Modelling C and N dynamics with MAGIC model from annual to seasonal/monthly time step Filip Oulehle,...
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Modelling C and N dynamics with MAGIC model from annual to seasonal/monthly time step Filip Oulehle, Jack Cosby, Chris Evans, Jakub Hruška, Jiří Kopáček,
Modelling C and N dynamics with MAGIC model from annual to
seasonal/monthly time step Filip Oulehle, Jack Cosby, Chris Evans,
Jakub Hruka, Ji Kopek, Filip Moldan, Dick Wright
Slide 2
Introduction Effective immobilization of deposited nitrogen is
a common feature of most acid sensitive catchments Saturation
hypothesis suggests that N immobilization should decline Nitrate
leaching may become important acidifying component Prediction of
future N immobilization is probably the biggest uncertainty in
acidification/eutrophication modelling
Slide 3
Modelling nitrogen with MAGIC MAGIC (Model for Acidification of
Groundwater In Catchments) -Developed to predict the long-term
effects of acidic deposition on surface water chemistry -Model
simulates soil and surface water chemistry in response to changes
in drivers such as deposition of S and N, land use practices,
climate - As sulphate concentrations have decreased, in response to
the decreased S deposition, nitrate (NO 3 ) has become increasingly
important. In acid soils much of the NO 3 leached from soil is
accompanied by the acid cations H+ and inorganic aluminium (Ali)
-In the early versions of MAGIC (version 1-5) retention of N was
calculated empirically as a fraction of N deposited from
input-output budgets -Later on fraction N retained was described as
a function of the N richness of the ecosystem (soil C/N ratio in
this case) version 7
Slide 4
Soil C/N and N leaching - empirical evidence Some limitations -
Soil C/N is vegetation specific - C/N ratio does not necessarily
reflect the N-richness of the actively cycling component of the
organic matter - C/N ratio does not appear to be useful in
understanding relatively short-term changes in N dynamics - hard to
detect changes in soil C/N under field conditions Soil C/N seems to
be a good predictor of N leaching on a spatial scale Lovett et al.,
Ecosystems (2002) 5: 712-718 Oulehle et al. Ecosystems (2008) 11:
410425
Slide 5
Modelling nitrogen with MAGIC In version 7 of MAGIC model C/N
soil ratio is the fundamental control on N leaching Limitation of
this approach example from ertovo Lake MAGIC v5: N retention
modelled as a first- order function of N deposition. MAGIC v7: N
retention modelled as a function of N richness of the ecosystem Two
shortcomings: 1) Over the short-term large changes in N leaching
cannot be accounted for by changes in the C/N ratio since the C/N
ration of soil organic matter changes only slowly. 2) The C/N ratio
of bulk organic matter is in reality a consequence rather than the
driver of the long-term retention and loss of N from the soil pool.
Oulehle et al. Environmental Pollution (2012) 165: 158166
Slide 6
Modelling nitrogen with MAGIC Alternative formulation of N
retention in new version of MAGIC (MAGIC v7ext) is based directly
on the microbial processes which determine the balance of N
mineralization and immobilization. Conceptually developed by Jack
Cosby - Inorganic N enters the model as deposition (wet and dry) -
Time series of plant litter and N fixation (litter C and N) are
external inputs to SOM. At each time step, decomposers process some
of the C and N content of SOM (FC1 and FN1). A portion of this C
and N turnover returns to the SOM as decomposer biomass (FC2 and
FN2), while the remainder is lost from SOM as CO 2 and NH 4 (FC3
and FN3) or as DOC and DON (FC4 and FN4).
