Summertime tidal flushing of Barataria Bay: Transports of water and suspended sediments

Abstract

[1] Inlets provide a critical ecological link between restricted bays and estuaries to the coastal ocean. The net fluxes of water and suspended sediment are presented in this study. These fluxes are obtained based on data from a multidisciplinary, full tidal cycle survey across Barataria Pass in southern Louisiana on 31 July to 1 August 2008. The velocity profiles were obtained with an acoustic Doppler current profiler mounted on a small boat continuously crossing the inlet, which contains swift and turbulent tidal currents. Water samples were collected six times in a 24 h period at three discrete depths and three locations across the inlet. The observations delineated a clear eddy on the western side of the inlet which causes a low R 2 value of the tidal harmonic analysis on the edges of the inlet. The net flux of total suspended sediment out of the bay was determined to be 8800 t of which 20% was organic matter, demonstrating a significant source of organic matter to the base of the coastal ocean detrital food chain. The time evolution and net fluxes of water, and suspended sediments showed that the net flow resembles conventional estuarine circulation patterns with net outward flow on the surface and shallow ends of the inlet and with net inward flow in the center and at the bottom of the center of the inlet. The west side has a much larger outward flow than the east side while the east side is fresher. These differences suggest that the Louisiana Coastal Current from around the Bird's Foot Delta derived from the mixing of shelf water with the Mississippi River freshwater may have entered the bay. This must have been mostly from the east side during the survey, which resulted in a smaller outward flow on the eastern side. A numerical experiment further confirmed this assumption and the model was verified by field observations on 5 May 2010.

The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

“…4 and 5), and we speculate that this was due to net export from the bay, a phenomenon that might be expected for a coastal ecosystem experiencing wetland loss (Ren et al, 2009). In the same cruise, Dagg et al (2008) also found that particulate organic carbon and nitrogen, Chl-a, and TSM (total suspended material) were high in the northern Louisiana Bight and argued that the particulate materials were representative of output from Barataria Bay, consistent with physical characterizations of exchange processes in this system (Das et al, 2010;Li et al, 2011).…”

“…The mean tidal discharge through the passes of Barataria Bay is ∼ 6950 m 3 s −1 , equivalent to 43 % of the average discharge of the lower Mississippi River (Das et al, 2010). Such strong tidal exchange also introduces Mississippi River-influenced shelf water into this estuary (Li et al, 2011). The dominant coastal current on the Louisiana shelf generally flows to the west, but a clockwise eddy occurs in the Louisiana Bight adjacent to the northwest of the Mississippi River birdfoot delta (Morey et al, 2003;Walker et al, 2005).…”

Seasonal Variation of Colored Dissolved Organic Matter in Barataria Bay, Louisiana, Using Combined Landsat and Field Data

“…Winds likely pushed bay water to the shelf through the tidal channels between barrier islands and that might have reduced salinity at Station 1 (daily mean salinity = ~14) due to the fresh and marine water mixing (Figure 8). [26,30]. The eastern part of the bay also experienced higher ag355 values likely due to the freshwater input from the DPFD and the numerous channels in the north and east (e.g., West Pointe à la Hache siphon diversion) regions of the bay during the high flow conditions of the MR [25].…”

“…An analysis of CDOM variability in 2010 revealed Barataria Bay, coupled with river and shelf water exchange near the mouth of the bay [26][27][28]. The generally shallow water depths of this aquatic system are also likely to make it susceptible to the physical forcings of wind, tides and currents, resulting in the release of CDOM trapped in the bottom sediments by water column mixing [23,29,30]. Since CDOM distribution in Barataria Bay is strongly influenced by the seasonality and the physical forcing, spatial and temporal monitoring of CDOM is necessary to study biogeochemical processes, sources and sinks of DOM, and to improve ocean color estimates of chlorophyll-a.…”

Will coastal wetlands continue to sequester carbon in response to an increase in global sea level?: a case study of the rapidly subsiding Mississippi river deltaic plain

“…As a result, most coastal marshes are being replaced by shallow open water area as sea level continues to rise. Conversions of marshes to open water releases a considerable amount of C into the adjacent estuary, where it is either decomposed to CO 2 , accumulated in bottom sediment of estuary, or exported to the coastal shelf (Li et al , 2011. Field studies in coastal North Carolina have shown that higher rates of erosion can contribute to large C fluxes to estuaries (Young 1995).…”