Abrupt alkalinization alters microbial diversity and promotes the proliferation of marine parasites in coastal microcosm experiments
Geoengineering News
Greg Rau
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Debora Iglesias-Rodriguez
Following up on James’ response below, I wanted to add a couple of
additional points:
In the paper you refer to, magnesium hydroxide was pumped directly
into the effluent of a wastewater treatment plant, and it appears that
the proof-of-concept field trial did not achieve measurable CDR.
Regarding your point about dilution, while it is true that alkalinity
will be diluted in-situ, whether re-equilibration occurs over minutes
or substantially longer timescales remains an open question and is
likely to vary considerably depending on deployment context. Factors
such as whether deployment occurs in a fjord versus an exposed coastal
environment, as well as seasonality and weather conditions, will
strongly influence outcomes in such highly dynamic systems.
Most importantly, framing this discussion as “biologists versus other
CDR practitioners” is unfortunate and risks polarizing a field that
fundamentally depends on interdisciplinary collaboration. Public trust
will depend heavily on transparency and on our collective willingness
to identify and communicate potential risks alongside potential
benefits.
While many researchers are understandably eager to move toward field
deployments, laboratory and mesocosm experiments remain essential for
addressing first-principles questions and for improving our
understanding of how biological communities respond to altered
carbonate chemistry.
Débora Iglesias-Rodríguez
--
________________________________
Professor M. Debora Iglesias-Rodriguez
Department of Ecology, Evolution and Marine Biology
Marine Biotechnology Building, 3151
University of California Santa Barbara
debora.igles...@lifesci.ucsb.edu
+1.805.893.4680
www.eemb.ucsb.edu/people/faculty/iglesias-rodriguez
https://labs.eemb.ucsb.edu/iglesias-rodriguez/debora/
__________________________________________
The Future of Marine Life in a Changing Ocean
World Scientific Press
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>
> ---------- Forwarded message ---------
> From: James Gately <jga...@ucsb.edu>
> Date: Mon, May 18, 2026 at 8:12 AM
> Subject: Re: [CDR] Abrupt alkalinization alters microbial diversity and promotes the proliferation of marine parasites in coastal...
> To: Greg Rau <gh...@sbcglobal.net>
> Cc: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com>
>
>
> Thanks for cc’ing me, Greg. I want to note that a couple of the points you raise are explicitly addressed in our paper. First, we gently aerated our microcosms with 0.22 um-filtered ambient air to facilitate air-sea CO2 exchange (see Methods). Although total alkalinity remained constant, the carbonate chemistry was dynamic, not static, as reflected in Figs. S7 and S8. Second, we state in the Introduction, Discussion, and Conclusions that our experimental design does not account for dilution. Our study was designed to reflect model-predicted alkalinity hotspots, not average in situ conditions post dilution -- a distinction we likewise discuss in Methods. While it is true that lab/microcosm experiments are unable to perfectly replicate in situ conditions, adaptive deployment strategies will only be possible if we understand where, when, and why harmful effects may occur. We hope our work contributes to that broader effort.
>
> Best regards,
> James Gately
> Postdoctoral Researcher
> University of California, Santa Barbara
> Department of Ecology, Evolution, and Marine Biology
> +1 (805) 893-5593
Greg Rau
Thanks for responding. I pasted in your comments below because I don't think they got through to the CDR Google group (but note, this not primarily an mCDR group). To Debora's point, by all means let's work together (and across silos) to design experiments that realistically reflect the chemical and biological (and CO2 reduction) effects of OAE. As a former biologist, that was the spirit of my question: Were the affects you observed due to the abruptness of alkalization or the unrealistic duration of the alkalization? This is obviously important because studies like this can and do influence hearts and minds and thus OAE policy, and if the experimental design is not realistic, then how can the resulting data, public opinion and resulting decisonmaking be relevant? This is not the first time that lack of realism has come up in the context of bio experimentation in OAE. From Bach et al's (2025) paper "Lethal by Design?....":
"...there is a disconnect between real-world ∆TA that can plausibly be invoked by OAE and the experimental ∆TA range frequently used in the context of the environmental OAE assessment. While “unrealistic” ∆TA can provide crucial insights into response patterns to OAE, they can also cause overestimation of OAE effects, if the unrealistic ∆TA is not contextualized appropriately."
