On the north beach of Spiekeroog, students led by marine physicist Prof Dr Oliver Zielinski are taking samples of pore water found in the fine cavities in the ground. Along two transects - on lines perpendicular from the high tide line to the dunes - they set 13 measuring points at intervals of five and ten metres. Photos: University of Oldenburg.

In order to access the water, so-called pore water lances are sunk into the ground - at a depth of one and two metres per measuring point. There are slits at the lower end of the lance through which the water can flow in.

A syringe is used to create a vacuum, which causes the water in the lance to rise and collect in the piston.

In order to be able to assign the measurements precisely later, the points are measured to within a few centimetres using GPS.

Samples of the pore water are filled at each measuring point for later laboratory analyses. A filter retains all particles larger than 0.2 micrometres. This means that only the dissolved organic matter (DOM) remains in the water.

On site, the students measure the temperature, conductivity, oxygen and iron content as well as the amount of DOM.

While they closely observe every movement during the first measuring points and familiarise themselves with the methods, later on everyone concentrates on a specific work step.

Oliver Zielinski explains that familiarising yourself as a team and developing a routine is the be-all and end-all of measurement campaigns.

Patience and care are also important in order to achieve good, clean results in the field: To measure the DOM using UV light, for example, the container must be free of fingerprints, dust and water.

To conclude the project, the students prepare a presentation. Some members of the group carry out a statistical analysis of the data, whilst others outline the methodological foundations. The participants’ conclusion: the exchange with other early-career researchers from different disciplines is particularly valuable.