Improved Microcosm Design for Performing Reservoir Water Quality Investigations

Abstract

Microcosms suspended in lakes and reservoirs have been effective for performing in situ water quality studies; these systems have also been proposed for the determination of rate constants for dynamic water quality models. A number of different microcosm designs have been used. The most common design consists of a polyethylene cylinder with external supports to which the plastic is glued. The primary problem with previous microcosm designs is their structural instability resulting in destruction during rough water conditions. The purpose of this paper is to report a strong and easily-assembled microcosm system. The microcosm design used 0.0152-cm (6-mil) clear polyethylene plastic heat sealed into a cylinder 0.776 m in diameter. The plastic cylinder was supported from inside by aluminum rings 0.0381-m wide, 0.0025-m thick, and 0.76-m in diameter. The rings were coated with spray plastic to negate leaching of aluminum and possible toxicity during experiments. The bands, which supported the microcosms at 1-m intervals, were held in place from the outside of the plastic cylinder by a second band similar to a large hose clamp. The microcosms performed well under extreme conditions, including winds to 110 km/hr, during water quality investigations at Lahontan Reservoir, Nevada.