Redox Chemistry in Minnesota Streams during Episodes of Increased Methylmercury Discharge

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• 作者：Steven J. Balogh ; Yabing H. Nollet ; and Edward B. Swain
• 刊名：Environmental Science & Technology
• 出版年：2004
• 出版时间：October 1, 2004
• 年：2004
• 卷：38
• 期：19
• 页码：4921 - 4927
• 全文大小：204K
• 年卷期：v.38,no.19(October 1, 2004)
• ISSN：1520-5851

文摘

Mercury (Hg) and methylmercury (MeHg) are flushedfrom watersheds during hydrological events, contaminatingdownstream surface waters and resident fish populations.We monitored total mercury (THg), MeHg, and ancillarywater chemistry parameters in two streams (Cedar Creekand Trott Brook) in east-central Minnesota on a weeklyor semiweekly basis from April through October 2003. Heavyprecipitation in late June resulted in discrete episodesof high concentrations (>1.2 ng/L) of MeHg in both streamsin early July. The MeHg/THg ratio increased from 0.15 to0.36 in Cedar Creek and from 0.13 to 0.46 in Trott Brook duringthe event. The high MeHg concentrations were accompaniedby low dissolved oxygen concentrations and increasedconcentrations of dissolved organic carbon, Mn, Fe, andorthophosphate. A prolonged absence of precipitation duringAugust and early September brought stream levels backto baseflow values, and MeHg concentrations decreased toless than 0.1 ng/L. These results suggest that warm-weather, high-discharge events are the primary route ofexport of MeHg from these watersheds, and baseflowcontributes much less MeHg to downstream waters. Theredox water chemistry during the events sampled heresuggests that MeHg in these streams is discharged fromwetland areas where anoxic/anaerobic conditions prevail.