Prescribed fire alters dissolved organic matter and disinfection by-product precursor in forested watersheds â€" part II. a controlled field study

Abstract

Forest detritus material is one of the major terrestrial sources of dissolved organic matter (DOM) in source waters. There is a health concern on DOM because it reacts with disinfectants to form a variety of potentially carcinogenic disinfection by-products (DBPs) during drinking water treatments. Prescribed fire is a common forest management practice in Southeastern US to reduce the risks of wildfire and beetle infestation. However, this forest management practice alters the composition and quantity of detritus materials on forest floor, changing the DOM and DBP precursors exports from those forested watersheds. In this book chapter, we discussed a prescribed fire study conducted in three 20m x 20m experimental plots in Hobcaw Barony, Georgetown, South Carolina. Litter and duff mixtures of field samples before and after prescribed fire were collected for water extraction experiments in the laboratory. In addition, water extracts were further exposed to sunlight for 15 days in order to understand the biogeochemical processes on the degradability of DOM and DBP precursors. The concentrations of water extractable organic carbon (WEOC) and water extractable total nitrogen (WETN) from unburned detritus (60.3 g-WEOC/m2 and 1.9 g-WETN/m2) were significantly greater than those from burned detritus (11.4 g-WEOC/m2 and 0.5 g-WETN/m2). Importantly, the yield of DBP was significantly reduced from 3651 mg-THM/m2 to 484 mg-THM/m2 after fire. There was no change in specific DBP formation in both burn and unburned samples after sunlight exposure although significant decreases in ultraviolet absorbance and fluorescence intensity were observed. This field study showed that prescribed fire could significantly decrease the production of dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) per unit area in forest floor and potentially decrease the DBP formation in water supply.