Diel cycling of zinc in a stream impacted by acid rock drainage: initial results from a new in situ Zn analyzer.

Recent work has demonstrated that many trace metals undergo dramatic diel (24-h) cycles in near neutral pH streams with metal concentrations reproducibly changing up to 500% during the diel period (Nimick et al., 2003). To examine diel zinc cycles in streams affected by acid rock drainage, we have developed a novel instrument, the Zn-DigiScan, to continuously monitor in situ zinc concentrations in near real-time. Initial results from a 3-day deployment at Fisher Creek, Montana have demonstrated the ability of the Zn-DigiScan to record diel Zn cycling at levels below 100 microg/l. Longer deployments of this instrument could be used to examine the effects of episodic events such as rainstorms and snowmelt pulses on zinc loading in streams affected by acid rock drainage.