Slope hydrology and permafrost: The effect of snowmelt N transport on downslope ecosystem
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In the permafrost-affected landscape, surface and near-surface water
movement links areas of higher elevation with lowlands and surface water
bodies. Water supply is dominated by snow melt and is thus highly
seasonal, as most water moves on the frozen surface in spring, passing
only a thin layer of thawed soil. Soluble nutrients mobilized by soil
thaw may thus be transported laterally from upslope to downslope
ecosystems, which in nutrient-limited cold ecosystems may affect
vegetation, ecosystem respiration and surface-atmosphere interaction. In
a nitrogen (N) limited ecosystem, however, released inorganic N may in
reality not travel far downslope. This study quantifies the potential
effect of the snowmelt water nutrient transport by tracing dissolved N
in meltwater moving downslope on the frozen surface in a W Greenlandic
slope with a snow fan supplying meltwater throughout most of the summer.
We use the stable isotopes 15N and D applied simultaneously on top of
the frozen surface upslope in a combined solution to investigate the
behavior of water and dissolved N flow patterns. We further address the
effect of season by tracing N supplied in the early thaw season (30 cm
to the frozen surface) and in the late thaw season (90 cm to the frozen
surface). Monitoring the slope in detail, we then use the numerical
coupled heat-and-mass transfer Coup model to simulate the biotics and
abiotics of the receiving ecosystem and study the importance of the
lateral N input and the effect of increased N transport in a warmer
future. About 50 % of the N tracer was retained in the ecosystem
immediately below injection in the early growing season (30 cm active
layer), whereas about 35 % was retained in the later growing season (90
cm active layer). Most of the applied 15N was rapidly immobilized by
microbes and into the bulk soil, whereas only a few percentages was
taken up by the vegetation. D recovery seemed to follow the pattern of
microbial N uptake, suggesting that N and D moved physically from the
frozen surface and to the immediate subsoil together.Modelling the
ecosystem based on measured N and C pool sizes, meteorology, soil
temperature and -moisture revealed a large N constrain on vegetation
growth. The current observed vegetation could not be explained with the
measured pools alone, suggesting an "invisible" source of N to support
the observed vegetation. We conclude that a substantial fraction of
lateral N input is transported further downslope, but that increases in
N release and transport might not affect vegetation immediately, as most
supplied N ends in the soil pool. Vegetation in the receiving ecosystem
relies on an external N source, which could be dissolved N transported
by snowmelt water on the frozen surface. Snowmelt redistribution of N in
the landscape may thus be a factor to account for when studying N
cycling in a spatial context.
Originalsprog | Engelsk |
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Publikationsdato | 1 maj 2020 |
Antal sider | 2 |
DOI | |
Status | Udgivet - 1 maj 2020 |
Begivenhed | EGU General Assembly 2020: Online - Online Varighed: 4 maj 2020 → 8 maj 2020 https://www.egu2020.eu/ |
Konference
Konference | EGU General Assembly 2020 |
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Lokation | Online |
Periode | 04/05/2020 → 08/05/2020 |
Internetadresse |
ID: 287005360