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Life in Freshwater

Ponds and Lakes - Static Water or Lentic Systems

It is very difficult to define a pond. Generally, they can be described as a small body of static water shallow enough to allow plant material to grow virtually across it. A lake would therefore follow on from this, i.e. where plants cannot grow across the entire area. Lakes are invariably fed by rivers but their outfall is less than the inflow allowing water to collect. Ponds are often the result of human activity and are normally fed by rain, groundwater or occasional inflow from small streams.

A Lowland Pond 
Lowland Pond surrounded by heath. Note the emergent vegetation around the edge, especially in the background. There is an extensive patch of lilies towards the middle with Potamogeton across the middle. Rushes and sedges in the foreground.

A large upland pond 
A large upland pond (or is it a lake?) at the end of a glaciated valley. There is a considerable amount of emergent vegetation of rushes and sedge. Where a stream runs in on the left there are trees (willows and alder) growing where a succession of plants (hydrosere) is developing.

The pond in the above picture is where china clay had been extracted 30 years previous. Gravel, peat and clay removal is a common way for ponds to occur. Other ponds may be located in the centre of villages for watering livestock and this is the reason for so-called "dew-ponds". This has little to do with dew but are places where a farmer has dug out an area and damned a small stream to fill with natural collections of water runoff. These can be used as watering holes or for crop irrigation in dry weather. A reduction in some human activities has led to fewer ponds although the up-surge in gardeners making ponds and water features has turned the tide slightly. Water power in the past has been used to create mill ponds for driving flour mills.

Constable's famous painting of the Haywain
 Constable's famous painting of the Haywain. Note that it is standing in the middle of the mill pond. This was a common maintenance procedure for carts so that the wheels would not dry out (causing the wood to shrink) because if they did the steel tyre would fall off. Another past reason for making ponds

The pond today outside the FSC field centre, Flatford Mill
 The pond today outside the FSC field centre, Flatford Mill. The building, also visible in the Haywain, is Willy Lots cottage. Taken in winter this picture shows a flooded pond. Ponds are often the result of human activity.

Ponds are transient, dynamic habitats. This means that they change with time. Invariably this leads to them gradually filling in with plants to form dry land. This succession is known as a hydrosere.

The large size of lakes means that they are less likely to be caused by human activity but are natural features. The exception is where damns have been built at the end of a valley to stop the river and streams to make a reservoir. Often used for recreational activity as well as human consumption they have a double function. A third might be to attract wildlife, especially birds, although for most the sides will be too steep for plants to grow. The valley above the reservoir might also have coniferous plantations growing to restrict the flow of minerals that could leach into the water and encourage plankton blooms.

Conditions in freshwater systems often blur and it is possible to find pond-like features near the edge of lowland rivers where the flow all but ceases. Plant and animal life will then display communities typical of the pond.

 


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