[IntrepidWorm]

Speaking strictly of mineral removal this rings true. However, processing large volumes of seawater can still have a detrimental effect on the local ecosystem, because pumping large volumes of seawater is extremely stressful to all of the seawater-loving organisms that get pulled along for the ride.

[jerf]

See also the trouble around desalinization plants.

In absolute terms, we couldn't hope to remove enough salt from the oceans to be even so much as detectable in the absolute sense, but in local terms water with increased salinity can cause problems. Oceans are not hives of life everywhere you look, it's really just in spots, and those spots are generally right where we want to be and to put our desalization plants.

Plus the high-salt and normal ocean water are much more resistant to mixing than our intuition would suggest. They will eventually mix, but the high-salt water can go a surprisingly long way first.

[rlucas]

See also, thermohaline circulation. A major factor in the global climate is the flow of water pulled north along the Atlantic's surface due to the sinking of denser, saltier water.

Not going to be an issue with your average desalination plant, but certainly proves the point that water masses can behave differently in big, non-trivial ways due to their salinity.

[scarby2]

there have been desalination trials with spreading the brine over a much larger area releasing much smaller quantities at each outlet. AFAIK these have been quite successful

I'm unsure on the impact of costs. Maybe we just pump it into the salton sea....

[jillesvangurp]

Depends. Shallow coastal waters without a lot of currents would be an issue. That's often the issue with desalination. The solution is running pipes to deeper waters where whatever you can pump there is going to be a drop in the ocean. Pipes and pumps are of course more expensive.