CHEMICAL-CRITERIA FOR MARINE EUTROPHICATION WITH SPECIAL REFERENCE TO THE OSLOFJORD, NORWAY

Results of a chemical and geochemical study of the Oslofjord system are presented to explore the possibility of qualitatively identifying a eutrophication gradient. Nutrient concentration and dissolved oxygen may indicate such a gradient in areas of similar hydrographies. Uncertainties due to minor differences in hydrography may be resolved by considering sedimentary organic carbon, C:N ratios and the accumulation of mineralisation products in the sediment pore water. The reliability of the sedimentary organic matter and the pore water composition as gradient indicators can be impaired by input of terrestrial organics, dispersal of mineralisation products by the benthic fauna or the apparent high levels of organic carbon and pore water nutrients in the absence of the benthic fauna under anoxic conditions.