Limnology Part 1

I arrived at Malham Tarn Field Studies Centre yesterday late afternoon for the start of a two and a bit day course in limnology - the science of the lakes. After dinner at 6pm, we had a short introductory lecture and then had an early night to settle in to the accommodation. I was very studious and did a past exam paper ... and picked out a few more things I need to revise.

This morning was a fairly leisurely start, with breakfast just after 8am and lectures starting just after 9am. Being Bank Holiday week, the centre is quite quiet and there are only seven delegates on our course, which is a good number. We had somewhat of an information download this morning, but it was very good revision for me covering the physics and chemistry of the lakes, including wave action, temperature profile, gas exchange and nutrients. 

After lunch, we carried out practical activities in alternate groups.  My group was first to take the rowing boat out on the lake and take some water samples. This was done using a ?Rettner tube, and dispensing the contents from various depths into glass collecting bottles. As we were measuring dissolved oxygen, the key was not to let there be an air gap/bubble at the top of the bottle. We also had a bit of a paddle around the lake looking at the adjoining peat bog - quite a unique juxtaposition to have an alkaline marl lake next to an acid peat bog.

Whilst the other group went on the boat, we had a graphing exercise to do which was to create a isopleth of temperatures for various depths and dates. It was a bit like an intellectual join the dots exercise, quite time consuming - I'm sure there must be a computer programme that does this now!

When the other group returned, we went to the lab to analyse the water. The first test we did was theWinkler method, which involves adding various chemicals in turn to the water sample, creating various reactions. At the end of the process, you can determine how much oxygen was in the sample by how much of the final chemical needed to be added to make the sample clear.  I took pictures of each stage, so will no doubt write up some more precise instructions in due course.

For the second test we used colormetry to determine the pH of water. This used various colour dyes, and the comparison against a colour chart to match to the closest colour and read off a value. It was accurate to 0.2 pH, but there was a little subjectivity in it, as different members of the group did not always agree on the colour match!  It is definitely more reliable that litnus paper, and allegedly more so that electronic meters that need to be constantly recalibrated.

After dinner, we had another short lecture on the history of Malham Tarn itself. We then had a walk out to the sluice gate, then on to a sink hole, a round trip of about 3km. It was getting dark when we got back, so I just settled down for the night, ready for another action packed day tomorrow ...