Use of in-stream reservoirs to reduce bacterial contamination of rural watersheds V.P.J. Gannon a , G.D. Duke b , J.E. Thomas c, T , J. VanLeeuwen d , J. Byrne b , D. Johnson b , S.W. Kienzle b , J. Little e , T. Graham a , B. Selinger c a Laboratory for Foodborne Zoonoses, Population and Public Health Branch, Health Canada, Box 640, TWP Road 9-1, Lethbridge, Alberta, Canada T1J 3Z4 b University of Lethbridge, Department of Geography, 4401 University Drive, Lethbridge Alberta, Canada T1K 3M4 c University of Lethbridge, Department of Biological Sciences, 4401 University Drive, Lethbridge Alberta, Canada T1K 3M4 d University of Prince Edward Island, Department of Health Management, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3 e Irrigation Branch Alberta Agriculture, Food and Rural Development, Agriculture Centre, #100, 5401-1st Avenue South, Lethbridge, Alberta, Canada T1J 4V6 Accepted 10 December 2004 Available online 9 March 2005 Abstract An investigation into bacterial water quality problems was conducted on an interconnected stream and irrigation system within the Oldman River Basin of southern Alberta, Canada. Levels of indicator bacteria, including fecal coliforms, generic Escherichia coli and fecal streptococci, were repeatedly measured in streams and irrigation return canals of this river basin during the summer of 2001. Bacterial-loading segments of the irrigation/stream system were identified through a comparison of indicator bacteria levels in pairs of upstream and downstream sites. Mann–Whitney U-tests indicated that reservoirs significantly reduced bacterial counts. A temporal comparison of E. coli counts and river discharges suggested that these indicator bacteria do not originate from within in-stream sediments. Site-specific as well as cumulative inputs from a variety of non-point sources are likely to be responsible for the high downstream levels of indicator bacteria in this water system. The use of management practices such as in-stream reservoirs may significantly reduce contamination, and increase the quality of limited rural water supplies to allow their reuse and safe discharge into downstream water sources. The identification of bacteria-loading river/canal segments could also be used to prioritize restoration projects. D 2005 Elsevier B.V. All rights reserved. Keywords: Water; E. coli ; Agriculture; Sediment; Irrigation; Fecal contamination 1. Introduction There is a growing concern about the environ- mental impacts that agriculture has on surface water 0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2004.12.076 T Corresponding author. Tel.: +1 403 329 2467; fax: +1 403 329 2082. E-mail address: thomas@uleth.ca (J.E. Thomas). Science of the Total Environment 348 (2005) 19– 31 www.elsevier.com/locate/scitotenv