Spatial And Temporal Variability Of Benthic Respiration In A Developing Deltaic Estuary (wax Lake Delta, Louisiana)
The Wax Lake Delta (WLD) is one of the few areas of land gain in coastal Louisiana and provides an analog for a naturally developing subdelta created by a river diversion. This study examined the spatial and temporal variability of benthic respiration to broaden our current understanding of the biogeochemical functioning of diversion-created estuarine systems. Spatial and seasonal benthic respiration rates were quantified during distinct periods of discharge and water temperature conditions, which included a spring period of peak river discharge (May 2012, 2013), a summer period of low discharge and maximum seasonal water temperatures (August/Sept, 2012), and an autumn period of low discharge and intermediate water temperatures (October 2013). Benthic respiration rates for the Wax Lake Delta ranged from 4.4 – 46.8 and averaged 16.7 (± 1.5) mmol O2 m-2 d-1 . Atchafalaya Bay sites ranged from 10.3 - 26.5 and averaged 17.1 (± 1.5) mmol O2 m-2 d-1 across all sites and seasons. Benthic respiration generally increased along two spatial gradients: 1) with distance offshore from the delta into Atchafalaya Bay, and 2) toward the interior of a mouth bar island. These patterns were related to similar increases in sediment OC and N content, which were derived from a mix of terrigenous and marine sources and varied with season. Sediment organic (OC and N) content and water temperature were identified as main drivers influencing benthic respiration in the Wax Lake Delta estuary. Seasonal changes in riverine discharge and wind-driven sediment resuspension events were likely to influence the seasonal variability of benthic respiration by governing water temperature and organic matter supply to the sediments. Benthic oxygen consumption rates in the Wax Lake Delta were most sensitive to increases in water temperature during low discharge conditions (< 2,000 m3 /s) of the MI-AR system. In context of coastal restoration, results from this study suggest that opening a sediment diversion during spring peak discharge conditions will have less of an effect on benthic oxygen consumption rates than during warmer low flow conditions.