Ullswater - the Lake

by Tim Clarke

Banner Image © Janet Wedgwood

Ullswater's beginnings

Ullswater is one of 16 major lakes in the Lake District, created about 10,000 years ago. Its ribbon-like shape was caused by glaciers carving deeply into the underlying rock as the overlying ice sheet melted and retreated. The basin of the lake is largely made up of a sedimentary mudstone created some 500 million years ago. These rocks, belonging to the so-called Eycott Group are related to Skiddaw and Borrowdale volcanic rocks. As the land rose, water was retained in the carved out valley bottom, along with the fauna and flora within it. Over time, rainwater and meltwater from streams around the lake changed its chemical composition. Even today this process is continuing.

Some Ullswater statistics

Ullswater is the second largest and second deepest lake in the Lake District.. It is about 14 km long and 1 km wide, with a characteristic dog-leg kink in the lake near Howtown associated with a geological fault in the underlying rocks. The average depth of the lake is 25.3 metres, with a maximum depth of 62.4 metres.

Ullswater is situated 145 metres above sea level. The lake water flows from South to North, flowing out into the River Eamont at Pooley Bridge and on to the River Eden. The water flows out of the lake at about 9.3 cubic metres per second, with the result that the bulk of the water (223 million cubic metres – the equivalent of abut 90,000 Olympic swimming pools!) is turned over less than once per year.

The importance of Ullswater's scientific and ecological status has been recognised since1984 when it was classified as a Site of Special Scientific Interest. It has been a National Nature Reserve since 1993.

Ullswater's inhabitants

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.

Above: Schelley Wikimedia CommonsBelow: Pike by Marcel Einig from Pixabay

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.

Food web illustration by Mark Richards

Monitoring the lake

There are several institutes in the region that regularly conduct surveys of the lake. These include the Freshwater Biological Association in Ambleside and the UK Centre for Ecology and Hydrology in Lancaster. They produce reports that can be consulted for more detailed information.

Their studies show that the water quality has been relatively stable over time. However there are significant seasonal variations that reflect the degree of mixing of the water and the variation in temperature.

The lake also changes in level. After heavy rains the level rises significantly as water from the surrounding hills flows into the rivers and becks that feed the lake. During Storm Desmond, in December 2015, continued heavy rain fell on land that was already saturated and the result was massive flooding and damage to Ullswater and some of the surrounding settlements.

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.

Pollen analysis of sediments has shown that, in the last 2,000 years, de-forestation around the lake, and ploughing of agricultural land, has increased run-off of nutrients such as phosphates into the water. In more recent times, the regular spreading in winter of grit and salt onto the A 592 road fringing the lake has increased the run-off of salt into the lake.

In general terms, Ullswater’s ecology is in good shape. There is relatively little human impact and so far the impact of climate change has been quite limited. Time will tell whether the Storm Desmond event in 2015 will be repeated. But for now, Ullswater remains, as many have claimed, the most beautiful lake in England. Long may it remain so!

by Tim Clarke

References:

Bagenal: The Ullswater Schelley. Field Naturalist 11. 18-20 (Year ?)

Bagenal: Notes on the biology of the Schelley in Haweswater and Ullswater. J Fish Biology 2 137-54 1970

Clarke, James : A survey of the lakes of Cumberland,Wesmorland and Lancashire 1789

Ellis & Cooper: Notes on the Lakeland Schelley Field Naturalist 1967 12, 35

Fryer G : A natural history of the lakes, tarns and streams of the English Lake District FBA 368 pg 5 1991

Moon :Mortality among Mute swans in Ullswater North West Naturalist 13, 25 1938

Ullswater 1885 Destruction of the gwyniad (schelley) by lead mine water Field 65 784 (year ?)

Maberly, Eliott & Thackeray: Options for the remediation of water quality in Ullswater and Derwentwater. May 2006

Hall et al Measurement , Modelling and prediction of water quality in Ullswater. 2000

Horne and Horne: Guide to publication ? 1985