Spatial Distribution of Bioavailable Inorganic Nitrogen From Thawing Permafrost

• Published in: Global Biogeochemical Cycles
• Main Authors: Hansen, Hans Frederik Engvej, Elberling, Bo
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: ammonium; Arctic; bioavailable nitrogen; permafrost; Ice; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/spatial-distribution-of-bioavailable-inorganic-nitrogen-from-thawing-permafrost(58ecaf9d-fa94-494d-907b-b5582fed285f).html; https://doi.org/10.1029/2022GB007589; https://curis.ku.dk/ws/files/340881172/Spatial_Distribution_of_Bioavailable_Inorganic_Nitrogen_From_Thawing_Permafrost.pdf

Arctic permafrost contains large amounts of nitrogen (N), which may be bioavailable upon permafrost thaw. Here, we have compiled inorganic N data from published studies on the active layer and permafrost layers combined with new data to quantify the spatial variability of bioavailable inorganic N in permafrost-affected ecosystems across the Northern Hemisphere. Ammonium (NH 4 + ) and nitrate (NO 3 − ) are typically extracted from samples using different agents and strength. The results of an extraction experiment are here used to recalculate published concentrations on NH 4 + and NO 3 − to a “water extractable fraction.” The results show that upper permafrost across all sites and samples contains significantly more NH 4 + compared to the root zone and was significantly and positively correlated with an increasing water/ice content despite a surprisingly high variation within and between sites. Based on the average reported permafrost thaw rates (0.4–0.8 cm y −1 ) for wet and dry landscape types, the average release of inorganic N (NH 4 + and NO 3 − ) from wet tundra ecosystems was calculated to be 2.0 [1.13–2.61] kg N ha −1 decade −1 and 1.3 [0.78–1.81] kg N ha −1 decade −1 for dry ecosystems. This brings permafrost-derived inorganic N on the same order of magnitude as biological nitrogen fixation in relatively dry tundra ecosystems but only marginally compared to nitrogen fixation in wet ecosystems. These landscape-specific variations highlight the need for improving the understanding of N mobilization linked to permafrost thawing, but also that N transfer from well-drained slopes to lower parts of the landscape can be important for the potential plant growth (greening) downslope from surrounding landscape types with faster permafrost thawing.