Microbial mediated sedimentary phosphorus mobilization in emerging and eroding wetlands of coastal Louisiana

The interactions between the microbial reduction of Fe (III) oxides and sediment geochemistry are poorly understood and mostly unknown for the Louisiana deltaic plain. This study evaluates the potential of P mobilization for this region during bacterially mediated redox reactions. Samples were collected from two wetland habitats (forested wetland ridge, and marsh) characterized by variations in vegetation structure and elevation in the currently prograding Wax Lake Delta (WLD) and two habitats (wetland marsh, and benthic channel) in degrading Barataria Bay in Lake Cataouatche (BLC). Our results show that PO₄^3- mobilization from WLD and BLC habitats were negligible under aerobic condition. Under anaerobic condition, there is a potential for significant release of PO₄^3- from sediment and wetland soils. PO₄^3- release in sediments spiked with Fe reducing bacteria Shewanella putrefaciens (Sp-CN32) were significantly higher in all cases with respect to a control treatment. In Wax Lake delta, PO₄^3- release from sediment spiked with Sp-CN32 increased significantly from 0.064±0.001 to 1.460±0.005μmolg^-1 in the ridge and from 0.079±0.007 to 2.407±0.001μmolg^-1 in the marsh substrates. In Barataria bay, PO₄^3- release increased from 0.103±0.006μmolg^-1 to 0.601±0.008μmolg^-1 in the channel and 0.050±0.000 to 0.618±0.026μmolg^-1 in marsh substrates. The PO₄^3- release from sediment slurries spiked with Sp-CN32 was higher in the WLD habitats (marsh 30-fold, ridge 22-fold) compared to the BLC habitats (marsh 12-fold, channel 6-fold). The increase in PO₄^3- release was significantly correlated with the Fe bound PO₄^3- in sediments from different habitats but not with their organic matter content. This study contributes to our understanding of the release mechanism of PO₄^3- during bacterial mediated redox reaction in wetland soils undergoing pulsing sediment deposition and loss.