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Thread: pH of lake

  1. #1

    Question pH of lake

    Last year I started a thread on the pH of my local lake, that I measured at 6.8 and worried that it might be too acidic. I've subsequently monitored the pH for 9 months. All through the winter it was around 8.4 - 8.6. However, since the weed has become prolific it has varied within the day, being acidic early in the morning and basic late afternoon. From my reading it looks as though this is typical of a lake in which there is insufficient calcium buffering capacity to neutralise the release of carbon dioxide in the night by the weed. The high pH in winter is due to the release of ammonia by the decaying weed. From talking to other members, it appears that the weed problem has only been critical in the last few years. The lake owner made a throw-away comment at our AGM that if we want the water level to be raised, he could again pump water from the neighbouring stream. So it looks as though his previous pumping efforts may have introduced fertilizer from the stream into the lake and encouraged the proliferation of the weed. The same thing happened at a carp lake I used to fish a few years ago. The only way I can see of reversing this change is to reduce the nutrient content by mechanically removing the weed and depositing it well away from the lake, so that the nitrogen released by the decaying weed does not get washed back into the lake. Although there is no evidence that this daily pH variation is toxic to fish or invertebrates, I'm sure it must be sub-optimal and could affect invertebrate population and health. The excessive weed is also a problem though it is being partially controlled by using a blue dye. Has anyone else experienced this and have any comments?
    Last edited by kingf000; 08-06-2019 at 12:45 PM. Reason: spelling mistake

  2. #2
    Join Date
    Oct 2007
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    Wiltshire
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    Default Re: pH of lake

    A pH of 6.8, while being on the acid side of a neutral 7, is by no means too acidic. 8.4 - 8.6 is well up the alkaline scale. pH values DO tend to fluctuate naturally, but what you descibe is quite a wide variation.

    You mention the farmer pumping in from a neighbouring stream and I wondered if it was not directly connected to the lake. That appears to be the case from your description and I wondered if you had taken pH readings from there as well to try to establish some sort of baseline. It seems more than likely that nutrient has got in from somewhere, but I am surprised that this has resulted in growth of rooted weeds rather than an algal bloom which would appear to be more likely.

    The use of Dyofix certainly helps to control both rooted weeds and algal growths by cutting down the available light reaching the plants. I would be inclined to continue that treatment rather than go down the path of mechanical removal which I have very recently heard quoted as between £550 and £750 per day, and you remove the cut weed from the banks afterwards.

    Mechanical removal won't cure the problem, but is likely to cause a surge in weedgrowth post-cutting with consequent effects on the pH of the water.

    If the fish and the inverts seem to be unaffected then I would not worry overmuch. You could consider the use of floating reed islands which suck nutrients directly from the water column due to the root curtain hanging down beneath the island. These need annual management but are worth the effort.

  3. #3
    Join Date
    Mar 2013
    Location
    Sussex
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    569

    Default Re: pH of lake

    Yes, we used blue dye. It was a waste of time and money. It looked toxic and nobody wanted to fish in the lake. It does not kill weed growing in water less than a metre deep as the sunlight still penetrates to that depth. We partially drained the lake and left it fallow over winter. The marginal weed died and the water cleared.
    https://sussex-trout-fishing.com/

  4. #4
    guest54 Guest

    Default Re: pH of lake

    It is a simple fact that any excess nutrients present in the water will encourage some organism to exploit it, be that weed or algae. Even mechanical or chemical effort to remove or kill the weed does not solve the problem of excess nutrients entering or being present in the water, you have to go back to basics and tackle the problem at source, only then do you have any chance of succeeding. Of course adding more fish will add the the nutrient load which is why aquarist's mature a tank or pond before even thinking of stocking with fish or invertebrates.
    Some success has been achieved in nitrate reduction on small bodies of water by the use floating reed beds which grow in the summer, absorbing nitrates and then the top growth is removed for composting before they die off in winter, the whole process has to be repeated year on year so is not particularly inexpensive and the floating reed beds need to be quite a size before they can be effective, they do however give shelter and a home for many creatures including fish. When large enough they also reduce evaporation, suppress underwater weed growth and keep the water cooler than would otherwise be the case.
    They would need to be anchored in place but if this is done in marginal water with spaces for fishing, it could well be part of the answer to controlling weed and excess nitrates/phosphates. It would also improve the fishing IMO.

  5. #5

    Default Re: pH of lake

    We would be delighted if we could get the pH of our loch as high as 6.8. It never gets as high as 6!

    Col
    Please note that any views expressed in this post may be those of the
    originator and do not necessarily reflect those of the reader.

  6. #6

    Default Re: pH of lake

    Many thanks for the comments. The stream runs alongside the lake in a ditch and is not directly connected to the lake. Although the blue dye worked well last year, this year it doesn't seem to have been as successful, with large growths of canadian pondweed and something that I think looks like watermilfoil, long strands of weed that covers the surface in the 8-10 ft deep water. It may be that the dye was added too late so the weed had already got established and so close enough to the surface to thrive. In summer, fishing deep can only be done with a boat right out in the middle of the lake. My thoughts about mechanically removing the weed would be that, similar to harvesting with the floating island, you would be removing the nutrients that make up the weed, and so not be there to decay in the winter. Hopefully we would get enough members to help with the clearance. However, as said, dying fish, of which there seem to be a lot over the summer, would replenish the nutrients.

