Water Quality in Bangs Lake: effects of recurrent phosphate spills to a coastal estuary

Author(s): Dillon, K.; Caffrey, J.; Carmichael, R.; Holcomb, S.; Griffin, C.; Allen, J.; Jones, T.; Price, K.; Baine, G.

Bangs Lake, an estuarine water body in the Grand Bay NERR, has been the site of three industrial phosphate spills from a nearby fertilizer plant since 2005. Due to restricted tidal exchange in Bangs Lake, these events have had long lasting effects on water column phosphate concentrations which may stimulate biological activity and alter the biogeochemical cycling of essential elements within the water column and the sediments. To determine the fate of excess phosphate from the industrial spills, we measured soluble reactive phosphate concentrations in sediment pore water and total particulate phosphate concentrations from sediment cores (0-25 cm depth) from four locations: North Bangs Lake (closest to spill locations), Bangs Lake, and two low impact reference sites (Bayou Cumbest and Bayou Heron). We also conducted phosphate adsorption experiments and measured benthic chlorophyll concentrations with sediments from these sites to determine if the excess PO4 was fertilizing benthic microalgae to determine the fate of this excess PO4. Pore water phosphate concentrations were highest (21 uM) from 10 to 20 cm depths in North Bangs Lake cores however pore water from the surface sections of these cores had much lower phosphate concentrations (<0.5 uM). Pore water from the Bangs Lake cores consistently had elevated phosphate concentrations (2 to 5 uM) throughout the core length while pore water phosphate concentrations from one reference site were much lower (<0.7 uM), likely reflecting background levels. Phosphate adsorption experiments show that surface sediments from North Bangs Lake and Bayou Cumbest rapidly stripped phosphate from solution to final concentrations of <3 uM while surface sediments from Bangs Lake had greatly reduced phosphate adsorption capacity with much higher final concentrations (24 to 32 uM) indicating these sediments are near saturation. In 2013 and 2014, Sediment chlorophyll a concentrations were higher in Bangs Lake compared to the reference site. Sediment chlorophyll a was significantly correlated with extractable phosphate concentration in sediments (r = 0.88). In addition, grow out experiments with amendments of phosphorus to water and sediment samples stimulated the growth of cyanobacteria capable of fixing nitrogen.

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