Particulate formation due to freezing humic waters

Abstract

Water samples were collected from a soft water highly humic pond, and all particulates of >0.15‐μm nominal diameter were removed by continuous flow centrifugation. Freezing caused the formation of brown particulates which could be removed by centrifugation. The particulates can be dispersed by sonification, but the size distribution of organic fractions is permanently altered by freezing.

Dissolved Organic Matter Chemistry and Transport Along an Arctic Tundra Hillslope

“…On 8 and 12 August 2016, we collected pore waters for detailed chemical analysis into sterile 60-ml amber borosilicate bottles, placed each bottle on ice in the field, froze them within 2 hr of collection and transported them to Colorado State University for analysis (described below). We feel our EEMS results are robust because (1) SUVA 254 values (<3.0 L·mg-C −1 ·m −1 ) were below the threshold where significant alterations have previously been found , (2) DOM chemical composition and aromatic characteristics are similar to previously reported values for unfrozen samples collected from the same sampling location (Imnavait watershed, Ward & Cory, 2015) and from other active layer soil horizons (low Arctic, Waldrop et al, 2010), (3) DOC concentrations are within range of groundwater samples collected the year prior from the same watershed (1,500-2,000 μM vs. 300-2,100 μM, respectively, Neilson et al, 2018) and DOC concentrations in unfrozen soil-water samples (Waldrop et al, 2010;Ward & Cory, 2015), (4) our NMR results support those found using EEMS, and (5) we observed no evidence of flocculation or production of brown particles in thawed samples, which is characteristic of abiotic particle formation and OM precipitation Giesy & Briese, 1978). More specifically, freeze-thaw dynamics may alter fluorescent DOM composition and concentration (>10%) when sample aromaticity is high (SUVA 254 > 3.5 L·mg-C −1 ·m −1 ; Fellman, D'Amore, & Hood, 2008; Pokrovsky et al, 2018), although evidence is mixed (Coble et al, 2014;Otero et al, 2007;Spencer et al, 2010).…”

“…More specifically, freeze-thaw dynamics may alter fluorescent DOM composition and concentration (>10%) when sample aromaticity is high (SUVA 254 > 3.5 L·mg-C −1 ·m −1 ; Fellman, D'Amore, & Hood, 2008; Pokrovsky et al, 2018), although evidence is mixed (Coble et al, 2014;Otero et al, 2007;Spencer et al, 2010). We feel our EEMS results are robust because (1) SUVA 254 values (<3.0 L·mg-C −1 ·m −1 ) were below the threshold where significant alterations have previously been found , (2) DOM chemical composition and aromatic characteristics are similar to previously reported values for unfrozen samples collected from the same sampling location (Imnavait watershed, Ward & Cory, 2015) and from other active layer soil horizons (low Arctic, Waldrop et al, 2010), (3) DOC concentrations are within range of groundwater samples collected the year prior from the same watershed (1,500-2,000 μM vs. 300-2,100 μM, respectively, Neilson et al, 2018) and DOC concentrations in unfrozen soil-water samples (Waldrop et al, 2010;Ward & Cory, 2015), (4) our NMR results support those found using EEMS, and (5) we observed no evidence of flocculation or production of brown particles in thawed samples, which is characteristic of abiotic particle formation and OM precipitation Giesy & Briese, 1978).…”

Freezing and Its Effect on Chemical and Biological Properties of Soil

“…This would not be limited to mineral soils, as the physical disruption of organic matter has also been reported. Both reversible and irreversible changes in the structure of soil-derived organic matter can occur (Forsyth and Fraser, 1947;Dergacheva and Dedkov, 1977;Giesy and Briese, 1978). The outcome would be a provision of new sites for ion fixation or the exposure of what used to be "unavailable" supplies of ions.…”

Changes in the chemistry of soil solution and acetic‐acid extractable P following different types of freeze/thaw episodes

“…Certain aspects of the freezing process are similar in nature to those that occur during dryinglrewetting episodes (Lehrsch et al, 1991). These include physico-chemical reactions such as irreversible precipitation involving organic matter (Giesy & Briese, 1978) or silicate (Wada & Nagasto, 1983). This occurs due to the increase in ionic concentration caused by the exclusion of solutes as the water freezes, a process enhanced by the migration of water and solutes to the freezing front from unfrozen soil (Taneli, 1967;Kemper et al, 1987).…”