If this example were used to discharge your +750 uM alkalinity into the ocean, the signal of this input, with or without air equilibration, would be undiscernible from ambient seawater alkalinity several minutes after discharge (at about 150X dilution), assuming a combined alkalinity analytical error and natural variability of +/- 5 uM. Probably ditto for pH and DIC. Such rapid rates of dilution and undetectability were confirmed in our UK field study. All of this says that biological exposure to elevated alkalinity, pH and anything else accompanying the alkalinity will be very brief for free-living pelagic organisms, especially considering that currently permitted discharges must be at pH<9. Where less diluted alkalinity and your "hot spots" do have relevance, and where your approach might be pertinent are sessile, benthic organisms living near a fixed OAE point source. These critters could obviously be exposed to less dilute discharge for their entire lifetimes, but these were not the focus of your study.
One last clarification, our UK study did not achieve net CDR because of the large CO2 footprint in the production and transport of the commercial Mg(OH)2 used. However, given the high pCO2 wastewater into which this alkalinity was placed, I can assure you that that alkalinity was fully carbonated/equilibrated with that bio CO2 after its 11.3 km pipeline journey to the ocean diffuser site. So, gross mCDR was clearly achieved, but via immediate reduction in biogenic CO2 emissions from the wastewater (measured) rather than eventual, direct air CO2 removal out in the ocean. Still, the CO2 emissions in alkalinity production and transport completely negated the gross CDR effected. We have subsequently accomplished verified, net OAE CDR (approaching 5 ktonnes worth) at our Halifax site, and, yes, we and others continue to look for biological impacts. Given your impressive analytical capabilities perhaps we could send you upstream, downstream and background samples for you to look for bio effects under real-world conditions?
Anyway, subtleties do matter, so let's design (and interpret) OAE experiments/trials accordingly.
Tom Goreau
Thanks for raising this very important point about inappropriate experimental time and space scales, Greg!
Your analysis of dilution and time scale effects on alkalinity dissipation and uptake is reminiscent of a claim in the 1970s that phytoplankton acquired almost all of their nitrogen when they drifted through micro-patches of concentrated zooplankton urine.
Proponents used molecular diffusion coefficients, which said clouds of high ammonium stayed around almost forever (on phytoplankton nutrient uptake time scales), so most phytoplankton nutrient uptake would come when they drifted through concentrated urine clouds. The claim got its chief advocate tenure at Harvard.
In fact ocean turbulent eddy diffusion coefficients are a million to a hundred million times higher than molecular diffusion coefficients, so the ammonium clouds dissipate practically instantaneously, MUCH faster than Los Angeles sewage, and these clouds would dissipate so quickly that only phytoplankton right next to the discharge point could possibly benefit. The claim was valid only in a completely stagnant ocean with NO motion!
It was therefore no surprise, from an evolutionary standpoint, that many of the micro-organisms MOST dependent on ammonium, the ammonium-oxidizing nitrifying bacteria and archaea, were later found to grow right on the zooplankton exoskeleton around the discharge point!
Since nitrifiers are also the major source of Nitrous Oxide, a very potent greenhouse gas and major regulator of the ozone layer, these microhabitats are important for global climate. Production of N2O is greatest the lower the oxygen concentration, so formation of dead zones in the ocean in recent decades will have greatly expanded their N2O production:
T. J. Goreau, W. A. Kaplan, S. C. Wofsy, M. B. McElroy, F. W. Valois, & S. W. Watson, 1980, Production of nitrite and nitrous oxide by nitrifying bacteria at reduced concentrations of oxygen, APPLIED ENVIRONMENTAL MICROBIOLOGY, 40: 526-532
Why is this relevant to CDR? Expansion of dead zones is also greatly increasing carbon storage in the underlying sediments, the largest global carbon sink, and the mechanism by which the Earth purges itself of CO2-driven hyperthermal events like that we are about to experience!
From:
carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> on behalf of Greg Rau <gh...@sbcglobal.net>
Date: Tuesday, May 19, 2026 at 00:35
To: James Gately <jga...@ucsb.edu>, carbondiox...@googlegroups.com <carbondiox...@googlegroups.com>, Debora Iglesias-Rodriguez <igle...@ucsb.edu>
Cc: Will Burt <wi...@planetarytech.com>, Lennart Bach <lennar...@utas.edu.au>
Subject: Re: [CDR] Abrupt alkalinization alters microbial diversity and promotes the proliferation of marine parasites in coastal...
