Ökologische Bedeutung von Oberflächenwellen

The project investigates the consequences of surface waves on the abiotic conditions in the littoral zone based on field measurements in Lake Constance. The research is focussed on wave-induced resuspension, the release of methane and phosphate due to pore water mobilization, and the effect of suspended particles and surface elevation on the light climate. Field data on wave properties will be employed to validate an existing surface-wave model which will then be applied to provide basin-wide estimates on the wave field characteristics, the release of phosphate and methane and the modification of the light regime by wave-induced resuspension.

The main objectives of the project are:

1) Identification of the direct and indirect consequences of surface waves on light intensities in the littoral zone including a characterization of the light climate on time periods from milliseconds to seasons. These measurements will also provide a basis for studies on light stress and primary production in the littoral zone.

2) Measurement of the wave-induced release of methane and phosphate from the sediments in the littoral zone and comparison of the concentrations in the littoral with those in the open water. These measurements will also reveal whether the littoral zone serves as a source of methane and nutrients for the entire lake and thus may contribute to the understanding of the origin of the elevated methane concentrations in the epilimnion in the open water observed in earlier investigations. Furthermore, the measurements will demonstrate the role of phosphate release in the littoral for phytoplankton growth during time periods of very low nutrient concentrations in the pelagial.

3) Validation of a nested-grid surface-wave model by comparing simulated and measured characteristics of surface waves in different sections of the littoral zone of Lake Constance.

4) Validation of the empirical relations that estimate resuspension from wave characteristics by using field measurements not only of turbidity but also of the particle size distribution in the water column.

5) Application of the surface wave model together with the empirical relations between wave characteristics and resuspension, methane and nutrient release and light climate to provide a spatially and temporally resolved estimate of the consequences of surface waves on the different abiotic factors. The calculations are intended to support an estimate of the overall wave-induced release of methane and nutrients in the littoral zone and will also provide information on the hydrodynamic conditions at different locations during different seasons.

Poster

(A) Schiffswellen induzierte Resuspension, (B) Windwellen induzierte Resuspension.