Microbial Changes in Selected Operational Descriptors of Dissolved Organic Matters From Various Sources in a Watershed

Abstract

Microbial changes in selected operational descriptors of dissolved organic matters (DOMs) from nine different sources (treated sewage, algae, soils, sediment, plants), which include a broad spectrum of potential organic precursors in the Han River watershed, were investigated using 28-day microbial incubation experiments. The DOM descriptors investigated were specific UV absorbance, fluorescence index, humification index, synchronous fluorescence spectra, apparent molecular weight (MW), and the extent of pyrene binding. The UV absorbance and the humification index values of most DOM samples increased after incubation, and their increases were more pronounced for algal- and plant-derived DOM compared with other sources. Microbial changes in fluorescence index were not consistent for the DOM samples investigated. Irrespective of the DOM sources, microbial changes resulted in the enhancement of humic substance-like structures and the associated characteristics. Microbial utilization of biodegradable organic substances appears to be prerequisite for the enhancement. Algal-derived DOM exhibited a substantial enhancement in MW value, whereas little changes or even decreases in the MW values were observed for terrestrial sources of DOM. Pyrene-binding reactivity and the microbial enhancement were observed only for algal- and plant-derived DOM. Our results are expected to provide basis for better understanding downstream microbial changes in DOM and the subsequent impact on the binding capabilities of DOM for hydrophobic organic contaminants in watersheds.