Hey, what ye doin’? Are ye fishin’?

Our team of scientists visited a number of lochs in Glasgow this summer. It may have looked a bit odd; a group of people moving around a raft in the middle of a loch, pushing things into the water and looking very pleased afterwards on the shore with giant tubes of mud. The reason? We were collecting lake sediments.

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June in Scotland, testing your waterproofs to the max

Lake sediments slowly fill up the deep parts of lakes and ponds with mud washed in by rivers and streams. The accumulation of mud over time incorporates the record of stuff washed and blown into the lake and the remains of algae, plankton and plant matter produced in and around the water. When environmental changes occur, lake sediments change their physical and chemical properties and incorporate different types of biological remains. If you are able to extract an intact sequence of mud (oldest at the bottom, youngest mud at the top) from the deepest point of the lake, scientific analysis of mud can tell us a lot about past landscapes, how they have changed over time and in many cases what effect human activity has had on the lake.

Our analyses for NERC Hydroscape on the cores have only started, so it will be a while until we have results from the mud, but we can already provide key facts about the Glasgow lochs studied; one, they were almost all shallow (<2.5 m) in comparison to Cumbria and Norfolk lakes, two, they were almost all full of submerged plants and three, they all contained a lot of mud.

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When collecting lake cores, it is usually a very good idea to sample the deepest point of the lake – where you often find the thickest amount of mud and most complete record of deposition. Many lakes (especially in the Lake District) have been surveyed before so the deepest areas are known. However, without any information, to find the deepest point of a lake, it’s a good idea to head towards the centre. To measure the water depth, we usually use a boat-mounted system with a simultaneous echo-sounder and GPS that records a lot of depth/location data while the boat travels around the lake. In shallow, plant-filled lakes, like our Glasgow ones, it becomes more difficult to move around the lake and the return data of the echo-sounder is telling you how much plant is below you rather than the depth of water. So the fool-proof, but longer time requiring process is to row around with a hand-held GPS and a measured line with a weight at the end. We ended up using both approaches in Glasgow. The preliminary bathymetries from Woodend Loch (near Drumpellier Country Park); Castle Semple Loch (Lochwinnoch) and Bardowie Loch (Milngavie) are shown below. Bardowie Loch is the exception to the Glasgow lakes surveyed this summer as it is 11m deep – a result of its formation by ice during the last glacial period.

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Bardowie Loch (pink circles indicate core locations, yellow crosses are soil samples).
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Castle Semple Loch
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Woodend Loch

 

Summary table of Glasgow loch, area of lake and max depth

Name of Loch Area of lake (ha) Max Water Depth found (m)
Possil Loch 4 ha 1
Hogganfield Loch 19 ha 2.2
Bishop Loch 23 ha 1.2
Woodend Loch 21 ha 1.2
Castle Semple Loch 79 ha 2.2
Loch Libo 9 ha 1.5
Bardowie Loch 21 ha 11
Dougalston Loch 3 ha 1

 

We’ll be using the measured depth and shape of the lakes (lake bathymetries) with the sediment data to calculate how much sediment has entered the lake over time and also how efficient they have been at capturing and storing atmospheric and water transported pollutants over the last 150 years.

We’ll keep you posted.

Dr Simon Turner, @samdavtur

University College London

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