The standard model for aquatic ecosystems is to link hydrologic connectivity to dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition and, ultimately, reactivity. Studies across effective precipitation gradients have been suggested as models for predicting how carbon cycling will change in Arctic aquatic ecosystems with projected drying (i.e., reduced hydrologic connectivity). To evaluate links between DOM dynamics and hydrologic connectivity, 41 stream samples from Greenland were analyzed across an effective precipitation gradient for DOM optical properties and elemental composition using ultrahigh‐resolution mass spectrometry. Sites with negative effective precipitation and decreased hydrologic connectivity exhibited elevated specific conductivity (SpC) and DOC concentrations as well as DOM composition indicative of decreased hydrologic connectivity, for example, lower aromaticity, assessed using carbon‐specific UV absorbance at 254 nm, decreased relative abundances of polyphenolic and condensed aromatic compounds, and increased relative abundances of highly unsaturated and phenolic compounds. Allochthonous inputs decreased as the summer progressed as exhibited by decreases in aromatic compounds. A decrease in molecular richness and N‐containing compounds coincided with the decrease in allochthonous inputs. DOC concentrations increased over the summer but more slowly than SpC, suggesting degradation processes outweighed combined evapoconcentration and production. The patterns in DOM composition suggest evapoconcentration and photodegradation are dominant controls. However, when hydrologic connectivity was high, regardless of effective precipitation, DOM reflected allochthonous sources such as snowmelt‐fed wetlands. These results highlight the challenges of modeling carbon cycling in aquatic ecosystems across effective precipitation gradients, particularly those with strong seasonality and regional variability in hydrologic inputs.
Arctic lakes store, modify, and transport large quantities of carbon from terrestrial environments to the atmosphere; however, the spatial and temporal relationships between quantity and composition of dissolved organic matter (DOM) have not been well characterized across broad arctic regions. Moreover, most arctic lake DOM compositions have been examined during the ice‐free summer, whereas DOM cycling between the ice‐covered winter months and summer have not been addressed. To resolve these spatial and seasonal uncertainties in DOM cycling, we sampled a series of arctic lakes from the North Slope of Alaska across a latitudinal gradient in the winter and summer over 3 years. Samples were analyzed for dissolved organic carbon concentration and DOM composition was characterized using optical and fluorescence properties combined with molecular‐level analysis using Fourier transform‐ion cyclotron resonance mass spectrometry. Tundra lake DOM properties including aromaticity and molecular stoichiometries were similar to other northern high‐latitude lakes, but optical parameters related to aromaticity and molecular weight were greater in major arctic rivers and in coastal lakes in the North Slope region. DOM composition was highly seasonal, with ice exclusion concentrating microbially processed DOM in the winter water columns, potentially influencing DOM cycling the following summer. However, the greatest variations in DOM composition were related to lake depth and likely other physical features including morphology and bathymetry. As the Arctic warms, we expect changes in hydrology and ice cover to enhance under‐ice microbial DOM processing, early summer photodegradation, and ultimately carbon fluxes to the atmosphere after ice‐out.
more » « less- PAR ID:
- 10367721
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 127
- Issue:
- 4
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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