Phosphorus Variability In the Area of Influence of the Mid-Barataria Sediment Diversion
Man-made levees along the lower Mississippi River prevent delivery of sediment from building and maintaining Louisiana’s coastal wetlands. The Mid-Barataria sediment diversions is designed to reintroduce Mississippi River water, sediment, and nutrients into the sediment-starved Barataria Basin. Phosphorus (P) is an important macronutrient for regulating primary production in coastal marine ecosystems. Wetlands can serve as a sink or source for phosphorus to the overlying water column through various retention and release processes, dependent on concentration. Louisiana coastal systems can be phosphorus limited due to much higher concentrations of bioavailable Nitrogen in river water. The high soluble molar N:P ( >50:1) ratio in the river water is offset by the high sediment total phosphorus load. The wetland soil P flux has the potential to decrease the N:P ratio of the surface water creating an optimum nutrient condition for increased algal bloom formation. We analyzed soil characteristics from 60 wetland stations in Barataria Basin, LA to include both vegetated marsh and open water stations. Total P and organic P was significantly higher by 11% in the marsh sites compared with the open water sites. Soil samples from twenty sites were analyzed for inorganic and organic P pools. Marsh sites had a higher organic P pool while open water sites had higher Iron (Fe) and Aluminum (Al) bound P. The Fe/Al bound pool is expected to release P months after the diversion operation has ceased increasing water column P concentrations. Both site types have relatively low equilibrium P concentrations indicating that the soil will take up P during sediment diversion operations. This research can help inform ecosystem modelers in accurately predicting diversion effects on the nutrient status of the coastal basin as well as serving as a wetland soil baseline condition prior to river reconnection for coastal restoration. Future research should explore changing P flux dynamics in the area of influence of the operating Mid-Barataria sediment diversion.