Dissolved and Particulate Organic Carbon in Icelandic Proglacial Streams: A First Estimate

Abstract

Here for the first time, we analyze the concentration of dissolved (DOC) and particulate organic carbon (POC), as well as its optical properties (absorbance and fluorescence) from several proglacial streams across Iceland, the location of Europe’s largest non-polar ice cap. We found high spatial variability of DOC concentrations and dissolved organic matter (DOM) composition during peak melt, sampling 13 proglacial streams draining the 5 main Icelandic glaciers. Although glacial-derived organic matter (OM) was dominated by proteinaceous florescence, organic matter composition was variable among glaciers, often exhibiting relatively higher aromatic content and increased humification (based on absorbance and fluorescence measurements) closer to the glacier terminus, modulated by the presence of glacial lakes. Additional sampling locations the in flow path of the river Hvitá revealed that while POC concentrations decreased downstream, DOC concentrations and the autochthonous fraction of OM increased, suggesting the reworking of the organic carbon by microbial communities, with likely implications for downstream ecosystems as glaciers continue to melt. Based on our measured DOC concentrations ranging from 0.11 mg·L−1 to 0.94 mg·L−1, we estimate a potential annual carbon release of 0.008 ± 0.002 Tg·C·yr−1 from Icelandic glaciers. This non-conservative first estimate serves to highlight the potentially significant contribution of Icelandic pro-glacial streams to the global carbon cycle and the need for the quantification and determination of the spatio-temporal variation of DOC and POC fluxes and their respective drivers, particularly in light of increased rates of melting due to recent trends in climatic warming.

The evolution of stream dissolved organic matter composition following glacier retreat in coastal watersheds of southeast Alaska

“…Typically, glacier DOM is associated with low SUVA254 (1.77 ± 1.16 L mg C -1 m -1 , n = 5) and high FI values (1.52 ± 0.09, n =11; Fegel et al 2016;Fellman et al 2014;Stubbins et al 2012). Similarly, parallel factor analysis of glacier DOM has shown that protein-like fluorophores dominate (typically > 70 %) total fluorescence (Chifflard et al 2019;Hood et al 2009;Kellerman et al 2020;Pautler et al 2012;Smith et al 2018;Stubbins et al 2012;Zhou et al 2019b). The broad shifts in optical and isotopic DOM properties, together with streamwater  O, likely reflected shifting sources of DOM and streamwater with time since glacier retreat.…”

Glacial Water: A Dynamic Microbial Medium

“…Nitrogen was also observed to decline in downstream glacial lakes in North America [ 199 ]. However, DOC increased during its flow in proglacial streams in Iceland, probably due to carbon mineralization and microbial transformation [ 212 ]. These contrasting results show how the processes in the proglacial streams are regulated by many local factors.…”

The influence of land cover, including Nootka lupin, on organic carbon exports in east Icelandic rivers

“…DOC and POC fluxes from a drained peatland in west Iceland (Borgarfjörður region) were quantified at 11.65 (± 1.98) and 9.57 (± 6.21) g m -2 yr -1 , making up 2.82 and 2.31% of the local carbon budget, respectively (Ólafsdóttir, 2015). In 13 proglacial streams in central and southwest Iceland DOC concentrations ranged from 0.11 to 0.94 (mean: 0.226) mg L -1 and POC concentrations ranged between 0.67 and 84.67 (mean: 0.37) mg L -1 (high POC concentrations were linked to high anthropogenic influences), resulting in an estimated DOC flux of 0.008 ± 0.002 Tg yr -1 from Icelandic glaciers (Chifflard et al, 2019). Kardjilov et al (2006) quantified fluvial organic carbon fluxes from three large inland catchments in NE Iceland, where DOC (0.23-0.30 g C m -2 yr -1 ) and POC (0.23-0.44 g C m -2 yr -1 ) fluxes were relatively low and close to detection limits.…”