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Planktonic regeneration was monitored in water hyacinth (Eichhornia crassipes Mart.) infested culture media treated with five different herbicidal products. All the herbicides forliarly applied at the recommended rates achieved virtually complete plant kill within 21 days after treatment (DAT). However, water hyacinth in the reference untreated control medium had healthy, bright green leaves and resilent stems. The phytoplanktonic flora observed in the culture media 28 DAT consisted of 8 chlorophytes, 7 diatoms and 4 blue-green algal genera. The presence of water hyacinth reduced the planktonic species diversity by half while treatment significantly increased the species richness. Glyphosate-treated medium contained the richest phytoplanktonic assemblages (SDI = 5.14) while the terbutryn-treated medium had the least species diversity (SDI = 1.75). Except in the glyphosate-treated medium, Synedra sp. was the most dominant species in the herbicide treated media. Only glyphosate-treated medium supported zooplanktonic growth 28 DAT. Key words: Phytoplankton, regeneration, herbicide, phytotoxic injury. Journal of Aquatic Sciences Vol.17(1) 2002: 21-26 |
