Bioassay Determination of Species Specific Phytoplankton Responses To The Herbicide Atrazine and Its Quantification in B. Everett Jordan Reservoir

Atrazine was quantified bi-weekly in samples from three locations in B. Everett Jordan Lake during March-July 1985 using gas chromatography. The presence in Segment 1 of atrazine and other previously identified Haw River constituents was verified by GC/MS. The highest concentrations were consistently found in Segment 1 (0.5-2.5 ug/L) and residue concentrations were generally higher in Segment 2 than Segment 3. Although atrazine concentrations declined rather rapidly following the field application runoff pulse in May, herbicide residue levels remained higher than those prior to that date. In vitro, natural population bioassays revealed species specific responses to atrazine. The population as a whole was severely inhibited at 50 ug/L atrazine. Results suggest low-dose (1 ug/L) growth stimulation for several members of the Cyanophyta. Several species of the Chlorophyta exhibited temporal growth lags at atrazine concentrations of 50 ug/L. However, maximum biomass was not severely depressed. Other species of green algae, Chlamydomonas in particular, exhibited resistance to the effects of atrazine at all doses. Competitive interactions between species affected individual responses to the toxicant. Species specific responses to atrazine levels commonly found in agricultural watersheds (0.25-10 ug/L) illustrate the potential of this important herbicide to alter the ecological basis of the food web.Master of Science in Public Healt