无磷洗衣粉并非控制水体富营养化的灵丹妙药

很多人认为，使用无磷洗衣粉便能有效解决令人烦恼的“水华”或“赤潮”问题。然而，无论是西方国家长达20年的实践经验，还是我国目前面临的现状显示，无磷洗衣粉对遏制水体富营养化现象作用并不十分明显!究其原因，面源污染和生活污水中的其它磷来源才是构成水体磷负荷的主要来源。因此，在国内外普遍兴建污水处理厂的前提下，是否有必要以洗涤效果不佳、可能会产生新的环境问题的无磷洗衣粉替代传统洗衣粉目前正遭到国外一些有识之士质疑。文章介绍了国外这方面的情况，并总结性地提出了我国在此方面应注意的问题。     

Determination of growth kinetics of microorganisms linked with 1,4-dioxane degradation in a consortium based on two improved methods

● Evaluated three methods for determining the consortia’s growth kinetics. ● Conventional method is flawed since it relies on the total biomass concentration. ● Considering only selected bacterial taxa improved the accuracy. ● Considering oligotrophs and copiotrophs further improved the accuracy. The conventional method for determining growth kinetics of microbial consortia relies on the total biomass concentration. This may be inaccurate for substrates that are uncommon in nature and can only be degraded by a small portion of the microbial community. 1,4-dioxane, an emerging contaminant, is an example of such substrates. In this work, we evaluated an improved method for determining the growth kinetics of a 1,4-dioxane-degrading microbial consortium. In the improved method, we considered only bacterial taxa whose concentration increase correlated to 1,4-dioxane concentration decrease in duplicate microcosm tests. Using PEST (Parameter Estimation), a model-independent parameter estimator, the kinetic constants were estimated by fitting the Monod kinetics-based simulation results to the experimental data that consisted of the concentrations of 1,4-dioxane and the considered bacterial taxa. The estimated kinetic constants were evaluated by comparing the simulation results with experimental results from another set of microcosm tests. The evaluation was quantified by the sum of squared relative residual, which was four orders of magnitude lower for the improved method than the conventional method. By further dividing the considered bacterial taxa into oligotrophs and copiotrophs, the sum of squared relative residual further decreased.     

The fungal microcosm of the internodes of Spartina alterniflora

The internodal area of growing cord grass (Spartina alterniflora Loisel) is a microcosm colonized by the mycelium and heretofore unreported hyphopodial appendages of the fungus Sphaerulina pedicellata. As the plant matures and this area senesces during the late summer and fall, sexual stages of this and other fungi develop. Scanning electron micrographs revealed that this biomass supports bacterial growth and is grazed by nematodes and mites.     

Environment-specific elasticity and sensitivity analysis of the stochastic growth rate

For matrix population models, analyses of how sensitive the population growth rate is to changes in vital rates (i.e. perturbations) are important for studies of life history evolution as well as for management and conservation of threatened species. There are two types of sensitivity analyses corresponding to absolute (sensitivity) or relative (elasticity) changes in the vital rates and both types can be applied to both deterministic and stochastic matrix population models. To date, most empirical studies of elasticity and sensitivity of the stochastic growth rate have examined the response to perturbations in the vital rates in a complete set of possible environments. However, it is often of interest to examine the response to perturbations occurring in only a subset of the possible environments. This has been done for periodic time-varying models elsewhere, but here we describe a recently published method for calculating the environment-specific sensitivity and elasticity of the stochastic growth rate and apply this method to data. These environment-specific perturbation analyses provide a logical way of dividing the sensitivity and elasticity among the environments. They give important insight into the selection regime in different environments and can provide valuable information for making management decisions and management evaluations in stochastic environments.     

Maintenance of a diverse harpacticoid copepod community in microcosm culture

The design and construction of a closed system circulating sea-water tidal estuarine sediment microcosm is described. The microcosm was used to culture mixed species populations of the Harpacticoida (Crustacea: Copepoda) and the evolution of the community and the successional changes are detailed. The communities that developed in each of four replicate microcosms were statistically indistinguishable with respect to the species richness, the numbers of individuals recorded, the log series diversity and the dominance diversity statistics. The most abundant species were the same in each microcosm with the same rank. A diverse community was maintained that did not tend to monoculture; however, the successional changes observed were not apparent in the estuarine communities from which the culture sediments was collected. Rather than a functional reorganisation of the community effecting this, gross environmental changes resulting from a decreased depth of sediment matrix are implicated. The success in maintaining a diverse community is attributed to a provision of a number of nutrient sources.     

