Sediment characteristics and wind-induced sediment dynamics in shallow Lake Markermeer, the Netherlands

In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake Markermeer were high, viz. on average ca. 1,000 g m-2 day-1. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with its large surface area (dynamic ratio = [H(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most of the lake's sediment bed. Indeed, near-bed currents can easily reach values[10 cm/s. Measurements of the thickness of the settled ''mud'' layer, as well as 137Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics were investigated in preliminary laboratory experiments in a small ''micro-flume'', applying increasing water currents onto five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour with respect to these currents.