(Received 25 September 1996; accepted in revised form 21 March 1997)
1
U.S. Fish and Wildlife Service, Northern Alaska Ecological Services, 101 12th Avenue, Fairbanks, Alaska 99701, U.S.A.; present address: U.S. Fish and Wildlife Service, Klamath Falls Ecosystem Restoration Office, 6600 Washburn Way, Klamath Falls, Oregon 97603, U.S.A.
2
U.S. Geological Survey, National Water Quality Laboratory, 5293 Ward Road, M.S. 407, Arvada, Colorado 80002, U.S.A; jrgarb@usgs.gov
3
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