『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