Virioplankton: Viruses in Aquatic Ecosystems

The discovery that viruses may be the most abundant organisms in natural waters, surpassing the number of bacteria by an order of magnitude, has inspired a resurgence of interest in viruses in the aquatic environment. Surprisingly little was known of the interaction of viruses and their hosts in nature. In the decade since the reports of extraordinarily large virus populations were published, enumeration of viruses in aquatic environments has demonstrated that the virioplankton are dynamic components of the plankton, changing dramatically in number with geographical location and season. The evidence to date suggests that virioplankton communities are composed principally of bacteriophages and, to a lesser extent, eukaryotic algal viruses. The influence of viral infection and lysis on bacterial and phytoplankton host communities was measurable after new methods were developed and prior knowledge of bacteriophage biology was incorporated into concepts of parasite and host community interactions. The new methods have yielded data showing that viral infection can have a significant impact on bacteria and unicellular algae populations and supporting the hypothesis that viruses play a significant role in microbial food webs. Besides predation limiting bacteria and phytoplankton populations, the specific nature of virus-host interaction raises the intriguing possibility that viral infection influences the structure and diversity of aquatic microbial communities. Novel applications of molecular genetic techniques have provided good evidence that viral infection can significantly influence the composition and diversity of aquatic microbial communities.     

Subsidies of Aquatic Resources in Terrestrial Ecosystems

Ecosystems - Floods, spatially complex water flows, and organism movements all generate important fluxes of aquatic-derived materials into terrestrial habitats, counteracting the gravity-driven...     

Consortia in Aquatic Ecosystems of the Transbaikalia

A survey in the basin of the Khilok River (a right tributary of the Selenga River) in 1999–2002 allowed us to reveal and describe the consortia of cyanobacteria Stratonostoc linckia f. linckia and Stratonostoc verrucosum, green alga Cladophora aegagropila, stonewort Nitella opaca, water moss Fontinalis sp., and duckweed Lemna trisulca. The relationship between the consort organisms and edificator plants can become the limiting factor in these communities. The long-term studies of the benthic communities of the Arakhlei Lake demonstrate the significance of the consortium approach in the long-term prediction of changes in the lake ecosystem.     

生态化学计量学在水生态系统中的研究与应用

生态化学计量学主要是研究碳、氮、磷等元素在各种生态过程中平衡的一门科学,其核心问题是揭示生物体元素组成的差异对生态功能的影响。由于生态化学计量学研究可以把生态实体的各个层次在元素水平上统一起来,因此生态化学计量学已成为许多生态系统的新兴研究工具。目前,生态化学计量学的研究与应用已深入到生态学的各个层次(分子、细胞、个体、种群、群落、生态系统及区域等不同尺度)。该文围绕生态化学计量学的两个重要组成理论,并结合笔者近年来的研究,归纳总结了生态化学计量学在水生态系统中的研究与应用及未来研究重点,希望有助于推动我国生态化学计量学在水生态系统中的应用研究。     

The Relation Between Adenosine Triphosphate and Microbial Biomass in Diverse Aquatic Ecosystems

By using autoradiographic examination of ¹⁴C labeled viable cells, natural phytoplankton communities were separated into living and non-living components. Comparisons of carbon to adenosine triphosphate (ATP) content of living cells yielded consistent ratios with depth, during periods of high and low nutrient supply at Lake Tahoe. Over time the ratio fluctuated by no more than ± 17% of the mean between the time of maximum nutrient supplies and nutrient depletion. The viability of specific phytoplankton groups was surprisingly low at times, indicating that conventional counting methods tend to overestimate live biomass. A survey of lakes differing in trophic states and having diverse phytoplankton and bacterial assemblages has shown that ATP measurements can be used as an accurate measure of total living microbial biomass.     

General Model of Microbial Growth and Decomposition in Aquatic Ecosystems

A model capable of simulating freely suspended and attached decomposers, particulate organic matter, labile and refractory dissolved organic matter, inorganic nitrogen, and phosphate in the open-water portion of lakes is presented. Examples are given showing the utility of the model when coupled to the whole-ecosystem model CLEANER.     

