AbstractThree small ponds in the boreal forest of southern Manitoba were treated with an aerial application of 2.1 kg/ha glyphosate. Two of the ponds had been treated the preceding year with 0.9 kg/ha glyphosate, whereas the third was previously untreated. Foliage samples of plants bordering the ponds were collected immediately after treatment, and water and sediment samples were collected over a period of 265 d after treatment. Samples were analyzed for glyphosate and its first metabolite, aminomethylphosphonic acid (AMPA). We found that glyphosate dissipated rapidly from the surface waters of all ponds (dissipation half‐lives of 3.5‐11.2 d). AMPA residues were detected in water samples during the first 14 d after treatment, suggesting that herbicide degradation was occurring in the water column. However, not all applied herbicide was accountable in residues in the water. Glyphosate and AMPA increased in sediment samples to day 36, suggesting that sediment adsorption was a major sink for the herbicide. Glyphosate dissipation from the water column was biphasic, with a rapid initial phase followed by a slower phase. We hypothesize this was due to herbicide sorption and partitioning between suspended particulate matter and bottom sediments. As was found after the first pond treatment, glyphosate dissipation was slower in chemically alkaline ponds than in a more dilute pond, suggesting that herbicide complexation with ions in solution may be a significant factor affecting the rate of dissipation in standing wa
展开▼
