TEMPORAL VARIANCE IN STREAM-HYPORHEIC INTERACTIONS IN STREAMS OF THE MCMURDO DRY VALLEYS ANTARCTICA – MODELING EXCHANGE FROM LONG-TERM STREAM GAUGE RECORDS OF FLOW AND ELECTRICAL CONDUCTIVITY

The streams of the McMurdo Dry Valleys of Antarctica connect their source glaciers to closed basin lakes on valley floors for 10-12 weeks per year during the austral summer. The streams are underlain by continuous permafrost, but during the flow seasons, hyporheic zones surround them, thawing to depths of <1m. However, these hyporheic zones are composed of relatively fresh sediment that is rapidly weathered. Glacial meltwater, which feeds these streams, is very dilute. Hence, the hyporheic zone is the primary source of dissolved solutes to stream waters. Here we develop conceptual and numerical models to quantify the influence of hyporheic exchange on stream water, informed by ~20 years of data collection (stream flow, electrical conductivity, temperature, stream and hyporheic water chemistry) on these streams. Our findings indicate that (1) short streams generally demonstrate little streamwater turnover (i.e., cumulative streamflow exchange through the hyporheic zone) compared to long streams, and (2) that hyporheic influence on streamwater varies on daily, seasonal, and interannual timescales. This work represents the first attempt to quantify cumulative impacts of hyporheic exchange on streamwater through time, and we propose that this is a starting point for developing similar models and applications for temperate streams.