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

There has been considerable discussion but little experimental evidence regarding the comparability of in-situ and remote (shipboard or laboratory) incubations for the determination of sediment oxygen consumption and benthic nutrient flux rates. This paper presents the results of such a comparison, using in situ chamber and shipboard chemostatic systems, for a shallow station on the Louisiana continental shelf during April 1992. Results indicated no methodological differences between rates of sediment oxygen consumption and nutrient flux (NH4+, NO3-, NO2-, P0(4)(3-), and SiO2/Si(OH)(2)) that could be attributed to the removal of cores from shelf sediments, This conclusion implies that subcoring from box cores is no more destructive of sediment structure and salient environmental characteristics than chamber emplacement. Differences between the methods occurred when ambient oxygen concentrations were low (<2 ml l(-1)), These differences were caused by initial reaeration of bottom water in the shipboard system and reflect the sensitivity of heterotrophic metabolism, dissolution kinetics, and diffusive fluxes to low oxygen concentrations. The differences in exchange rates observed in this study reiterate the importance in maintaining ambient conditions in the experimental apparatus. The results of this study corroborate the small body of data that addresses this issue and extends methodological similarities to include nutrient exchanges. Given the comparability of rates, use of remote chemostatic systems is more advantageous for work in shelf environments than in-situ batch methods due to increased statistical rigor, logistical convenience, and the ability to minimize changes in experimental conditions during incubations.