Why am I getting blanketweed?

Where did this come from?

Rather to my surprise, the New Pond is getting quite a bit of blanket weed growing on it.

I’d expected not to be suffering from this as I’d assumed that the both the Old and New Ponds had the low nutrient levels you expect in unpolluted waters. This winter phosphorus and nitrogen concentrations in the New Pond were low with just 28  microgrammes of phosphorus in each litre of water – and under one milligramme of nitrogen.

But this week we’ve measured the phosphorus levels in the pond again. Phosphorus is essential for plant growth but too much of it is like living just on burgers. Because of this, phosphorus is both a fertiliser and also one of the most widespread and pernicious pollutants in ponds, lakes and rivers.

And now phosphorus has risen to around 200 microgrammes per litre in the New Pond. What I haven’t worked out is where it has come from – although its possible its simply the result of the low water levels leading to chemicals becoming more concentrated.

Fortunately the blanketweed doesn’t seem to be causing too many problems at present: Lesser Pondweed and Small Pondweed are both growing well, as is the stonewort we added from the local gravel pits. We’ve also still got a little bit of Water-violet as well.

Having four kinds of submerged water plants is quite a bit better than the most ponds in the countryside which, sadly, are too degraded by pollution to support this variety of water plants.


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