SEDIMENT O-2 DEMAND, DENSITY AND BIOMASS OF THE BENTHOS AND PHYTOPIGMENTS ALONG THE NORTHWESTERN ADRIATIC COAST - THE EXTENT OF PO ENRICHMENT

Sediment oxygen demand (SOD), silicate and ammonia fluxes, benthic mac ro- and meiofauna and phytopigments were measured during two cruises i n March 1992 and August 1993 in the northwestern Adriatic Sea. Nine, m ostly shallow (< 50 m) stations, on a transect stretching from the Po mouth southwards, were visited. Two major issues were addressed: (1) T o what extent does the river Po affect the benthic communities along t his transect ? and (2) Is there any indication of an eutrophic situati on as described in earlier studies ? The spatial patterns of SOD (rang e +/- 100 to 1450 mu mol O-2 . m(-2). h(-1)) and benthic fauna do not provide evidence for a simple latitudinal decrease in organic enrichme nt from the Po to the south. However, northern stations generally had the highest SOD, faunal densities and biomass. Water column characteri stics (temperature, salinity, phytopigments) in August 1993 indicate a rough partition of the transect into two groups of stations, of which the northern cluster experiences the direct influence of Po water. Th is is in conformity with the vision of existing deviations of the gene ral anticyclonic flow regime in the northern Adriatic in summer, where by Po water is directed offshore instead of southwards. Compared to th e southern North Sea, the present SOD and benthic fauna figures are mo derate and do not indicate any alarming situation in terms of enrichme nt.