Production by microphytobenthos in the Swan-Canning Estuary

Intact sediment cores containing microphytobenthos, dominated by episammic diatoms, were collected from shallow sand flats of the Swan-Canning Estuary , Perth, southwestern Australia, and their photosynthesis-light relations d educed from changes in oxygen (17 cores) or pH (13 cores). The theoretical saturating light intensity I-k determined from O-2 was 107 muE m(-2) s(-1), and the light intensity at which photosynthesis is saturated, I-sat, was a bout 1100 muE m(-2) s(-1). Mean gross production and respiration increased with temperature. Infaunal contributions to total respiration were measured for two cores at about 30%. The sediment photic zone was estimated as 0.5 mm in fine sediments of the u pper estuary and 3.5 mm in coarse sediments of the lower estuary. Microalga e from below the photic zone photosynthesized on exposure to light. Biomass (measured as chlorophyll a) decreased down the sediment profile and was li nearly correlated with net and gross maximum photosynthesis. Relative photo synthetic efficiencies were high, and light compensation increased with inc reasing depth in the sediment. Q(10) values estimated from both net oxygen and carbon dioxide flux decreas ed with increasing temperature. Highest and lowest Q(10) values were for re spiration and net production derived from pH measurements. Copyright (C) 20 01 John Wiley & Sons, Ltd.