Modelling the terrestrial nitrogen and phosphorus cycle in the UVic ESCM
Nitrogen (N) and phosphorus (P) biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In Earth system models (ESMs) the implementation of nutrient limitations has been shown to improve the carbon cycle feedback representation and, hence, the fidelity of the response...
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Published in | Geoscientific Model Development Vol. 16; no. 14; pp. 4113 - 4136 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
20.07.2023
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | Nitrogen (N) and phosphorus (P) biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In Earth
system models (ESMs) the implementation of nutrient limitations has been shown to improve the carbon cycle feedback representation and, hence,
the fidelity of the response of land to simulated atmospheric CO2 rise. Here we aimed to implement a terrestrial N and
P cycle in an Earth system model of intermediate complexity to improve projections of future CO2 fertilization feedbacks. The
N cycle is an improved version of the Wania et al. (2012) N module, with enforcement of N mass conservation and the merger
with a deep land-surface and wetland module that allows for the estimation of N2O and NO fluxes. The N cycle module
estimates fluxes from three organic (litter, soil organic matter and vegetation) and two inorganic (NH4+ and NO3-) pools and accounts for inputs from biological N fixation and N deposition. The P
cycle module contains the same organic pools with one inorganic P pool; it estimates influx of P from rock weathering and losses from
leaching and occlusion. Two historical simulations are carried out for the different nutrient limitation setups of the model: carbon and nitrogen
(CN), as well as carbon, nitrogen and phosphorus (CNP), with a baseline carbon-only simulation. The improved N cycle module now
conserves mass, and the added fluxes (NO and N2O), along with the N and P pools, are within the range of other studies
and literature. For the years 2001–2015 the nutrient limitation resulted in a reduction of gross primary productivity (GPP) from the carbon-only value of 143 to
130 Pg C yr−1 in the CN version and 127 Pg C yr−1 in the CNP version. This implies that the model
efficiently represents a nutrient limitation over the CO2 fertilization effect. CNP simulation resulted in a reduction of 11 %
of the mean GPP and a reduction of 23 % of the vegetation biomass compared to the baseline C simulation. These results are in better
agreement with observations, particularly in tropical regions where P limitation is known to be important. In summary, the implementation of
the N and P cycle has successfully enforced a nutrient limitation in the terrestrial system, which has now reduced the primary
productivity and the capacity of land to take up atmospheric carbon, better matching observations. |
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ISSN: | 1991-9603 1991-959X 1991-962X 1991-9603 1991-962X |
DOI: | 10.5194/gmd-16-4113-2023 |