The Cumberland Marsh Region (CMR), located on the coast of the Bay of Fundy, is a major feeding ground for waterfowl and contains significant coastal wetland systems. In this study, concentrations of lead (Pb) and arsenic (As) were assessed in the bottom sediments of various open water wetlands across the CMR, and gastropods were sampled from the same wetlands to assess bioaccumulation of these nonessential trace elements and the potential for transfer to higher trophic level species. It was predicted that gastropods would have higher concentrations of Pb and As from wetlands with higher concentrations of these elements in sediments. Although wetland sediments and gastropods had elevated Pb and As concentrations, in some cases above the Canadian Sediment Quality Guidelines for the protection of aquatic life, there were no significant correlations between sediment and gastropod trace element concentrations. Gastropod to sediment ratios of Pb and As concentrations were highest in the brackish wetlands, but overall, levels were not of toxicological concern. Wetland chemistries and gastropod physiologies are hypothesized to be driving factors in determining the level to which Pb and As will bioaccumulate and merit careful consideration when developing wetland management strategies.
Freshwater marshes are prevalent and important stores of carbon. They
bury carbon in deeper soils, although reported rates of carbon
accumulation are significantly higher over recent (decadal) versus
longer (centennial and millennial) timescales. Intrinsic organic matter
degradation, long-term climatic and ecological changes, and recent
anthropogenic impacts on sediment fluxes and organic matter production
may have a role in explaining this discrepancy, yet remain poorly
understood for freshwater marshes. We collected a 4-m core from a
riverine-influenced marsh in the watershed of Big Creek which drains
into Lake Erie in southern Ontario, Canada, and conducted radiometric
dating, elemental analyses, and programmed pyrolysis for organic matter
characterization. Over the past 5,710 calibrated years, burial of
organic (on average 26 ± 34 g C m-2 yr-1) and inorganic (22 ± 25 g C m-2
yr-1) carbon fractions has resulted in high rates of carbon
accumulation. We found that elevated recent rates of organic carbon
accumulation are driven by fractions that have low thermal stability and
are predominantly from aquatic sources. This type of organic carbon is
buried intermittently in deeper marsh sediments and corresponds to major
hydro-fluvial events (e.g., Nipissing highstands), which coincide with
regional marsh development. We deduce that lower fractions of labile
carbon in deeper soils reflect long-term degradation, which underscores
the notion that high recent rates of carbon accumulation are generally
not sustained over centuries and millennia. Our research demonstrates
the importance of identifying various carbon fractions in understanding
carbon burial in freshwater marsh soils, and informing marsh
conservation.
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