Biogeochemical cycling of copper associated with particulate matter in Lake Superior

The biogeochemical cycling of trace metals in natural systems is strongly associated with biotic- and abiotic-particles being created and released by weathering, anthropogenic and biological activities. Particles act as metal sinks and sources. Particulate species may undergo several chemical reactions that affect the bioavalablility and toxicity of trace metals to aquatic biota. A billion tons of metal-rich mine tailings were discharged along the shore of the Keweenaw Peninsula over a 100-year period due to copper mining activity. Several decades after cessation of the tailing discharges, high concentrations of trace metals in sediments are still found along the coastal areas. This thesis focuses on the release of copper from the mine tailings, the movement of copper in the lake, and the ultimate fate of the copper.; The major objective of this study was to determine the processes governing concentrations of dissolved copper in the west coastal area of the Keweenaw Peninsula. The two major processes were found to be dissolution of copper from the mine tailings and scavenging of copper by suspended particles. Spatio-temporal patterns of suspended particles were examined to determine the influence of environmental factors on the dynamics and distribution of the suspended particles. River inputs, texture of sediments, thermal structure, bathymetry, and weather conditions were shown to be the major factors that regulate suspended particles and sediments in the study area. To identify the pathway of particle/sediment movements, chemical and mineralogical fingerprints of the major sediment source materials were developed and used as tracers. Longshore transport of suspended particles and sediments in conjunction with currents and waves was shown to be the predominant process in the study area; some cross-margin transport was also shown to occur. Spatio-temporal patterns of dissolved copper concentrations revealed nearshore/offshore gradients that result from the coastal contamination with copper tailings. Unlike in the oceans, uniform depth profiles of total dissolved copper and high Cu:C ratio of settling particles were observed. These profiles indicate that copper is controlled by the suspended particles via sorption (scavenging) rather than biological activity (uptake by algae).