Microbial Degradation of Plant Leachate Alters Lignin Phenols and Trihalomethane Precursors

Abstract

Although the importance of vascular plant-derived dissolved organic carbon (DOC) in freshwater systems has been studied, the role of leached DOC as precursors of disinfection byproducts (DBPs) during drinking water treatment is not well known. Here we measured the propensity of leachates from four crops and four aquatic macrophytes to form trihalomethanes (THMs)-a regulated class of DBPs-before and after 21 d of microbial degradation. We also measured lignin phenol content and specific UV absorbance (SUVA(254)) to test the assumption that aromatic compounds from vascular plants are resistant to microbial degradation and readily form DBPs. Leaching solubilized 9 to 26% of total plant carbon, which formed 1.93 to 6.72 mmol THM mol C(-1). However, leachate DOC concentrations decreased by 85 to 92% over the 21-d incubation, with a concomitant decrease of 67 to 92% in total THM formation potential. Carbon-normalized THM yields in the residual DOC pool increased by 2.5 times on average, consistent with the preferential uptake of nonprecursor material. Lignin phenol concentrations decreased by 64 to 96% over 21 d, but a lack of correlation between lignin content and THM yields or SUVA(254) suggested that lignin-derived compounds are not the source of increased THM precursor yields in the residual DOC pool. Our results indicate that microbial carbon utilization alters THM precursors in ecosystems with direct plant leaching, but more work is needed to identify the specific dissolved organic matter components with a greater propensity to form DBPs and affect watershed management, drinking water quality, and human health.

The Genesis and Exodus of Vascular Plant DOM from an Oak Woodland Landscape

“…Average weighted carbon-normalized yields in the other six sample types ranged from 1.72 to 2.56 mg 100 mg OC −1 . These values are consistent with previous studies involving plant leachates (Hernes et al, , 2013aPellerin et al, 2010). Carbon-normalized yields in the litters and duffs prior to leaching ranged from 0.72 mg 100 mg OC −1 in the annual grass duff to 6.05 mg 100 mg OC −1 in the annual grass litter, and averaged 3.82 mg 100 mg OC −1 , while post-leaching values were 1.03-6.87 mg 100 mg OC −1 with an average of 4.17 mg 100 mg OC −1 , indicating preferential leaching/degradation of non-lignin plant constituents ( Table 1).…”

“…In contrast, calculated stream yields from HS and other similar streams at the research site indicate a DOC export of approximately 0.03 kg ha −1 DOC. Rapid microbial remineralization of plant leachates has previously been demonstrated (Cleveland et al, 2004;Pellerin et al, 2010). Our study shows that DOM produced on the landscape is nearly quantitatively retained or remineralized, and DOM that does flow into adjacent streams has the potential to be highly modified by biotic and abiotic processes.…”

Relationships between molecular weight and fluorescence properties for size-fractionated dissolved organic matter from fresh and aged sources

“…The possibility of such controls on the structure of biologically processed DOM, with a corresponding relationship between size and optical properties, is of interest in drinking water treatment systems that incorporate biological processing. In particular, it has been shown that DOM leached from different leaf species has different DBP formation potentials that are modified by microbial processing (Reckhow et al, 2004;Chow et al, 2009;Pellerin et al, 2010;Beggs and Summers, 2011;Hur et al, 2012).…”

Prescribed Fire Alters Dissolved Organic Matter and Disinfection By-Product Precursors in Forested Watersheds - Part I. A Controlled Laboratory Study

“…As DOM is an important precursor reacting with disinfectants during water treatment to yield carbonaceous (e.g., trihalomethanes; THMs) and nitrogenous disinfection by-products (N-DBPs) (e.g., haloacetonitriles; HANs) (17)(18)(19) increasing studies are focusing on the sources of DOM and the associated chlorine reactivity (20,21). Litters have been identified as a significant watershed source of DOM contributing to the downstream water supply and DBP precursors (14,(22)(23)(24). Different plant species can have a diverse amount and composition of organic compounds such as polysaccharides, lignin, tannin, and aliphatic biopolymers (25).…”