Our pond has had a green bloom for the last year. The bloom is composed of microscopic algae, tiny single celled plants. When the bloom first occurred last April, I thought the bloom, by cutting out light, might kill off underwater plants. But there was no effect over a month or two, so I forgot about it.
A few days ago, I looked for elodea (Canadian pond weed) and couldn’t find any at all in the pond. A year ago, we had lots of it in various areas of the pond. Elodea is an underwater plant that roots in the bottom of the pond. It is probable that poor light, due to the bloom, has killed it off. Which is unfortunate as elodea has been a valuable oxygenator in the pond.
All plants give off oxygen when they photosynthesise as in this simplified equation:
Carbon Dioxide + Water + Sunlight = Glucose + Oxygen
Those plants which are under water give their oxygen to the water, and so we call them oxygenators. Plants above the water like pond irises give off oxygen too, but it goes into the air.
Oxygenators are necessary in a pond to supply oxygen to animals such as tadpoles, newt larvae, damsel and dragon fly larvae, and other animal life in the water. Elodea was not the only oxygenator, we have hornwort, a free floating underwater plant, but there seems to be less of it.
Another oxygenator we have is starwort. I have not noticed this one before. We don’t have much starwort and so should encourage it. It has rosettes of star like leaves, and floats on the water with some leaves submerged. It is the submerged ones that supply oxygen to water, those floating give it off to the air. There’s also a few strands of crowfoot, and I mean a few; another to be encouraged, as some of its leaves are underwater and so oxygenating.
We are considering what further plants we might add to the pond, having lost a prime oxygenator in elodia. Excluding plants that root in the water, fearing they will suffer elodea’s fate, we want free flowing underwater plants. Willow moss is a candidate. It is rootless, so is what we require, but we don’t want it sinking to the bottom especially in deeper areas, where it would likely die because of lack of light. It would be worth getting some and experimenting.
If we get willow moss, that would give us as oxygenators: hornwort, starwort, crowfoot and willow moss. That hopefully would improve matters but a further problem is that the deeper areas of the pond are virtually plant deserts, poor in oxygen. There is little mixing in the pond, as unlike say a stream, there is no flow. This means oxygen rich areas are unable to assist the oxygen poor areas. We need to bring about flow. My remedy would be a solar powered oxygenator. I have looked on Amazon, there are a number which might be suitable, costing £30 to £50. Such an oxygenator would aerate the pond, supplementing that from the oxygenating plants, and bring about flow in the pond giving us mixing of the water in order to aerate the whole pond.