Buoy-Based Temperature Profiling in the Bavarian Lakes

Researchers use OTT buoys and the OTT net DL datalogger to study the long term effects of climate change on the Bavarian lakes.

Buoy-Based Temperature Profiling in the Bavarian Lakes

Background

In summertime, a temperature stratification occurs in deep lakes – the surface is warm, deep down the water is cold – which has considerable influence on the nutrient balance and the biological habitat in these lakes. Due to generally higher air temperatures induced by the climate change, both will change and hence also the life conditions of the ecosystems in the lakes.

The Bavarian State Office for the Environment (Bayerisches Landesamt für Umwelt) cooperated with the Water Management Authority Weilheim (WWA Weilheim) and OTT Hydromet, which was responsible for detailed planning and system integration, to implement a measurement project for the continuous monitoring of water temperature profiles in Lake Ammersee, Bavaria.

As long‑term, proven methods for buoy‑based temperature profiling were largely unavailable at the time, new technical approaches had to be developed to meet the project requirements. With considerable effort, a monitoring buoy was installed at the deepest point of Lake Ammersee, at a depth of 81 meters. The buoy is securely anchored using three concrete weights, each weighing 750 kilograms.

A measurement chain mounted beneath the buoy continuously records water temperature at 16 different depths, providing a detailed vertical temperature profile of the lake. In addition, a compact weather station installed on the buoy measures meteorological parameters. This atmospheric data supports the interpretation and analysis of the water temperature measurements collected by the profiling system.

Monitoring Solution

As a solution, a buoy was installed at the deepest point of the Ammersee (81 m) which is held in position by three concrete weights (750 kg each). A measurement chain was then fixed on the underside of the buoy, to continuously measure the water temperature at 16 different depths.

The measurement buoy is anchored at the deepest point of the lake (81 m). At its underside there is a measurement chain with 16 temperature sensors, evenly distributed down the water column right to the bottom of the lake.

The buoy delivered by OTT HydroMet is equipped with extensive measurement technology:

Compact weather station for monitoring the meteorological parameters: air temperature, air pressure, relative humidity, global radiation, wind direction and wind speed
Solar panels for autonomous power supply
Measurement chain with 16 temperature sensors
Data logger OTT netDL500 with remote data transmission

The temperature sensors of the measurement chain and of the compact weather station are continuously collecting data (average values in 15 minutes intervals). The measured data is stored in the OTT netDL data logger which is installed inside the buoy. Several times a day, the data are transferred via mobile communication from the measurement site to a database of the Water Management Authorities where they are immediately available for evaluation.

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Implementing the Measurement Project

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Buoy-Based Temperature Profiling in the Bavarian Lakes

Background

Monitoring Solution

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