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  1. #1

    Default ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    New research identifies the impact of agriculture on mayfly -




    Musha rig um du rum da

  2. #2
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    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    wonder what is does to spawning fish then ? easker1

  3. #3

    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    I don't suppose it helps, eh?

    Blue Planet did the trick with plastic packaging - albeit with a very extended time line for a ban - I wonder what would raise awareness to bring about some thing similar to "The Silent Spring" for damaging farming practices. No one gives a twopenny for a low birth rate in insects but the causal link to reduced otter and kingfisher populations might just do it ... but i wouldn't bet on it.
    Musha rig um du rum da

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    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    diawl bach,

    Check out one of my posts on the Ambridge saga.I wrote about a project we did back in the mid-'90's where we fingerprinted fine sediments entering artificial trout redds. 80%+ was of agricultural origin.

    Now trout ova are in the gravels for about 90 days or so and so I'm not sure how much P will attach itself to the fines in that time, and how much impact it might have on the ova. If I were you I'd be talking to the Centre of Ecology and Hydrology about it.

    A few years before the above project we had a visit from an American sedimentologist named Fred Theurer. Most of his work was on Pacific Salmon in the North West USA, but he said that the basic principles would still apply.

    One of the things he said that stuck in my mind was that a trout will dig a redd about 6" deep, and the resulting gravel is clean of sediment. Once the eggs are laid and covered over fine sediments will penetrate the interstices between the gravels and will fill the redd from the bottom up. Therefore if you are going to do any gravel cleaning it is a good idea to clean to twice the depth that the fish will use. Doing so will create a "sump" that can fill with sediments leaving the egg layer untouched.

    The nature of the gravels will have some impact. The gravels in the Cotswold rivers are flattened like a pack of cards and trap sediments like crazy. Even buying in clean gravel we'd have to wash it over and over and we'd still get fine yellow sediment out of it. Kennet valley flint gravel is angular and doesn't seem to hold sediment. I did a project putting gravels back into the Kennet and the dumper was tipping a ton at a time of gravel into the river. There was a few seconds of mild turbidity when the machine levelled the gravels off and that was it.

    I've printed off that item you posted off and am sending it to a friend in Austria. They are starting to have problems with grayling recruitment particularly. They are convinced it is otters, and the otter population has increased significantly over the last few years. However, the brown trout population has increased and the rainbows have remained stable. It is difficult trying to convince them that Austrian otters do not ONLY eat grayling!

  5. #5

    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    One of the things he said that stuck in my mind was that a trout will dig a redd about 6" deep, and the resulting gravel is clean of sediment. Once the eggs are laid and covered over fine sediments will penetrate the interstices between the gravels and will fill the redd from the bottom up. Therefore if you are going to do any gravel cleaning it is a good idea to clean to twice the depth that the fish will use. Doing so will create a "sump" that can fill with sediments leaving the egg layer untouched.
    That's worth knowing, good one.

    I'm busy trapping silt with ye old brash bundles, allegedly prehistoric but amazingly effective in winter as filters and excellent fry habitat in late spring. Soddin' maize.....
    Musha rig um du rum da

  6. #6
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    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    Bit difficult to describe but there is a small stream nearby that flows clean, when it flows, until it reaches a small inlet that used to be where a small pond outlet drained into it, the pond is gone and the land is now farmed(arable), the water that flows from it is more than cloudy, it is pure yellow clay coloured sludge.

  7. #7
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    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    I would be more worried about the increased Phosphates, if it is a slow moving river then the fine sediment could impinge on the ova, we had a similar problem in a hatchery , when the forestry was cut down, we had a lot of cleaning to do , easker1

  8. #8
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    Default Re: ‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

    easker1

    Phosphates (P) mainly come from washing machines and dishwashers. Most sewage works will only clean to a consented standard, which in the case of small works, can be very high. 6 parts per million was common in England and even on large works consents as high as 2 or 3 ppm were not uncommon.

    P strippers will get this down to 1ppm but they are expensive to install and maintain which is why they were limited to works serving at least 10,000 people - about the size of two reasonable sized villages or one small town.

    Even 1ppm is too high according to the people at CEH with whom I worked on a couple of projects back in the day. They would suggest 0.6ppm, but the technology at the time didn't permit that.

    P is definitely a major problem which isn't going away anytime soon. What effect it has on fish ova in a redd I do not know. Worth a chat with CEH.

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