Biodiversiteit en abiotische metingen op de Slow Mill locatie off-shore Texel in 2019. NIOZ Report 2020-06

In 2019 NIOZ was involved in biodiversity research and the measurement of abiotic conditions at a location where a wave energy converter device (SLOWMILL) will be placed. The location lies 4 km offshore Texel and has a water depth of 12 meter. In February 2019. Fauna was sampled with a boxcore. The analyses of these samples showed that abundance and biodiversity is relatively low, and typical for the high energetic coastal environment. The addition of hard substratum, being a measurement frame, showed that local abundance and biodiversity increased enormously. With 18 species which were not found in the sandy bottom, biodiversity increased with ~ 50%. The densities of macro faunal specimens on the hard substratum was 400 times higher than densities in the natural soft sediments. The measurements of the physical environment showed that the location is dominated by along shore tidal currents of approximately 0.5 m/s. The residual current is in northward direction. During a south westerly storm (8 Bft) near bottom currents were over 1 m/s. Significant wave heights during the storm was 2.5 meter, with a maximum of 4.8 meter. Mean wave period was 3.5 seconds. Peak period is 5.8 seconds and linked to waves from a northerly direction. Temperature, salinity and turbidity measurements show a well defined tidal periodicity. The turbidity data clearly show the effect of wind and wave conditions on the total suspended matter. Peak concentrations were measured after the storm when resuspended material resettles. The data also suggest that there is lateral transport of suspended material, most likely derived from the bordering shallow Wadden Sea.