This is an electronic version of an article published in /Freshwater Biology/: complete citation information for the final version of the paper, as published in the print edition of /Freshwater Biology/, is available on the Blackwell Synergy online delivery service, accessible via the journal's website at http://www.blackwellpublishing.com/FWB or http://www.blackwell-synergy.com

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Last modified: Mon Dec 12 18:43:58 PST 2005