Abstract
Dissolved organic matter (DOM) is ubiquitous in aquatic environments, whose behaviors and fate are highly related to the chemical compositions and size distribution. In this study, the UV-induced photodegradation properties of DOMs with different origins (i.e., macrophyte- and algae-derived) were investigated using absorption and fluorescence spectroscopy as well as flow field-flow fractionation (FlFFF). Results showed that, irrespective of DOM origins, the chromophoric components could be more effectively photo-degraded than the non-chromophoric ones. Though the two DOMs were characterized with similar fluorophores, the photodegradation properties showed obvious heterogeneities in DOM origins and molecular weights (MWs). Compared to macrophyte-derived DOM (MDOM), the algae-derived DOM (ADOM) exhibited a higher degradation rate and efficiency due to the abundance of labile components like newborn protein-like substances. The FlFFF results revealed a high photo-preferability of 100 kDa-0.45 μm protein-like MDOM and same photo-sensitivity of the size-fractionated humic-like moieties, testifying the reduction of molecular sizes during the photodegradation. However, the increase in relative percentage for 100 kDa-0.45 μm protein-like components and 5–15 kDa humic-like moieties implied a possible enhancement of molecular sizes for ADOM during the early period (i.e., the first hour) of photodegradation. This study provides new insights into the origin-related heterogeneities in compositions and size distribution for DOM transformation.
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