SEASONAL FLUXES ACROSS THE SEDIMENT-WATER INTERFACE, AND PROCESSES WITHIN SEDIMENTS

Measurements of oxygen uptake across the sediment-water interface sugg ested that between 17-45% of the net primary production in the souther n North Sea was degraded in the bottom sediments. Similar measurements of nutrient exchange fluxes showed that the sediments were significan t sources of nutrients transferred to the water column. The sediments are. therefore, important sites of organic matter degradation and nutr ient recycling, and must be included in any models for the North Sea. The sediments are also accumulators of radionuclides, particularly ass ociated with the silt/clay fraction. At one site in the more central a rea of the North Sea where the water column stratifies during summer, vertical profiles of radionuclides (Cs-137, Pu-239, Pu-240, Pb-210) su ggested a deposition rate of sediment of 0.3-0.6 cm a-1, but at other sites vertical sediment profiles were unsuitable to measure deposition .