Once this snow melts the rivers will be f@cked again

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Stevie

would that not depend on the severity of the melt?

Not much chance of that happening round here for a while. Current 'cold snap' forecast to last for a few more weeks. It's currently -5C and yippee! It's started to snow again!

Andy

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GAIC Single Handed Casting Instructor

http://www.andygreyfishing.com/

It will depend on that, however all this grit has to go somewhere, I'm not an expert so don't know whether it ia acid or alkalie, I expect the latter. Either way the balance will be upset.

Does anybody know more?

When you stop to think about it the level of salinity entering the rivers during a snow melt will be thoroughly diluted. In any event fish are well capable of tolerating a moderate level of salinity, otherwise we wouldn't have SEA trout would we? How about salmon? Ever heard of steelhead, ie sea-run rainbows? How come many of our tidal estuaries are stuffed with coarse fish?

If it melts I suspect we will get some flooding as the ground underneath is thoroughly frozen and the melt water will be able to go one way only and that is not to soak in to the ground where it might do some good.

I think that insect life will suffer though Bob. They should not be exposed to any type of salinity.

but not for fly fishing at the momment if yer brave enough czech nymphing will come into its own and if your out on the beats and there is no wind there could be oppurtunity to get some grayling on the dry (that will really test you)
10 days averag -5 and temperatures are predicted to rise which will bring the thaw i reckon it will be back online for perfect fishing 1st week of feb

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lets fish the clydeGuide

That's what I meant, it's not just the fish themselves it's everything in the waterway that supports them.

Yes it will be dilluted but they have used alot more salt than usual by along way. Maybe in the countryside the roads are not so numerous but here in the city and surrouning area it's farely concentrated.

Plain old NaCl, assuming that's the major component of the grit, shouldn't affect the pH, as far as I can see. It can't dissociate into hydrogen caions and some other kind of anion, which would cause the pH to decrease (become more acidic).

If high levels of organic matter are washed into the river, which might accompany the high overland flow arising from frozen topsoil, then the acids these release when rotting might affect the pH of the water.

Salinity is another issue, I suppose it will affect the fluid balance in an invertebrate's tissues, but I'm not sure if this would affect an invertebrate more or less than the megafauna (e.g. trout) which inhabit a river. Can any of the entomologists clear this up?

Salt runoff probably is not brilliant for the rivers but also not awful either. Off the top of my head, some work done in Sweden (where the pollutants build up in the snow pack for up to 11 months of the year on/next to roads - and are then released in a short sharp period of thawing) detected some relatively subtle impacts on receiving watercourse invertebrates. This would be a very much worst case scenario and probably not one that occurs frequently in this country.

However, there could be localised instances where road runoff goes into small discharge streams (offering little dilution) that some localised acute effects were in evidence (perhaps having a bad effect if the thaw polluted redds in a small spawning burn). Such an effect would be likely to disappear within a fairly short distance downstream of the drainage outfall though (i.e. be very localised).

The main mechanism that would cause negative impacts is likely to be not direct toxicity of the salt itself - rather the "mobilising" effect salt might have on toxic metals that are bound to sediment/soil particles. These can become more water soluble in the presence of salt.

However, on a positive note the 5-year research that I ran out of Sheffield University to characterise/mitigate the effects of motorway runoff did not find many cases where drainage outfalls significantly impacted the invertebrate and fish communities (if road salt had a bad impact - you would see it at all of the streams that we monitored intensively).

Where impacts did occur, they tended to be associated with very sluggish, tiny streams which accumulated sediment rich in petrol combustion products (PAHs). It was these PAHs, rather than metals, that seemed principally responsible for toxicity. It also means that riffle flows that are required for spawning habitat are likely to be unaffected, as it was the accumulation of very fine sediment that was the best predictor of negative impacts.

Without going into massive detail - and regressing to my previous line of work - aquatic toxicity is not only a function of chemical concentration in water. It is also a function of the duration of exposure (among other things). In an over simplistic example, you might get the same degree of toxicity by exposing a creature to 100mg/l of chemical for 24 hours as you would by exposing it to 50 mg/l for 48 hours.

So - the good news is that the exposure profile in terms of "duration" for road salt is likely to be short enough for invertebrates and fish to cope with and recover from. It will have nowhere near the same impact as a continuous (i.e. permanent year-round) discharge of toxic effluent from a factory or inadequate sewage treatment works.

Finally - be thankful that the precipitation has fallen as heavy snow instead of heavy rain!! At least we can go grayling fishing loads of times before snow melts (rather than waiting for the rain-induced floodwaters to subside!). To me - the snow makes the "fishable" gaps in the weather longer. Plus, its good to have some nice "robust" flows to kick the stream bed around a bit and keep things nice and varied.

The glass is half full.