After more than two years of ERW experiments we still fail to measure carbon dioxide removal with traditional chemical analyses and electronic soil sensors. But when we started to monitor CO₂ concentrations in soil gas we found a signal immediately!

WORKING PAPER - V3.1 - Dirk Paessler, Ralf Steffens, Jens Hammes, Ingrid Smet - May 17th 2023

Preface

Here we publish a working paper about our preliminary results of 2.5 years of weathering experiments in close-to-nature settings. We have decided to go for direct publishing on our blog because a formal scientific publishing process with proper peer-review would take at least several months and the climate does not have time. Nevertheless, several scientists from Project Carbdown and numerous experts from ERW companies we are working with have given their feedback as a form of peer review. Thanks to (in no particular order): Maria-Elena Vorrath, Karen Strassel, Benedikt Kratochwil, Jelle Bijma, Henry Liu, Adam Wolf, Lily Schacht, Johannes Barth, Jens Hammes, Ralf Steffens, Philipp Swoboda, Mathilde Hagens, Philip Pogge von Strandman, Jacob Rietzler, Tim Jesper Suhrhoff, Mark Baum, Mary Yap, Dimitar Epihov, Jörg Rickli, Jens Hartmann and Thorben Amann for their input. If you have comments or suggestions please contact us at info@carbon-drawdown.de.

Summary

This paper discusses the challenges we have faced in the past 2.5 years of field-experiments trying to measure the speed of Enhanced Rock Weathering (ERW) in agricultural settings for removing CO₂ from the atmosphere.

Measurements using traditional, lab-based methods have not given us any significant signal yet and may take years to show a relevant signal. To address these issues, we propose using CO₂ sensors placed inside the soil in combination with automated CO₂ flux meters on top of the soil as a new method to assess the Carbon Dioxide Removal (CDR) effects resulting from ERW treatments in agricultural settings.

In the future, this novel approach could provide a faster way to assess the effectiveness of ERW in removing CO₂ from the atmosphere. In turn, this would expedite ERW experiments, could make large-scale/multi-variant experiments feasible, and could eventually become a new methodology for MRV (monitoring, reporting and verification) of ERW. This approach may also enable a faster collection of the large datasets that are needed for the creation, calibration and validation of accurate ERW models.

What you are about to read

In our working paper we will show ERW data derived from

• in situ field experiments,

• large lysimeter experiments set up in open nature,

• hundreds of smaller lysimeter experiments in a greenhouse (in Fürth/Germmany) and

• simultaneous soil column experiments at the University of Hamburg.

These data will show you that after two years we are still not able to identify a clear “CDR signal” in soil water leachate chemistry and/or in EC/pH sensor data. A sister experiment in Greece showed quite similar results.

Although it is possible that we made unfortunate choices regarding our soils and rocks, the fact that we have the same situation of “no-signal” across several experiments makes this less plausible. Instead, it indicates that we need a much better understanding of ERW under (semi) field conditions. Our latest greenhouse experiment with - so far - 15 soils and 12 rock types is designed specifically to improve this understanding.

And there is also good news: our XXL lysimeter and greenhouse experiments seem to deliver a proper signal from CO₂ gas sensors buried at a depth of 15 cm into the soil. Even better: this signal becomes visible as early as days or weeks after rock dust is applied and mixed into the soils. Best of all? This ERW monitoring approach is available at a fraction of the cost of the still ongoing chemical analyses.

Based on initial observations, we seem to be able to qualitatively assess the weathering rate of different soil/rock variations and might be able to quantify the actual CDR rates in tons of CO₂ per hectare per year soon! By looking directly at the effect of ERW on the soil’s carbon cycle - namely the reduction of CO₂ respiration from the soil - we circumvent the otherwise required understanding of the complex bio/geochemical soil processes and hopefully acquire a novel, straightforward MRV approach for ERW.

Download the working paper (PDF)

Here is the link to the PDF (4 MB).

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