Our blog often refers to the experimental ponds at Hauxley Nature Reserve. They consist of 30 ponds, each ~ 1 metre square, dug out in autumn 1994 to create replicates in which the colonisation and development of animal and plant communities could be followed. Here is a view of the site with the ponds visible as squares in the middle distance and, below, the day they were dug.
The small size was primarily because I had for five years studied the pondlife of similar sized ponds created by the removal of coastal defence anti-tank blocks at Aberlady Bay, a reserve near Edinburgh. The Aberlady ponds showed a striking variation of animals and plants even between adjacent pond; ponds the same age, size, shape and (almost) location. Below is a photo of two of the Aberlady ponds, the nearest with clear water above a sward of Pondweed,
Potamogeton lucens, the furthest choked with bright green stonewort,
Chara sp. For an ecologist interested in why plants and animals are where they are this startling difference was an irresistible topic. Trouble was that at Aberlady the ponds were already ~25 years old. The Hauxley ponds would allow me to track their history from their origins onwards.
The main work at Hauxley consisted of regular sampling of the invertebrates in early summer, trying to catch the ponds before they dried out. The sampling was simple, recording presence/absence rather than taking away samples to record the populations of different species. The early summer plants communities have also been recorded along with the dates at which ponds dried or reflooded. The main animal sampling was kept up for ten years. Plants have been recorded every year. The ponds have endured years of drought and flood and provided the nearest we can get to an ecological time machine. More recently we have realized their value for exploring the impact of extreme events and carbon capture in ponds with a recorded history, a classic example of how science often works out serendipitously.
The Hauxley ponds have revealed complex patterns of colonisation and change by both animals and plants. Part of the pattern is classic ecological succession, a sequence of species establishing starting with pioneer species that arrive quickly and survived in the bare, exposed mud to be followed by slower colonists and species that require the shelter of aquatic plants. Super-imposed on this pattern are ups and downs associated with dry or wet years. The photos below show one pond photographed every year in early summer to give a feel for the changes.
In the first two years the substrate remained largely bare, drying out in late summer. In June 1997 unusually heavy rainfall stopped the ponds drying out. Aquatic grasses, e.g. sweet reed grass
, Glyceria fluitans, and spike rush
, Eleocharis palustris, formed thick swards. The ponds only dried out again in summer 1999. The pioneer animals of the first two years, including several ostracods and copepods, had been largely replaced by invertebrates typical of more permanent ponds. However with the resumption of summer dry phases these animals started to be lost from ponds, although it took two years for these losses to be widespread. The grasses and spike rush also declined, as you can see in the pictures, suffering not just from the drying out but also grazing by rabbits. By 2010 the pond looks increasingly terrestrialised, most obviously with the colonisation by docks plants
, Rumex sp
. The pioneer animals that thrived in the ponds during their early years dry phases did not return, perhaps unable to establish in the dense moss mats which had covered the bottom of the pond creating dark, anoxic mud
. The Hauxley ponds have provided a window into the reponses of both animals and plants to variations across the years, including heatwaves as in 2006 or very wet years such as 2012.
No comments:
Post a Comment