Clear water question

[ramidg]

My pond is a large hole dug into the clay layer through the two feet or so of top soil in what I guess is the wider flood plain for the Trent, we are about a half mile from the river and 50 feet above current river level. The pond clear water depth is about 5 feet maximum late spring and about 3 feet minimum late summer. There is about 2 feet of rotting leaves in the deepest parts below this. Last winter all the fish (carp)perished. The heron was very busy this spring, but is no longer visiting, so I suspect the fish were weak after the hard winter but are now all eaten. I have not seen any fish all summer. Frogs toads and newts all turned up as usual and have bred in abundance, dragon flies too, so their larvae clearly survived the winter. The king fisher still visits so is catching enough to make his trip worth the effort, on the occasions I have been close enough to watch it is not fish he is catching. All the usual weeds have grown. I limit maintainence to keeping the middle third of water surface clear once the tadpoles arrive, just raking the excess growth to the margins. This year for the first time ever the water has remained crystal clear all summer. It is normally clear early in the year and goes cloudy as temperatures rise in spring, but it has not happened this year. Is this because there are no fish in the pond? Forgot to say when I first posted that I have never added any food to the the pond.

[Wild-Woman]

Cloudiness or an algae bloom that occurs in ponds/lakes is a result of growth during sunny weather. Photosynthesis that produces food for growth sometimes causes overgrowth of algae/plants which die, are broken down by bacteria in the pond which in turn raisies the nitrate level therefore the dissolved oxygen level goes down, which inturn kills off more living organisms and the balance of the pond is unfavourable.
Your pond is probably well balanced. It may be that there just hasn't been so much sun.

[ramidg]

W-W thanks for the response. It does not feel like we have been short of sun this year, but there is another clue in your response, (another thing I forgot to mention in my initial post). The pond is surrounded by trees, the trees were started after the pond was dug about 25 years ago, with predominantly broad leaf on the south west side, and so the amount of tree shade will be increasing year on year cutting down the amount of light to the pond. The branches do not extend over the water, but the trees are higher than the pond is wide.

[JohanJ]

Yes, your water is clearer because the carp have gone - which had a variety of effects. The obvious one, carp produce a lot of waste so eventually that becomes food for algae. But other less obvious effects are that carp eat bloody everything so you've probably got a few more weed in the water itself than before, which itself means more shade so less light for algae. And carp are also bottom mulling creatures so they murk up sediment etc. So, given you didn't feed them, it's unclear precisely which of these three effects is the main factor for your clear water - probably a bit of everything - but it's the carp absence that's key.

[King Edward]

It does sound as if the absence of fish is related to the clear water. Apart from turbidity caused directly by their rooting in the mud, the disturbance to the sediment was probably also releasing nutrients from the bottom back into the water, resulting in more algal growth.

If you search online there are some photos of Kingfishers catching and eating Great Crested Newt larvae, so it may be those they are after (if you have them). I guess they'd probably take adult Smooth Newts as well.

Do you intend to replace the fish, or leave it without for the time being?

[ramidg]

Thanks for your interest and replies.
Johan: Last year there were pink clouds of what I took to be water fleas but this year much fewer, is this another indicator of lower nutrient levels? The pond is not linered and weed grows everywhere. I rake the floating stuff as completely as I can until the tadpoles arrive, used to be mostly duckweed, nowadays its mostly frogbit, then hook the stuff that grows from the bottom and pull it to the margins to keep the middle water surface clear. This is slowly exposed and dries as the water level drops through the summer. The pond is donut shaped and I keep some clear water all round for the wind to circulate the water.
KE:My eyesight isn't good enough to tell what the kingfisher is catching currently, but they are definitely not silvery and wriggly like a fish. Looking in the water the newt tadpoles are the probable prey, they still have their gills but some are starting to take a gulp of air from the surface now. I think they are common newts, they are all over the garden, I have never seen a GCN in there. I have been reading other watery posts on here and came across the comment in one that GCN will not inhabit a pond with fish, I was contemplating stocking with sticklebacks for the kingfisher's benefit, but after seeing the GCN comment decided not to. There definitely seems to be more insect activity this year, I counted over 20 of the big dragonfly larvae skins a couple of weeks into the warm spell a couple of months ago, definitely more than normal, and the group of whirlygig(?) beatles is about 4 times bigger than usual, in conjunction with the clear water its getting more interesting without the fish.

[King Edward]

My grandfather's goldfish pond here has quite a lot of Great Crested Newts, but their breeding success appears to be very low with only a few large larvae visible. Fish were temporarily absent last year, so hopefully they had much better breeding success then. Overall, the amount of visible life in this pond is far, far less than in the new fish-free pond I made earlier this year, which is teeming with Daphnia, Mayfly larvae, Water Beetles & larvae and more. Should be even more next year once amphibians and dragonflies are breeding. The water clarity is also far superior without fish - some blanketweed but sparkling clear water, compared to constant suspended sediment in the fish pond.

'Pink clouds' does sound like a good description of water fleas (Daphnia), so fewer of them would indicate less suspended algal growth in the water. So I think you're right that this also indicates that nutrient levels are lower overall. Presumably the carp don't bother the Daphnia, feeding mainly on the bottom.

It'll be interesting to see how the numbers of Dragonflies and other insects continue to build up without the fish - hopefully a lot more 1st year nymphs will survive this year and give you a bumper quantity next summer. What plants do you have in there apart from the Frogbit?

[ramidg]

Plants I introduced are Canadian pondweed and a few lillies. Millfoil arrived by itself. There is also a millfoil that is long strings but I'm not sure if it is different to the ordinary millfoil or another part of the same plant. Curly leaf also arrived a few years ago. I did have bullrushes arrive but they grew from one side to the other and stopped the water movement so I dug them out. I also dug out the large white lillies for the same reason, the remaining lillies are garden centre varieties which are smaller and do not spread into the deep water. I can see a few clumps of blanket weed growing from the bottom (now the water is clear). Yellow iris grows in and around the edges. Any of the duckweed/frogbit/Canadian pondweed would fill the pond by mid summer if I did not rake it.