Estimation of sediment–water exchange of solutes in Lake Veluwe, The Netherlands

Two methods for the determination of sediment–water exchange of dissolved components –(a) laboratory column experiments and (b) calibration of a model for vertical transport of dissolved components in pore water– are discussed. The three parameters of the transport model –the effective dispersion coefficient at the sediment–water interface, the attenuation constant of dispersion in the sediment and the advective flow rate– were highly correlated. Estimates for the dispersion coefficient at the sediment–water interface in the shallow Lake Veluwe, The Netherlands, showed a large variability, but were always one to two orders of magnitude larger than the molecular diffusion coefficient. Dispersive transport dominated advective transport at the sampled sites. The dispersion coefficient at the sediment–water interface in shallow lakes can be enhanced by several mechanisms, such as pressure gradients caused by wind stress. Exclusion of this turbulent dispersion, as in laboratory column experiments with intact sediment cores, can therefore result in an underestimation of the real flux. For reactive compounds the introduced error may be partly compensated by adjustment of the concentration gradient due to reaction during transport and incubation.