CSDMS 2016 annual meeting poster AngangLi
Effects of In-stream Mixing on Carbon Photo-mineralization in Arctic Rivers
Abstract:
Photo-mineralization, the oxidation of dissolved organic carbon (DOC) to CO2 by light, is an important mechanism of CO2 production in arctic inland waters. Current estimates of arctic CO2 production assume that DOC is well-mixed in the water column, which overlooks circumstances when vertical mixing is not strong enough to replenish DOC in the photo-active near-surface region. To determine conditions for which the well-mixed assumption is valid, we used a physically based model that numerically computes whole-stream effective reaction rates as an integrated effect of spatial patterns of photo-chemical reaction and mixing limitations, and quantified the difference in these rates with and without mixing limitations. The well-mixed assumption holds when the mixing timescale is sufficiently smaller than photo-mineralization timescale. However, mixing limits effective whole-stream photo-mineralization rates when total light attenuation over depth is strong and when the reaction rate is faster than the mixing rate. We applied this analysis to estimate whole-system photo-mineralization of DOC in the Kuparuk River, Alaska. We found that the well-mixed assumption is valid for photo-mineralization of DOC in the main stem of the Kuparuk River, and upscaling of available observations with this assumption yields a total DOC photo-mineralization rate of 1.26×105 mol CO2 day-1. Scaling analysis indicates that photo-mineralization rates in other arctic systems with similar photon attenuation over depth but longer mixing timescales will be limited by hydrodynamic mixing rates.
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