Sinking wood into a lake won't remove the carbon unless you have a very deep lake, and you'd need many, many of them to have any impact on the CO2 levels whatsoever. The scale of wood that would need to be harvested is far beyond dropping some logs in a lake.
They need to go into a deep enough pit where the methane produced from anerobic breakdown won't reach the atmosphere.
The conditions that created the lignite coal and peat simply aren't that easily reproducible, especially with large volume of wood (rather than ferns over thousands and millions of years).
So sink them in the ocean. Or better, burn off the hydrogen and use the energy to dry the wood, leaving the bulk of the carbon, and then mix that in with the soil.
Recreating the lignite era process could be as easy as genetically engineering an alternative,presently indigestable version of lignin.
But my point is that the claim above that sequestering wet wood will somehow take meaningful quantities of water (fresh or otherwise) out of the ecosystem is just plain silly.
> Recreating the lignite era process could be as easy as genetically engineering an alternative,presently indigestable version of lignin.
Ah yes, so easy. Why on earth have we been treating wood with chemicals to prevent rot in our structures when we could have just engineered them to not rot all along?
"Easy" is relative. If the comparison is completely abandoning fossil fuels, launching continent sized parasols into space, running a significant fraction of the atmosphere through a magic filter, etc. the bar is quite different than your moved-goalposts of "compared to spraying something on some fraction of our lumber".