Wednesday, 27 November 2013

Flood, drought ... and now the plough

 The modestly named Small pond weed, Potamogeton berchtoldii, (or, less modestly, Berchtold’s pond weed, because that is what the Latin says) is nonetheless a canny plant, turning up in ponds across Druridge Bay, including unlikely sites in the middle of arable fields. The delicate, filigree strands of stems and leaves seem ideal to fragment, stick to birds and be carried between sites. This little pondweed also seems able to tough it out in exposed shallows or ponds with slightly higher salinity, which seems to come up from underground springs. Although it is a flowering plant this species relies on cloning to spread using ramets; individual plants that, together, form the whole vegetative colony. To over-winter the pondweed sets turions, essentially a bud, but a bud adapted to tough it out during the lean times, functionally akin to a seed or bulb  in other species. Just how tough this overlooked pondweed can be is under severe test in some of the subsidence ponds at Blakemoor Farm. The warm summer has seen water levels fall far enough for several subsidence ponds to be ploughed through, including the wide but shallow site featured on the blog as it began to dry out.

The cracked, dried soil from the sequence earlier in the year (2nd September blog, compare the drying sequence in the photos above to the latest ploughed state of the pond at the top of the blog) is now tilled and turned, the pond which was once the summer hang out for avocets , teal and black headed gulls is barely detectable. Whether ramets and turions cope well with ploughing I do not know, although I suspect the plant will recolonise once the pond refills. On the 20th November the site was just the bare, ploughed ridges but by the 27th a silver flash of water had puddle across the lowest part of the shallow basin. Potamogeton berchtoldii is not a rare plant: the map shows the national records from the NBN gateway data base since 1980. If anything it may be overlooked given the small size and identification challenges

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