Forest Fire Altered Dissolved Organic Matter and Disinfection Byproduct Precursor Exports From Forested Watersheds.

Prescribed fire is commonly used in the southeastern US as part of silvicultural regimes and habitat management. Forest fire reduces the thickness of detritus layer and changes foliar litters into pyrogenic organic matter (PyOM) on the forest floor, resulting different quantity and quality of DOM exported from forested watersheds. In this study, we compared characteristics of DOM from raw and burned foliar litters commonly found in the Southeastern United States, including longleaf pine (Pinus palustris), ash (Fraxinus caroliniana), Boxelder (Acer negundo), sweetgum (Liquidambar styraciflua), baldcypress (Taxodium distichum), and water tupelo (Nyssa aquatica), and evaluated their disinfection byproduct formation potential (DBPFP) using a uniform formation condition test.  In addition, waters from a recent prescribed burned watershed (WS77) and a control watershed (WS80) in the Santee Experimental Forest in South Carolina were sampled for DOM characterization and DBPFP tests. Laboratory analysis using pyrolysis gas chromatography mass spectrometry showed that PyOM contained a greater aromatic carbon but less nitrogen contents than their originally unburned materials. PyOM also yielded fewer amounts of DOM but containing greater aromaticity, and fulvic-like and humic-acid like fractions. This DOM extracted from PyOM, definitely dissolved black carbon in this study, was recalcitrant against photo and microbial degradation and had a greater reactivity in forming nitrogenous DBPs (N-DBPs) such as haloactonitriles (HANs). Field measurements also showed that DOM exported from WS77 was more reactive in forming HANs in chlorination than those from WS80. Results of our studies demonstrated that forest fire could change DOM exported from watersheds, resulting different characteristics of DOM in source water. Water treatment facilities using these source waters could produce more N-DBP in their finished waters.