In:
Biogeosciences, Copernicus GmbH, Vol. 20, No. 2 ( 2023-01-24), p. 365-382
Abstract:
Abstract. Across the Arctic, vast areas of permafrost are being degraded by climate
change, which has the potential to release substantial quantities of
nutrients, including nitrogen into large Arctic rivers. These rivers heavily
influence the biogeochemistry of the Arctic Ocean, so it is important to
understand the potential changes to rivers from permafrost degradation. This
study utilized dissolved nitrogen species (nitrate and dissolved organic
nitrogen (DON)) along with nitrogen isotope values (δ15N-NO3- and δ15N-DON) of samples collected
from permafrost sites in the Kolyma River and the six largest Arctic rivers.
Large inputs of DON and nitrate with a unique isotopically heavy δ15N signature were documented in the Kolyma, suggesting the occurrence
of denitrification and highly invigorated nitrogen cycling in the Yedoma
permafrost thaw zones along the Kolyma. We show evidence for permafrost-derived DON being recycled to nitrate as it passes through the river,
transferring the high 15N signature to nitrate. However, the potential
to observe these thaw signals at the mouths of rivers depends on the spatial
scale of thaw sites, permafrost degradation, and recycling mechanisms. In
contrast with the Kolyma, with near 100 % continuous permafrost extent,
the Ob River, draining large areas of discontinuous and sporadic
permafrost, shows large seasonal changes in both nitrate and DON isotopic
signatures. During winter months, water percolating through peat soils
records isotopically heavy denitrification signals in contrast with the
lighter summer values when surface flow dominates. This early year
denitrification signal was present to a degree in the Kolyma, but the ability
to relate seasonal nitrogen signals across Arctic Rivers to permafrost
degradation could not be shown with this study. Other large rivers in the
Arctic show different seasonal nitrogen trends. Based on nitrogen isotope
values, the vast majority of nitrogen fluxes in the Arctic rivers is from
fresh DON sourced from surface runoff through organic-rich topsoil and not
from permafrost degradation. However, with future permafrost thaw, other
Arctic rivers may begin to show nitrogen trends similar to the Ob. Our
study demonstrates that nitrogen inputs from permafrost thaw can be
identified through nitrogen isotopes, but only on small spatial scales.
Overall, nitrogen isotopes show potential for revealing integrated catchment
wide nitrogen cycling processes.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-20-365-2023
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2158181-2
Permalink
