Before we address this subject, I highly recommend that you watch this extremely well presented in-depth video, “Sinking of the city of Venice”, Part 1 published by Nova. Parts 2, 3 and 4 are also available on YouTube.
The following excerpts are taken from Water Canada (with RenewCanada) ~ “Fake Plastic Reefs”.
Ray Hesslein, limnologist, offers his thoughts on how using protocells to make limestone structures might affect water bodies.
Rachel Armstrong wants to use synthetic biology and smart chemistry to save decaying buildings in the Italian city of Venice.
Water Canada’s sister publication, ReNew Canada, recently profiled Armstrong’s TEDTalk, wherein the scientist details how she proposes to grow artificial limestone reefs under those buildings and use them as support structures. The metabolic materials Armstrong’s team designs are based on the protocell. One of the reef-building organisms Armstrong and her team have engineered naturally moves away from light and towards darkness. This behaviour would keep reefs out of Venice’s navigable canals and have them grow in the darkness under its buildings, essentially petrifying, and sustainably reclaiming, the city’s foundations.
We wondered how the approach might affect the water in the canal system and asked Dr. Ray Hesslein, recent recipient of the Society of Canadian Limnologists’ Frank H. Rigler Award, to give us a lesson in calcium carbonate.
Water Canada: Can you tell us a bit about how limestone works?
Dr. Hesslein: The ease with which organisms can produce precursors to limestone really depends on how much calcium carbonate is in the water. At the Experimental Lakes Area [in Ontario], where there is very little calcium carbonate in the water, organisms have a huge difficulty developing this material. Even clams and mussels have difficulty making shells. That’s one extreme. At the other end of things, the ocean is at the point of saturation. That’s why we have coral reefs. It’s relatively easy for organisms to produce shells or that kind of thing by precipitating calcium carbonate from the water.
What do you make of Armstrong’s protocells?
The greater concern is not whether you produce an enzyme package that can precipitate calcium carbonate, but whether you can control it. How do you make it go where you want it to? How do you stop it from growing wildly in the canals?
How might the introduction of limestone affect the surrounding ecosystem?
If you put calcium carbonate into fresh water, it will corrode and dissolve gradually. If the water body is not saturated or near saturation, that water body will corrode the limestone. That’s a concern in the ocean right now. When you add more CO2 into the atmosphere, it goes into the ocean and acidifies it slightly. Some areas where calcium carbonates were stable in the past have become corrosive, and that is having an effect on reefs. An estuary is more complex and variable. There may be times when things will be stable or under-saturated and begin to corrode. If you have organisms in that area and it’s semiclosed, this process will compete with them. Other organisms will have difficulty precipitating unless you put in amendments. This is not to say Armstrong’s process won’t work in some places. The concept is interesting, but in my mind, there are more questions than answers. One would have to look at the situation in Venice, checking for seasonal variability and doing a proper engineering assessment.
Any other thoughts you’d like to share?
Armstrong talks about continuous renewal being something biology does that is different from manmade structures. Organisms die and are replaced. In Venice, we might want to preserve everything forever, but I’m not sure I agree with the whole notion of being able to make things last. Biology evolves as well.