SEDIMENT OXYGEN-CONSUMPTION AND BENTHIC NUTRIENT FLUXES ON THE LOUISIANA CONTINENTAL-SHELF - A METHODOLOGICAL COMPARISON

There has been considerable discussion but little experimental evidenc e regarding the comparability of in-situ and remote (shipboard or labo ratory) incubations for the determination of sediment oxygen consumpti on and benthic nutrient flux rates. This paper presents the results of such a comparison, using in situ chamber and shipboard chemostatic sy stems, for a shallow station on the Louisiana continental shelf during April 1992. Results indicated no methodological differences between r ates of sediment oxygen consumption and nutrient flux (NH4+, NO3-, NO2 -, P0(4)(3-), and SiO2/Si(OH)(2)) that could be attributed to the remo val of cores from shelf sediments, This conclusion implies that subcor ing from box cores is no more destructive of sediment structure and sa lient environmental characteristics than chamber emplacement. Differen ces between the methods occurred when ambient oxygen concentrations we re low (<2 ml l(-1)), These differences were caused by initial reaerat ion of bottom water in the shipboard system and reflect the sensitivit y of heterotrophic metabolism, dissolution kinetics, and diffusive flu xes to low oxygen concentrations. The differences in exchange rates ob served in this study reiterate the importance in maintaining ambient c onditions in the experimental apparatus. The results of this study cor roborate the small body of data that addresses this issue and extends methodological similarities to include nutrient exchanges. Given the c omparability of rates, use of remote chemostatic systems is more advan tageous for work in shelf environments than in-situ batch methods due to increased statistical rigor, logistical convenience, and the abilit y to minimize changes in experimental conditions during incubations.