Benthic fluxes and nutrient budgets for sediments in the Northern Adriatic Sea: burial and recycling efficiencies

Abstract

The Northern Adriatic Sea, between Italy and Yugoslavia, has been plagued by problems of eutrophication. Anthropogenic nutrient loading in rivers (the Po River being the largest) entering the northern Adriatic has increased nutrient input to this system and stimulated algal growth. This area is relatively shallow (maximum depth = 60 m), but becomes stratified during the summer months, inhibiting oxygen transport to bottom waters. During September 1988 in situ benthic flux measurements were made at five stations in the region south of the Po River Delta, and cores were collected for studies of pore water and solid phase chemistry at 6 stations. 210Pb was used to constrain sediment accumulation rates and a range of 0.2-0.8 g/cm2/year was determined at different stations. These rates must be considered to be upper limits because bioturbation may be active, although 234Th and 7Be showed little evidence of this process. Pore water profiles show evidence of irrigation, and mean diffusive fluxes for radon, oxygen, TCO2, silica, phosphate and ammonia are generally 20-90% of the fluxes obtained from benthic chamber measurements. This is consistent with previous work in this area in which studies of radon fluxes indicated that irrigation plays an important role in sediment–water exchange.