Effects of tidal currents on chlorophyll a content of sandy sediments in the southern North Sea

Observations of high growth rates among benthic species living on sandy bottoms in turbulent areas of the southern North Sea suggested the hypothesis that transient deposition of suspended organic matter during period of slack current might provide a food source for these animals. Over a 24 h period, changes in chlorophyll levels in the water, on the sediment surface, and in 3 sediment layers were measured. The results not only confirmed the hypothesis, but also revealed that with each tidal cycle, high levels of chlorophyll were alternately being buried in the sediment (to a depth of 5 cm) and then resuspended Laboratory experiments suggest that the mechanism by which this occurs is related to the format~on of sand ripples on the sediment surface. Varlous implication of these findings are discussed.