Microphytobenthos production potential and contribution to bottom layer oxygen dynamics on the inner Louisiana continental shelf

To investigate the relative importance of microphytobenthos (MPB) oxygen (O₂) production on a river-dominated shelf, we made sediment core incubation measurements of MPB O₂ production and sediment O₂ consumption, and compared these to water-column measures of primary production and respiration during one spring and two summer cruises. Sites were located across a light attenuation (Kd) gradient on the inner Louisiana shelf (<25 m depth) with three sites on the eastern shelf and one site on the western shelf. MPB production rates were highest (range = 0.7–33.4 mmol O₂ m^–2 d^–1) at the western site where light attenuation was lowest (range = 0.13–0.16 m^–1). Near the river plumes, where Kd was higher (range = 0.17–0.64 m^–1), MPB production was lower (range = 0–2.0 mmol m^–2 d^–1). MPB production influenced the magnitude and direction of sediment O₂ exchanges at the western site and was observed to be a function of light availability. Overall, though, in comparison with integrated bottom layer production and respiration rates, MPB photosynthetic O₂ production as a percentage was small (range of means = 0%–2%) at the eastern shelf sites. At the western site, MPB production was larger, and more variable, 39% (SE 34%) of bottom layer O₂ production. Though based on a small data set, results suggest distinct differences between eastern and western shelf Kd and MPB contributions to bottom water O₂ due to proximity to the freshwater discharges of the Mississippi and Atchafalaya rivers.