Biogeochemistry & Environmental Quality Research Group Clemson University

Watershed Perturbation on Drinking Water Quality

Forested watersheds are critically important to supply clean drinking water to millions of people in the US. Extreme weather such as extensive drought and intense rainstorms, resulting in severe wildfire and flooding respectively, has threatened these important natural resources.  In addition, population and economic growths have significantly altered land uses and management practices of many watersheds. These climatic and anthropogenic stresses modify the vegetation composition and soil organic matter within watersheds, affecting the quantity and quality of terrestrial DOM exports, and eventually altering downstream biogeochemical processes and the fate of many inorganic and organic chemical constituents in source waters. My research program is to increase an understanding of how climate change and corresponding management strategies affect the production and export of DOM from forested watersheds. The ultimate goal is to develop effective source water control strategies to optimize source water quality such that the use of disinfectants, formation of DBPs, and concentrations pollutants in finished waters could be minimized.

1. Drinking Water Safety during Hurricane and Flooding Events

Coastal blackwater rivers, characterized by high concentrations of natural organic matter, are source water for millions of people in the southeastern US. In October 2015, large areas of coastal South Carolina were flooded by Hurricane Joaquin. This so-called “thousand-year” rainfall mobilized and flushed large amounts of terrestrial organic matter and associated pollutants (e.g. mercury) into source water, affecting water quality and safety of municipal water supply. To understand the dynamics of water quality and water treatability during this extreme flood, water samples were collected from Waccamaw River (a typical blackwater river in the southeastern US) during rising limb, peak discharge, falling limb, and base flow. Despite decreasing water flow after peak discharge, dissolved organic carbon (DOC) levels (increased by up to 125%), and formation potentials of trihalomethanes and haloacetic acids (increased by up to 150%) remained high for an extended period of time (>eight weeks after peak discharge), while variation in the N-nitrosodimethylamine (NDMA) FP was negligible. Coagulation with alum and ferric at optimal dosage significantly reduced concentrations of DOC by 51e76%, but up to 10 mg/L of DOC still remained in treated waters. For an extended period of time, elevated levels of THMs (71-448 mg/L) and HAAs (88-406 mg/L) were quantified in laboratory chlorination experiments under uniform formation conditions (UFC), exceeding the United States Environmental Protection Agency's (USEPA) maximum contaminant level of 80 and 60 mg/L, respectively. Results demonstrated that populations in coastal cities are at high risk with disinfection by-products (DBPs) under the changing climate.

2. Watershed Management Reduce the Risks of Wildfire and Disinfection Byproducts

Detritus in forest watersheds is the major terrestrial source of DOM and nutrients in source waters but it is also the fuel igniting a forest fire. Fuel reduction techniques, including broadcast burning, pile burning, and mechanical thinning, could reduce the amount of DOM exports and the risks of wildfire. Accordingly, the frequency of fuel reduction practices can affect the accumulation of detritus material in forest floor and the amounts of DOM exports. The frequency and magnitude of post-treatment rainstorms also control the quantity and quality of DOM exports from a forest watershed. DOM is a great concern in source water because it affects many water treatment and aquatic processes, such as formations of carcinogenic disinfection byproducts (DBPs) during water disinfection, as well as transports and fates of toxic metals and organic pollutants. The ultimate goal of my research program is to develop effective watershed management strategies that can optimize source water quality such that the use of disinfectants, formation of DBPs, and concentrations pollutants in finished waters could be minimized. Detritus in forest watersheds is the major terrestrial source of DOM and nutrients in source waters but it is also the fuel igniting a forest fire. Fuel reduction techniques, including broadcast burning, pile burning, and mechanical thinning, could reduce the amount of DOM exports and the risks of wildfire. Accordingly, the frequency of fuel reduction practices can affect the accumulation of detritus material in forest floor and the amounts of DOM exports. The frequency and magnitude of post-treatment rainstorms also control the quantity and quality of DOM exports from a forest watershed. DOM is a great concern in source water because it affects many water treatment and aquatic processes, such as formations of carcinogenic disinfection byproducts (DBPs) during water disinfection, as well as transports and fates of toxic metals and organic pollutants. The ultimate goal of my research program is to develop effective watershed management strategies that can optimize source water quality such that the use of disinfectants, formation of DBPs, and concentrations pollutants in finished waters could be minimized.

Biogeochemistry & Environmental Quality Research Group

Clemson University

Last Updated: 1/30/2021

By Kenneth Chow