Photochemical degradation of dissolved organic matter (DOM) to carbon dioxide (CO2) and to partially degraded compounds is an important component of the aquatic carbon cycle in the Arctic. Controls on the photodegradation of DOM remain poorly understood, but recent work suggested that photodegradation of DOM varied consistently by water type in the Arctic. In small streams DOM was mainly mineralized by sunlight to CO2, while in lakes the main fate of DOM was partial photo-degradation. Factors contributing to this pattern may include iron and DOM composition. Analysis of photochemical conversion of DOM to CO2 across several hundred streams, rivers, thaw ponds, and lakes in the Arctic over the past seven summers has revealed that the best predictor for photochemical conversion of DOM to CO2 was high iron (i.e., “red zinger”) vs. low iron waters. Interactions between iron and DOM may enhance photochemical reactions that convert DOM to CO2 in high iron waters. In low iron rivers and lakes, there is evidence of extensive prior processing of DOM by sunlight (i.e., photo-bleaching and photochemical alteration of DOM in these “chamomile” waters). Together, these results suggest that after easily photo-mineralized moieties are removed due to interactions between iron and DOM in headwater streams and ponds, DOM fate shifts toward partial photo-degradation and downstream export in rivers and lakes. Providing a molecular understanding of the controls on DOM degradation across the Arctic landscape is needed to predict how aquatic carbon cycling may change as the Arctic continues to warm.

Watershed tea in arctic lakes: Comparing carbon chemistry and cycling in red zinger vs. chamomile waters

253rd National Meeting (2017)

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