XTREME STREAMS AS INPUTS TO XTREME LAKES: QUANTIFYING THE DAILY DOSE OF PARTICULATE ORGANIC MATTER TO LAKES IN THE DRY VALLEYS OF ANTARCTIC

Due to the lack of terrestrial vegetation algal mats growing in streams and under lake ice are the primary inputs of organic matter to the closed basin lakes of the McMurdo Dry Valleys in Antarctica. Streamflow in the dry valleys is highly dynamic and can vary by as much as 5 to 10 fold during a single day depending on the orientation of the face of the source-water glacier and the solar trajectory. The objective of this study was to quantify the daily fluctuations in suspended particulate organic matter (POM) concentration from one of these streams in order to investigate the significance of changing flow regimes on the daily dose of organic matter to the lake ecosystems. Organic matter was collected using a plankton net placed in the stream for periods of approximately 4 hours throughout the day. A total of six individual daily flood events were observed in this way over three seasons with peak flows ranging from less than 1 L/s to over 200 L/s. The results showed a rapid increase in the concentration of POM on the ascending limb of the hydrograph for all but the largest flood events. The peak concentration for the largest flood event occurred after the flood peak suggesting a potential critical flow threshold for the input of organic matter from different sources in the stream. In general, higher concentrations of POM were observed during the low flow seasons. This resulted in similar overall organic matter transport rates for high and low flow years. The results from this study enable us to make the first quantitative assessment of variations in the daily dose and seasonal organic matter input to the extreme lakes of the Dry Valleys that takes into account the dynamic nature of the extreme streams in Antarctica.