Permanently Intermittent Streams of the McMurdo Dry Valleys, Antarctica - Extreme Stream Ecosystems Responding to Annual and Intra-seasonal Intermittency

The streams of the McMurdo Dry Valleys (MDVs), Antarctica are fed by glacial melt water for 6-10 weeks per year, and are therefore intermittent on an annual basis. However, because of fluctuations in surface energy balance during the austral summer, they can also experience intermittent flow during the flow season, which is more typical in long streams (>2 km) than short streams (<2 km). These streams are underlain by continuous permafrost, though sediments adjacent to the stream thaw to depths of 0.75-1 m in the austral summer. This accommodation space serves as a reservoir that must be saturated prior to flow continuing downstream. Hence, long streams have larger subsurface pore-reservoirs to fill than short streams, leading to greater intra-season intermittency on long streams than short ones. Flow intermittency has significant impacts in the MDV streams, controlling diatom community make up, and altering temporal biogeochemical patterns of streams. These ecosystems are fairly resilient as algal mats in the stream begin metabolism almost immediately after being re-wetted annually. These streams serve as a poor corollary to warm desert intermittent streams as the rewetting periods are fairly consistent in timing and length. This regularity in intermittency is likely the key to the biological resilience of these ecosystems.