Topping up problems and tadpoles

A couple of thoughts about dead tadpoles and topping up.

One thing that might be responsible for tadpoles dyng is heat. The lethal temperature for tadpoles is around 35 – 36 C: for young tadpoles, water at this temperature can kill 80% or more. Older tadpoles are more resilient.

We saw mortalities in our (open to full sun) New Pond in the very hot days we had in May; although we weren’t measuring temperature at the time, measurements we’ve been making during the latest warm weather suggest that the pond was at, or very close to, the tadpole-killing temperature in May. And we certainly had quite a lot of dead tadpoles, although some did survive – an outcome which was pretty consistent with the idea that their deaths were due to the high temperatures. We also had dead water slaters and it seems pretty likely to me that this was also due to heat. There are lab studies showing Daphnia are killed by water temperatures around the mid 30s, so it seems quite possible slaters could go the same way.

The possibility raised by Alison is that her dead tadpoles were due to the chemicals added to tapwater to disinfect it – to kill bacteria and viruses. Traditionally, chlorine was used to do this. Chlorine is still used in water treatment but modern processes also include the addition of ammonia to generate chloramines.

Chloramines are used to treat drinking water because they reduce the risk of what the water industry slightly coyly calls ‘disinfection by-products’. These are the chemicals inadvertently formed when chlorine (amongst other things) is added to the water and reacts with organic matter to form by-products which are implicated with causing cancer – obviously not a good thing to have in drinking water.

Unfortunately chloramines are both toxic to aquatic organisms and don’t simply evapoarate – they have to be positively removed.

I haven’t have a chance to look at what data are available on chloramine toxicity to amphibians – beyond seeing lobby group websites which claim they are toxic. So whether adding tapwater equivalent to 10% of the volume of the pond (which is what Alison did) is enough to kill tadpoles I don’t know yet: my suspicion is that it wouldn’t be, since it’s not something a lot of people have reported. But I will dig a bit deeper here.

What all this does point to is that it seems increasingly important to me that the first thing you have to think about with making a pond is not the size, shape, depth, location or plants. It’s how to locate a clean, unpolluted, water supply which is safe for wildlife and which will be available throughout the drier times of the year.

In a world where a lot of the water that comes out of taps contains contaminants, obtaining this water requires a bit of planning.


9 Responses to “Topping up problems and tadpoles”

  1. Diana Says:

    Our new pond which has only rainwater is diminishing quite quickly now as there has been so little rain. We had a shower this evening but not much change in the level of the pond. It’s not in full sun until mid-day thankfully otherwise there might be little water left. I was hoping to plant some marginal plants but the water has retreated. I shall have to stick to floating plants I think this year or at least until we get more rain. As the pond is new, life is limited to beetles and we do have a few beetle larvae or at least what I think are beetle larvae. Not the great diving beetle but one of the lesser beetles I think. We are really trying not to top up with tap water but I wouldn’t like the pond to dry out completely. I never thought I would be praying for rain! Our old pond has always been topped up with tap water but only in very hot weather and is much deeper with a lot more vegetation. At the end of last week, we did have two or three small frogs but I have not seen them this week. There are also still tadpoles developing and beetle larvae. It has probably not been quite so hot up here in the north.

  2. Jeremy Biggs Says:

    Hi Diana

    I can’t remember whether we discussed before the condition of your tap water. I seem to remember you’re in Scotland – is that right? If so, it might be that your tapwater isn’t so bad.

    Or you could see whether you could scrounge some rainwater butt water from a neighbour – people quite often have some they don’t use!


  3. Robert Says:

    Here in rented accommodation in the inner city (London), we have no choice but to top up our wild life pond with tap water. It would be very useful to know how we can remove the unwanted chemicals from this tap water.

    • Jeremy Biggs Says:

      Hi Robert

      I’d be interested to know where you are roughly. I guess you have a garden? Are there any roofs nearby that water could be sourced from?


      • Robert Says:

        Hi Jeremy,

        In a garden flat in Deptford, London. There are no downpipes from the roof in our garden, and we can’t place anything for collection in the communal area. The roof is filthy from pigeons and from the dirt raised by the passing traffic. Perhaps there is some quick and easy way to filter the tap water?


  4. Alison Says:

    Hi Jeremy

    Thanks for the interesting and helpfull information regarding topping up/dead tadpoles. The timing of the dead tadpoles coincides perfectly with the uncomfortably hot weather that we were having at Poulton-Le-Fylde, Lancashire at the time. The pond is small but does spend some time in the shade.
    I am now going to collect rainwater from my greenhouse guttering in a bucket and use this to top up as often as it rains.


  5. Diana Stevens Says:

    We have been lucky – yesterday and last night it rained so we have two full rainwater tanks so pond can be topped up a bit. Won’t be completely full but at least it will not getting any worse, just yet. Hope other people have had some rain too.

  6. christine taylor Says:

    We have a small pond in our garden (Widnes Cheshire) it was full of tadpoles, but I noticed last week a lot of them had died. I emptied the pond and removed all the dead ones but I filled the pond up with tap water. But what could have caused them to die in the first place. I look every day and they are still dying??

    • Jeremy Biggs Says:

      Hi Christine

      It wasn’t quite clear. Are they still dying? Let me know, and I’ll come back with some suggestions – though I’m not sure its going to be possible to give a definitive answer.


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