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

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

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

6. THMFP in August (A) and October (O) 2000 in the Ohio River and major tributaries Oh1GrOh2KYOh3WaCuTn

7. Chlorophyll concentrations in August (A) and October (O) 2000 in the Ohio River and major tributaries Oh1KyOh2GrWaCuTnOh3

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

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

11. High Light Amb. Light Dark

14. Results zComparative 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  m)

15. Relevance to Ecosystem Questions zFactors controlling DOC flux from drainage zRole of allocthonous and autochthonous sources of DOC in rivers zInput-output budgets to determine carbon transformations and THMFP production

16. Acknowledgements zThanks to Rich Schultz for analysis work zWe 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.