title: Copper Complexation Capacity and Copper Speciation in Freshwater Lakes (Lake Western Branch and Lake Prince)
Creators: name: Sultana, Rachide Ibrahimo Abdul
Publisher: name: Old Dominion University
publisherIdentifier: https://ror.org/04zjtrb98
publisherIdentifierScheme: ROR
Year: 1995

description: This research examines the copper complexation capacity, copper speciation and dissolved copper concentrations in Lake Western Branch (WB) and Lake Prince (LP) both located in Suffolk, Virginia. These lakes are drinking water reservoirs for the cities of Suffolk and Norfolk, and they experience blooms of algae which can deplete them of oxygen and affect treatment of their waters for drinking. Copper sulfate has regularly been added to control the algae, but the effectiveness of these additions is uncertain. For environmental management implications, knowledge of speciation (i.e., the concentrations of the various chemical forms) is important in studying the effects of copper (and other trace metals) on algae. Trace metals in natural waters can be complexed by inorganic and organic ligands, and their chemistry can be affected by phytoplankton in different ways: by surface reactions, metal uptake, and production of exudates (extracellular organic matter) with metal complexing properties. Therefore, the uncertain effects of trace metals on algae result from lack of definitive knowledge of the actual chemical forms (i.e., free ions, inorganic and organic complexes) of copper in these lakes, and their concentrations. Information on copper speciation will lead to a more complete understanding of the interactions of copper with aquatic biota and its biogeochemical cycling.

A very sensitive and accurate analytical technique capable of distinguishing the forms of copper and their concentration levels in natural waters, ligand competition/ differential pulse cathodic stripping voltammetry (LC/DPCSV), was used in this research. This technique has several advantages over others for determining trace metal concentrations and speciation.

Surface (2 m) lake water samples were collected in different seasons: Fall 1994, Spring 1995, and Summer 1995 at four stations in Lake Western Branch and three stations in Lake Prince. Total dissolved copper ranged from 7.13+ 0.11 to 65.25+0.74 nM in Lake Western Branch, and from 5.96+0.60 to 59.2+0.29 nM in Lake Prince. LC/DPCSV determinations of the natural copper complexing organic ligands in Lake Western Branch and Lake Prince indicated the presence of two classes of ligands. In Lake Western Branch, the stronger class, L1, had concentrations (CL1) ranging from 33.33±0.10 to 83.44+0.04 nM, with a conditional stability constant (expressed with respect to Cu2+) ranging from (log K' CuL1 values) 12.45 +0.37 to 14. 71 +0.03. The weaker class, L2, in Lake Western Branch had concentrations (CL2) ranging from 27.76±0.25 to 49.72+0.19 nM, with log K'CuL2 values ranging from 7.27+0.08 to 8.25+0.30. In Lake Prince, CL1 ranged from 26.51±0.96 to 78.74+0.66 nM, and log K' CuL1 ranged from 12.43+0.14 to 14.58+0.04. CL2 ranged from 10.81 +0.47 to 16.56+0.44 nM, and log K'CuL2 ranged from 7.98+0.76 to 8.35±0.29. The results indicate that over 99 % of the total dissolved copper in the water surface (2 m) of both lakes is organically complexed, and copper speciation is dominated by organic complexes formed with the stronger ligand class, L1. Because of the high extent of organic complexation, fractions of inorganic copper are reduced to less than 2 % of the total dissolved copper. Free cupric ion concentrations ranged from 0.35+0.02xl0-14 M to 0.83±0.0SxI0-9 M in Lake Western Branch, and from 0.113+0.006xl0-14 to 15.4+0.22xI0-13 M in Lake Prince.