Effect of organic matter source and salinity on dissolved organic matter isolation via ultrafiltration and solid phase extraction |
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Authors: | Brittany R Kruger Brent J Dalzell Elizabeth C Minor |
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Institution: | (1) Large Lakes Observatory, University of Minnesota, Duluth, 2205 E 5th St, Duluth, MN 55812, USA;(2) Department of Soil, Water, and Climate, University of Minnesota, 439 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108, USA |
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Abstract: | In this study, samples were taken from three contrasting freshwater sources and amended with salt in order to determine the
influence of salinity and dissolved organic matter (DOM) composition on DOM recovery via ultrafiltration and solid phase extraction
(SPE) with C18 disks. Salt addition caused variable recovery of DOM when using C18 SPE, and ultraviolet–visible spectroscopic characterization of the extracted material showed spectral responses that varied
among sample sources. In contrast, increasing sample salinity from 0 to 30 ppt consistently caused a 15–25% reduction in the
amount of high molecular weight DOM isolated by ultrafiltration for both dissolved organic carbon (DOC) and chromophoric DOM
(CDOM), regardless of DOM composition. We hypothesize that a change in conformation (such as coiling or disaggregation) of
DOM molecules occurs in the presence of salt, allowing them to pass through the ultrafiltration membrane and thereby decreasing
the DOM retained by ultrafiltration. These results are important because they demonstrate that changes in salinity can influence
DOM recovery in estuaries. Interpretation of DOM characteristics along estuarine gradients needs to account for potential
artifacts introduced by sample isolation techniques. |
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