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Abstract
Measurements of the production of organic matter by the microalgae (phytoplankton and microbenthos) have been carried out in the Smålandshavet - a shallow water area in the southern part of Denmark. Measurements of dissolved oxygen and the vertical penetration of the green light have also been made.
The area investigated can be divided into two parts, an open area with a good exchange of water and an enclosed fjord with poor possibilities of water renewal. Both areas are recipients for loaded waste waters.
In none of the areas investigated is the microalgal production particularly high. The ineffective water exchange in the fjord makes the watermass very sensitive to larger amounts of oxygen-consuming substances. Because of outlet of sewage the concentration of dissolved oxygen is low and the turbidity high. This causes the biological diversity to be very restricted. Calculations show that the oxygen deficit observed is mainly due to loaded oxygen-consuming substances. The decomposition of in situ produced organic matter is of less importance.