Sedimentation in Mariager Fjord, Denmark: The impact of sinking velocity on system productivity

Mariager Fjord (cast coast of Jutland, Denmark) is a sill Fjord with a cent ral, permanently stratified basin. The upper mixed laver of the water colum n shows unusually high levels of primary production and phytoplankton throu ghout the summer season. Plankton blooms takes place at intervals of 2-3 we eks during the entire growth season although the external load of mineral n utrients is not very high. It is shown here that the high production result s from overall low sedimentation rates and consequently long retention time s of suspended particulate matter within the mixed layer. The low sinking v elocities of suspended particles thus constitute the base for an efficient in situ re-mineralization and high regenerated production. Plankton communi ty structure is therefore more important for system productivity than is th e external nutrient load per se.