Ullswater - the Lake
by Tim Clarke
Some Ullswater statistics
Every lake has its own characteristic fauna and flora, depending upon a range of variables. These include the composition of the underlying rock, the nutrients in the water, temperature, acidity/alkalinity, rainfall, depth, turbidity, and water flow. The impact of human activities has an influence too. Offtake of water, inputs from agriculture, sewage outfalls, fishing, tourism, all affect the ecology of the lake.
Ullswater has a number of distinguishing features, including an endemic fish, the Schelley.
However, unlike most other Lake District lakes it has no Pike – a top predator. Freshwater ecologists have been intrigued by these and other peculiarities for over a century.
The Arctic Char used to be present in Ullswater but scientists think it became extinct before 1940, probably due to lead pollution from the Greenside Mine.
Food Webs in Ullswater
Ecologists will often describe the relationship between the flora and fauna of an ecosystem in terms of a Food Web.
At the base of Ullswater's food web are the phytoplankton. They float in the surface waters and are made up of one-celled diatoms and blue-green algae (Cyanobacteria). They get their energy from photosynthesis. The phytoplankton are fed on by zooplankton – a diverse group, including water fleas, copepods and rotifers. Many are predators, feeding on each other as well as on the phytoplankton.
The zooplankton are in turn fed on by small fish such as minnows and the minnows are eaten by larger fish and by birds, such as herons and cormorants, as well as otters.
There are also floating and submerged plants which form food for a variety of invertebrate species, as well as birds such as mute swans, coots and others who feed on both the plants and the animal life on it.
When dead plant and animal material falls to the lake bed it forms food for a variety of decomposers who break it down and return the nutrients to the system.
Monitoring the lake
An analysis of the sediment at the bottom of the lake yields fascinating information about the history of the lake over time. A core sample taken in 1979 showed that whilst in general terms the ecology of the lake has been quite stable, during the last 5,000 years the pH has changed from 7.6 to 6.7 – the lake has become more acid.
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