用微宇宙法研究稀土元素在富营养化水体中的归趋

本文利用静态实验室水生微宇宙的方法研究了轻、中、重三类五种稀土混合物（La,Ce,Sm,Gd,Y）在富营养水体、底泥、浮萍、大型蚤、螺蛳和金鱼中的分布和富集。结果表明,稀土在水生微宇宙各组分中的分布和积累的趋势为轻稀土>中稀土>重稀土。稀土元素在水体中6h后基本趋于平衡,其大部分为底泥所吸附;不同生物对稀土的分布和富集存在着较大的差异,其趋势为浮萍>大型蚤>螺蛳>金鱼。     

Prey-predator dynamics in rotifers: density-dependent consequences of spatial heterogeneity due to surface attachment

Classical models of prey-predator interactions assume that per capita prey consumption is dependent on prey density alone and that prey consumption (functional response) and consumer proliferation (numerical response) operate on the same timescales and without time lags. Several modifications have been proposed for resolving this timescale discrepancy, including variants where the functional response depends on both prey and predator densities. A microcosm system with the rotifer Brachionus 'Nevada' feeding on the prasinophyte Tetraselmis sp. showed significant (P < 0.0005) increases in steady-state biomasses of both prey and predators with increasing carrying capacity (represented by total phosphorus of the growth medium), which is inconsistent with predictions based on the traditional prey-only-dependent functional response. We provide data indicating that surfaces where the predator can attach provide a high-quality habitat for rotifers, which can result in a predator-dependent functional response. We also show that partitioning between the attached and free-swimming habitats was fast compared to the timescale of the numerical response. When attached to surfaces, rotifers maximized net energy gain by avoiding the high cost of swimming and by increased food capture due to reduced viscous drag. A mathematical model with prey-dependent functional response and wall-attached and free-swimming fractions of the population describes our data adequately. We discuss the implications of this finding for extrapolating microcosm experiments to systems with other surface-to-volume ratios, and to what extent our findings may apply to other popular model organisms for prey-predator interaction.     

Biodegradation of Hexachlorocyclohexane by two species of Bacillus isolated from contaminated soil

Biodegradation of α, β, γ and δ hexachlorocyclohexane (HCH) isomers was studied in broth medium and soil microcosm by Bacillus circulans and Bacillus brevis isolated from contaminated soil. Degradation of α and γ isomers by both the bacterial isolates was higher than thermodynamically stable β and δ isomers. However, B. circulans was found more effective than B. brevis for β and δ isomers. Maximum rate of degradation was recorded at 150 mg/L followed by 100 and 50 mg/L. Soil microcosm study revealed maximum degradation of HCH isomers in the treatment containing natural soil, pesticide and bacterial inocula than the treatment having sterilised soil, pesticide and bacterial isolates. Chloride release was positively co-related with HCH degradation in broth medium as well as in soil microcosm, suggesting that B. circulans and B. brevis hold promising potential by having efficient enzyme(s) required for dechlorination of HCH from contaminated sites.     

Application of microcosm and species sensitivity distribution approaches in the ecological hazard assessment of 4-tert-butylphenol

In order to evaluate the ecological hazard of 4-tert-butylphenol (4-TBP), species abundances and physicochemical properties were monitored for 63 days in a microcosm system containing planktonic algae, rotifers, shrimps and Daphnia. The 63 days-NOEC (no observed effect concentration) of 4-TBP for this system was calculated. At the same time, species sensitivity distribution curves were constructed based on the toxicity data of EC₁₀, EC₅₀ and NOEC derived from laboratory single-species toxicity tests, which further gives no obvious hazard concentrations for 95% species in the ecosystem (HC₅). In both the microcosm and the single-species tests, the shrimp (Neocaridina sp.) was the most sensitive species to 4-TBP exposure, while most algae species were relatively insensitive compared to the zooplankton. For the microcosm exposed to 4-TBP, significant changes occurred to the community structure instead of the community function, resulting in a NOEC_microcosm of 265.38?μg?L^–1 which approached the EC₁₀-based HC₅ (0.376?mg?L^–1). Nevertheless, EC₅₀-based HC₅ was higher than the NOEC_microcosm, and the NOEC-based HC₅ was lower. The data showed that the EC₁₀-based HC₅ was protective at the similar level with the result of microcosm for 4-TBP, providing supportive data for chemical risk assessment.     

