The redox potential of sediment from the Middle Adriatic region

Sediment redox potentials (EH) at stations of different trophic status in the central Adriatic from 2001-2007 were investigated in this paper. For most part of the year at open sea and channel stations EH values were mainly positive (+150 to 0 mV), even to 10 cm sediment depth. Positive EH (absence of sulphate reduction with very low sulphide concentrations) at these stations is probably caused by low to medium organic matter sedimentation rates. Negative EH values (presence of sulphide and appearance of anoxic conditions in sediment) and shallow redox transition depths in sediment were found in areas with higher productivity and organic matter sedimentation such as eutrophicated Kaštela Bay after a winter plankton bloom, a near shore station exposed to a city wastewater outlet and stations located under fish farm cages. Vertical profiles of sediment EH, ironbound phosphorus fraction and Fe(III)OOH investigated at a middle Adriatic tuna farm indicated a relationship between redox potential and phosphate adsorption/desorption processes.