Seasonal Arsenic Accumulation in Stream Sediments at a Groundwater Discharge Zone

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• 作者：Allison A. MacKay ; Ping Gan ; Ran Yu ; Barth F. Smets
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：January 21, 2014
• 年：2014
• 卷：48
• 期：2
• 页码：920-929
• 全文大小：525K
• ISSN：1520-5851

文摘

Seasonal changes in arsenic and iron accumulation rates were examined in the sediments of a brook that receives groundwater discharges of arsenic and reduced iron. Clean glass bead columns were deployed in sediments for known periods over the annual hydrologic cycle to monitor changes in arsenic and iron concentrations in bead coatings. The highest accumulation rates occurred during the dry summer period (July鈥揙ctober) when groundwater discharges were likely greatest at the sample locations. The intermediate flow period (October鈥揗arch), with higher surface water levels, was associated with losses of arsenic and iron from bead column coatings at depths below 2鈥? cm. Batch incubations indicated iron releases from solids to be induced by biological reduction of iron (oxy)hydroxide solids. Congruent arsenic releases during incubation were limited by the high arsenic sorption capacity (0.536 mg_As/mg_Fe) of unreacted iron oxide solids. The flooded spring (March鈥揓une) with high surface water flows showed the lowest arsenic and iron accumulation rates in the sediments. Comparisons of accumulation rates across a shoreline transect were consistent with greater rates at regions exposed above surface water levels for longer times and greater losses at locations submerged below surface water. Iron (oxy)hydroxide solids in the shallowest sediments likely serve as a passive barrier to sorb arsenic released to pore water at depth by biological iron reduction.