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Ecology

The following article was prepared for the Radley Lakes Exhibitions staged by
Save Radley Lakes in August 2005 in aid of rescuing these lakes from destruction.

 

The Radley Lakes were formed by the extraction of limestone gravel over the second half of the last century. The gravel deposits lie on top of the Kimmeridge Clay belt, so the underlying substrata are water impermeable. Excavations below the water table will therefore result in the formation of lakes.

In the early 1980s, these gravel pits were considered an eyesore and measures were started to fill them in.

However, left to themselves, water-filled limestone gravel pits provide an important habitat for wildlife. First of all the water is very alkaline (hard) and clean as a result of natural filtering by the gravel. Provided that the surrounding land is not subject to any form of intensive agriculture that could give rise to pollution of groundwater and surface water by fertilisers, composted matter, etc, it will also typically be low in nutrients. This gives rise to a specific habitat type known as “hard oligo-mesotrophic water”. Such waters can support an unusual type of primitive aquatic plant-life called stoneworts. In this event, the habitat type is known as “hard oligo-mesotrophic water with benthic vegetation of Chara spp.” Chara being the scientific name for some stoneworts. The Bullfield Lake and, very likely, the larger Thrupp Lake are of this habitat type. This combination of factors, is, it seems, sufficiently unusual for such habitats to be so rare as to qualify for protection under the European Habitats Directive as a Special Area of Conservation.

The Radley Lakes have become interesting for several other reasons: Their age (the majority of gravel pits are younger or have been filled in) the lack of agriculture affecting the surrounding land and the fact that they and their surroundings have, for the most part, been neglected by human activity, or have got on quite well in spite of it. The in-filling of the nearby lakes has had an effect too. The Last Lakes have become a refuge for species that have been displaced from the lake areas that have been destroyed. This is believed to have resulted in significant local species enrichment and accounts partly for the unusual biodiversity within what is quite a small area. Also, the lakes provide a wetland habitat only in their immediate vicinity, where they support a range of hydro-philic trees such as Willow and Poplar. Only a short distance away, the free draining gravel subsoil dries out in summer, so that one then finds wetland and dryland habitats in close proximity. The poor quality of the soil, disturbed or removed during the gravel extraction, also means that lush vegetative growth does not occur widely and a range of plants adapted to this type of environment can thrive.

Central to this are the lakes themselves. Under the water, they support benthic vegetation, molluscs, fish and insect larvae. The lakes are a habitat for birds. Many birds demand expanses of water for refuge. Others need to feed on what they can find in the water. Aquatic mammals, such as otters and water voles do likewise. Perhaps the most important way that the lakes affect the surrounding ecology is through insects. Many insects breed in still water. These lakes support huge populations of damselflies in particular, also dragonflies, mayflies, and some smaller insects that may sometimes be less welcome. These insects are a principal food source for many creatures that inhabit the lake surroundings, including insectivorous birds, spiders, and, very particularly, bats. Go down to these lakes on a summer’s evening at dusk and you will find bats everywhere they can fly and where there are insects to be found. Insects are also pollinators and are often specific or partially specific to a range of plants.

The insect biodiversity around the lakes is quite staggering, and is reflected in many of the photographs on show at the exhibition.

The trees around the lakes depend on the lakes for sustenance and provide refuges and roosting places for birds and bats. They also sustain a range of additional insect species, as well as provide food and refuge for animals and birds.

The lakes and their surroundings are now a self-sustaining ecological system. No proper management of the site for conservation has ever taken place, apart from some maintenance of the lakesides by fishermen, and the keeping of paths clear. The lakes remain clean with a healthy stock of fish. There is thriving biodiversity.

Take away the lakes, the trees will die or be destroyed in the process; most of the insects will disappear; the birds and bats that depend on water, insects, or trees will disappear. One will be left with a relatively impoverished semi-dryland habitat.

RWE Npower have offered to “restore” the area to nature conservation. “Restore” is not an appropriate word in these circumstances, nor perhaps is “conservation”. After infilling is completed and the fences taken down (an estimated quarter of a century hence) the area will require intensive management in order to achieve a respectable result in an acceptably short time. A proposed “wetland area”, on top of the ash, will not be permanent throughout the year and will require management to maintain correct water levels. What will be found there will be the result of gardening, not nature.

What is there now is entirely down to nature, albeit with a little inadvertent “help” from man along the way. This is what makes it so important and interesting to ecologists and conservationists and so valuable to true lovers of wildlife.

 

Permanent link to this article: http://www.radleyvillage.org.uk/ourvillage/nature-2/the-radley-lakes/ecology/