Benthic fluxes of dissolved inorganic carbon, nutrients and oxygen in the Gulf of Trieste (northern Adriatic)

Benthic fluxes of dissolved inorganic N, Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O-2 from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly in the period September 1995 - August 1996 using in situ incubated light benthic chambers. The highest efluxes of DIC, NH4+, PO43-, Si(OH)(4), and NO3- influxes encountered in late summer - early autumn were the consequence of degradation of benthic microalgae, and in autumn mostly of sedimented phytoplankton. High NO3- eflux was observed in spring. Only NH4+ and Si(OH)(4) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality and quantity of sedimentary organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIG, NH,+ and Si(OH), effluxes observed in July 1996 were due to the late spring - early summer degradation of sedimentary organic matter produced by benthic microalgae, while the autumn phytoplankton bloom was quickly reflected in enhanced benthic fluxes due to higher temperature. Significant correlations between NH4+, PO43- and Si(OH)(4) fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes were linked to O-2 consumption, suggesting that aerobic oxidation processes were important at the sediment-water interface in the Gulf. The N, P and Si nutrients released from sediment pore waters are probably utilized in benthic microalgal and bottom-water primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other.