LONG-TERM, HIGH-FREQUENCY OBSERVATIONS REVEAL SHIFTS IN HYPORHEIC WEATHERING SOLUTE CONCENTRATION-DISCHARGE DYNAMICS IN MCMURDO DRY VALLEY STREAMS, ANTARCTICA

The response of conservative solute concentrations to discharge variability results from the interactive influence of hydrologic, hydraulic, and biogeochemical processes, especially those that occur in the critical zone. The typical reliance on a few events or narrow time-spans for the analysis of concentration-discharge (C-Q) relationships limits the certainty with which the long-term evolution of critical zone structure or processes may be inferred solely from hysteresis curves. To overcome this challenge we apply a time-flexible C-Q classification scheme to long-term, high-frequency records of discharge and electrical conductivity from ephemeral streams in the McMurdo Dry Valleys, Antarctica across sub-daily to decadal timescales. Dry Valley streams are characterized as a two end-member system wherein weathering solutes are predominantly sourced from the hyporheic zone, such that electrical conductivity serves as a surrogate for weathering solute concentrations. We find that C-Q relationships during diel pulsing events can be explained only through a combination of hydrologic and hydraulic mechanisms that mix hyporheic and glacial end-members during the rise and recession of flood waves. At the decadal scale, our analysis identifies an inter-annual freshening signal that partially corresponds with an increase in cumulative annual discharge across five streams in Taylor Valley, Antarctica. Our results demonstrate the value of long-term, high-frequency data in identify critical zone evolution through C-Q relationships.