Production by microphytobenthos in the Swan–Canning Estuary

Abstract

AbstractIntact 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 deduced from changes in oxygen (17 cores) or pH (13 cores). The theoretical saturating light intensity Ik determined from O2 was 107 µE m−2 s−1, and the light intensity at which photosynthesis is saturated, Isat, was about 1100 µE 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 upper estuary and 3·5 mm in coarse sediments of the lower estuary. Microalgae from below the photic zone photosynthesized on exposure to light. Biomass (measured as chlorophyll a) decreased down the sediment profile and was linearly correlated with net and gross maximum photosynthesis. Relative photosynthetic efficiencies were high, and light compensation increased with increasing depth in the sediment.Q10 values estimated from both net oxygen and carbon dioxide flux decreased with increasing temperature. Highest and lowest Q10 values were for respiration and net production derived from pH measurements. Copyright © 2001 John Wiley & Sons, Ltd.