This research presents the first data on mercury (Hg) concentration and speciation in North Carolina for a southeastern US blackwater estuary. Water column data for Hg speciation and ancillary parameters were determined on 11 cruises between July 2004 and September 2006. Average surface water concentrations for total dissolved Hg (TDHg) were 7 pM and ranged from <1 to 37 pM, while the average particulate Hg (Hgpart) concentrations was 11 pM with a range of <1 to 46 pM. Average methylmercury (MeHg) surface water concentrations were 0.42 pM and ranged from <0.1 to 1.7 pM. TDHg concentrations are highest under medium flow conditions, where as Hg part concentrations are highest under high flow conditions.
Sediment analyses throughout the estuary revealed elevated concentrations of Hg at freshwater stations M61, HB and LVC. Hg concentrations are similar throughout the lower estuary when normalized to organic carbon content, however concentrations at LVC are elevated suggesting a local point source from a defunct chlor-alkali plant. Benthic flux experiments conducted at M61 and HB indicate that sediments act as both a source and sink for total Hg in the estuary, having one of the highest TDHg flux out of sediments in comparison to other estuaries. However, sediments were never a source of MeHg in the Cape Fear River estuary (CFRE) unlike many other systems where sediments are a significant input of MeHg to overlying waters.
Photolysis experiments indicate that irradiation of CFRE water does not impact the speciation or concentration of water column TDHg. Photolysis of estuary water containing ambient particles and resuspended bottom sediments show no clear increase or decrease of water column Hg concentrations. Irradiation of unfiltered CFRE surface waters produces significant concentrations of dissolved gaseous Hg (DGHg) and demethylates Hg at a rate dependent on initial MeHg concentration.
Mass balance calculations indicate that riverine input is the primary source of Hg and MeHg to the estuary. The primary sink for TDHg is benthic flux. Tidal exchange transports approximately 20% of total Hg and 40% of MeHg to the coastal ocean. Comparison with other estuaries indicates that the CFRE is a moderately impacted industrialized estuary.
|Advisor:||Willey, Joan D.|
|Commitee:||Benninger, Larry K., Kieber, Robert J., Martens, Christopher S., Skrabal, Stephen A.|
|School:||The University of North Carolina at Chapel Hill|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 70/05, Dissertation Abstracts International|
|Keywords:||Cape Fear River estuary, Estuaries, Fluxes, Mercury cycling, Methylmercury, Photochemistry|
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