Variations in high‐latitude riverine fluorescent dissolved organic matter: A comparison of large Arctic rivers

Abstract

[1] Given the pace of climate change, it is important to better understand dissolved organic matter (DOM) storage and cycling in high-latitude rivers and its subsequent export to the Arctic Ocean. To address this concern, excitation/emission matrix spectroscopy and parallel factor analysis (PARAFAC) coupled with optical indices were used to characterize the optical properties of fluorescent DOM (FDOM) and colored DOM (CDOM) in five large Arctic rivers over two seasonal cycles. Five PARAFAC components were identified and proved useful indicators for the quantitative and qualitative descriptions of DOM sources and modification processes within Arctic watersheds. In comparing Pan-Arctic relationships between the optical properties and chemical properties of DOM, three components traced terrigenous biomarkers and two components are introduced as potential indicators for microbial processing. Conversely, no individual PARAFAC component could be directly linked to a specific plant source or river and simpler absorbance indices (i.e., a 350 ) proved to be better suited to quantify dissolved organic carbon and lignin phenol concentrations. Differences in FDOM character between the rivers could be explained by general watershed characteristics, including vegetation, topography, and hydrology. Based on these differences, the influence of coniferous vegetation on DOM character is most apparent in the Lena and Yenisei Rivers and bog-derived FDOM sources are more important in the Ob River. This study illustrates how increased hydrological connectivity in the Ob catchment and the abundance of lakes within the Mackenzie watershed may influence FDOM concentrations and the microbial processing of DOM within these watersheds.

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

“…with earlier results (Spencer et al, 2009;Stedmon et al, 2011;Walker et al, 2013). The raw EEMs acquired with Aqualog R were corrected for inner-filter effects and for the Raman and Rayleigh scattering (Murphy et al, 2013).…”

“…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).…”

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

“…The riverine input can be monitored by optical methods with absorption, fluorescence, or remote-sensing measurements (Spencer et al, 2012;Walker et al, 2013;Fichot et al, 2013;Mann et al, 2016). The largest DOC concentrations were found in the Siberian rivers Lena -1300 µmol L −1 , Yenisey -842 µmol L −1 , and Ob -950 µmol L −1 , and the concentrations were lower in the North American Yukon -816 µmol L −1 and McKenzie -648 µmol L −1 rivers Mann et al, 2016).…”

Trends in Levels of Allochthonous Dissolved Organic Carbon in Natural Water: A Review of Potential Mechanisms under a Changing Climate

“…In the spring and summer seasons, DOC found in rivers shows signs of more terrestrial inputs (i.e., increased lignin phenols) [159], suggesting a more connected landscape where water carries solutes from all regions of a watershed. Further, the IPCC has predicted that runoff resulting from the thawing of permafrost in the arctic and subarctic areas and subsequent formation of new ponds and lakes will increase the availability of stored carbon stocks [121] through increased hydrologic connectivity [160]. As permafrost thaws, the hydrologic connectivity of arctic and subarctic regions will increase, resulting in greater export of allochthonous DOC to fluvial networks, and ultimately, to the ocean.…”

“…Likewise, phenolic portions of humic acids from the International Humic Substance Society (IHSS) were identified with fluorescence/PARAFAC and reagent-based phenol assays [53] and lignin phenols found in several large artic rivers have been attributed to a PARAFAC-derived component [160]. In kinetic studies of THM formation upon chlorination of natural waters, it was shown that resorcinol components make up 15%-30% of THM precursors in natural water and are likely fast reacting (formed within first hours) THM precursors [4], while other phenolic compounds are likely slow reacting (from hours to weeks) THM precursors [4].…”