Light-induced conversion of refractory, high molecular weight lake water constituents

Abstract

High molecular weight DOM (apparent mol wt. ≥1500) was isolated from lake water, both in summer and in winter. Sephadex G-15 gel permeation chromatography with 0.02 M phosphate buffer yielded one peak. Elution with distilled water gave rise to distinct smaller sized subfractions. It was concluded that these compounds are weakly bound subunits of the macromolecules, which are liberated on elution with distilled water. The macromolecules were not stable in the dark. Exposing them to daylight in the laboratory and to sunlight, in quartz bottles enhanced conversion. During 6 weeks' exposure to weakly photolytic conditions (daylight >300 nm), organic carbon of the high molecular bulk substances decreased by 15% (winter) and by 25% (summer), while the concentrations of the apparent low molecular weight substances increased accordingly. Such a slow but continuous transformation may reduce also the <in situ> persistence of the macromolecules gradually.