Kerr,S.C., Shafert,M.M., Overdier,J. and Armstrong,D.E.(2008): Hydrologic and biogeochemical controls on trace element export from northern Wisconsin wetlands. Biogeochemistry, 89, 273-294.

『ウィスコンシン湿地北部からの微量元素流出に対する水文学的および生物地球化学的コントロール』


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』

Introduction
Methods
 Site description
 Field sampling preparation
 Field sampling
 Laboratory analysis
  Trace/major elements
  DOC
  SUVA
  Nitrogen speciation
  SPM
  Oxygen-18 isotopes
  Sulfur species
  Iron speciation
 Statistical analysis
Results
Discussion
 Water source
 Mineral weathering and groundwater flowpath
 Metal transport by DOC
 Metal transport by SPM
 Redox status and precipitation/dissolution/adsorption processes
 Seasonal events
Conclusions
Acknowledgements
References


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