Comparative Physiology of Respiration in Aquatic Fungi

A comparative study of terminal respiration was undertaken in five genera of aquatic fungi in the Leptomitales. The cytochrome system in this group of fungi contained cytochrome a-a₃ (605 nm), cytochrome c (551 nm), cytochrome b (557 nm), and cytochomo b (564 nm). A representative of each of three aerobic genera, Leptomitus, Apodachlya, and Sapromyces, had a total cytochrome content of about 2×10^?10 mol/mg dry weight. An endogenous respiration rate of 21 μl O₂ uptake/ (h × mg dry weight) at 21.7°C was found in Leptomitus and Apodmhlya and 14 in Sapromyces. The strain belonging to the fermenlative genus Mindeniella had approximately one-third of the total cytochrome content and one-third of the endogenous respiration rate observed in Leptomitus and Apodachlya. Mindeniella and Sapromyces contained less total cytochrome when grown under reduced oxygen tension than when grown in air. Only about one-half of the b-type cytochrome was redueible by endogenous substrates. Both cytochrome a₃ and an unidentified pigment bound CO. The endogenous respiration of Leptomitus, Apodachlyo, and Sapromyces was strongly Inhibited by sodium cyanide, sodium azide, antimycin A, and sodium fluoroacetate.     

Herbivores Enforce Sharp Boundaries Between Terrestrial and Aquatic Ecosystems

The transitions between ecosystems (ecotones) are often biodiversity hotspots, but we know little about the forces that shape them. Today, often sharp boundaries with low diversity are found between terrestrial and aquatic ecosystems. This has been attributed to environmental factors that hamper succession. However, ecosystem properties are often controlled by both bottom-up and top-down forces, but their relative importance in shaping riparian boundaries is not known. We hypothesize that (1) herbivores may enforce sharp transitions between terrestrial and aquatic ecosystems by inhibiting emergent vegetation expansion and reducing the width of the transition zone and (2) the vegetation expansion, diversity, and species turnover are related to abiotic factors in the absence of herbivores, but not in their presence. We tested these hypotheses in 50 paired grazed and ungrazed plots spread over ten wetlands, during two years. Excluding grazers increased vegetation expansion, cover, biomass, and species richness. In ungrazed plots, vegetation cover was negatively related to water depth, whereas plant species richness was negatively related to the vegetation N:P ratio. The presence of (mainly aquatic) herbivores overruled the effect of water depth on vegetation cover increase but did not interact with vegetation N:P ratio. Increased local extinction in the presence of herbivores explained the negative effect of herbivores on species richness, as local colonization rates were unaffected by grazing. We conclude that (aquatic) herbivores can strongly inhibit expansion of the riparian vegetation and reduce vegetation diversity over a range of environmental conditions. Consequently, herbivores enforce sharp boundaries between terrestrial and aquatic ecosystems.     

Experimental Approach to the Role of Protozoa in Aquatic Ecosystems

In enrichment batch experiments, samples from three water bodieswere alternatively supplemented by various amounts of organicmaterial and incubated at 20 C. Colpidium campylum reached itshighest total cell volumes in cultures with the highest initialtotal cell volumes in cultures with the highest initial concentrationsof organics; Cyclidium glaucoma preferred lower concentrations;and Glaucoma chattoni occupied the intermediate position. Noneof the species preferred any special type of organic material.In two-stage continuous-flow units, a mixed culture of bacteriawas kept in stage I and the clones of ciliates were maintainedin stage II. The interrelations between the total cell volumesof ciliates at various concentrations of bactopeptone were inaccordance with the results from the enrichment experiments.Since the growth of bacteria continued in the presence of ciliates,a four-stage apparatus was constructed in which a bacterialculture was raised and diluted in three stages before enteringthe culture ofColpidium. The bacterial growth in the presenceof Colpidium was not eliminated even by this arrangement, asdemonstrated by dosing antibiotics along with bacteria. An effectof ciliate metabolites on bacterial growth rate is suggested,completing a metabolic cycle in the bacteria-protozoa system.     