Organic and inorganic phosphorus uptake by bacteria in a plug-flow microcosm

Phosphorus (P) is a vital nutrient for sustaining natural water productivity. Both particulate and dissolved forms of organic and inorganic P are potentially important sources of bioavailable P for primary and secondary producers. A microcosm system to imitate the bacterial community in Plym river sediment and pore water is described and bacterial uptake rates for inorganic and organic phosphorus are presented in this paper. The aim of this study was to investigate the uptake of two organic phosphorus compounds (phytic acid and D-glucose-6-phosphate) by freshwater bacteria. The bioreactors comprise glass columns packed with two types of small glass beads on which bacterial biofilm can develop. The glass beads with different porosity were introduced to simulate River SPM. The selected P compounds spiked into the inflow of the microcosm, and measured the step change of P concentration in the outflow to investigate the behavior of bacterial uptake of nutrients. The results showed that organic phosphorus was converted into inorganic phosphorus but the conversion rate depended on the type of phosphorus species. One experiment suggested that phytic acid (refractory) could displace phosphate from the biofilm surface; the other experiment showed that D-glucose-6-phosphate (labile) could be hydrolysed and utilized easily by the bacteria. The results also suggested that bacteria might break down the C-P bonds to utilize the carbon. Further experiments should investigate the effect of varying the C:N:P ratio in the microcosm system to determine which nutrient limits bacteria uptake.     

Epiphytic cyanobacteria maintain shifts to macroalgal dominance on coral reefs following ENSO disturbance

Macroalgal dominance of some tropical reef communities in the Eastern Pacific after coral mortality during the 1997-1998 El Ni?o Southern Oscillation (ENSO) was facilitated by protection from herbivory by epiphytic cyanobacteria. Our results do not support that reduction in number of herbivores was a necessary precursor to coral reef decline and shifts to algal reefs in this system. Rather, macroalgae dominated the community for several years after this pulse disturbance with no concurrent change in herbivore populations. While results of microcosm experiments identified the importance of nutrients, especially phosphorus, in stimulating macroalgal growth, nutrient supply alone could not sustain macroalgal dominance as nutrient-stimulated growth rates in our in situ experiments never exceeded consumption rates of unprotected thalli. In addition, thalli with nutrient-enriched tissue were preferentially consumed, possibly negating the positive effects of nutrients on growth. These tropical reefs may be ideal systems to conduct experimental tests distinguishing phase shifts from alternative stable states. Shifts were initiated by a large-scale disturbance with no evidence of a changing environment except, perhaps, dilution in herbivory pressure due to increased algal cover. Community establishment was most likely stochastic, and the community was likely maintained by strongly positive interaction between macroalgal hosts and cyanobacterial epiphytes that uncoupled consumer control of community structure.     

Efficient algorithms for statistical estimation in compartmental analysis: Modelling 60Co kinetics in an aquatic microcosm

A mathematical model of radionuclide kinetics in a laboratory microcosm was built by systems identification techniques. Insight into the functioning of the system was obtained from analysis of the model. Methods employed have allowed movements of radioisotopes not directly observable in the experimental system to be distinguished. Results are generalized to whole ecosystems.     

Revealing how species loss affects ecosystem function: the trait-based Price Equation partition

Species loss can alter ecosystem function. Recent work proposes a general theoretical framework, the "Price Equation partition," for understanding how species loss affects ecosystem functions that comprise the summed contributions of individual species (e.g., primary production). The Price Equation partition shows how the difference in function between a pre-species-loss site and a post-loss site can be partitioned into effects of random loss of species richness (species-richness effect; SRE), nonrandom loss of high- or low-functioning species (species-composition effect; SCE), and post-loss changes in the functional contributions of the remaining species (context-dependence effect; CDE). However, the Price Equation partition is silent on the underlying determinants of species' functional contributions. Here we extend the Price Equation partition by using multiple regression to describe how species' functional contributions depend on species' traits. This allows us to reexpress the SCE and CDE in terms of nonrandom loss of species with particular traits (trait-based SCE), and post-loss changes in species' traits and in the relationship between species' traits and species' functional contributions (trait-based CDE). We apply this new trait-based Price Equation partition to studies of species loss from grassland plant communities and protist microcosm food webs. In both studies, post-loss changes in the relationship between species' traits and their functional contributions alter ecosystem function more than nonrandom loss of species with particular traits. The protist microcosm data also illustrate how the trait-based Price Equation partition can be applied when species' functional contributions depend in part on the traits of other species. To do this, we define "synecological" traits that quantify how unique species are (e.g., in diet) compared to other species. Context dependence in the protist microcosm experiment arises in part because species loss alters the diet uniqueness of the remaining species.     

Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.     

Population growth rate and carrying capacity for springtails Folsomia candida exposed to ivermectin.

