Journal
BIOGEOCHEMISTRY
Volume 123, Issue 1-2, Pages 1-14Publisher
SPRINGER
DOI: 10.1007/s10533-014-0049-0
Keywords
Arctic; Lena Delta; Permafrost; DOM; FT-ICR MS; Molecular markers
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Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490 +/- A 75 A mu mol C L-1 for riverine and bay samples and 399 +/- A 115 A mu mol C L-1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 +/- A 7.1 A mu mol N L-1) in comparison to the river and the bay (both 13.2 +/- A 2.6 A mu mol N L-1). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/C-wa, H/C-wa, C/N-wa) highlighted preliminary sample discrimination. The highest H/C-wa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/C-wa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/N-wa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers.
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