Use of large enclosures for perturbation experiments in lentic ecosystems: A review.

Available literature on use of field enclosures in freshwater and marine systems is reviewed to assess how accurately enclosures mimic ecological conditions and process rates occurring in adjacent open habitat. Among- and within-replicate variability of ecological parameters in field enclosures is compared to those in laboratory microcosms and open field habitat respectively. Results concerning the potential ecological effects and fate of pollutants indicate that perturbation studies using field enclosures can provide defensible data at the population and community levels over time periods of several months and spatial scales of tens of meters. The degree of ecological realism that can be achieved, however, is variable. Chronic effects of some pollutants may be difficult to separate from nonspecific effects due to enclosure. Determination of cause/effect pathways for observed toxicant impacts generally will require supplemental laboratory studies.