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Impact of sediment resuspension and photochemistry on dissolved organic carbon and copper speciation

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Michelle Leigh Smith (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Stephen Skrabal

Abstract: Changes in dissolved organic carbon (DOC) and Cu speciation caused by sediment resuspension and photochemistry in the highly turbid, organic rich waters of the Cape Fear River Estuary (CFRE) have been investigated. The concentration of DOC in filtered estuarine samples exposed to simulated sunlight decreased 4 -27 mM compared with dark controls which also decreased but to a lesser extent. This indicated that organic carbon was being converted to inorganic carbon in light exposed samples and consumed in dark controls. Unfiltered irradiated samples containing ambient river particles experienced an increase in DOC relative to samples with no particles, indicating particles are capable of producing DOC upon exposure to light. When suspended sediments (2 g wet sediment per L) were present, 3-145 mM DOC was released in light exposed samples relative to dark controls. The DOC released was directly related to the percent organic carbon in the sediment. When resuspended sediment samples were exposed to photosynthetically available radiation (PAR) rather than full spectrum light, there was significantly less DOC produced suggesting UVA/UVB light is the most effective at engendering changes in DOC. A series of photolysis experiments were also conducted to determine the effects of irradiation and resuspended sediments on total dissolved copper (TDCu) concentrations. In relatively uncontaminated environments, there was little or no effect of sediments or irradiation on TDCu levels in the estuary. In more contaminated environments, such as seen in San Diego Bay and the Port of Wilmington in the CFRE, there was a significant increase in TDCu production after irradiation in 0.2 mM filtered water containing sediments. These results suggest that the impact of sediment resuspension on TDCu concentration depends to a large extent on how much Cu is present in the irradiated sediments. In addition to TDCu, the impact of light exposure and sediments on Cu(I) was also investigated. Copper(I) concentrations in filtered CFRE water increased in light exposed samples suggesting production of reduced Cu from other dissolved Cu species. Little impact of ambient particles or sediments on Cu(I) concentrations were observed. The effect of full spectrum and PAR on the photodegradation of strong Cu binding ligands was also studied in filtered water with no added sediments. When exposed to full spectrum light, ligand concentrations decreased from 55 nM to 10 nM, whereas samples exposed only to PAR decreased from 50 nM to 19 nM, indicating that PAR is very effective at the degradation of Cu ligands in the water column.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Keywords
Carbon--Speciation, Copper--Speciation, Photochemistry, Sedimentation and deposition--North Carolina--Cape Fear River Estuary
Subjects
Copper -- Speciation
Carbon -- Speciation
Photochemistry
Sedimentation and deposition -- North Carolina -- Cape Fear River Estuary