Identifying Drivers of Seasonality in Lena River Biogeochemistry and Dissolved Organic Matter Fluxes.

Juhls, Bennet, Stedmon, Colin A., Morgenstern, Anne, Meyer, Hanno, Hölemann, Jens, Heim, Birgit, Povazhnyi, Vasily and Overduin, Pier P. (2020) Identifying Drivers of Seasonality in Lena River Biogeochemistry and Dissolved Organic Matter Fluxes. Open Access Frontiers in Environmental Science, 8 . Art.Nr. 53 . DOI 10.3389/fenvs.2020.00053.

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Abstract

Warming air temperatures, shifting hydrological regimes and accelerating permafrost thaw in the catchments of the Arctic rivers is affecting their biogeochemistry. Arctic river monitoring is necessary to observe changes in the mobilization of dissolved organic matter (DOM) from permafrost. The Lena River is the second largest Arctic river and 71% of its catchment is continuous permafrost. Biogeochemical parameters, including temperature, electrical conductivity (EC), stable water isotopes, dissolved organic carbon (DOC) and absorption by colored dissolved organic matter (aCDOM) have been measured as part of a new high-frequency sampling program in the central Lena River Delta. The results show strong seasonal variations of all biogeochemical parameters that generally follow seasonal patterns of the hydrograph. Optical indices of DOM indicate a trend of decreasing aromaticity and molecular weight from spring to winter. High-frequency sampling improved our estimated annual fluvial flux of annual dissolved organic carbon flux (6.79 Tg C). EC and stable isotope data were used to distinguish three different source water types which explain most of the seasonal variation in the biogeochemistry of the Lena River. These water types match signatures of (1) melt water, (2) rain water, and (3) subsurface water. Melt water and rain water accounted for 84% of the discharge flux and 86% of the DOC flux. The optical properties of melt water DOM were characteristic of fresh organic matter. In contrast, the optical properties of DOM in subsurface water revealed lower aromaticity and lower molecular weights, which indicate a shift toward an older organic matter source mobilized from deeper soil horizons or permafrost deposits. The first year of this new sampling program sets a new baseline for flux calculations of dissolved matter and has enabled the identification and characterization of water types that drive the seasonality of the Lena River water properties.

Document Type: Article
Keywords: Lena River, Arctic, DOC, CDOM, optical indices, stable water isotopes
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.3389/fenvs.2020.00053
ISSN: 2296-665X
Projects: CATS
Date Deposited: 03 Jan 2021 19:51
Last Modified: 08 Jan 2021 11:02
URI: http://oceanrep.geomar.de/id/eprint/51341

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