An Analysis of Soil CO₂ Efflux and Leachate Alkalinity Data
Dirk Paessler, Jens Hammes, Anna Anke Stöckel, Ralf Steffens, Ingrid Smet
ABSTRACT:
In order to better understand Enhanced Weathering (EW) we ran an extensive greenhouse experiment with more than 400 pots with grass plants (Lollium perenne) for 24 months throughout 2023-2024. Every month we measured multiple parameters in the soil leachate water (total alkalinity (TA), pH, electrical conductivity (EC), and cations) as well as soil CO₂ effluxes.
With a focus on carbon transport we present here the data from 67 rock-soil variations with 4 replicates each, based on the lab results from 6,500 leachate samples and almost 1 million CO₂ efflux measurements from our custom-built army of autonomous fluxmeters.
Here we present data for soil CO₂ efflux based on nighttime measurements only, i.e. without photosynthesis. This CO₂ efflux integrates multiple processes, including SOM decomposition, root respiration, and inorganic carbon reactions, all of which may be influenced by rock dust treatments (e.g. rock dust causes larger/smaller plants or more/less weathering). The relative contribution of these components cannot be resolved from our data. It shows that in year 1 and
especially in the first 10-20 weeks after setup all pots, including controls, exhibited much higher CO₂ effluxes than in year two with a fade-out trend over time. This is likely caused by the disturbance/aeration of the soil column during the homogenisation of the soil and the experiment build up process. Increased soil CO₂ efflux is known to occur naturally when dry soil is rewetted after a period of drought (Birch effect1) and when soil structure is disturbed and aerated, exposing more soil organic matter to decomposition by microbes (“tilling-like” effects). We also found that CO₂ efflux data of the first year usually did not correlate with the measurements of the second year.
