Use of Siltex

Has anyone got practical experience of using Siltex to improve fisheries?
I have heard that the EA have stopped recommending it - any truth to these rumours?
Martin J Lees Waterscapes - Siltex
Cheers!

Crushed Limestone is cheaper, you use less and it seems to work just as well.

Both Siltex and crushed limestone stimulate the development of decomposition bacteria, enabling them to break down the organic matter in the silt, thereby causing a reduction in silt depths.

They also increase ph levels and the calcium is a building block for invertibrates and snails etc.

We lime approx 25% of our lakebed every year and the increase in natural food has been incredible.

Stu

I am skeptical of the claims made for it - but have no first hand observations of its effects upon waters i have fished. I stopped fishing some local lakes just before it was used there and never been back - they were getting "gardened" too much for my liking (tree removal, installation of platforms etc) and were way too busy for my liking anyway.

To my mind the best and only way to reduce silt depth is to suction pump it out or to dredge it. Unless you were using siltex in some upland or acidic waterbody there is likely to be no beneficial effect on snails etc - virtually all waterbodies in the midlands or south are fine for snails and have ideal pH without liming.

As for invertebrates, it is the edges of lakes and ponds that are important - especially if theres lots of emergent plants - for wide range of invertebrates, water fleas etc etc. Bare silt is only good for bloodworms, mussels and a few other animals - a limited diversity - though large numbers will make good food source.

If the need is to get oxygen into the silt (to promote aerobic decomposition of silt by bacteria etc) then a good raking could work better. Also, dont forget natural aeration caused by fish stirring up the sediment as they feed, and from burrowing invertebrates that live in the silt.

A common problem is small ponds so heavily overstocked with large fish (eg carp) or birds (eg waterfowl) that a huge volume of excrement causes deoxgenation at the lake bed. In such conditions i would reduce the source of the excrement, increase the flushing rate (throughput of clean water), or introduce aeration.

Although i havent fished them, I have seen the after effects of using Siltex (or crushed limestone) on several lakes when coupled with use of herbicide targeting blanket weed. It has turned clear-watered lakes full of weedbeds including lillies into a barren pea soup as phytoplankton flourished.

Thanks for the input lads,
Still wondering why EA have done such an about-face on this in the last 10 years.
Anyone else got any info on this?
Cheers.

Re. the EA position, i didnt know they had a view - never mind that it has changed.

I know a fisheries expert (an academic with a small but highly regarded ecological consultancy) and his views mirror mine.

In cases such as the Broads where siltation is a partially man-made issue and where some Broads can have 5ft of silt above a peat bed and only 2-3ft of open water above the silt surface, then it is major issue!.

In one of the Norfolk Broads, Cockshoot Broad (yes, silly name, i dont make these things up - honest) the lake was separated from the River Bure by a dam in the late 1980s (to prevent ingress of silt and nutrients from sewage discharges etc) and a humungous volume of silt was pumped out increasing the depth from 18" to over 4ft across a very large area. The water subsequently cleared and weedbeds not seen for over 80 years re-established from seeds previously buried deep in the peat/lower silt.

chub_on_the_block said:

I am skeptical of the claims made for it - but have no first hand observations of its effects upon waters i have fished

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Where to start! Firstly I have managed a lake in the south of England for 22 years, I have plenty of first hand experience. It depends on the type of silt. Liming only works on organic matter, it won't work on non organic silt, there is nothing for bacteria to work on. But it does work on the former. Pumping silt is a massive task, behond most.

As for your points on snails and invertibrates, all I can say is that in my experience, liming has resulted in a massive increase in both and a resultant increase in fish growth.

The pea soup is likely a result of killing the blanket weed. Unused nutriant is the usual cause of algea. Liming, in my experience if anything has the opposite effect. The extra zooplankton clears the phytoplankton.

But, I'm only a reasonably experienced amateur, my comments are only based on my own observations and experience. I'll carry on liming.

Stu

I cant argue with first hand experience - without any scientific investigations that is all we can go on. Glad it worked on you water Stu.

Here's an extract from an EA publication:

"Hydrated lime, crushed limestone and
slag all produce an alkaline reaction in
water and in pond soil. This aids the
release of nutrients for plants. Do not
use these products unless you have
evidence of acidic or poorly buffered
water chemistry, or that organic matter
is accumulating in acid soil conditions."

It's on page 11 of a note on Fisheries Habitat Improvement.


I'm a member of a club which, after advice from a fishery consultant, used crushed limestone on an estate lake to reduce the thick deposits of silt. This was done for a few years. One year, after applying lime, some of the fish died. The use of lime was abandoned, and the silt deposits are getting thicker.

http://therrc.co.uk/MOT/References/EA_Fisheries_habitat_improvement.pdf

Hi Greenie,
The case Chub highlights is a superb example of how science can solve a problem and it demonstrated clearly the way forward for the embryonic Norfolk Broads National Park.

In the 1980's I visited Cockshoot Broad both before, during and after the restoration work and fully support what Chub has written.
The work undertaken was immense, with huge amounts of silt pumped out onto the surrounding land.
Initially there was just an anti angler barrier (essential because the local anglers respected nothing) across the entrance, later the ingress of disturbed water from the connecting waterway made a physical barrier essential.
The work on the Broad provides a superb example how applied science (English Nature staff) can have such a dramatic and beneficial effect on a water body.

If you can I strongly suggest a visit, if nothing it demonstrates the destruction motor boats can cause to a sensitive ecosystem and how man can reverse it.

As for crushed limestone, a few lorry loads of chalk would provide a similar effect though don't expect it to dissolve decades of silt and decaying vegetation, physical removal is the only answer Im afraid.

Good luck.

.

keora said:

Here's an extract from an EA publication:
......It's on page 11 of a note on Fisheries Habitat Improvement.
http://therrc.co.uk/MOT/References/EA_Fisheries_habitat_improvement.pdf

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Thanks for the reference Keora - I've not seen that document before - an interesting read - as is the whole RiverRestorationCentre site the River Restoration Centre - worth having a look at to check over the status of projects planned/performed on your rivers.

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As for crushed limestone, a few lorry loads of chalk would provide a similar effect though don't expect it to dissolve decades of silt and decaying vegetation, physical removal is the only answer Im afraid.

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Thanks Mick - I'll let the membership know that they are in for some hard mucky labour and not just barrowing in some 'miracle Siltex' - I wonder if there will be a better turn-out for work-parties - or will it be the usual "can't I've got a match"!

Thanks Lads!

I am always skeptical of chemical solutions such as using herbicide. For example, If you dont physically remove the plant material that you kill the decomposing remains will deoxygenate the water and kill the fish and invertebrates. That is unless you do it like nature does - in winter - when the water is cold, holds more oxygen, and the microbial breakdown is slower. But in winter problem weed growth isnt an issue!.

Re Cockshoot, it was the truly great UK freshwater ecologist and limnologist Dr Brian Moss at the University of East Anglia who came up with the idea and i think the work was undertaken in association with the fledgling Broads Authority. Its a pity we never get to hear more about, or from, the likes of Brian Moss (recently retired prof at University of Liverpool) as we only see on our telly's those academics concerned with space exploration or the never-ending stream of inane politicians or wannabee celebrities from the opposite end of the human spectrum.

keora said:

One year, after applying lime, some of the fish died

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Did they find out what killed the fish? I ask because there are all sorts of reasons that can cause a fish kill.

On advice, we only lime about 20% of the lake at any one time, means the fish can get away if they need to when it first goes in.

Stu