So far, we’ve had no blanketweed

The old pond

The old pond

Following heavy rain both ponds are now as full as they get.

The old pond has been clear since the tadpoles became less abundant in the summer.

The new pond has only just cleared – until recently single-celled free floating algae were colouring the water. I expect these will return in spring until there is a reasonable population of water fleas, and other plants get going to compete for nutrients.

Conductivity of the old pond is still very low: just 70 micro Siemens. This is really very good.

The new pond is a bit higher: 155 micro Siemens.

The new pond: looks awful but is developing well

The new pond: good points - the water is clear, plants are beginning to take, there's plenty of animals including some quite uncommon things; bad points - the butyl is showing in places and its hard to keep it covered.

Conductivity is a rough guide to how clean the water is – but you do have to be careful in interpreting the measurements. Water draining from soft rocks such as clay or chalk, will naturally have more chemicals dissolved in it, giving a higher conduvtivity, than water draining from hard rocks e.g granite. But if the water is free of pollutants this doesn’t matter. In any given area – where its unsual to see big differences in background conductivity – then high conductivities are often a clue to the presence of pollution. In the south you start to get suspicious when conductivity is over 250-300.

I don’t actually know why the conductivity is higher in the new pond. It maybe that some soluble chemicals have washed in from the grass turves while they were bare, or it maybe something from the gravel (we did wash it, but it may be that it still had some soluble compounds on it). These may be harmless: calcium, sodium, magnesium. But there may be nutrients too. Only a proper laboratory analysis of the water will allow me to tell.

Interestingly we have never had any blanketweed or filamentous algae in the ponds: I put this down to the presumed low nutrient levels. Although I don’t know if this is the reason for certain, I’m sure it must help.


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