High Temporal and Spatial Nitrate Variability on an Alaskan Hillslope Dominated by Alder Shrubs

• Main Authors: McCaully, Rachael E., Arendt, Carli A., Newman, Brent D., Salmon, Verity G., Heikoop, Jeffrey M., Wilson, Cathy J., Sevanto, Sanna, Wales, Nathan A., Perkins, George B., Marina, Oana C., Wullschleger, Stan D.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; permafrost; Seward Peninsula; Tundra; Alaska
• Online Access: https://doi.org/10.5194/tc-2021-166; https://tc.copernicus.org/preprints/tc-2021-166/

In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems is of critical importance, yet many details about the form, location, and availability of N from these shrubs remain unknown. To address this knowledge gap, the spatiotemporal variability of nitrate (NO 3 − ) and its environmental and edaphic controls were investigated at an alder ( Alnus viridis spp. fruticosa ) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and compared to soil pore water collected from locations outside ( upslope, downslope, and between ) the alder shrubland. δ 15 N and δ 18 O of soil pore water were consistent with the predicted range of NO 3 − produced through microbial degradation of N-rich alder shrub organic matter. Soil pore water collected within alder shrubland had an average NO 3 − concentration of (4.27 ± 8.02 mg L −1 ) and differed significantly from locations outside alder shrubland (0.23 ± 0.83 mg L −1 p < 0.05). Temporal variation in NO 3 − within and downslope of alder shrubland corresponded to precipitation events, where NO 3 − accumulated in the soil was flushed downslope during rainfall. Enrichment of both δ 15 N and δ 18 O isotopes at wetter downslope locations indicate that denitrification buffered the mobility and spatial extent of NO 3 − . These findings have important implications for nutrient production and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.