What changes might we see as sea level rise = increased salinity?

April 21, 2015 10:50 AM

So I've read predictions about how sea level rise will increase the salinity of current freshwater outlets. What might be some changes one would see underwater as a result of change? Would freshwater flora/fauna migrate upstream? Would salt water species migrate in? Or would there be some dead zone where the water is too fresh for ocean folk and too salty for river folk?

As is probably evident, I am not a scientist, but rather a clueless short fiction writer. So answering this question involves no actual saving of fishes, unfortunately.

THANK YOU

posted by angrycat to Grab Bag (4 answers total)

Best answer: A good starting point would be to read about estuaries, which, to quote the article, is the "transition zone" between salt and freshwater, thus "subject both to marine influences - such as tides, waves, and the influx of saline water - and to riverine influences - such as flows of fresh water and sediment."
posted by barchan at 11:24 AM on April 21, 2015 [1 favorite]

Best answer: would there be some dead zone where the water is too fresh for ocean folk and too salty for river folk?

If by "folk", you mean animals, not this won't happen.

Some fish, like salmon, dig both environments.

Air breathers will be unaffected. There are cetaceans pretty far up the St. Lawrence Seaway.

You might be interested to know that in places such as Millford sound in New Zealand, where lots of fresh water sits on top of the ocean water, sea mammals (and penquins) congregate for a kind of natural de-lousing. Since they breathe air, they are unfazed by the change in salinity, but their skin parasites are mostly not adapted to fresh water; they die.

Would freshwater flora/fauna migrate upstream?

There is nowhere to migrate to. There would simply be less habitat for them.

Would salt water species migrate in?

Hmm, some would, yeah. Whenever there's a change in the environment, more adaptable species adapt; more specialized species will die out.

Zebra mussels and sea lamprey are, unfortunately for the Great Lakes, both adaptable to either salt or fresh water and accomplished shipborne stowaways.

Here's a word for you: euryhaline: able to adapt to a wide range of salinity.
 
posted by Herodios at 11:42 AM on April 21, 2015 [3 favorites]

Best answer: There was a big paper in Science in 2012 that looked at about 50 years of historical data on world salinity changes. Here's a summary of it. The short summary is that salinity is showing anthropogenic change, with some areas, wetter ones dropping in surface salinity, and some, dryer ones, rising. There's no over all pan-oceanic trend, but there are significant regional ones.

Now, that in mind, what you're asking about is usually called saltwater intrution. There's evidence in the literature supporting increasing estuarine salinities in a number of studies. Salt water intrusion happens when rising levels of salt water in the sea push and displace fresh water aquifers, underground. This can cause the water table to shift to salt or brackish rather than fresh. This process increases salinity in coastal wetlands and river mouths.

Further, there are studies warning that human over-use of ground water exacerbates the problem. Remove fresh water from the ground and more salt can intrude, basically. This is still an area of debate for modellers and field science alike.

The effects on organisms seem to be displacement of fresh or brackish habitats and species with high salt or salt tolerant ones. This will have mostly deleterious effects on existing coastal ecosystems as organisms find themselves increasing maladapted for the new normal salinities and water levels (don't forget rise too). This affects not just natural species distributions, but also commercial and aquifarm species ranges too. To give a sense of how wide ranging these effects can be, I've also seen predictions of human health impacts caused by shifting fresh and salt mosquito populations, thus altering disease transmission vectors.

Rather than turn this into a primary source linkfest, I've tried to give a 10 km summary of a very big, very rapidly changing field. Most of the work has been done in the last decade, and we're still just finding the edges of what's important here. Coastal and near-shore ecological change is one of the most significant results of climate change and will be/is incredibly dynamic.
posted by bonehead at 12:25 PM on April 21, 2015 [3 favorites]

Response by poster: Yikes, NPR is addressing this issue right now w/r/t the degradation of the Everglades in Florida. Thanks all so much for your most learned responses.
posted by angrycat at 3:18 PM on April 21, 2015