Production and fate of extracellular polymeric substances produced by benthic diatoms and bacteria: A laboratory study

It is well known that benthic diatoms and bacteria are able to affect the stability of cohesive sediments. Their production of new extracellular polymeric substances (EPS) increases the erosion threshold and decreases the erosion rate. To predict this build up of biostability in cohesive sediments, it is therefore vital to understand the EPS production rates for both diatoms and bacteria under different ecological conditions. The present study examined the production of EPS as function of light intensity and linked this to biostabilisation. Microbenthos was sampled from a Danish marine embayment at 5-m depth. A 10-day comparison of EPS production under light and under dark conditions showed that the bacterial EPS production hardly changed during the experiment, while the algal EPS production was significantly high already from day 1 and reached a maximum production on day 10. Erosion threshold of natural cohesive sediments was determined in annular flumes after variable consolidation periods under similar light/dark conditions. The evolutions of erosion threshold and EPS concentration correlated well under light conditions, while the development in dark conditions showed no significant correlation, indicating that diatoms are more efficient in sediment stabilisation than bacteria. Further it seems, that the studied biological-sedimentary system needs 2e3 days of acclimatisation before the production of EPS can be well correlated with the increase of sediment stability.