Sulphide tolerance of benthic diatoms in relation to their distribution in an estuary

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Abstract
Benthic diatoms from the Eems-Dollard estuary were tested for their ability to survive in solutions of free sulphide. The unialgal cultures and mixed populations of diatoms tested were isolated from field stations on different parts of the estuary; some of these stations were exposed to organic waste water. Toxic concentrations of free sulphide were found in the range of 0·9–6·8 mm (5–48 h incubation in the dark); these concentrations of free sulphide are among the highest reported from marine sediments. Relatively tolerant benthic diatom species survived 6·8 mm of free sulphide during 5–24 h, whereas relatively sensitive species were strongly inhibited by 0·9 mm during more than 24 h. Two estuarine plankton diatom species were equally resistant, whereas two oceanic species were the most sensitive tested. The occurrence of a few benthic diatom species on mudflats with very strong organic pollution (and hence superficial black layers) was related to their relatively high sulphide tolerance. However, other species dominating on mudflats were relatively sensitive. Data on sulphide tolerance, capacity for heterotrophic growth in the dark, tolerance of high ammonia concentrations, capacity to survive prolonged darkness and anaerobiosis, together with salinity preference indicate that diatom species have different combinations of these capacities and these are responsible for their distribution in gradients of organic enrichment in the Eems-Dollard estuary.