7322894074

53

r*=0,72

y = 1,014- 0,0004x

Log glyphosate concentrations (pg f¹)

Figurę 3.3 Uelationship bctween the Shannon’s divcrsity index and glyphosate concentrations added to the growth media in an agricultural stream phytoplankton community after a 96 hours cxposure to various concentrations of glyphosate-based

herbicide.

3.6.6 Interspccific variations

As shown in figurę 3.4 (A), the phytoplankton community was composed of six dominant phytoplankton classes. The control treatment was dominated by the Chlorophyceae (40%), Bacillariophyceae (25%), Chrysophyceae (22%) and Chryptophyceae (10%) classes. Euglenophyceae (0.8%) and Cyanobacteria (2.2%) presence was marginal. The relative biomass of Chrysophyceae, Bacillariophyceae, Euglenophyceae and Cryptophyceae gradually decreased up to a glyphosate concentration of 100 pg f¹, while the relative biomass of Chlorophyceae was inereased. Above 100 pg I'¹ of glyphosate, the relative biomass of Chlorophyceae decreased, while an inerease was observed for the other four phytoplankton

classes. At the highest glyphosate concentration (1000 pg l'¹), the phytoplankton community

%

was composed of Bacillariophyceae (35%), Chryptophyceae (30%), Chrysophyceae (14.5%), Chlorophyceae (12.7%), Euglenophyceae (5.6%) and Cyanobacteria (2%).