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PreprintImpacts of Hurricanes Katrina and Rita on the microbial landscape of the New Orleans area( 2007-03-20) Sinigalliano, Christopher D. ; Gidley, M. L. ; Shibata, T. ; Whitman, D. ; Dixon, T. H. ; Laws, Edward A. ; Hou, A. ; Bachoon, D. ; Brand, Larry E. ; Amaral-Zettler, Linda A. ; Gast, Rebecca J. ; Steward, Grieg F. ; Nigro, Olivia D. ; Fujioka, Roger S. ; Betancourt, W. Q. ; Vithanage, G. ; Mathews, J. ; Fleming, Lora E. ; Solo-Gabriele, Helena M.Floodwaters in New Orleans from Hurricanes Katrina and Rita were observed to contain high levels of fecal indicator bacteria and microbial pathogens, generating concern about long-term impacts of these floodwaters on the sediment and water quality of the New Orleans area and Lake Pontchartrain. We show here that fecal indicator microbe concentrations in offshore waters from Lake Pontchartrain returned to prehurricane concentrations within 2 months of the flooding induced by these hurricanes. Vibrio and Legionella species within the lake were more abundant in samples collected shortly after the floodwaters had receded compared with samples taken within the subsequent 3 months; no evidence of a long-term hurricane-induced algal bloom was observed. Giardia and Cryptosporidium were detected in canal waters. Elevated levels of fecal indicator bacteria observed in sediment could not be solely attributed to impacts from floodwaters, as both flooded and nonflooded areas exhibited elevated levels of fecal indicator bacteria. Evidence from measurements of Bifidobacterium and bacterial diversity analysis suggest that the fecal indicator bacteria observed in the sediment were from human fecal sources. Epidemiologic studies are highly recommended to evaluate the human health effects of the sediments deposited by the floodwaters.