Settling velocity and residence time of particles in Lake Constance

Seasonal and spatial aspects of the net settling velocities of particles in Lake Constance were investigated by measurements of settling fluxes and estimates of the concentrations of suspended matter. Annual mean sinking velocities ranged from 2.6 m d^?1 in the euphotic zone to 7.5 m d^?1 in the aphotic zone. Summer maxima of 36.6 m d^?1 were caused by settling calcite crystals, while minima of 0.4 m d^?1 during the clear water phase resulted from particulate matter consisting mostly of phytoplankton and organic debris. Winter settling velocities averaged 1,2 m d^?1. The mean residence time for the bulk of particles calculated on an annual basis was 27.8 days. The net settling velocities in this study were higher than those calculated for phytoplankton in other investigations but agreed with estimates for particles from Lake Zürich obtained by an approach similar to this study.