The use of field enclosure experiments to study the effect of pesticides on lake phytoplankton

Abstract

AbstractAn outdoor enclosure experiment was carried out to study the effect of some selected pesticides on phytoplankton of Lake Omdalsvann, Norway. The experiment lasted 2 weeks during 1990 July/August). The pesticides tested were chlorosulfuron (herbicide), propiconazole (fungicide), dimethoate (insecticide) and glyphosate (herbicide). The pesticides were tested at three concentration levels (1 μg L−1, 10μg L−1 and 100μg L−1) of their active ingredients. Samples for phytoplankton analysis were collected twice each week. The species richness differed greatly among the experimental bags. All treatments resulted in a significant (P < 0.05) decrease in species number compared with the results of the control. At the same time, great differences did exist in algal biomass in response to different pesticides tested. The pattern of biomass deviation from control (positive or negative) and magnitude (significant or non‐significant, at P= 0.05) were mainly dependent on toxicant type, concentration and the exposure time. Shannon‐Wiener diversity indices ranged between 2.69 and 2.76. The index values decreased significantly at all pesticide treatments with lowest values usually recorded 2 days after adding the pesticides. The biomass of some natural algal taxa varied quite independently not only to the different pesticides but also to their concentrations; a finding which supports the concept of species‐dependent variation in algal sensitivity to chemicals. In situ toxicity testing seems to be a reliable protocol to generate more realistic data necessary for environmental protection.