Sampling an alpine lake
A CASE STUDY
The Site
La Roche-de-Rame is located in the Hautes-Alpes department in southeastern France at the eastern border of the Parc National des Ecrins.
Due to its location and the direct connection of the lake to a camping site, it was possible to directly communicate our research to interested local people, as well as tourists.
Sampling procedure (in the field)
Taking sediment core samples in the field requires quite a lot of equipment and teamwork. The specialists at the EDYTEM designed a platform to be mounted on a rubber boat to make the core extraction easier.
Depending on the planned sampling depth of the sediment, a long plastic linertube is prepared and fit in the coring system. The attached ropes have to be long enough to cover the maximum water depth of the sampling point and to give enough way for moving the hammering weights and holding the corer in place.
An example for such a coring system, and the one we used to core Lac La Roche-de-Rame, is the UWITEC gravity corer. This corer allows to add different weights as a hammer, to force the tube into the sediment.
The general sampling approach is to row out on the lake and systematically measure the water depth to find the deepest point of the lake. The deepest spot of the lake is the ideal area to sample, as it is assumed that everything washed into or accumulated in the lake will eventually end up here.
Sample preparation (in the laboratory)
Once the sediment cores are extracted from the lake and transported to the laboratory, they are stored at +4° C.
The cores are cut into halves and separated into one working half and one archive half. At least one of them is being photographed to high-resolution. This image is then used to create a detailed sedimentological description of the core.
Sediment samples are taken from the working half of the core, for DNA extraction and pollen analysis. Currently, we only took sediment samples for DNA extraction. Furthermore, macrofossil remains are picked throughout different sediment layers of the core for radiocarbon dating.
The DNA is extracted in a dedicated ancient DNA laboratory and then used for different analyses to estimate the quantity of certain sequence types and metabarcoding.