What happened to the pH of the samples during the week after sampling?

In the previous post the conclusion was that the water of our lake (Weerwater) is definitely alkaline. But will the pH change during the days after sampling? A little bit of air was available in the bottle, but it remained sealed, meaning no additional oxygen was present. Measuring during the days after was not planned, but turned out to be a good exercise. I had to know the pH meter and its behaviour, so I measured again the next day, the day after and so on. It turned out that the pH moves towards neutral, but very slowly. Most likely this is the result of biological processes, performed by micro-organisms, like bacteria. Either the alkaline factor is being removed, or neutralising acid is being produced – or both. I don’t see a relationship with the amount of organic matter at the sample location. Especially the “Fantasie beach” (actually I sampled at the end of a jetty) was rather clear, but it is the area where a lot of water skiing is going on!

The first couple of times I was calibrating before the measurement and checked the pH of the buffers afterwards. When I realised there is a small deviation rather soon (minutes), which doesn’t change in the days after I didn’t calibrate the next time, but checked whether the values for the buffers were unchanged. They were.

Next time I will tell about the water samples taken from different lakes in Almere. The old hypothesis of slightly acidic water was revitalised. I expected the “Weerwater” to be anomaly