Longterm effects of the herbicides Atrazine and Dichlobenil upon the phytoplankton density and physico-chemical conditions in compartments of a freshwater pond.

Atrazine (1.1 mg · L-1) and Dichlobenil ("DBN") (4.3 mg · L-1) were dosed in triplicates into the water of a compartimentalized pond. Maximum concentrations of the chemicals detected were 200 μg · L-1 Atrazine and 4.2 mg · L-1 DBN (on day 3 - 5 after dosing). Residues were monitored for 55 days, amounting to 60 μg Atrazine and 1.5 mg DBN per litre at the end of observation. O2- and H+-concentrations were significantly lower for 35 and 30 days resp. in the treated water as compared to controls. The conductivity of the dosed water was significantly higher for at least 65 (DBN) and 120 days (Atrazine) than in the untreated compartments. Differences in phytoplankton abundance and diversity could be evaluated between controls and treated biotopes