| Summary: | The phytotoxicity of atrazine, paraquat, glyphosate, and alachlor to sago pond-weed (Potamogeton pectinatus), a submerged aquatic macrophyte, was tested under three types of laboratory culture conditions. In each case, tests were conducted in static systems, the test period was four weeks, and herbicide exposure was chronic, resulting from a single addition of herbicide to the test vessels at the beginning of the test period. The three sets of test conditions employed were: (1) axenic cultures in 125-mL flasks containing a nutrient media and sucrose; (2) a microcosm system employing 18.9-L buckets containing a sand, shell, and peat substrate; and (3) an algae-free system employing 0.95-L jars containing reconstituted freshwater and a nutrient agar substrate. The primary variable measured was biomass production
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