Biogeochemistry of Copper In Lake Pontchartrain Water and Sediments.

Copper exists in various physico-chemical forms in nature waters. These different forms likely have different bioavailability implication to aquatic organisms. In this study, we investigated speciation of Cu in the dissolved phase and chemical forms in the sediment phase of the lake. Water and sediment samples in subsegments of the Lake Pontchartrain were collected and the speciation in water was performed using a modified resin column approach.  Copper in sediments was sequentially fractionated into exchangeable, reducible, oxidizable, or residual Cu using a modified European Community Bureau of Reference (BCR) procedure. The labile Cu form in water, which dissociates and contributes to the free Cu ion flux, accounted for 32-70% of the total dissolved Cu in water. The opening of Bonnet Carré Spillway increased total Cu in the water along a transect from the shore (the Spillway),  suggesting of increasing Cu concentration due to sediment brought in by the opening up of Bonnet Carré Spillway. On the other hand, average percentage of dissolved Cu as of total Cu in water was generally increasing towards the center of the Lake. Sediment fractionation showed that the Cu was present predominately in oxidizable fraction followed by residual fraction, reducible fraction, and exchangeable fraction. The presence of the largest pool of oxidizable Cu suggests that appreciable amount of sediment Cu was also associated with redox-sensitive materials such as ferrous minerals. Copper in the sediment likely control the long-term average labile Cu levels in water.