Resuspension created by bedload transport of macroalgae

Earlier studies have quantified that plant bound transport in shallow lagoons and estuaries may periodically be the dominating nutrient transport form. In some of these field studies turbidity increased when plant transport increased. The hypothesis in this study is therefore that macroalgae erode surface sediment while drifting as bed load. To improve the understanding of this ballistic effect of moving plants on the sediment surface, controlled annular flume experiments were performed. Plant transport was measured together with turbidity and suspended particulate matter during increasing water currents. In all experiments the plant induced sediment erosion started earlier than at bare bottoms. The turbidity increased when the plants started to move (2-4 cm s-1). Depending on the plant type the turbidity increased from a background concentration of 7-10 mg SPM l-1 to 30-50 mg SPM l-1 for Ulva lactuca, Chaetomorpha linum and Ceramium sp., while the more rigid macroalgae like Fucus vesiculosus caused much higher turbidities (50-150 mg SPM l-1).This phenomena may explain the appearance of turbid waters in estuaries and lagoons in the absence of wind and wave action.