Origin-specific molecular signatures of dissolved organic matter in the Lena Delta

Abstract

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 ± 75 lmol C L-1 for riverine and bay samples and 399 ± 115 lmol C L-1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 ± 7.1 lmol N L-1) in comparison to the river and the bay (both 13.2 ± 2.6 lmol 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 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.

From Fresh to Marine Waters: Characterization and Fate of Dissolved Organic Matter in the Lena River Delta Region, Siberia

“…Both CDOM and DOC were highly correlated, displaying a similar relationship as found for the coastal Canadian Arctic (Walker et al, 2009; see Figure 2), although with a higher a 350 relative to DOC in the Lena delta waters. The presented values are comparable to other studies previously conducted in this region, with a 350 (a 440 ) values of about 15 m −1 (2.9 m −1 ) at low salinity and DOC concentrations ranging from 500-700 to 100 µM at low and high salinity, respectively (Alling et al, 2010;Stedmon et al, 2011;Semiletov et al, 2013;Walker et al, 2013;Heim et al, 2014;Dubinenkov et al, 2015a).…”

“…Subsequently, with an enhanced input of DOM (especially CDOM) into the Arctic Ocean, changes in the radiant heating in the upper meters of the ocean as well as a possible increase in the sea-ice melt rates might be foreseen (Granskog et al, 2015). Furthermore, the characteristics of DOM have been shown to be a powerful proxy for tracing organic substances with permafrost origin O'Donnell et al, 2014;Dubinenkov et al, 2015a). Moreover, long-term studies concerning the quantification, composition and dynamics of DOM, from fresh to marine waters in the main rivers flowing into the Arctic Ocean, are needed to improve the understanding of DOM dynamics, its role in the carbon cycle pathways.…”

“…The Lena Delta region and Laptev Sea have high DOC concentrations (>500 µM) and high CDOM associated with low salinity waters (Alling et al, 2010;Stedmon et al, 2011;Semiletov et al, 2013;Walker et al, 2013;Heim et al, 2014;Dubinenkov et al, 2015a), decreasing toward higher salinities through conservative mixing (Cauwet and Sidorov, 1996;Kattner et al, 1999). This is a characteristic also thought to be shared by other Arctic rivers (Dittmar and Kattner, 2003).…”

Chemical composition of dissolved organic matter draining permafrost soils

“…4, 5, 6, and 7). These differences in DOM composition between organic mat and permafrost soil layers were consistent with previous observations in arctic (Mann et al, 2012;Cory et al, 2013;Hodgkins et al, 2014;Spencer et al, 2015;Dubinenkov et al, 2015) and subarctic soils (e.g., Kaiser et al, 1997;Cory et al, 2004;D'Andrilli et al, 2010;Tfaily et al, 2013). For instance, Cory et al (2013) used optical proxies to show that organic mat DOM contained higher aromatic C and higher average molecular weight compared to permafrost DOM.…”

“…Furthermore, multiple studies have suggested that bacterial growth rates and efficiencies are inversely correlated to the average oxidation state of DOM (Meyer, 1994;Vallino et al, 1996;Sun et al, 1997). Given that aromatic C, molecular weight, and oxidation state of DOM have been reported to differ between permafrost and organic mat DOM in arctic soil waters (Hodgkins et al, 2014;Spencer et al, 2015;Dubinenkov et al, 2015), a more detailed view of DOM chemical composition is needed to identify the organic compounds that govern the susceptibility of DOM to aquatic bacterial degradation.…”