The role of algal carbon in the formation of THMs

1. The role of algal carbon in the formation of THMs J.D. Jack, T. W. Sellers, P. A. Bukaveckas, D. McGaha and J. Shostell Department of Biology and Center for Watershed Research, University of Louisville Louisville, KY (USA)

2. Trihalomethanes (THMs) • Chlorination of water supplies is commonly used as a disinfection practice worldwide • While effective, this process can also produce potentially harmful disinfection by products such as trihalomethanes (THMs). THMs include chloroform etc.

3. Trihalomethanes • Previous observational and experimental work with THM formation potential (THMFP) in source waters: • THMFP is directly proportional to TOC, temperature and pH • THMFP may be influenced by CHLa and algal extracellular products • Evidence for both autochthonous and allocthonous sources of THM precursors

4. Research Approach • Comparative: Survey of THMFP and other parameters in the Ohio River mainstem and 5 major tributaries during different hydroperiods • Experimental: Mesocosm studies at three hydroperiods in which we assessed THMFP under different light regimes

6. Oh1 KY Oh2 Gr Wa Cu Tn Oh3 THMFP in August (A) and October (O) 2000 in the Ohio River and major tributaries

7. Oh1 Ky Oh2 Gr Wa Cu Tn Oh3 Chlorophyll concentrations in August (A) and October (O) 2000 in the Ohio River and major tributaries

8. Experimental Study • Experiments performed at the Ohio River Experimental Station in 2000 L mesocosms • Experiments were conducted in July, August and September to capture range of river conditions • River water pumped into mesocosm and mixing maintained by submersible pumps

10. Experimental Study • Tank covers were used to create different light environments and thus indirectly control algal bloom development • Dark-tank covered, no light (N=3) • Ambient-simulates light in deep portions of the river (N=3) • High light-simulates light in shallow portions of river (N=3) • Tanks sampled for THMFP, CHLa, DOC, POC, TN and TP on days 0,3,6,10

11. High Light Amb. Light Dark

14. Results • Comparative data: consistent with hypothesis that algal production promotes THMFP (both CHLa and THMFP were highest in Wabash). • Experimental data: consistent with above hypothesis. High light tanks exhibited larger increases in CHLa and greater changes in THMFP than those observed in low light tanks. Minimum of 96% of THM in the dissolved form (< 0.45 mm)

15. Relevance to Ecosystem Questions • Factors controlling DOC flux from drainage • Role of allocthonous and autochthonous sources of DOC in rivers • Input-output budgets to determine carbon transformations and THMFP production

16. Acknowledgements • Thanks to Rich Schultz for analysis work • We gratefully acknowledge USEPA, the Technical Assistance Center for Water Quality at Western Kentucky University and CSX Corporation for funding of this research and the Ohio River Experimental Station.