Water Quality in Bangs Lake: effects of recurrent phosphate spills to a coastal estuary: Year 2

Author(s): Dillon, K.; Caffrey, J.; Carmichael, R.; Dzwonkowski, B.; Holcomb, S.; Berry, T.; Baine, G.; Sleek, J.; Capps, R.

In 2015 we continued to examine the effects of industrial phosphate spills to Bangs Lake in the Grand Bay National Estuarine Research Reserve. Higher phosphate concentrations in sediments and porewater were measured in Bangs Lake compared to the reference site in Bayou Heron (while other nutrient concentrations were similar or lower). Peaks in particulate organic phosphorus (POP) concentrations in southeastern Bangs Lake corresponded in time to at least one known major phosphate spill (2005). In an effort to examine transport of a contaminant plume we also conducted a fluorescent dye tracer study using fluorescein in the northern portion of Bangs Lake. Transport and dilution rates on the day of the study were strongly affected by tidal action and a very strong western wind. Although the known source of phosphorus to the estuary is on the western side of Bangs Lake, hydrological processes that flush sediments and nutrients from the Lake may concentrate finer sediments and associated particulate phosphorus in the southeastern part of the Lake. Pb 210/ Cs dating conducted on the sediment cores were corroborated by Th isotope data, which confirmed greater pollution associated with spill material from the facility at sites in Bangs lake. Phytoplankton nutrient bioassay experiments showed that phytoplankton in Bangs Lake were very strongly limited by nitrogen. Preliminary results suggested that both ammonium and nitrate were effective at stimulating growth, and grazing by microzooplankton was sometimes significant. Benthic microalgae in Bangs Lake appeared to be decreasing, although they were still generally higher than at the reference site. Benthic microalgal growth was not stimulated by addition of ammonium, phosphate or both.

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