Maps in Geophysics - Phase 2 (2004-2007)

Sub-Project 1 Ulrike Feudel

Nonlinear Dynamics in Models for Tidal Flats: Pattern Formation, Complexity and Critical Transitions

Our study of the interaction of biological and physical processes in tidal flats focusses on the role of biological compared to physical processes. Firstly, we study the biogeochemical degradation of different substrates in the Wadden Sea sediment with respect to the emergence of temporal, spatial or spatio-temporal patterns, which result from a non-linear interaction between reaction, bioturbation, diffusion and advection. Within this study we estimate the influence of the sediment's structure (sand or mud flat) on the process of advection. Environmental conditions that change with time are of particular interest: We study the effect of seasonal fluctuations in the environmental conditions as well as the influence of changing penetration depths of specific chemicals (e.g. oxygen) that are affected by the tides. Our second goal is the modelling of the effect of aggregation on sedimentation processes, specifically on the size distribution of aggregates. We estimate the impact of the biological activity of microorganisms inhabiting the sedimenting particles on the size distribution and the velocities of sedimentation. In particular we investigate how this activity is affected by the strength of the antagonistic forces determining the size of the aggregates (coagulation, shear stress). From the results we derive an estimate how the sizes will change along the season.