Sampling along the dyke

Previously the pH of the Markermeer turned out to be really high. Even when putting the pH-values of all primary samples together, those values were really high in comparison with the other lakes and the river IJssel. Of course I could take some additional samples at the same location, but why not sample along the whole dyke (in Almere)? Starting in the Northern part where the municipality of Lelystad begins and then sampling every couple of kilometres (if possible) until we hit Zeewolde.

Parking Kernplaats

This time I went by car, because it would be a trip of over 50 km (it turned out to be 75), and the wind was really strong. Apart from this now I know that taking and measuring three samples, marking the bottles and taking a picture of the environment takes about a quarter of an hour, so ten samples would add two and a half hours to the journey. The disadvantage is that a car can only be parked at specific parking spots, but the day before sampling I checked all the nice locations on Google maps and sent myself a list of addresses.

The parking places are often at viewpoints, having their own names (in Dutch) like “ Nonnetje”,  “Kuifeend” (both names of birds) or more prosaic names like “Pampushaven” (just meaning Harbour of Pampus). Below I show a map of all the locations where I actually took my three samples, with locations in degrees.

Again, I discarded sample 0 as it was only for rinsing the bottle, then I measured samples one to three and kept the third. Values were written down in a notebook, together with the time. A picture of the location was taken for reference and the bottles were marked.

When I came home, a second measurement was done, but only to exclude potential errors (third sample only of course). All values turned out to be very close to the original one for sample 3 – mostly about 0.04 points lower as expected (based on previous investigations, showing a gradual pH drop over time). The high values were moving a bit more towards a lower pH. Of course the earliest samples were older (about four hours) than the later ones (less than an hour), but the pH-shift was not really different. Before measuring again, the pH meter was checked (not calibrated) with two buffer values (6.86 and 9.18). The deviation was still only a couple of hundreds and afterwards (measuring in two rounds) the values were still very close, so no doubt about the accuracy of the pH meter. I present the pH values with two decimals, but keep in mind that the precision is not: the standard deviation will take care of it.

However, one was an exception, because the pH went up, but this was a special sample, taken closely to the Blocq van Cuffeler, the huge pumping station. The three samples had the lowest values measured in the whole series, but were very different from each other, suggesting the water was not very homogeneous. That’s not a surprise, being close to a pumping station bringing (rain-) water from the canals into the lake. Then the third sample was also the one with the lowest original value of those three samples.

Here we will stick to the average of the three values obtained directly after sampling.

The averages and standard deviations (of the population) were calculated and the averages were put on the map. For those who care about significance the averages and standard deviations (for significance testing keep in mind that dividing by the square root 3 provides the standard error of the mean) will be available in a table below. Here we present the pH values in the map, because it offers the best visualisation.

There is no doubt that the pH gets up when we get closer to parking IJmeerdijk near Almere Poort (a very nice parking by the way, where a lot of people are chilling out). Despite this local high, it’s very clear now that the pH will never be below 8.00 in this area (and probably this applies to all Dutch lakes and rivers, let’s see). For the IJmeerdijk value of 8.70 (again!), the question is whether some kind of dump is lowering the pH locally. It could also be the opposite, this being the spot where hardly any fresh water comes in. We could see the effect of fresh water close to the pumping (pH relatively low) station and around it’s outlet to the lake.

Below pictures of the environment of the sampling points are presented. Be aware that the actual sampling point may be a hundred metres arpart. The real sampling point is just a bunch of basalt rocks, like the picture at “Kuifeend”. I get as close to the water as possible (sometimes really dangerous because of slippery algae and unstable rocks) and I use a stick with a cord to be able to sample as far from the rocks as possible. Then I will avoid beaches, harbours and closed areas as much as possible, staying close to the open water. The sampling point “near da Vincipad is an exception and so is the small bay close to the pumping staion “Blocq van Cuffeler”. At the map it is al very clear, especially when using the coordinates.


Blocq van Cuffeler (outside dam)
Blocq van Cuffeler (inside bay)
Pampushaven near da Vincipad

IJmeerdijk, parking

Near Musweg

2 thoughts on “Sampling along the dyke

  1. Pingback: More surprises: details along the dyke | Scientassist

  2. Pingback: More surprises: details along the dyke – Site Title

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