BENTHIC FLUXES OF NUTRIENTS IN THE NORTHWESTERN BLACK-SEA

The exchange of O-2, NH4+, Si(OH)(4), ortho-phosphate, Fe2+, Mn2+ and H2S between the sediment and the overlying water (benthic flux) was de termined at 6 locations on the northwestern shelf of the Black Sea usi ng an in situ benthic lander. Oxygen consumption by the sediments rang ed from 0 to 33 mmol m(-2) d(-1) depending mostly on the initial oxyge n concentration in the bottom water. During the time period of deploym ent of 22 h, no reduction of sulfate was observed within the lander an d no release of methane. H2S was released from the highly eutrophic se diments close to the Dniester river with a flux of 0.3 mmol m(-2) d(-1 ). Fluxes of phosphate, ammonia and silica close to the mouths of the Danube and Dniester rivers were high (0.5, 2.6-4.4 and 6.0 mmol m(-2) d(-1), respectively) and comparable with values measured in other estu aries such as Naragansett and Chesapeake Bay, but higher than fluxes m easured in shelf-slope seas like the Skagerrak. The benthic fluxes of phosphorus and silica are in the same order of magnitude as the annual nutrient input by the Danube river, whereas ammonia fluxes from the s ediment amounted to similar to 10% of the Danube input. Hence, benthic fluxes from the sediments are responsible for a significant flux of n utrients to the waters of the northwestern shelf of the Black Sea. (C) 1998 Elsevier Science B.V. All rights reserved.