Physiographic Controls and Wildfire Effects on Aquatic Biogeochemistry in Tundra of the Yukon-Kuskokwim Delta, Alaska

Zolkos, Scott, MacDonald, Erin, Hung, John D., Ludwig, Sarah, Mann, Paul, Treharne, Rachael and Natali, Susan (2022) Physiographic Controls and Wildfire Effects on Aquatic Biogeochemistry in Tundra of the Yukon-Kuskokwim Delta, Alaska. Journal of Geophysical Research: Biogeosciences, 127 (8). e2022JG006891. ISSN 2169-8953

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Northern high-latitude deltas are hotspots of biogeochemical processing, terrestrial-aquatic connectivity, and, in Alaska’s Yukon-Kuskokwim Delta (YKD), tundra wildfire. Yet, wildfire effects on aquatic biogeochemistry remain understudied in northern delta regions, thus limiting a more comprehensive understanding of high latitude biogeochemical cycles. In this study, we assess wildfire impacts on summertime aquatic biogeochemistry in YKD tundra using a multi year (2015–2019) dataset of water chemistry measurements (n = 406) from five aquatic environments: peat plateau ponds, fen ponds, fen channels, lakes, and streams. We aimed to (i) characterize variation in hydrochemistry among aquatic environments; (ii) determine wildfire effects on hydrochemistry; and (iii) assess post-fire multi-year patterns in hydrochemistry in lakes (lower terrestrial-freshwater connectivity) and fen ponds (higher connectivity). Variation in hydrochemistry among environments was more strongly associated with watershed characteristics (e.g., terrestrial-aquatic connectivity) than wildfire. However, certain hydrochemical constituents showed consistent wildfire effects. Decreases in dissolved organic carbon (DOC) and CO2, and increases in pH, specific conductance, NH4 +, and NO3– indicate that, by combusting soil organic matter, wildfire reduces organics available for hydrologic transport and microbial respiration, and mobilizes nitrogen into freshwaters. Multi-year post-fire variation in specific conductance, DOC, and CO2 in lakes and fen ponds suggest that watershed characteristics underlie ecosystem response and recovery to wildfire in the YKD. Together, these results indicate that increasing tundra wildfire occurrence at northern high latitudes could drive multi-year shifts toward stronger aquatic inorganic nutrient cycling, and that variation in terrain characteristics is likely to underlie wildfire effects on aquatic ecosystems across broader scales.

Item Type: Article
Additional Information: Funding information: We acknowledge and are grateful for the opportunity to conduct research on traditional lands of the Yup'ik, who have stewarded this land for generations. This study was supported by National Science Foundation grants (NSF 1915307, 1624927 to S.M.N., P.M., J.D.S.; 1561437 to S.M.N. and J.D.S) and the Gordon and Betty Moore Foundation (#8414 to S.M.N.).
Subjects: F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: Rachel Branson
Date Deposited: 05 Jul 2022 14:46
Last Modified: 10 Feb 2023 03:30

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