Short-term response of benthic bacteria and nanoflagellates to sediment resuspension: an experimental study

Abstract

We investigated benthic bacterial abundance, biomass and activities and heterotrophic nanoflagellate (HNF) abundance and biomass during sediment resuspension and after a resilience period through short-term laboratory experiments. The strong sediment resuspension increased bacterial carbon production only slightly (Tukey's test, P < 0.05) but somehow interfered with microbial growth. During sediment resuspension, after an initial increase (at 48 and 72 h) bacterial abundance and biomass decreased until the end of resuspension. Sediment resuspension also altered the relationship between HNFs and bacteria (increase in the ratios of bacterium to HNF abundance and biomass after sediment resuspension; Tukey's test, P < 0.01). After sediment resuspension, the fraction of bacterial C production removed by flagellates decreased, whereas bacterial turnover did not change significantly, suggesting that HNF pressure on bacteria decreased. These results are consistent with the significant decrease in both HNF abundance and biomass (Tukey's test, P < 0.01) and suggest that this small benthic component is less resilient to sediment resuspension than bacteria. Sediment resuspension also determined significant changes in sediment organic matter pools (proteins and carbohydrates). Sediment resuspension determined a decrease in total protein concentrations, whereas total carbohydrate concentrations did not change significantly. Sediment resuspension had significant effects on extracellular enzymatic activities, as aminopeptidase increased and β-glucosidase activity decreased. Based on total protein and carbohydrate concentrations and enzymatic activities, we observed that sediment resuspension resulted in an increase in protein turnover and a decrease in carbohydrate turnover. These results indicate that sediment resuspension plays a major role in the early diagenesis of sediment organic matter.