Microcosm Design Research Articles

Characterisation of the dynamics of C-partitioning within Lolium perenne and to the rhizosphere microbial biomass using 14C pulse chase

The dynamics of C partitioning with Lolium perenne and its associated rhizosphere was investigated in plant-soil microcosms using 14C pulse-chase labelling. The 14CO2 pulse was introduced into the shoot chamber and the plants allowed to assimilate the label for a fixed period. The microcosm design facilitated independent monitoring of shoot and root/soil respiration during the chase period. Partitioning between above- and below-ground pools was determined between 30 min and 168 h after the pulse, and the distribution was found to vary with the length of the chase period. Initially (30 min after the pulse), the 14C was predominantly (99%) in the shoot biomass and declined thereafter. The results indicate that translocation of recent photoassimilate is rapid, with 14C detected below ground within 30 min of pulse application. The translocation rate of 14C below ground was maximal (6.2% h-1) between 30 min and 3 h after the pulse, with greatest incorporation into the microbial biomass detected at 3 h. After 3 h, the microbial biomass 14C pool accounted for 74% of the total 14C rhizosphere pool. By 24 h, approximately 30% of 14C assimilate had been translocated below ground; thereafter 14C translocation was greatly reduced. Partitioning of recent assimilate changed with increasing CO2 concentration. The proportion of 14C translocated below ground almost doubled from 17.76% at the ambient atmospheric CO2 concentration (450 ppm) to 33.73% at 750 ppm CO2 concentration. More specifically, these changes occurred in the root biomass and the total rhizosphere pools, with two- and threefold 14C increases at an elevated CO2 concentration compared to ambient, respectively. The pulselabelling strategy developed in this study provided sufficient sensitivity to determine perturbations in C dynamics in L. perenne, in particular rhizosphere C pools, in response to an elevated atmospheric CO2 concentration.

A comparison of the responses of two microcosm designs to a toxic input of copper

Two microcosm designs were compared for their sensitivity to toxic concentrations of copper. One design simulated a littoral zone, including macrophytes, sediment, and associated organisms. The other design used a periphyton community collected on polyurethane foam artificial substrata. Microcosms were dosed with copper sulfate (0–300 µg Cu 1−1, nominal concentrations) and monitored for changes in several structural and process variables. Coefficients of variation of responses measured from the littoral microcosms were greater than from responses measured from the artificial-substrata microcosms. Effects were detected more frequently at lower concentrations of copper in the artificial-substrata microcosms than in the littoral microcosms. Lowest observable effect concentrations (LOECs) for measures of community structure ranged from 20.2–42.8 µg Cu 1−1 in the artificial-substrata microcosms and from 24.0–98.5 µg Cu 1−1 in the littoral microcosms. LOECs for measures of community process ranged from 42.8–310.3 µg 1−1 in the artificial substrata microcosms. Significant differences from controls for community process were detected only at 304.7 µg Cu 1−1 in the littoral microcosms. While there were differences between the two microcosm designs in the concentrations of copper that resulted in adverse effects, response trends were similar. Often, dose-response relationships between variables and copper concentrations were not log-linear, but showed stimulations at intermediate concentrations of copper (10–100 µg 1−1, nominal concentrations). The choice of microcosm design should be dependent on the particular research question, as the designs differ in complexity and in the ease of construction and maintenance.

Statistical concerns in the design and analysis of multispecies microcosm and mesocosm experiments

AbstractMicrocosm and mesocosm experiments are useful in the environmental analysis of the effects of toxicants on ecological communities. While there has been much interest in the biological approaches to microcosm design, there seems to have been little thought given to statistical issues in the design of these experiments. Here, some statistical design issues are considered. Some criteria are proposed, and optimal or near optimal designs suggested. Of particular interest is the choice of doses in the experiment, choices that allow for tests with high power and also provide good estimates of effect levels and other parameters. Also, some analytical techniques recently suggested for the analysis of community data are criticized and alternate methods suggested.

Improved Microcosm Design for Performing Reservoir Water Quality Investigations

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.

A unique laboratory method for evaluating agro-ecosystem effects of an industrial waste product

This paper describes the design, extraction, and maintenance of intact soil-core microcosms which accurately predicted biomass reduction, nutrient loss and trace element enrichment in field-grown crops amended with acidic precipitator fly ash. These agricultural microcosms sustain ecosystem-level interactions while offering a cost-effective, manageable, experimental unit which can be subjected to laboratory controls.

Pelagic Diatom Populations in Lentic Freshwater Microcosms

AbstractThree experiments, involving simultaneous monitoring of selected biological and chemical parameters in 50 l laboratory microcosms and the epilimnia of their parent reservoirs, were carried out from the autumn of 1978 to the winter of 1980. Experiments lasted 8‐13 weeks, their aim being to ascertain degree of similarity between laboratory and field systems. Microcosm dynamics, specifically diatom dynamics, most closely paralleled that found in reservoirs during late spring and early summer, a time of thermal stratification. During winter months when thermal stratification was absent or less pronounced, microcosm diatom populations diverged significantly from reservoir populations within 24 days. It is inferred that microcosm design and operating conditions have a major bearing on microcosm usefulness for environmental assessment.

Review and evaluation of microcosms for assessing effects of stress in marine ecosystems

Representative estuarine-marine microcosms were reviewed and evaluated to provide recommendations and guidance for use in assessing effects of perturbations on coastal zone ecosystems. Properly designed marine microcosms can be effective assessment tools for evaluating the effects of stresses on coastal ecosystems. Critical design considerations include scaling of important physical factors, such as turnover rate and circulation, inclusion of appropriate trophic groups, minimization of side growth, and maintenance of realistic nutrient regimes. Selection of communities or major components to be included in design of microcosms should be based on the experimental hypothesis, ecologically and economically important organisms, ability to interpret test results, difficulties involved in scaling, and sensitivity of the community to the stress being investigated. In selection of response parameters, emphasis should be placed on key ecological components, particle size distribution, and those variables that reflect aggregate responses at the population or community level.

Some considerations in the design of aquatic microcosms for plankton Studies

Some of the most important problems facing aquatic microcosm research are those resulting from the small size of laboratory microcosms because not all biological and physical processes present in natural ecosystems can be scaled down to laboratory size. Three major problems of scale are: (i) problems arising from the shallow depth of most microcosms; (ii) the difficulty of including higher trophic levels; (iii) the dominance of chemical and biological activity occuring on the sides and bottom of microcosms. The most severe of these problems is the third: in particular, the growth of periphyton on the sides of the container. Periphyton growth exerts a significant effect on the metabolism of microcosms within 40–50 days after inoculation. Biological control of periphyton growth has been largely unsuccessful and the efficacy of mechanical means is uncertain. A possible resolution of the problem of side activity is to focus on the plankton bloom which occurs shortly after inoculation. Since side growth is not...