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Torrens, Christa L. ¹ ; Gooseff, Michael N. ²

¹ INSTAAR - University of Colorado, Boulder
² INSTAAR - University of Colorado, Boulder

Glacial meltwater streams in the McMurdo Dry Valleys [MDV], Antarctica flow 4-12 weeks per year during the austral summer. Instream algal mats provide most of the primary production; there are no vascular plants. Extensive hyporheic zones host microbial communities, which may provide significant heterotrophic respiration. During the austral summer, there is continuous daylight and potentially continuous photosynthesis. Temperature, streamflow [Q] and specific electrical conductance [EC] all vary on diel timescales. Little is known about interactions between these diel fluxes and whole-stream metabolism in MDV streams.

To examine the temporal patterns of hyporheic exchange and stream metabolism in this system, we measured water temperature, EC, Q, and instream and hyporheic dissolved oxygen [DO] on Von Guerard Stream. Von Guerard is a relatively long MDV stream with a well-developed hyporheic zone and abundant algal mats. EC is a common proxy for hyporheic exchange as meltwater is dilute, and hyporheic water has relatively high EC due to rapid weathering in the hyporheic zone. DO is a proxy for whole-stream metabolic processes: primary productivity adds DO to the system while respiration consumes it.

We expected instream DO to follow diel irradiation patterns, decreasing at “night” when the solar aspect is relatively low. We also expected instream DO and EC to be negatively correlated, as hyporheic exchange would add both dissolved solutes and less-oxygenated water to the stream. However, we found that instream DO levels remained high regardless of solar aspect or EC fluxes; this indicates consistently high primary productivity and relatively low levels of respiration, regardless of hyporheic influx. Hyporheic DO flux patterns are more complex and appear to be more strongly influenced by hyporheic exchange.