Deciphering riverine dissolved organic matter biodegradation: Evidence from three-dimensional fluorescence

Biological degradation contributes significantly to aquatic dissolved organic matter (DOM) turnover. Yet to date, the specific biological pathways involved in DOM degradation are still obscure. Here, we show how DOM changes in response to 28-d incubation in a karst river, via the combined fluorescent excitation-emission matrix (EEM) with parallel factor analysis (PARAFAC) and peak picking. Tyrosine-, tryptophan-and UV humic-like components were identified as the primary DOM in original waters. Notable decreases of protein-like compo-nents were observed after 15 & DEG;C incubation, suggesting preferential consumption of biogenic DOM. Elevated temperature (30 & DEG;C), however, caused significant decreases in visible humic-like and terrestrial fulvic-like components, but an increase in UV humic-like components in comparison to 15 & DEG;C incubation (p < 0.05). Hu-mification index (HIX) decreased dramatically after 15 & DEG;C incubation, indicating that biological processes regulated river DOM properties. Our results highlight the significant biogenic signals in karst rivers, and evidence that fluorescence measurement can decipher riverine DOM biodegradation as a useful approach.

Automated summary

Biological degradation plays a significant role in the turnover of aquatic dissolved organic matter (DOM). The specific biological pathways involved in DOM degradation, however, remain unclear. In this study, the changes in DOM during a 28-day incubation in a karst river were analyzed using fluorescent excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) and peak picking. Different components of DOM were identified, and the results indicated that biogenic DOM was preferentially consumed during the incubation. The study also demonstrated the usefulness of fluorescence measurement in deciphering riverine DOM biodegradation.