The city has been sinking for quite a long time, are any businesses surprised when the floods come?
It really doesn't need a source. If Venice takes too much water from an aquifer then subsidence is unavoidable. The city is sitting on top of a sponge, after all. This is true for any city that's not built on bedrock (which I believe includes half of Manhattan and Miami. NYC of course draws from the Hudson)
Anyway, as the paper states the subsidence exasperates rising sea levels.
If the claim is that it is the main problem, I think it does need a source, and by reading the abstract it doesn't seem like yours is one.