Charge Balance and power law?

I've come across a statement in a paper\* that's poorly explained, and I can't work out the reasoning behind it. I suspect this is embarrassingly basic, but could anyone please explain the theory behind the following (from the bottom of the second paragraph of the discussion)?



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> For a reaction involving B(OH)4- and CO32-, a B(OH)4- can balance the charge of only 1/2 a CO32-, thus a dependence *[of the B/Ca ratio in synthetic aragonite]* on [B(OH)4-]/[CO32-]0.5 would be expected.
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I'm unsure why a power law applies here.


\* Holcomb, M.; DeCarlo, T. M.; Gaetani, G. A.; McCulloch, M. Factors affecting B/Ca ratios in synthetic aragonite. *Chem. Geol.* **2016,** *437,* 67–76. [DOI: 10.1016/j.chemgeo.2016.05.007](https://doi.org/10.1016/j.chemgeo.2016.05.007).


