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Hydrologic and biogeochemical controls on trace element export from northern Wisconsin wetlands
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original article
Hydrologic and biogeochemical controls on trace element export from northern Wisconsin wetlands
Sara C. Kerr1 , Martin M. Shafer1 , Joel Overdier1 and David E. Armstrong1 
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Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park St., Madison, WI 53706, USA |
Received: 5 August 2007 Accepted: 17 June 2008 Published online: 17 July 2008
Abstract Wetlands play an important role in determining the water quality of streams and are generally considered to act as a sink
for many reactive species. However, retention of chemical constituents varies seasonally and is affected by hydrologic and
biogeochemical processes including water source, mineral weathering, DOC and SPM cycling, redox status, precipitation/dissolution/adsorption,
and seasonal events. Relatively little is known about the influence of these factors on trace element cycling in wetland-influenced
streams. To explore the role of wetlands with respect to the retention/release of trace elements to streams, we examined temporal
and spatial patterns of concentrations of a large suite of trace elements (via ICP-MS) and geochemical drivers in five streams
and wetland rivulets draining natural wetlands in a northern Wisconsin watershed as well as in their groundwater sources (terrestrial
recharge, lake recharge, and older lake recharge). We performed principal components analyses of the concentrations of elements
and their geochemical drivers in both the streams and rivulets to assist in the identification of factors regulating trace
element concentrations. Variation in trace and major element concentrations among the streams was strongly related to the
proportion of terrestrial recharge contributing to the stream. A dominant influence of water source on rivulet chemistry was
supported by association of groundwater-sourced elements (Ba, Ca, Cs, Mg, Na, Si, Sr) with the primary statistical factor.
DOC appeared in the first principal component factor for the streams and in the second factor for the rivulets. Strong correlations
of Al, Cd, Ce, Cu, La, Pb, Ti, and Zn with DOC supported the important influence of DOC on trace metal cycling. A number of
elements in the rivulets (Al, La, Pb, Ti) and streams (Al, Ce, Cr, Cu, La, Pb, Ti, Zn) had a significant particulate cycle.
Redox cycling and precipitation/dissolution reactions involving Fe and Mn likely impacted Cu and Mo as evidenced by the low
levels in the rivulets. Variance in Fe, Mn and the metal oxy-anions was associated with factors related to redox cycling and
adsorption reactions in the wetland sediments. In streams, DOC and metals with a high affinity for DOC were associated with
a factor which also included negative loadings for groundwater-sourced elements, reflecting the importance of seasonal hydrologic
events which flush DOC and metals from wetland sediments and dilute groundwater sourced metals. Redox processes were of secondary
importance in the streams but of primary significance in the rivulets, documenting the importance of anoxic conditions in
wetland sediments on groundwater en route to the stream.
Keywords Trace elements - Metals - Wetlands - Streams - Biogeochemistry
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