The federal government is testing a measuring buoy in Lake Aegeri

Last Friday, the Federal Office for the Environment installed a new type of measuring buoy in the middle of Lake Aegeri. It will stay there for two years and record data that will help create a better understanding of climate change.

A mobile crane slowly lifted the 250 kilogram buoy into the air last Friday. The crane operator then gently manoeuvred the measuring buoy into the cold Lake Aegeri. He took great care, as this prototype cost around CHF 100,000. But everything went according to plan.

The measuring buoy is equipped with various sensors that will record the water temperature and oxygen content. It is all part of a pilot project run by the Federal Office for the Environment (FOEN/BAFU) in cooperation with the cantonal agencies and Eawag, the water research institute of the ETH. The goal: to collect more precise data in order to better understand the effects of climate change and to be able to take any necessary measures.

The buoy supplements cantonal measurements
The Confederation has recorded water temperatures on numerous rivers in Switzerland up to now, but not in lakes. With this pilot project, the federal government now wants to test whether the monitoring network can also be extended to lakes.

"The federal measurements supplement the existing cantonal temperature measurements, which are carried out four times a year at the same time as the measurements of chemical water quality at the deepest point of Lake Ägeri," says Thilo Herold, who works for the Hydrology Department of the FOEN.

"The buoy is used to continuously measure the seasonal change in water temperature," he adds. With the help of a motorised winch that is integrated into the buoy, a measuring probe is moved up and down several times a day, so that the temperature can be recorded "in a high temporal resolution from the surface to the lake bottom". Small solar panels and a battery provide the necessary energy. "We are now testing how many times a day the probe can be moved up and down – and that depends heavily on the weather."

Martin Schmid from Eawag, the water research institute of the ETH Domain (left) and Thilo Herold from the Hydrology Division of the Federal Office for the Environment are in charge of the pilot project.
The buoy is lowered into the water
The buoy's sensors
The buoy will remain in Lake Ägeri for two years.                               Photos: Mathias Blattmann

Another test field relates to the anchoring. The measuring buoy is anchored to the seabed with thick nylon ropes with two metal weights weighing 80 kilograms. "We hope that the buoy will be stable enough to withstand a more violent storm," says Thilo Herold.

Thilo Herold's team in Oberägeri had prepared a boat to tow the measuring buoy and its anchorage to its intended location. This lies approximately between Oberägeri and the mountain forest on the other side of the lake. The set-up took around two hours. The buoy is equipped with a signal light so that it can be seen by swimmers and ships.

Temperature change has many effects
And what will the more accurate data be good for?

"The stratification of a lake, i.e. how the layers of water at different temperatures are distributed, has a major influence on the ecosystem of a lake," explains Martin Schmid from Eawag. The stratification influences the oxygen supply of the deeper water and thereby also affects the habitat for oxygen-dependent aquatic animals, such as fish.

If the water is less mixed as a result of global warming, algal blooms can occur. "These effects, in turn, can, for example, influence the water supply, fishing or the recreational use of the lake," says Thilo Herold. Based on the more accurate data, more comprehensive forecasts can be made and any necessary measures can be initiated.

Lake Aegeri is one of three lakes selected by the FOEN for the pilot project: buoys have already been installed in Lake Murten (Fribourg) and Lake Hallwil (Aargau). Thilo Herold explains the decision: "The three bodies of water were selected because they are representative of a large number of lakes." The buoys there are also prototypes that are currently being tested.

The data from all measuring buoys are sent to a server in real time and can be viewed publicly on the Internet. "It's great that the installation work in the three lakes has now been completed with the Lake Aegeri buoy, and that we can continue the project with Eawag. We are looking forward to including this good and reliable data in our monitoring," says Thilo Herold after the successful installation of the Lake Aegeri measuring buoy.