Saturday, 12 January 2013

Airborne pondweeds

The farm fields so rich in shallow subsidence ponds (9th Jan blog) are a snapshot of the ecology we seldom witness. When the oil seed rape was harvested several pools were exposed that had spent the summer behind an impenetrable thicket of brittle stems, shards of seed cases and broadsides of splinters. The ponds seemed caught out, their summer secrets revealed, their inhabitants easy pickings. Two ponds right in the middle of the arable fields were unvieled as home to clumps of fine leaved pondweeds, probably Potamogeton berchtoldii, rather meanly known as Small Pondweed, which is widespread along Druridge Bay, although I’ve not fished out a piece to check. The dense wefts of leaves wallow just below the surface of the shallow water, each leaf a thin, glistening, delicate frond, slightly translucent. The pondweed was not in the ponds in springtime nor had been there in the previous two autumns (although the ponds themselves are sometimes not entirely there, due to the ups and downs of water levels and ploughing). It seems the pondweeds must have arrived this summer. The ponds in summer are the private venues of ducks and seagulls, heron and swans, behind the wall of crops. The sudden establishment of the pondweed looks like an example of colonisation via a vector that has unwittingly given the plants a lift. I cannot be wholly sure; the plants are evidence of possible processes, but this is tricky to demonstrate definitively. I am reassured by the possibility of this hard-to-see ecology going on around us; pond plants have always been good at getting around the landscape. The sheer number of ponds create the opportunity for them to expand out from core sites suring wetter years. The winter wheat shoots are already greening across the field for this year's crop. The Small Pondweed may have found a new pond all to itself or settled in a doomed trap. I'll be keeping an eye on its fate.

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