Of course Almere is only a part of the Netherlands. Going on a trip to the North I selected some other sample points, which I would visit during my trip. The Ijsselmeer was sampled at two points: Lelystad and Lemmer. It’s separated from the Markermeer, so I wondered if the pH would be very different. Then in Frisia the Tjeukemeer was sampled at the parking “De Lanen” (actually under the A6). Traffic was not as good as expected and I had to ignore the other sample points planned for, but for now it will do.
Let’s see what the results were. It would be a rather long day and the measurement of the samples at home would be ten hours later. For the other lakes we already noticed that the pH drops a little bit during the days after, so I decided to take my pH meter with me and do the first measurement right after sampling.
By now it won’t be a surprise that the IJsselmeer is also was in the higher pH range, but the same applied to the Tjeukemeer! Back at home I measured the samples again and two days after another time (of course measurements were done in duplo, taking all precautions). The results are shown below.
The calibration was not an issue anymore. The buffers provided very stable values during the last week or so. I don’t put in the graph, because it might be boring. Of course all the data are available in a spreadsheet and I keep my original log papers.
Having collected enough samples to know that al least not all surface water in the Netherlands is acidic, I went looking for explanations. Ammonia seemed to be a possibility, but it’s not very likely, because the water quality is sufficient. Moving to soil samples in the future, it will be interesting to determine the inorganic Nitrogen (NO2–, NO3– and NH4+) and I read a lot about all kinds of methods (hoping to find a less complex and less dangerous method than the classic Berthelot in dozens of scholarly articles). Limestone, concrete and all kinds of waste water could explain local elevations of the pH, but not in several different lakes at the same time.
The I found an interesting site saying “An additional cause of elevated pH is high photosynthetic activity, which removes carbon dioxide from water and raises pH”. This would mean that the pH differs throughout the day. Biological activity is also a good explanation for the pH-drop of the samples, because I keep them in the dark, but not cool.
The next investigation might be (very) local again, now looking at the factor time!