Hydrologic and Landscape Controls on Dissolved Organic Matter Composition Across Western North American Arctic Lakes

Northern high-latitude lakes are hotspots for cycling dissolved organic carbon (DOC) inputs from allochthonous sources to the atmosphere. However, the spatial distribution of lake dissolved organic matter (DOM) is largely unknown across Arctic-boreal regions with respect to the surrounding landscape. We expand on regional studies of northern high-latitude DOM composition by integrating DOC concentrations, optical properties, and molecular-level characterization from lakes spanning the Canadian Taiga to the Alaskan Tundra. Lakes were sampled during the summer from July to early September to capture the growing season. DOM became more optically processed and molecular-level aromaticity increased northward across the Canadian Shield to the southern Arctic and from interior Alaska to the Tundra, suggesting relatively greater DOM incorporation from allochthonous sources. Using water isotopes (d(18)O-H2O), we report a weak overall trend of increasing DOC and decreasing aromaticity in lakes that were hydrologically isolated from the landscape and enriched in d(18)O-H2O, while within-region trends were stronger and varied depending on the landscape. Finally, DOC correlated weakly with chromophoric dissolved organic matter (CDOM) across the study sites, suggesting that autochthonous and photobleached DOM were a major component of the DOC in these regions; however, some of the northernmost and wetland-dominated lakes followed pan-Arctic riverine DOC-CDOM relationships, indicating strong contributions from allochthonous inputs. As many lakes across the North American Arctic are experiencing changes in temperature and precipitation, we expect the proportions of allochthonous and autochthonous DOM to respond with aquatic optical browning with greater landscape connectivity and more internally produced DOM in hydrologically isolated lakes.

Automated summary

Northern high-latitude lakes are important in cycling dissolved organic carbon (DOC) from outside sources to the atmosphere. However, the distribution of dissolved organic matter (DOM) in Arctic-boreal regions is mostly unknown. This study expands on regional studies by investigating the composition of DOM in lakes across the Canadian Taiga to the Alaskan Tundra. The results show that DOM becomes more processed and aromaticity increases towards the north, indicating greater incorporation of DOM from outside sources. Additionally, the study found that hydrologically isolated lakes had different trends in DOC and aromaticity compared to lakes with connectivity to the surrounding landscape.