Dear James and Debora,
Thanks for responding. I pasted in your comments below because I don't think they got through to the CDR Google group (but note, this not primarily an mCDR group). To Debora's point, by all means let's work together (and across silos) to design experiments that realistically reflect the chemical and biological (and CO2 reduction) effects of OAE. As a former biologist, that was the spirit of my question: Were the affects you observed due to the abruptness of alkalization or the unrealistic duration of the alkalization? This is obviously important because studies like this can and do influence hearts and minds and thus OAE policy, and if the experimental design is not realistic, then how can the resulting data, public opinion and resulting decisonmaking be relevant? This is not the first time that lack of realism has come up in the context of bio experimentation in OAE. From Bach et al's (2025) paper "Lethal by Design?....":
"...there is a disconnect between real-world ∆TA that can plausibly be invoked by OAE and the experimental ∆TA range frequently used in the context of the environmental OAE assessment. While “unrealistic” ∆TA can provide crucial insights into response patterns to OAE, they can also cause overestimation of OAE effects, if the unrealistic ∆TA is not contextualized appropriately."
As for your point about non-air-equilibrated vs equilibrated OAE, the chemical differences here can indeed be significant, but with open-ocean discharge these differences are likely to be quickly dwarfed by dilution. Here (also attached) is one example from a SoCal wastewater discharge to the coastal ocean:
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Debora Iglesias-Rodriguez
Thank you for your messages, Greg and Will.
Greg:
1. You make reference to unrealistic alkalinity but, again, we don’t actually know the dilution timeframes. Incidentally, from the paper you cite (Bach et al. 2025):
- “…OAE within a ∆TA range of 300-1000 μmol kg-1 could be observable for minutes to weeks near TA point-sources. It could also be observed in semi-enclosed basins (e.g. Baltic Sea) where many large-scale OAE operations occur along the coastline for decades (Table 2). These levels could be locally/regionally important when water exchange with the bulk ocean volume is limited.”
- Table 2 also notes that 300-1000 μmol kg-1 discharges could last: “Minutes to weeks in proximity to the release site. Years in enclosed basins under sustained gigatonne-scale deployment.”
2. Importantly, in a real-world implementation of OAE, we are not talking about a single deployment event, but rather semi-continuous deployments—potentially occurring every few minutes, hours, or days—over extended periods of time (years), thereby making elevated pH a chronic exposure, especially at Gt scale deployments (Table 2, Bach et al. 2025). In this context, our experimental design may underestimate real-world conditions.
3. You also emphasized that permitted discharges must remain below pH 9. Notably, our highest measured pH values were approximately 8.9, which declined over the course of both experiments due to aeration. We further highlight that, because TA remained approximately the same, the responses we observed were likely driven by shifts in carbonate chemistry—particularly pH—rather than by TA itself. This distinction is explicitly clarified in Box 1 for readers who may skim the paper. As TA is a derived construct, organisms are likely more directly affected by parameters such as pH, CO₂, and HCO₃⁻.
At present, the experimental and modeling literature remains limited and points to a wide range of possible outcomes. We will continue to adapt our experimental design as new data emerges.
