Date of Award

Summer 1996

Document Type


Degree Name

Master of Science (MS)


Chemistry & Biochemistry



Committee Director

John R. Donat

Committee Member

David Burdige

Committee Member

Patricia A. Pleban

Call Number for Print

Special Collections LD4331.C45 H46


This is the first research to examine the horizontal, vertical, and temporal variability of total dissolved zinc, organic complexation of zinc, and zinc speciation in the Chesapeake Bay. Filtered (0.45μm) surface and bottom water samples were taken along the salinity gradient of the Chesapeake Bay in October 1993, March 1995, July 1995, and October 1995. Analysis by Differential Pulse Anodic Stripping Voltammetry (DP ASV) indicated that total dissolved zinc concentrations in the Bay ranged from 2.9 ± 0.7nM to 38.8 ± 2nM. Total zinc was highest at the northern end of the Bay (low salinity), approximately 10 times lower at the Bay mouth (high salinity), and showed both conservative (October 1993 and March 1995) and non-conservative (July and October 1995) behavior as a function of salinity. The concentration of total zinc was generally highest in the spring (March 1995) and decreased through the summer and fall (July 1995 and October 1995). In the bottom waters, concentrations of total dissolved zinc were either slightly higher or the same as those at the surface.

Zinc titrations monitored by DP ASV indicated that 84-99% of dissolved zinc was organically complexed by a single ligand class whose concentration ranged from 11.9 ± 0.3nM to 54.0 ± 5. 7nM. Total ligand concentrations generally showed conservative behavior with salinity (i.e., high ligand concentrations at low salinity and 2.5-5 times lower ligand concentrations at the high salinity end-member). Ligand concentrations appeared to increase from spring to summer (March to July 1995) and decrease slightly in the fall (October 1995). Ligand concentrations showed either slight decreases or no changes with depth.

The conditional stability constants (log K' ZnL. zn 2+) of zinc ligands ranged from 8.7 ± 0.2 to 10.0 ± 0.2. The calculated free zinc ion concentrations ranged from 17 ± 12pM to 266 ± 77pM. Free zinc ion concentrations determined in 1995 showed minima between 15-25 salinity units. In July and October 1995, both end-member zinc ion levels were high, whereas in March 1995, the north Bay free zinc ion level was low, decreased through a minimum at 20 ipsu, and increased nearly 100 times in the Bay mouth (high salinity end-member). All free zinc ion concentrations determined in the Chesapeake Bay fell within a range between the concentration causing neritic growth limitation and that causing naupliar toxicity.


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