UV-Protected Moorings: Years of Monitoring in the Baltic Sea

For six years, Björn Elsässer, and the team at DHI A/S, Denmark, have used AML-6 instruments fitted with AML's Street Lamp UV anti-fouling system to monitor a dredge disposal site in the Baltic Sea on behalf of Germany's Federal Administration of Waterways and Shipping (WSV). The site sits beside a major widening project on the Kiel Canal, the world's busiest artificial waterway - and the monitoring program exists to make sure the canal's expansion isn't quietly damaging the Baltic seabed around it.

First opened in 1895, the canal saves ships a detour of roughly 250 nautical miles around the Jutland peninsula, cutting fuel use and CO2 emissions along with it. It has been widened several times since to keep pace with growing ship sizes and increasing traffic. The most recent project, which began in 2020, is expanding the canal's bed to a minimum width of 70 metres in an area often described as the last remaining bottleneck on the waterway.

Six monitoring stations are spread across the disposal site: four around the disposal area itself, one at the edge of a Natura 2000 protected nature site, and one further away as a reference point. Each station carries two units, one near the surface and one near the seabed. The Natura 2000 designation - part of the EU's network of protected habitats - is a key reason the program is held to such a demanding standard: one-second sampling, one-minute averaging, with data transmitted in near real time to a central database.

AML's involvement began in 2018 with a trial deployment of a MetrecX unit - part of AML's legacy instrument line, since succeeded by the X2•Series - run alongside the program's existing monitoring equipment to see how it performed under real site conditions. In 2020, the program upgraded to two AML-6 units fitted with an external dissolved oxygen sensor. Sitting outside the AML-6's built-in UV coverage, that sensor fouled - while the UV-protected sensors on the same units stayed clean. It's exactly why the program's next upgrade, in 2022, brought every sensor inside that same protection.

That upgrade scaled into a full fleet of AML-6 units - twelve mounted across the monitoring stations, with six more in rotation for servicing and calibration. Three are fitted with a PAR sensor, every one of them paired with AML's Street Lamp UV anti-fouling system. Each AML-6 measures conductivity, temperature, and pressure, alongside dissolved oxygen, chlorophyll-a, and turbidity.

Five months submerged in the same conditions that cover the surrounding frame in mussels and barnacles, and the protected sensor face stays clear.

Across eight years of continuous monitoring, the data has shown that the environmental impact of the disposal activity is, if anything, very localized.