Environmental controls on observed spatial variability of soil pore water geochemistry in small headwater catchments underlain with permafrost

• Published in: The Cryosphere
• Main Authors: Conroy, Nathan Alec, Heikoop, Jeffrey M., Lathrop, Emma, Musa, Dea, Newman, Brent D., Xu, Chonggang, McCaully, Rachael E., Arendt, Carli A., Salmon, Verity G., Breen, Amy, Romanovsky, Vladimir, Bennett, Katrina E., Wilson, Cathy J., Wullschleger, Stan D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Arctic; permafrost; Seward Peninsula; The Cryosphere; Alaska
• Online Access: https://doi.org/10.5194/tc-17-3987-2023; https://noa.gwlb.de/receive/cop_mods_00068846; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00067258/tc-17-3987-2023.pdf; https://tc.copernicus.org/articles/17/3987/2023/tc-17-3987-2023.pdf

Soil pore water (SPW) chemistry can vary substantially across multiple scales in Arctic permafrost landscapes. The magnitude of these variations and their relationship to scale are critical considerations for understanding current controls on geochemical cycling and for predicting future changes. These aspects are especially important for Arctic change modeling where accurate representation of sub-grid variability may be necessary to predict watershed-scale behaviors. Our research goal is to characterize intra- and inter-watershed soil water geochemical variations at two contrasting locations in the Seward Peninsula of Alaska, USA. We then attempt to identify the key factors controlling concentrations of important pore water solutes in these systems. The SPW geochemistry of 18 locations spanning two small Arctic catchments was examined for spatial variability and its dominant environmental controls. The primary environmental controls considered were vegetation, soil moisture and/or redox condition, water–soil interactions and hydrologic transport, and mineral solubility. The sampling locations varied in terms of vegetation type and canopy height, presence or absence of near-surface permafrost, soil moisture, and hillslope position. Vegetation was found to have a significant impact on SPW NO 3- concentrations, associated with the localized presence of nitrogen-fixing alders and mineralization and nitrification of leaf litter from tall willow shrubs. The elevated NO 3- concentrations were, however, frequently equipoised by increased microbial denitrification in regions with sufficient moisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. The redox conditions in both catchments were generally limited by Fe reduction, seemingly well-buffered by a cache of amorphous Fe hydroxides, with the most reducing conditions found at sampling locations with the highest soil moisture content. Non-redox-sensitive cations were affected by a ...