Separate dissolved and particulate trace metal budgets for an estuarine system: an aid for management decisions

The sources and sinks of dissolved and particulate Pb, Cu and Zn were determined for the main basin of Puget Sound to understand the effect man has had on metal concentrations in both the water column and in the sediments. Municipal, industrial and atmospheric sources contributed about 66% of the total Pb added to the main basin of Puget Sound during the early 1980s. Advective inputs were the major sources of total Cu and Zn (approximately 40%) while riverine and erosional sources contributed about 30%. The discharge of the particle-bound trace metals from rivers minimized the influence of particulate anthropogenic sources, which constituted 50%, 23% and 18% of the total particulate Pb, Cu and Zn inputs, respectively. While advective transport was the major source of dissolved Cu and Zn (approximately 60% of all dissolved inputs), industrial, municipal and atmospheric inputs contributed about 85%, 30% and 38% of the dissolved Pb, Cu and Zn inputs, respectively. The sources of dissolved and particulate Cu and Zn were comparable with the sinks within the errors of the analyses indicating their quasi-conservative nature. Advection removed about 60% of the total Cu and Zn added to the main basin while 40% was deposited in the sediments of Puget Sound. Because of this quasi-conservative nature of Cu and Zn, anthropogenic inputs of Cu and Zn were dispersed from the system more than they were contained within main basin sediments. About 75% of the dissolved Pb discharged into the main basin of Puget Sound was lost from the dissolved phase and was balanced by a similar gain in the particulate phase. Because of this extensive scavenging and the effective retention of particles within the main basin, about 70% of the total Pb added to the main basin was retained within its sediments. These separate mass balances have utility in management decisions because they show the relative contributions from different sources and demonstrate whether the influences of dissolved and particulate inputs are reflected solely in the water column or the sediments, respectively.