SS4.06 Speciation, Bioavailability, and Impacts of Atmospheric Trace Metals in Aquatic Systems
Date: Wednesday, June 12, 2002
Time: 3:15:00 PM
Location: Esquimalt
 
WilleyJD, University of North Carolina at Wilmington, Wilmington, USA, willeyj@uncwil.edu
Kieber, R, J, University of North Carolina at Wilmington, Wilmington, USA, kieberr@uncwil.edu
 
DECREASE IN IRON AVAILABILITY TO PHYTOPLANKTON IN OLIGOTROPHIC SEAWATER CAUSED BY RAINWATER HYDROGEN PEROXIDE
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Laboratory experiments mixing 5% iron-enriched (100 nM ferric nitrate) synthetic rain (pH 4.5 sulfuric acid) with 95% of Bermuda Area Time Series Station (BATS) Seawater increased in dissolved iron concentrations two times above concentrations predicted based on dilution due to release of Fe(II) from seawater particles, probably Saharan dust. This soluble iron increase was maintained for more than 24 hours. When rainwater contained both added iron and environmentally relevant concentrations of hydrogen peroxide, the increase in soluble iron did not occur. The dramatic influence of rainwater hydrogen peroxide on iron in seawater impacts the availability of atmospherically deposited iron to phytoplankton in iron replete waters. This was clearly demonstrated in bioassays conducted with BATS surface seawater in March 2000. Chlorophyll a concentrations in three-day bioassays increased approximately 50% relative to controls after addition of synthetic rain containing either ferrous or ferric chloride (50 or 100 nM) added as a 2% dilution by rain. Rainwater hydrogen peroxide completely removed this iron stimulation suggesting hydrogen peroxide plays a critical previously unknown role in the solubility and bioavailability of atmospherically deposited iron in seawater.