Abstract

Abstract. The Kolyma River in northeast Siberia is among the six largest Arctic rivers and drains a region underlain by vast deposits of Holocene-aged peat and Pleistocene-aged loess known as yedoma, most of which is currently stored in ice-rich permafrost throughout the region. These peat and yedoma deposits are important sources of dissolved organic matter (DOM) to inland waters that in turn play a significant role in the transport and ultimate remineralization of organic carbon to CO2 and CH4 along the terrestrial flow-path continuum. The turnover and fate of terrigenous DOM during offshore transport largely depends upon the composition and amount of carbon released to inland and coastal waters. Here, we measured the ultraviolet-visible optical properties of chromophoric DOM (CDOM) from a geographically extensive collection of waters spanning soil pore waters, streams, rivers, and the Kolyma River mainstem throughout a ∼ 250 km transect of the northern Kolyma River basin. During the period of study, CDOM absorption coefficients were found to be robust proxies for the concentration of DOM, whereas additional CDOM parameters such as spectral slopes (S) were found to be useful indicators of DOM quality along the flow path. In particular, the spectral slope ratio (SR) of CDOM demonstrated statistically significant differences between all four water types and tracked changes in the concentration of bioavailable DOC, suggesting that this parameter may be suitable for clearly discriminating shifts in organic matter characteristics among water types along the full flow-path continuum across this landscape. However, despite our observations of downstream shifts in DOM composition, we found a relatively constant proportion of DOC that was bioavailable ( ∼ 3–6 % of total DOC) regardless of relative water residence time along the flow path. This may be a consequence of two potential scenarios allowing for continual processing of organic material within the system, namely (a) aquatic microorganisms are acclimating to a downstream shift in DOM composition and/or (b) photodegradation is continually generating labile DOM for continued microbial processing of DOM along the flow-path continuum. Without such processes, we would otherwise expect to see a declining fraction of bioavailable DOC downstream with increasing residence time of water in the system. With ongoing and future permafrost degradation, peat and yedoma deposits throughout the northeast Siberian region will become more hydrologically active, providing greater amounts of DOM to fluvial networks and ultimately to the Arctic Ocean. The ability to rapidly and comprehensively monitor shifts in the quantity and quality of DOM across the landscape is therefore critical for understanding potential future feedbacks within the Arctic carbon cycle.

Highlights

  • There is increasing evidence that inland freshwater ecosystems play a significant role in the global carbon cycle owing to the metabolism of terrestrially derived organic matter as it moves through fluvial networks from land to ocean (Cole et al, 2007; Battin et al, 2009a, b)

  • A variety of conceptual and pragmatic issues complicate the study of Arctic rivers, including: (i) large seasonal variations in discharge accompanied by large seasonal variations in nutrient and organic matter inputs from rivers to the coastal ocean (e.g., McClelland et al, 2012); (ii) the heterogeneity of vegetation, permafrost extent, topography, and soil attributes within Arctic watersheds (e.g., Frey and McClelland, 2009); and (iii) spatial and temporal inaccessibility hindering comprehensive sampling; among others

  • We present a full suite of dissolved organic carbon (DOC), bioavailable DOC, and chromophoric DOM (CDOM) parameters throughout the permafrostdominated Kolyma River basin in northeast Siberia with the purpose of helping to elucidate the processing of dissolved organic matter (DOM) along a full flow-path continuum from soil pore waters to the mainstem

Read more

Summary

Introduction

There is increasing evidence that inland freshwater ecosystems play a significant role in the global carbon cycle owing to the metabolism of terrestrially derived organic matter as it moves through fluvial networks from land to ocean (Cole et al, 2007; Battin et al, 2009a, b). Selective processing and loss of permafrostderived DOM has been shown to occur via microbial metabolism throughout the Kolyma River basin, as waters move downstream through the fluvial network (Mann et al, 2014, 2015; Spencer et al, 2015). We complement these previous studies by providing extensive spatial characterization of DOM along a flow-path continuum from soil pore waters to the Kolyma River mainstem during midsummer (July) baseflow. We explore a full suite of CDOM parameters as well as concentrations of dissolved organic carbon (DOC) and bioavailable DOC as they vary across a full flow-path continuum in the Kolyma River basin in northeast Siberia

Data and methods
Results
Discussion and conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call