『Abstract
In many modelling studies on N cycling, denitrification is considered
by a simplified process model. A widely used model describes denitrification
as potential denitrification reduced by the soil conditions nitrate
N content (N), degree of water saturation (S) and temperature
(T). Henault(eの頭に´) and Germon, 2000 [Henault(eの頭に´)C. and Germon,J.C., 2000. NEMIS, a predictive
model of denitrification on the field scale. Eur. J. Soil Sci.,
51: 257-270.] showed that this model worked satisfactorily for
two data sets where parameters had been specifically derived for
these data sets. This paper demonstrates that it may not always
work well for other data, i.e., Dutch data sets. The model was
parameterized for each of eight Dutch data sets, consisting of
three sand, two heavy loam and three peat sites. After parameter
optimisation the model is not able to predict individually measured
actual denitrification rates. However, for sand and loam soils,
but not for peat soils, the correspondence between measured and
predicted average actual denitrification is good. This means that
the calibrated model can predict, for those specific locations,
cumulative denitrification rather well, provided that detailed
information on soil conditions is available, either from measurements
or from simulation models. The parameters and thus the reduction
functions differed between the data sets. Parameter values within
a class of soils, say sand, loam, and peat, were different. So
care should be taken when using parameter values obtained from
other studies. Albeit simple in its mathematical formulation,
a widely used simplified denitrification process model needs to
be parameterized for each location.
The parameter optimisation is likely to be influenced by errors
in the data. Therefore, an analysis on the effect of errors is
presented based on an artificial data set. This data set was constructed
consisting of 100 realisations of the soil conditions N, S and
T, each drawn from a (long-) normal distribution based on the
mineral Dutch data sets. For each realisation the relative denitrification
rate (Dr) was computed based on a ‘true’
set of parameters. Next, measurement errors were introduced on
Dr, N, S and T, either from a uniform or
a normal distribution. For each of the 100 data sets the data
were perturbed 100 times with newly drawn measurement errors.
The perturbed data sets (10,000) were then optimised by the model.
The coefficients of variation belonging to the estimates were
large. This exercise can only be used to demonstrate possible
directions of effects from errors, but it cannot be used to fully
judge results obtained from real data sets.
Keywords: Actual denitrification; Parameter identification; Potential
denitrification; Reduction functions』
1. Introduction
2. Materials and methods
2.1. Parameter identification
2.2. Effect of measurement errors
3. Results and discussion
3.1. Parameter optimisation for real data sets
3.2. Parameter optimisation for artificial data set
4. Summary and conclusions
Acknowledgements
Appendix A. Stoichiometry factor between potential denitrification
and carbon decay rate
Appendix B. Estimate of measurement error in S
References