Dynamics of photochemical and microbial processing of newly exposed terrestrial DOM in arctic surface waters (Invited)
Abstract
Surface freshwaters act as conduits of terrestrially derived carbon to the atmosphere, and are susceptible to climate change impacts on the water and carbon cycles. For example, climate change in the Arctic is causing melting permafrost, thermokarst failures, and increased fire, all of which will release previously frozen or buried carbon to surface waters as dissolved organic matter (DOM). As previously-frozen DOM is released into relatively warm sunlit surface waters, photodegradation is expected to enhance the rates of DOM processing by bacteria. This close-coupled synergism between photo and bio-oxidation of the DOM is likely particularly important in the Arctic where photochemical interactions abound in the shallow, unshaded streams that transport DOM across the landscape. To test this, we manipulated the UV light exposure of freshly exposed DOM and measured the responses in bacterial production and respiration and characterized the DOM with parallel factor analysis (PARAFAC) of fluorescence spectra. Exposure to light significantly enhanced bacterial processing of DOM, and the magnitude of the positive response was greater for recently exposed DOM compared to resident surface water DOM. These results suggest that turnover rates of newly released DOM depend on water residence time in sunlit surface waters. However, how water movement from soils to small streams and lakes controls the coupled photo- and bio-degradation of DOM is too poorly known to predict the fate of DOM, either to the atmosphere as CO2 or to the ocean as altered, recalcitrant carbon. As a first step in evaluating these hydro-bio-photo linkages and controls, we used DOM fluorescence as a proxy to trace the source and estimate the lability of the DOM in natural and thermokarst-disturbed environments. Results showed that the chemistry and reactivity of DOM was altered by both light exposure (as expected) and also by microbial processing even over short time periods similar to water residence times in streams, which was unexpected. We propose that this substantial and rapid processing of DOM by both light and microbes is related to the chemical nature of the newly exposed soil carbon, and will have important implications for the fate of carbon in a warming world. Thermokarst gully slump releases previously frozen carbon to surface waters
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B11I..07C
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0428 BIOGEOSCIENCES / Carbon cycling