Hypolimnetic aeration is a widely used technique for lake restoration and fisheries enhancement. However, system design still depends on application of “safety factors” to observed oxygen demand rates, in large part because actual oxygen demand may be greater after aeration than before. Laboratory incubations of sediment show that sediment oxygen demand (SOD) rates follow mixed order kinetics, with an initial period of zero order reaction, followed by first order kinetics. The transition from zero to first order kinetics may correspond to the transition from laminar to turbulent flow. This suggests that SOD reaction kinetics are governed by thickness of the diffusive sublayer adjacent to the sediments. Therefore, zero and first order reaction regions correspond with oxygen diffusion limitation and substrate limitation, respectively. Such a mechanism would account for the induced oxygen demand observed following hypolimnetic aeration and would reconcile differences in SOD reaction orders noted in the literature. This paper describes development of equations based on laboratory SOD incubations for predicting induced oxygen demand following hypolimnetic aeration.
Ponderosa pine trees growing on the bank of the Spokane River, Idaho, have been used to monitor the river's past concentrations of Hg, Cr, Ag, Rb, Zn, Co, and Fe. Sections of cores and tree rings were neutron-activated to determine the trees' metal content as a function of tree ring age. Analysis of these data indicates that they are in rough agreement with sediment core data for Coeur d'Alene Lake and the volume of ore mined in the Coeur d'Alene mining district if allowances are made for metal holdup in Coeur d'Alene Lake.
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