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To what extent can soil moisture and soil Cu contamination stresses affect nitrous species emissions? Estimation through calibration of a nitrification–denitrification model

Abstract. Continental biogeochemical models are commonly used to predict the effect of land use, exogenous organic matter input or climate change on soil
greenhouse gas emission. However, they cannot be used for this purpose to investigate the effect of soil contamination, while contamination affects
several soil processes and concerns a large fraction of land surface. For that, in this study we implemented a commonly used model estimating soil
nitrogen (N) emissions, the DeNitrification DeCompostion (DNDC) model, with a function taking into account soil copper (Cu)
contamination in nitrate production control. Then, we aimed at using this model to predict N2O-N,
NO2-N, NO-N and NH4-N emissions in the presence of contamination and in
the context of changes in precipitations. Initial incubations of soils were performed at different soil moisture levels in order to mimic expected
rainfall patterns during the next decades and in particular drought and excess of water. Then, a bioassay was used in the absence or presence of
Cu to assess the effect of the single (moisture) or double stress (moisture and Cu) on soil nitrate production. Data of nitrate
production obtained through a gradient of Cu under each initial moisture incubation were used to parameterise the DNDC model and to estimate
soil N emission considering the various effects of Cu. Whatever the initial moisture incubation, experimental results showed a
NO3-N decreasing production when Cu was added but depending on soil moisture. The DNDC-Cu
version we proposed was able to reproduce these observed Cu effects on soil nitrate concentration with r2 > 0.99 and RMSE < 10 % for all treatments in the DNDC-Cu calibration range (> 40 % of the water holding capacity) but
showed poor performances for the dry treatments. We modelled a Cu effect inducing an increase in NH4-N soil concentration and
emissions due to a reduced nitrification activity and therefore a decrease in NO3-N, N2O-N and
NOx-N concentrations and emissions. The effect of added Cu predicted by the model was larger on N2-N
and N2O-N emissions than on the other N species and larger for the soils incubated under constant than variable moisture. Our
work shows that soil contamination can be considered in continental biogeochemical models to better predict soil greenhouse gas emissions.
