheic flow is more important because it turns over far more conduit flow and does so with much shorter and possibly more important residence times.