By ‘terrestrial’ I meant ecosystems on the island, whether they are aquatic, riparian, or whatever. I should have been more explicit and simply said ‘land-based’. True terrestrial ecosystems may be impacted because the SW-GW relationships may be changed, water tables changed, etc. This will be exacerbated if they decide to pump GW.

Near-shore ecosystems will be impacted because the SW flow into the sea will be reduced, which could cause problems to an ecosystem adjusted to a certain amount of fresh water input from the land.

As for the implications… I doubt terrestrial ecosystems will be bothered. Aquatic ecosystems and geomorphology might be, depending on what parts of the hydrograph are siphoned from and when, and where along the reaches. As for coastal ecosystems, the rain would have fallen there anyway, so it’s just the nutrients and sediment that might be lacking, and this could be ameliorated somewhat provided the material is returned to the river after being pumped into the bottling facility.