the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Mar 2026
Synergistic effects of basalt and earthworms: enhanced nutrient availability and altered heavy metal dynamics
Abstract. Enhanced weathering (EW), the application of crushed silicate rocks such as basalt to soils, has been proposed as a carbon dioxide removal (CDR) strategy. Besides CO2 sequestration, EW can influence soil chemistry and crop nutrition, providing agronomic co-benefits, but it may also release heavy metals with potential risks for food safety. Soil organisms such as earthworms, which strongly influence nutrient cycling, and mineral dissolution, may further interact with EW processes, yet their role remains poorly understood. Here, we conducted a full-factorial experiment to test the combined effects of basalt and earthworms on soil chemistry, and growth, nutrients and heavy metal concentrations of Zea mays. Basalt significantly increased porewater pH, alkalinity, and nutrient concentration (Ca, Mg, Na, and Si). Earthworms further amplified most of these responses, suggesting increased weathering rates. Plant nutrient concentrations were in general positively affected by basalt and earthworms, while plant biomass remained unaffected. Furthermore, basalt decreased heavy metal concentrations in the aboveground plant parts, but V, Ni, and Al accumulated in their roots with basalt application. Basalt and earthworms thus show promise in improving agricultural soils, but trade-offs related to heavy metal accumulation must be addressed to optimize their use in sustainable agriculture.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 23 Aug 2026)
- RC1: 'Comment on egusphere-2026-603', Anonymous Referee #1, 22 Jul 2026 reply
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- 1
Generally I enjoyed reading this study. The Results section is quite dense as you document each analyte in turn and I wonder whether this could be better summarised. There is a lack of experimental detail in places, particularly about things like the earthworm species, unless I missed it, and a significant lack of quality control data to accompany your analytical results. I think, given your data you could add in a mass balance to quantify the expect of basalt weathering and whether this is accelerated by earthworms.
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Title (and throughout): don't use the term "heavy metal", it is unscientific - see https://publications.iupac.org/pac/2002/pdf/7405x0793.pdf
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Abstract
This needs to be far more quantitative - we don't know the soil pH or organic matter content, the duration of the experiments, whether differences between treatments were statistically significant, what concentrations in plant biomass actually were.
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Introduction
2nd para - there are instructions left in the text "Click or tap here to enter text" - this needs proof reading properly.
Line 31 - I think the statement that there is good evidence for EW benefiting plant growth in the tropics but weak evidence in temperate regions is not accurate. There are lots of published experiments in temperate conditions as well. Perhaps the authors mean field trials (though I don't think this paper is about a field trial either). The statement seems at odds with line 41 where the well documented benefits of EW are acknowledged.
Line 33 - I not that the first author is citing a very limited number of papers here but 2 out of 3 are their own. There's nothing wrong with self citation but it is important to acknowledge others work in the field as well.
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Methodology
Line 63 - justify this choice of amendment level - is it typical of what is advised when EW is being done at scale in the field?
Table 1 - caption needs to state how many replicates were used for each measurement and what the uncertainty is - std err or std dev. Also methods used to determine these parameters need to be cited and, for chemical measurements quality control data should be given.
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Line 76 - how old and what growth stage were the maize plants at when added?
Line 80 - how does this fertilisation rate compare to what is typically used in the field?
Line 84 - at destructive sampling what was earthworm recovery like and was there a mass change? (Line 89 - at the end of the experiment were the remaining mesocosms destructively sampled as well as the plants being harvested?)
Line 87 - first mention of the earthworm additions - needs far more detail - species, mass added, how this compares to typical field densities, source of earthworms, how their identity was confirmed etc.
Line 101 - how were the cores taken? Were the mesocosms excavated and, when a certain depth was taken a core was taken or something else?
Line 106 - can you justify this assumption by citing some studies which have tested it?
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Line 113 - chemical analysis of biomass needs quality control - accuracy and precision
Line 119 - similarly for soil analysis
Line 152 - why wasn't presence / absence of earthworms and basalt included in your model for explaining differences in plant biomass?
Fig 1 - state what the error bars represent and give a value for n, i.e. number of reps.
Line 167 - list the exceptions
Line 168 - perhaps the detail is in the SI but here give average no. of earthworms recovered and average weight change between start and end of experiment. Initial mass of earthworms should have been added to the methods section
Line 197 - was this increase significantly greater?
Fig 2, 3 (all figures) - the "*" are not needed as you show the p values. - typically these sorts of subscripts are used to show significant differences between treatments. Need to state what the error bars represent and always ensure number of replicates (n) is given (sometimes it is but e.g. Fig. 8 it isn't).
Line 351 - go back to the Methods section and state how limits of quantification were determined and list what these were for all analytes in the SI.
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Typically if concentrations are below quantification you can set the concentrations at limit of detection divided by the square root of 2 - did you do this and then carry out your statistical analysis for e.g. Ni. (Croghan, C. & Egeghy, P. P. 2003. Methods of Dealing with Values Below the Limit of Detection Using Sas. 602 Southern SAS User Group, 22, 24.)
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Line 404 - it's probably worth reminding the reader here which variables were included in the PCA but didn't appear in PC1 or PC2, e.g. pH
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Fig 9, 10, 11, 12, i.e. all box plots - need to state what the various whiskers, tails, horizontal lines represent in the caption
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Discussion
Lind 723 - careful with the word "synergistic" - do you men that the effect of basalt and earthworms was greater than the sum of the individual effects, or was the effect additive, i.e. the effect of basalt and earthworms was equal to the sum of the indivdual effects, or was the effect of the two, less than the sum of the individual effects. Synergism is a technical term and should be used correctly.
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Line 725 - it is highly unlikely that simply burrow breaks down silicate minerals - what evidence is there for this and do you mean chemically or physically? If you mean chemically then yes moving basalt to a different environment may accelerate weathering but there is no reason why burrowing and resultant displacement of silicate minerals (or basalt grains) would result in their physical breakdown.
There is a little evidence in the literature of earthworms reducing mineral size - the paper of Suzuki et al is rather unconvincing, I've yet to meet an earthworm ecologist who believes the results, people think the results are an experimental artefact of either preferential feeding or retention of particles in the earthworm gut. The Carpenter et al papers on earthworms and mineral weathering do hint at some grain size reductions, but not consistently.
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Line 747 - but I don't think you've told us which ecotype (or species) of earthworm were used in your study.
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Line 758 - first mention of watering of the mesocosms - this detail should be mentioned in the methods. Thinking about it, it would also be useful to document the leachate volumes collected over time, it would be interesting to see if there was more leaching in the earthworm treatments, so please incorporate this into your Results section.
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Line 762 - 765 - I don't follow the logic of why, just because respiration has increased in your mesocosms you think earthworms would migrate to these areas in the field. You could argue that an increase in CO2 (which has a negative impact on earthworms) would decrease migration into such areas.
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Line 800 - 805 - more sustainable agricultural practises will also likely elevate soil organic matter content
Line 880 - but in nutrient poor or degraded soils how likely is it that there will be a thriving earthworm population?
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The main thing missing from this study is, I think, an attempt at mass balance, You have pore water data, leachate data, exchange site data and plant composition and biomass data so you could attempt a mass balance similar to that of Kelland et al (2020) Global Change Biology 1 – 19. Doi.org/10.1111/gcb.15089 to determine a) basalt weathering rates and b) whether earthworms increase these or not.
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