CDR Measurement for ERW via Alkalinity in Leachate (Data From Our Greenhouse Experiment, Part 2)

Join us on our endeavor to reliably measure the climate-positive effect of enhanced rock weathering (ERW) in agricultural settings by analyzing the water that leaches from the soil! In this blogpost we explain how the carbon dioxide removal (CDR) effects of rock weathering can be estimated using alkalinity measurements of leachate water and what early results we see in our greenhouse experiment.  

Introduction

In this paper we delve into Enhanced Rock Weathering (ERW) and its potential for Carbon Dioxide Removal (CDR) in agricultural settings. We present the first results of our extensive greenhouse experiment that was started early 2023 with the goal to measure the climate-positive effects of ERW on relatively short timescales (months to a few years). To achieve this we are experimenting with several measurement approaches. One of them is based on analyzing alkalinity in leachate waters, the topic of this paper where we both explain how it works and what our first results tell us.

In our experiment we encountered the challenge of developing an approach to measure CDR from leachate alkalinity. As there doesn’t seem to exist a published standard method for this, we had to formulate our own process together with our scientific advisors.

Our leachate alkalinity measurements indicate substantial variability in weathering rates, influenced by differing soil and rock types, which surpasses our presumptions. This unexpectedly large variability underscores the complexity inherent in reliably measuring ERW's CDR effect which is likely not fully represented by today’s models.

We conclude that while alkalinity measurements in leachate waters seem to provide a viable indicator of ERW's CDR impact in controlled environments, its applicability in real-world, large-scale agricultural settings necessitates further exploration and development. The variability and complexity highlighted in our findings emphasize the need for ongoing research to refine these methodologies and explore alternative, more feasible approaches as proxies for CDR assessment in the context of ERW.

Even though weathering models will most likely be needed for MRV at full ERW deployment scale in a decade or two, we will initially need extensive measurement data from greenhouse experiments and real life field trials to train and verify such models. In this paper we publish some of the first empirical alkalinity datasets that might bring us a little closer towards the establishment of a scalable and reliable monitoring and reporting framework for CDR via ERW.

Download the PDF file (V1.1, Dec 18th 2023, 3 MB). Here is a PDF of V1.1 with the marked changes since initial publication of V1.0.

In summary, our exploratory research in the greenhouse offers promising insights into the measurement and effectiveness of ERW for CDR. However, the complexity and variability of natural processes present significant challenges that need to be addressed before this approach can be diligently applied on a larger scale.

Download the paper

For more detailed information and data, please download and review the full paper (3 MB PDF, V1.1, Dec 18th 2023). Stay tuned for more updates as we continue our journey into understanding and harnessing ERW for carbon dioxide removal and its climate benefits.

Update Dec 18th 2023

We have updated the article, see here for details.

Update October 2024

After reading this blog post please also look at our blog article Why measuring alkalinity is not the same as quantifying HCO₃⁻ (How to avoid confusion about the seemingly straightforward use of alkalinity to quantify CO₂2 removal).

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