Erodibility of soft fresh water sediments: the role of bioturbation by meiofauna

Markermeer is a large and shallow fresh water lake in The Netherlands. It has a 680 km2 surface and a 3.6 m mean water depth. Markermeer is characterized by its high turbidity, which affects the lake ecosystem seriously. As part of a study that aims to mitigate this high turbidity, we studied the water bed exchange processes of the lake’s muddy bed. The upper cm’s – dm’s of the lake bed sediments mainly consist of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of the soft anoxic mud. This oxic layer is believed to be responsible for Markermeer high turbidity levels. Our hypothesis is that the oxic layer develops from the anoxic mud, and due to bioturbation. In particular we will refer to bioturbation caused by meiobenthos. The objective of this study is to determine the influence of the development of the oxic layer on the water-bed exchange processes, as well as the role of bioturbation in this processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the erosion rate of Markermeer sediments, and therefore affects the fine sediment dynamics of the lake.