Bacteria and organic matter dynamics during a bioremediation treatment of organic-rich harbour sediments

We studied the dynamics of bacteria and organic matter in the Ancient Port of Genoa (Italy) during a bioremediation treatment of sediment (during summer–autumn 1998) in an area characterised by continuous sewage discharge. A strong increase in total benthic bacterial density (TBN) was recorded at the end of the study, from 14108 to 58–172108 cell g1 in different parts of the treated area. The TBN increase was linked to organic matter depletion, from more than 40 to less than 20 mg g1. In order to highlight the main ecological mechanisms involved in bioremediation, a laboratory experiment based on both water and sediment from the basin studied was carried out. We observed an increase in TBN during the first 20 days and a decrease in sediment organic matter (up to about 20%). Increases of organic matter (about 2-fold) and TBN (from 21 to 33109 cell l1) occurred in the overlying water, suggesting a strong association between the sediments and water column processes. Hydrolytic activities, which double in the sediment and increase up to a 300-fold in the water, are consistent with the decrease in sediment organic matter and with the water fraction dynamics.