Slide 7
Modelling nitrogen with MAGIC Oulehle et al. Environmental
Pollution (2012) 165: 158166 Constant carbon turnover (FC1) The
simulation can be further improved by including the negative effect
of acidification on turnover of SOM during the period of peak S
deposition rationale well explained in Kopek et al. (2013)
Biogeochemistry 115: 33-51
Slide 8
Modelling nitrogen with MAGIC Summary: The new formulation of C
and N processes in the soil gives a more satisfactorily simulation
of the observed trends in NO3 in water compared to previous
versions of the MAGIC model. The new formulation simulates both
rapid (and amplified) ecosystem responses to changes in deposition
of N, as well as the long-term changes in soil C/N resulting from
chronic N deposition and accumulation in SOM. Limitations: Balanced
C cycle, i.e. a constant soil C pool DOC and DON adjusted to fit
the measured data
Slide 9
Modelling nitrogen with MAGIC Preliminary testing of MAGIC
performance in monthly time step Soil organic matter decomposition
and N uptake driven by changes in soil temperature Q10 fce
(calculated externaly) potential application in climate change
scenario assessment ertovo lake
Slide 10
Modelling nitrogen with MAGIC Seasonal MAGIC applied on four
sites: ertovo lake (CZ) seasonal data available 1998-2010 Gwy
(Cymru) 1980-2010 Storgama (Norway) 1975-2010 Grdsjn NITREX
(Sweden) 1990-2010 DIN annual deposition
Slide 11
Modelling nitrogen with MAGIC The 4 sites are at various stages
in N saturation
Slide 12
Modelling nitrogen with MAGIC ertovo Lake
inletGwyStorgamaGrdsjn Inputs mmol m -2 % of inputmmol m -2 % of
inputmmol m -2 % of inputmmol m -2 % of input N depositon* 139 122
69 338 Outputs N-NO 3 leaching 96693730913226 N-NO 3 leaching
observed100 25 8 19 DON leaching 271924201725227 Denitrification
867671072 Soil accumulation 1184940355131292 * In respect of Grdsjn
= deposition + fertilizer input N saturation ertovo Lake >>
Gwy > Storgama > Grdsjn
Slide 13
Modelling nitrogen with MAGIC
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Summary Despite reasonable model fit of cumulative N leaching
across sites, only ertovo calibration has shown satisfactory fit
between modelled and observed NO 3 dynamic. This might be a result
of uniform Q10 fce used across sites need to try site specific Q10
for decomposition and N uptake Generally overestimation of N
leaching during the winter months in Gwy - lack of proper winter?
Decomposition and N uptake more tightly coupled at this heathland
site? Presented examples pointed out that in ertovo and Storgama
catchments N dynamics behave quite similar, despite different level
of N saturation (in other words Strogama might be fairly sensitive
to N deposition). In respect of Grdsjn, lack of seasonality in NO 3
leaching might be a consequence of artificial fertilizing. Are N
addition experiments able to mimic altered N soil transformations
caused by gradual enrichment through N deposition? Current MAGIC
version is able to reproduce N seasonality as a result of coupled C
and N dynamic Further development should focus on: soil C dynamic
(C sequestration more C soil pools?) feedback between soil acidity
and C decomposition
Slide 18
Linkages between DOC availability and soil heterotrophic
respiration Three mechanisms could lead to lower amount of
bioavailable dissolved organic C (DOC) for the microbial community
(Kopek et al., 2013) (1)Increased abundance of N for plant uptake,
causing lower C allocation to plant roots (2)Chemical suppression
of DOC solubility by soil acidification (3) Enhanced mineralisation
of DOC due to increased abundance of electron acceptors in the form
of sulphate and nitrate - in anoxic soil micro-sites. Week 1Week
2Week 3Week 4 Soil analysis Leachate analysis Treatment addition CO
2 measurements Control H 2 SO 4 HClNaOHNaCl 800 ueq L -1
Slide 19
Linkages between DOC availability and soil heterotrophic
respiration
Slide 20
Solution applications had immediate effect on DOC concentration
in soil water.
Slide 21
Linkages between DOC availability and soil heterotrophic
respiration Solution applications had immediate effect on DOC
concentration in soil water and on soil respiration. In the end of
the experiment, alkaline solution enhanced soil respiration by 20%
compared to control, whereas acid treatment suppressed soil
respiration by 15% compared to control. Neutral treatment has only
short-term effect (suppression) on soil respiration.