Dissolved Organic Carbon Chemostasis in Antarctic Polar Desert Streams
In the McMurdo Dry Valleys [MDV], Antarctica, little is known about concentration-discharge (C-q) relationships for biological solutes such as DOC. Because MDV streams are low in organic carbon and experience large diel fluctuations in discharge (q), we expected that the MDV DOC-q relationship would be dilution-based and limited by the DOC generation rate, not the fluid transit time. To evaluate the DOC-q relationship in these glacial-meltwater streams, we fit the long-term DOC-q data to two models: a power law and an advection-reaction model. We then used model outputs and other common metrics to quantify the DOC-q relationship. Surprisingly, our results show that this relationship is chemostatic; however, they do not provide a clear explanation why. After examining and eliminating various potential DOC-q drivers, we propose a conceptual model where hyporheic carbon storage, hyporheic exchange rates, and net DOC generation rates are key interacting components that enable chemostatic DOC-q behavior in MDV streams. This model clarifies the role of autochthonous carbon stores in maintaining DOC-q chemostasis and may be useful for examining these relationships in temperate systems, where the role of autochthonous carbon is masked by a far larger allochthonous signal.