Forecasting the effects of stressors on the dynamics of natural populations requires assessment of the joint effects of a stressor and population density on the population response. The effects can be depicted as a contour map in which the population response, here assessed by population growth rate, varies with stress and density in the same way that the height of land above sea level varies with latitude and longitude. We present the first complete map of this type using as our model Folsomia candida exposed to five different concentrations of the widespread anthelmintic veterinary medicine ivermectin in replicated microcosm experiments lasting 49 days. The concentrations of ivermectin in yeast were 0.0, 6.8, 28.8, 66.4, and 210.0 mg/L wet weight. Increasing density and chemical concentration both significantly reduced the population growth rate of Folsomia candida, in part through effects on food consumption and fecundity. The interaction between density and ivermectin concentration was "less-than-additive," implying that at high density populations were able to compensate for the effects of the chemical. This result demonstrates that regulatory protocols carried out at low density (as in most past experiments) may seriously overestimate effects in the field, where densities are locally high and populations are resource limited (e.g., in feces of livestock treated with ivermectin).     

An energetic perspective on the relationship between disturbance and ecosystem productivity

Previous ecological models for disturbance from energetic perspectives have focused on destructive pulses by which storages in a system are quickly drained during disturbance events and recovered thereafter. However, considering the wide range of disturbance intensities, frequencies, and durations in nature, disturbance effects on ecosystem energetics would be better understood by diversifying the disturbance effects on specific system configurations or energy pathways. Based on two hypotheses, we built simulation models of the variable disturbance-productivity relationships observed in a freshwater aquatic microcosm study. First, we hypothesized that disturbances will differentially alter the intrinsic rates of energy pathways in a system. Second, we hypothesized that there is a disturbance threshold where response of the intrinsic rates changes abruptly. Simulation results showed variable patterns of gross primary productivity (GPP) during the disturbance and post-disturbance periods under the diverse scenarios of disturbance effects on the intrinsic rates. Simulation results confirmed that the second hypothesis (i.e., disturbance threshold) was essential to achieve a U-shaped or peaked disturbance-productivity relationship. We evaluated the models by comparing them with the results of the microcosm tests, and suggested possible mechanisms of the variable disturbance-productivity relationships by varying parameters related to the disturbance effects on the intrinsic rates and the disturbance thresholds.     

Persistence for ecosystem microcosm models

A qualitative analysis of a system of autonomous differential equations modelling an ecosystem microcosm is carried out from the point of view of persistence. Necessary and sufficient conditions are given that no trajectory with positive initial conditions has a component that tends to zero asymptotically or reaches zero in finite time. The results are stated in terms of threshold levels for the input nutrient parameter in the system.     

Predicting water quality data in an unfilled reservoir using microcosm sediment-water simulation

The technique of microcosm sediment-water simulation was used to obtain predictive water quality data for the proposed Jordanelle Reservoir, Heber City, Utah. Sediment-water microcosms were prepared for four sites located in the north arm of the reservoir basin, including two sites located in an abandoned acid mine tailings pond. Data obtained from the tailings pond microcosms indicated that low pH water and high trace metal concentrations may exist in this area of the reservoir. These data suggested that the tailings material should be contained or removed prior to reservoir filling. Other sites in the reservoir basin exhibited water quality considered normal for reservoirs of similar elevation and basin geology. Near the proposed dam, anaerobic conditions could develop rapidly due to available concentrations of organic carbon, and the subsequent release of Zn, Fe, and Mn may pose a water quality problem. At the sampling site near Keetley, simulation data indicated that anaerobic conditions will not develop as quickly or be as severe as conditions expected near the dam. Overall, the availability of nitrogen and phosphorus in the Provo River and Jordanelle sediments indicated that problems with algal blooms may exist in the reservoir. Also presented is a brief discussion of the advantages and disadvantages associated with microcosm sediment-water simulation.     

Interactive effects of disturbance and dispersal directionality on species richness and composition in metacommunities

Dispersal among ecological communities is usually assumed to be random in direction, or to vary in distance or frequency among species. However, a variety of natural systems and types of organisms may experience dispersal that is biased by directional currents or by gravity on hillslopes. We developed a general model for competing species in metacommunities to evaluate the role of directionally biased dispersal on species diversity, abundance, and traits. In parallel, we tested the role of directionally biased dispersal on communities in a microcosm experiment with protists and rotifers. Both the model and experiment independently demonstrated that diversity in local communities was reduced by directionally biased dispersal, especially dispersal that was biased away from disturbed patches. Abundance of species (and composition) in local communities was a product of disturbance intensity but not dispersal directionality. High disturbance selected for species with high intrinsic growth rates and low competitive abilities. Overall, our conclusions about the key role of dispersal directionality in (meta)communities seem robust and general, since they were supported both by the model, which was set in a general framework and not parameterized to fit to a specific system, and by a specific experimental test with microcosms.