Benthic fluxes in San Francisco Bay

Benthic fluxes were measured in San Francisco bay (South Bay), using in situ flux chambers. Fluxes of silica, ammonium and alkalinity were mainly due to deep irrigation of the burrows of macrofauna. Fluxes of oxygen and nitrate were dominated by exchange along steep gradients near the sediment/water interface. Interannual variation in benthic fluxes could be as large as seasonal variations. This variability was difficult to separate from spatial variability. Extensive nitrification and denitrification were presumed to occur in the sediment column. About 55 per cent of fixed particulate nitrogen reaching the sediments was converted to nitrogen. Large fractions of the net annual productivity of carbon (90 per cent) and silica (65 per cent) were recycled by the benthos.