Research

J. März, U. Feudel, K. W. Wirtz

Understanding aggregate dynamics in turbulent shallow waters using a new modelling approach

Suspended particulate matter aggregates in turbulent shallow water systems are composed of inorganic and organic substances. They play an important role in the benthic-pelagic coupling as well as in the pelagic ecosystem. Concentration, size and composition of these aggregates exhibit large fluctuations on many time scales reflecting a complex interplay of both ecological and physical factors. In order to quantify the relative importance of those factors we developed a zero dimensional model using as a new approach the effective variable approximation (EVA). The average radius as a key property of the particle size distribution is introduced as an effective variable deriving its dynamics from traditional size class models. By avoiding explicit size classes the approach allows a better description of mutual dependencies without extensive parameterization effort and is computationally inexpensive. The model takes biologically and physically mediated aggregation, disaggregation, erosion, resuspension and advection into account. Diurnal and seasonal variations in the relevance of the different processes are identified. Model results agree fairly well with observations in the back barrier tidal flat of Spiekeroog island in the German Wadden Sea.