Release of Dissolved Organic Matter from Melting Ice

摘要

The elution behavior of dissolved organic matter (DOM) from melting ice, as well as the effect of freezing and thawing temperatures on the elution behavior of DOM from melting ice, was evaluated. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydro-phobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The bulk DOM and its five fractions, as well as ultraviolet (UV)-absorbing substances, trihalomethane (THM) and haloace-tronitrile (HAA) precursors, and fluorescent materials in DOM exhibited a first flush behavior during ice melting, i.e., preferential elution with the early melt water fractions; the first flush behavior of DOM was stronger at higher freezing temperatures and/or at lower thawing temperatures, whereas DOM was eluted from the ice more uniformly at lower freezing temperatures and/or at higher thawing temperatures. The higher dissolved organic carbon (DOC) concentration in ice was, the higher degree of enrichments of DOM within the first melt water fraction was. HAA precursors were more strongly enriched in the early melt water samples than THM precursors during ice melting. The fluorescent materials were released more uniformly over the entire melt period, as compared with the bulk DOM.