EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

A model for three-way carbon flux partitioning in calcareous soils using stable isotope measurements

Guy Kirk1, Chris McCloskey1,2, Wilfred Otten1, and Eric Paterson2
Guy Kirk et al.
  • 1Cranfield University, School of Water, Energy, and the Environment, Cranfield, Bedfordshire, United Kingdom
  • 2The James Hutton Institute, Craigiebuckler, Aberdeen, Scotland, United Kingdom

In order to understand and model soil carbon (C) dynamics it is essential that we are able to partition net ecosystem C exchange by individual organic and inorganic fluxes under field conditions. Stable isotope methods provide a reliable means to separate fluxes from two sources, such as plant respiration and soil organic matter (SOM) mineralisation. In many soils, however, plant and soil respiration are not the only sources of C efflux, as breakdown of carbonate minerals provide a third, inorganic, C source. We currently lack methods and models to allow us to untangle plant, inorganic soil, and organic soil C fluxes in the field. This limits our ability to gather field-scale plant and soil C flux data to soils without inorganic carbonates, rendering calcareous soils a major gap in our understanding of, and ability to model, soil C dynamics.

To remedy this we have developed a novel three-way partitioning model to account for inorganic carbonate dissolution in a planted soil. Analysis of a mechanistic model of lime (CaCO3) dissolution showed differences in CO2 pressure in the soil, arising from differences in soil respiration as influenced by differences in temperature and moisture, to be a major control on dissolution rates. The thee-way partitioning model we have developed derives the CO2 flux from CaCO3 dissolution from SOM mineralisation and below-ground plant respiration fluxes.

To test this model we used cavity ring-down spectroscopy to measure CO2 fluxes from soil mesocosms containing C3-origin SOM and planted with a C4 grass, both with and without CaCO3, and unplanted soil mesocosms containing CaCO3. As previously field measurements revealed temperature to be the strongest control on soil respiration this was carried out at four temperatures (15, 20, 25, and 30oC). Using the distinct δ13C values for CaCO3 dissolution, C4 grass respiration, and C3 SOM mineralisation, fluxes were partitioned from mesocosms containing two C fluxes to parameterise the model. The model was tested through application to flux data from mesocosms containing C fluxes from CaCO3, SOM, and plants in order to assess its suitability for generating novel field datasets of C fluxes from calcareous soils.

How to cite: Kirk, G., McCloskey, C., Otten, W., and Paterson, E.: A model for three-way carbon flux partitioning in calcareous soils using stable isotope measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22627,, 2020