Deposit Accumulation Testing System

The primary pathway of Hg to aquatic systems is considered to be atmospheric transport and subsequent deposition, which has caused an accumulation of Hg in watershed soils (Mason, et al., 1994). Recent work has shown that watershed disturbance such as clear cutting results in the increased export of Hg from the watershed to aquatic systems (Porvari, et al., 2003) and others have found agricultural and urbanized land use to be important factors influencing Hg export (Fitzgibbon, et al., 2008 Mason Sullivan, 1998). Thus the recovery of aquatic systems from anthropogenic Hg may depend on watershed characteristics which will differ among watersheds. Therefore we compared time to recovery to watershed attributes (e.g., %urban, susceptibility to erosion, watershed to lake area ratio, etc...) to test the hypothesis that the rate of recovery from Hg enrichment is influenced by watershed controlled pathways and stressors. 

These deposits which act as a poison constitute a measurement of the accumulated work of the catalyst, their analysis and pilot plant tests allow to obtain information which contributes to a better understanding of the poisoning and aging mechanisms of these systems. 

Given that the product of the tip reaction, Fe(CN)g-, did not deposit on the UME surface (unlike the Cu2+/Cu procedure discussed above), this system represented a useful model for testing the abilities of SECM to image the dissolution activity over selected areas of a crystal surface. For these experiments, the current for the diffusion-limited oxidation of Fe(CN)g was recorded as a function of position in the x, y plane, as the probe UME was scanned over the surface at a constant height. The solution conditions were as defined above. Problems that might have arisen from the accumulation of the electrolysis product, Fe(CN)s , in the tip-substrate gap, with the possible deposition of potassium ferricyanide, were largely alleviated by careful choice of a relatively fast tip scan speed and moderate initial UME/crystal separation. 

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