ABSTRACT
Springborn Laboratories, Inc., and the University of Kansas have collaborated on a series of microcosm studies to evaluate the fate and ecological effects of pesticides in littoral ecosystems. Microcosms fill a role in the ecological assessment process intermediate between laboratory toxicity tests and pond mesocosm studies. The microcosms are contained in fiberglass tanks (11-m3 volume, 1.4-m depth) immersed in a flat-bottomed pond. We place 10 cm of pond sediment, seasoned pond water, and 40 juvenile bluegill sunfish in each tank. Macrophytes, plankton, and macroinvertebrates are present in the water and sediment, and additional colonization occurs after the microcosms are assembled.
After four to eight weeks, we apply the pesticide to the tanks in a manner simulating spray drift and/or surface runoff. Three or more treatment levels are included in each study, usually with three replicate microcosms at each treatment level. Application rates and treatment frequencies bracket the exposure conditions expected from normal agricultural practice. Pesticide residues are measured in microcosm water and sediment over time.
Ecological conditions are monitored before, during and after the pesticide treatment. The monitoring program includes water chemistry (pH, dissolved oxygen, conductivity, hardness, alkalinity, and suspended solids), biomass and taxonomic abundance of phytoplankton and periphyton, macrophyte biomass, zooplankton abundance, benthic macroinvertebrates, emergent insects, and fish growth and survival. Treated microcosms are compared with untreated controls to evaluate the effects of the pesticide.
The taxonomic diversity of zooplankton, benthic macroinvertebrate, and emergent insect communities in the microcosms is approximately equal to that in mesocosms. When direct comparisons have been made, similar ecological effects and disappearance rates of pesticides have been observed in the two types of experimental systems.
