Spatial distribution in sediment characteristics and benthic activity on the northwestern Black Sea shelf

The influence of the River Danube as a major source of nutrients and suspended solids to the continental shelf of the Black Sea has been analyzed. In the framework of the EC project EROS-2000, sediment cores from 33 stations on the northwestern continental shelf were sampled in August 1995. Spatial patterns in structural sediment characteristics, macrobenthos composition and benthic mineralization rates were examined using ordination techniques. Three general areas could be distinguished according to the distribution of abiotic sediment characteristics and macrobenthos community: (1) The area just in front of the Danube Delta where large amounts of nutrients and suspended solids are discharged. High sedimentation rates of fine-grained sediments and high benthic mineralization rates characterized this area. The macrobenthos community was dominated by deposit feeders. (2) The northern part of the continental shelf where an anticyclonic gyre is located. The majority of the Danube discharges are transported to this region. This area was characterized by low sedimentation rates. However, the deposited material contained a larger fraction of fresh organic matter compared to the delta area, resulting in high benthic mineralization rates. Suspension feeders dominated the macrobenthos community. (3) The southern part of the continental shelf was characterized by low sedimentation rates and low rates of benthic mineralization. In this area suspension feeders dominated the macrobenthos community. Oxygen fluxes into the sediment ranged between 2 and 52 mmol O-2 m(-2) d(-1) (average 21 mmol O-2 m(-2) d(-1)) decreasing with water depth. Macrobenthos accounted for 20% of the total benthic oxygen consumption. In the northern part of the continental shelf and in the coastal stations, microorganisms, and micro- and meiobenthos dominated benthic community respiration, while macrobenthos became relatively more important in terms of oxygen consumption in the southern part of the continental shelf.