DOM characteristics along the continuum from river to receiving basin: a comparison of freshwater and saline transects |
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Authors: | Brandon M Stephens Elizabeth C Minor |
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Institution: | (1) Large Lakes Observatory, University of Minnesota-Duluth, 2205 East 5th St., Duluth, MN 55812, USA;(2) Large Lakes Observatory, Department of Chemistry and Biochemistry, University of Minnesota-Duluth, 2205 East 5th St., Duluth, MN 55812, USA; |
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Abstract: | The chemical characteristics of bulk (sterile-filtered) and high molecular-weight dissolved organic matter (HMW DOM) were
analyzed for freshwater (St. Louis River, Minnesota to Lake Superior) and saline (Elizabeth River, Virginia to Chesapeake
Bay) river-to-receiving basin transects. Dissolved organic carbon concentrations and UV–Visible spectroscopy of bulk DOM demonstrated
a reduction in organic carbon, colored DOM and aromatic compounds downstream in both transects. The proportion of DOM recoverable
via ultrafiltration as HMW material also decreased downstream in both transects, although there was an offset in recoveries
between the transects that may be explained by the effects of ionic strength and/or differences in ultrafiltration technique.
The analysis of HMW DOM by Fourier transform infrared spectroscopy illustrated similar trends between transects, with a general
shift from aromatic/carboxylic compounds nearshore to aliphatic/carbohydrate materials offshore. The parallel changes observed
along saline and freshwater transects imply that similar processes play significant roles in the down-gradient alteration
of DOM and that ionic strength or pH changes cause second-order effects. |
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