Grit/road salt effects on river

Apologies if this has been asked before or another thread same.

Last year the council where I live used or put on the local roads 1,400 tonnes over 40 gritting operations, so was wondering what happens to this salt once its been deployed?

Does motorway run off go to sewerage or does it enter the rivers?

Will salt affect breathing of fish and as fish take in water from osmosis does the salt interfere with this delicate process?

Thanks.

wes79 said:

Does motorway run off go to sewerage or does it enter the rivers?

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That would depend on how and where any water drains. Some will enter the water drainage system, plenty will just drain into adjacent land.

wes79 said:

Will salt affect breathing of fish and as fish take in water from osmosis does the salt interfere with this delicate process?

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I doubt that quantities of salt actually entering watercourses would ever be significant enough to have such serious results. I've yet to hear of fish struggling to survive because of it. However, there's plenty of anecdotal evidence that suggests that fish don't feed particularly well following periods where large scale gritting of roads takes place.

I deliberately add salt to my pond water to help them through the winter and to reduce the parasite loading. My koi are thriving as anyone who has seen them will agree. The salt is added at a recommended dose of 1/2oz per gallon which if you care to do the sums is a lot of salt (around 14kg per 1000 gallons off the top of my head and my pond at 3mX3mX1.5m is roughly 3000 gallons). Taking those numbers into account I would suggest that the run off from the roads into the dilution of a river will be negligible, depending on the flow rate of the river of course.

More damaging imo will be the other chemicals and residue which build up on the roads during a prolonged period of snow and are washed into the river following a sudden thaw. That nasty brew is probably what accounts for the fishes reluctance to feed in those circumstances.

Of course all this is my own conjecture and I expect to be lambasted for it as soon as the resident ecologist reads it.