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2. USDA and NRCS 2003 National Handbook of Conservation Practices http://www.nrcs.usda.gov/technical/Standards/nhcp.html
3. Vegetation analysis of the irrigation and drainage canals in eastern Saudi Arabia;Shaltout;J. Univ. Kuwait,1993
4. Spirogyra species and accompanying algae from pools and ditches in The Netherlands;Simons;Aquat. Bot.,1990