Sincerely,
Hi all,Thanks for tagging me in here Greg. James/Debora, it's been a while since we chatted, but hope all is well with you both.I really appreciate the spirit of this email chain.On the one hand, fully agree with that James/Debora have said here, understanding where the limits/thresholds are is very valuable, and this recent paper highlights interesting findings in that regard.On the other hand, the struggle we face as practitioners is that many people can be lazy when it comes to reading papers (I admit I've always been a bit like this....scanning rather than thorough reading). When one reads 'alters microbial diversity and promotes the proliferation of marine parasites' in the title, the reaction is one of significant concern. Perhaps the phrase in the abtract 'reflecting model-predicted OAE scenarios that produce severe localized impacts' is intended to clarify that the tests were done at 'high/severe concentrations', but that's not very clear to me, and thus i suspect its lost to others too. I really appreciate that you've made it clear in the paper itself, in multiple locations, these caveats in regards to dilution and 'severe' treatment.I suppose it is not the job of the academic community to contextualize their results to real-life deployements. And of course there are SO few deployments to actually compare to!I'm hoping I can help solve here by taking our actual TA/pH data from the field site to contextualize to studies like yours. We can use field data to show the kinds of pertubations we create in different parts of the harbour, and then compare to the published thresholds (500umol/kg for OAE-PIIP, 750umol/kg for your study).Better yet, if we publish that in peer-review, then folks like yourself could cite that to better contextualize your studies. I (with help from my colleague Tim) are hoping to present simple graphics that do this in the coming weeks, and maybe just maybe we will find time to actually write a paper!Apologies for the long email, I hope this was helpful. Happy to discuss further anytime.And regardless, its nice to be in touch with you again.CheersWill
--Will BurtVice President - Science and Product, PlanetaryAdjunct Professor (FGS) - Department of Oceanography -
Dalhousie University
Tom Goreau
I should add that many people who are naïve about ocean mixing processes incorrectly calculate the spread of alkalinity, nutrients, heat and other physical and chemical parameters using molecular diffusion coefficients, and so underestimate their spread by a factor of a million to a hundred million. This is not a small error!
Tom Goreau
To be clear, this refers to horizontal diffusion along isopycnal density surfaces, not vertical diffusion perpendicular to the density gradient.
Mallory Ringham
Hi folks, here to echo that this conversation highlights the need for better communication between mCDR technology developers and academic laboratories. While OAE dilution will vary widely across sites and by various dispersion methods, we absolutely do have tools to identify relevant dilution timeframes, and a lot of work is being done to characterize both current and potential alkaline release strategies.
One published example from 2024 is here: Khangaonkar et al., 2024: https://iopscience.iop.org/article/10.1088/1748-9326/ad7521/meta#erlad7521f3. The Salish Sea Model group ran a series of high-resolution simulations at small (0.164 Mmol TA) and large (164 Mmol TA) scales at two different locations in Sequim Bay, WA. Locations were chosen to represent both a tidally energetic channel and more quiescent conditions, with a 1000 fold scale up from an existing field trial to a hypothetical full-scale deployment, using a discharge rate realistic to wastewater treatment of 40 million gallons per day. The simulations represent continuous one-year dispersion of ∆TA ≈ 869 mmol m−3, at a max pH 9 (avg ∆pH ≈ 1.06). There are some maps in the paper showing the distribution of alkalinity within these studies, and I attached a figure that indicates the spatial scale of pH and TA anomalies from alkaline release. Keep in mind that pH and TA both vary naturally in Sequim Bay: samples collected at the mouth of the Bay throughout this project ranged by up to Δ0.3 and Δ200 umol/kg in pH and TA, respectively—the annotations on the attached figure are mine, including the overlay of measured TA range.
In this case, sessile organisms near the alkaline point source will certainly experience altered carbonate chemistry, but we should not assume that pelagic / mobile species are continuously bathed in this chemistry-- Sequim Bay has a flushing time of about ten days, so currents and tides will have a significant impact on exposure to marine organisms. I’d note as well that this study hypothesizes a standalone alkaline release— OAE technology developers aim to integrate with other coastal infrastructure, adding additional dilution on top of these effects.
This study is hypothetical and there are many improvements that could be made to this modeling exercise, but there are several other examples that look at realistic exposures, including work at Halifax Harbor, Tasmania, and Port Angeles (model studies in preparation for submission now). [C]Worthy has shown some fantastic simulations on potential OAE development throughout the Salish Sea as part of community engagement and education efforts in the region.
Finally, a correction on Greg’s earlier comment in this thread ‘that currently permitted discharges must be at pH<9’. This is not true—Ebb's research pilot, Project Macoma, is permitted for up to 9.8 for routine, continuous alkalinity release, and up to 12 under certain scientific conditions. We have extensive near-field models and field data indicating rapid dilution from this small scale pilot, on order of meters and minutes away from a not-insubstantial alkaline outfall. I'm not suggesting that this is the path OAE will take, but that blanket statements on pH thresholds from a regulatory perspective lose a lot of nuance when it comes to mCDR research.
Cheers,
Mallory
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Greg Rau
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Institute of Marine Sciences
Univer. California, Santa Cruz
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