The impact of scavenging on trace metal budgets in Puget Sound

Abstract

The distributions of dissolved and particulate Mn, Pb, Cu and Zn in Puget Sound, its tributaries, and its sediments were determined to illustrate the impact of scavenging reactions on trace metal budgets of a large fjordlike estuary. About 75% of the dissolved Pb discharged into the main basin of Puget Sound was scavenged from the dissolved phase. The high particulate Pb concentrations in regions of high particulate Mn concentrations and the significant correlations between Pb and Mn concentrations on suspended particles demonstrate the importance of hydrous manganese oxide phases in scavenging dissolved Pb. Since particles are effectively retained within the main basin, scavenging results in the sedimentation of about 70% of the total Pb added to the main basin. Only isolated instances of scavenging of dissolved Cu and Zn were observed and the discharge rates of dissolved Cu and Zn from known sources were equal to their rates of advective removal within the errors of the budget. The remineralization of organically-bound particulate Cu is partly responsible for its quasi-conservative behavior within the main basin of Puget Sound. The fates of Cu and Zn are controlled mainly by physical processes such as advection and settling of particles. Advection removes about 60% of the total Cu and Zn added to the main basin while 40% is deposited in the sediments of Puget Sound.