    There is much debate in the club over whether there is a lot of food in the lake or not. Some members get quite upset at the suggestion that there is insufficient food for the fish population, even though this is the case with 90% of stocked lakes. Their argument is that a lot of the fish survive and grow, I have seen trout feeding on dead fish on the bottom of lakes. However, my observations are that there is rarely a prolific buzzer hatch, either from the number of midges around or the absence of huge numbers of floating shucks. There are often quite a lot of fish topping and tailing, but buzzer patterns, whether emergers or others, catches well in early spring but doesn't later on, or at least only with recently stocked fish. I've seen a few sedges and olives, but not that many. Other food sources are sticklebacks and damsels. Some members say there are also freshwater snails, but I've only ever seen a few great pond snail shells. For most of the year, the vast majority of fish are caught on lures, damsel nymphs and hoppers. I don't think anyone has caught on, or even tried, snail patterns. Might be worth trying for the top and tailers?
    Normally high pH is good for invertebrates, but that is where the basicity is due to high levels of calcium bicarbonate and carbonate, eg in chalk streams etc. I haven't been able to find out whether high pH due, I presume, to ammonium carbonate and bicarbonate, is beneficial or harmful, though free ammonia is harmful. Also large changes in pH between night and day doesn't seem to be toxic, but I'm unaware of any studies on effects on growth rate etc. of fish or invertebrates.

  7. #7
    Join Date
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    Default Re: pH of lake

    We have a 3 acre lake with similar issues, namely excessive weed growth and filamentous algae. Over several years of trying various remedies including chemicals, dye, cutting and removal we have settled on a solar powered "algae buster" which uses sonic waves to break up the algae and effectively removed algae as a problem. The downside of this is that the resulting clear water promotes weed growth (mostly Canadian Pondweed) so we cut the weed once around mid-June and remove as much as possible. We don't cut the whole lake but concentrate on a smaller area near popular bank fishing locations as leaving a weedy area gives some protection from cormorants. We were having some success with chemicals but every time we found one that worked it was banned! As our water is typically 10 - 20 feet deep we use blue dye as a growth inhibitor but many members don't like it.

    The pH is usually around 7.2, there is plenty of food, we have snails, damsels, buzzer, sedge and a few ephemerids and fish over-winter quite well. There is a pair of resident swans that eat some weed.

    You will never really get on top of excessive weed growth and unless you have many willing hands, removing cut weed can be a problem

    - - - Updated - - -

    We have a 3 acre lake with similar issues, namely excessive weed growth and filamentous algae. Over several years of trying various remedies including chemicals, dye, cutting and removal we have settled on a solar powered "algae buster" which uses sonic waves to break up the algae and effectively removed algae as a problem. The result of this is that the clear water promotes weed growth (mostly Canadian Pondweed) so we cut the weed once around mid-June and remove as much as possible. We don't cut the whole lake but concentrate on a smaller area near popular bank fishing locations as leaving a weedy area gives some protection from cormorants. We were having some success with chemicals but every time we found one that worked it was banned! As our water is typically 10 - 20 feet deep we use blue dye as a growth inhibitor but many members don't like it.

    The pH is usually around 7.2, there is plenty of food, we have snails, damsels, buzzer, sedge and a few ephemerids and fish over-winter quite well. There is a pair of resident swans that eat some weed.

    You will never really get on top of excessive weed growth and unless you have many willing hands, removing cut weed can be a problem
    Last edited by sewinbasher; 11-06-2019 at 03:45 PM.
    “There is no more lovely country than Monmouthshire in early spring. Nowhere do the larks sing quite so passionately, as if somehow inspired by the Welsh themselves. There is a blackbird on every thorn and a cock chaffinch, a twink as they call him there, on every bush...... It moved me profoundly. I had been spared to see another spring, and I thank God for it.”

    Oliver Kite
    “A Spring Day on the Usk”
    A Fisherman’s Diary

  8. #8
    Join Date
    Oct 2007
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    Wiltshire
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    Default Re: pH of lake

    Don't forget that as soon as you disturb the bottom sediments which is very likely to occur as part of the weed removal process, you will free up any nutrients that are locked in to that sediment. Thus the whole process with start over once more. In fact probably worse as those freed nutrients are likely to be used up by an algal bloom.

    Mechanical cutting is like pruning roses - it encourages fresh growth.

    I don't know if anyone is still using grass carp to control weed growth in a stillwater fishery. I was involved in an early experiment using that species and it certainly worked well and furthermore, as they grow they become worth more money per fish. I still have some of the reports on how that went tucked away somewhere.

    After a rapid search I have found the summary document that covers 14-15 years of work at a gravel pit trout fishery using grass carp as a biomanipulation method. PM me your email and I'll send it to you.

    Chemical treatment MAY be possible but this depends on a lot of factors and needs to be discussed at some length with experts in that field AND needs to be undertaken with great care to avoid DO sags due to the weed breaking down and the consequent mortalities that can go with it.
    Last edited by BobP; 11-06-2019 at 04:03 PM.

  9. #9
    guest54 Guest

    Default Re: pH of lake

    Using dye as you described is a sticking plaster over an amputation. Sure it worked last year but holding the weed back for one year only allowed the nitrates and other nutrients to build up so that the following year there is an abundance for the weed to feed on, hence the increase in growth rate. As I said you have to get to the root cause to understand what is happening, only then you can make some sort of informed decision on how to proceed. Cutting back the weed just makes things worse the following year because the nutrients are still there waiting for whatever weed is left to exploit, remove all the weed and algae will take over.
    A prime example of nature at it's best in these circumstances was an Irish lough in the west of Ireland, gin clear with healthy weed growth around the margins and fantastic fish stocks, including trout, it was surrounded by huge reed beds so dense that the only access to the water was by boat of platform, which were neglected and very unsafe, that didn't stop me though, four hours of non-stop fish. Given the chance nature will find a place for reed beds to take hold, learn from nature.

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