EFFECTS OF PYRACLOFOS (AN ORGANOPHOSPHOROUS INSECTICIDE) ON NUTRIENT ENRICHED ECOSYSTEMS

Bag type floating microcosms were used to study the effects of an orga nophosphorous insecticide, pyraclofos on a pond plankton community. To amplify the effects one group of bags was enriched with nitrate and p hosphorus, which brought about increases, in phytoplankton and subsequ ently zooplankton. The enrichment also changed water quality condition s such as dissolved oxygen and pH. Higher densities of phytoplankton e nhanced the break down of the insecticide. The insecticide generally s uppressed zooplankton population growth but some species increased dur ing the course of the experiment due to the interspecies interactions. The altered zooplankton densities facilitated the outbreak of certain species of phytoplankton which otherwise might have been heavily graz ed. This outbreak occurred regardless of nutrient enrichment, although enrichment generally increased the density of most phytoplankton spec ies.