Establishing Causality between Environmental Stressors and Effects on Aquatic Ecosystems

Establishing causal relationships between environmental stressors and observed effects in natural systems is difficult due to the many intrinsic environmental factors that can hinder this process and because there are no widely accepted and proven approaches for determining such relationships. Several types of approaches or combinations of approaches, each with their own sets of advantages and limitations, have been applied in a variety of ecological systems to investigate possible causal relationships between stressors and effects. These include controlled laboratory studies (including acute and chronic bioassays), experimental field manipulations, field studies based on synoptic field surveys, mathematical simulation modeling, statistical associations, various combinations of laboratory, experimental, and field studies, and the ecoepidemiological (weight or evidence) approach. The use of ecoepidemiological (“forensic toxicology”) principles is becoming increasingly attractive as a method to help establish causality because it does not involve the same limitations of other approaches and it can also be used to integrate disparate information within a logical framework so that scientifically and defensible regulatory decisions can be made. The objective of this Commentary series of papers on the issue on causality is to demonstrate the application of the ecoepidemiology approach, using a variety of case history studies, for establishing causal relationships between specific stressors and biological effects. For each case history provided in the following series of papers, the authors describe their study situation, summarize the results supporting a causal relationship, and then compare their study results against seven standard causal criteria.     

Prevalence of Heterotrophy and Atmospheric CO2 Emissions from Aquatic Ecosystems

Recent, parallel developments in the study of freshwater and marine ecosystems have provided evidence that net heterotrophic systems (those in which respiratory organic matter destruction exeeds photosynthetic production) are more prevalent than hitherto believed, including most rivers, oligo- to mesotrophic lakes and some oligotrophic regions of the ocean. In parallel, these aquatic ecosystems have been shown to act as CO₂ sources to the atmosphere, as expected from the heterotrophic nature of the communities they contain. The prevalence of net heterotrophic aquatic ecosystems indicates that they must receive significant inputs of organic carbon from adjacent ecosystems, assigning an important role to the lateral exchanges of carbon between land and aquatic ecosystems, between coastal and open ocean ecosystems, as well as internal redistribution within large or complex aquatic ecosystems in determining their metabolic status and the gaseous exchange with the atmosphere. The examination of the carbon budget of ecosystems requires, therefore, an integrative approach that accounts for exchanges between compartments often studied in isolation. These recent findings conform a new paradigm of the functioning of aquatic ecosystems, and the metabolic connectivity between ecosystems in the biosphere.     

Identifying and Predicting Biological Risks Associated With Manufactured Nanoparticles in Aquatic Ecosystems

Nanotechnology has great potential for revolutionizing the treatment of disease, optimizing manufacturing processes and consumer products, and remediating polluted environments. Increased use and disposal of products containing nanoparticles will inevitably result in their accumulation in aquatic ecosystems via direct input and runoff from contaminated soils. Aquatic organisms are particularly susceptible to pollutants due to their large, fragile respiratory epithelium. This potential toxicity can be exacerbated by common stressors, such as changes in water temperature, salinity, pH, and oxygen levels, and must be considered in environmental risk assessments. The unique properties of manufactured nanoparticles present serious problems for risk assessment strategies, and there is a concern in the regulatory community that standard toxicological methods may be inadequate to address these compounds. Our capacity to detect and quantify nanoparticles is extremely limited, especially in complex biological, soil, or water samples. The distinctive chemistry and physical structure of each nanomaterial will determine its bioavailability, and these parameters can be altered over time or with changes in water chemistry. The use of advanced analytical techniques, such as functional genomics, proteomics, and metabolomics, can provide a global assessment of the biological response to a novel chemical and will be important in determining the potential toxicity of nanoparticles. Industry should adopt a proactive approach to identifying potential risks to aquatic ecosystems so that the benefits of nanotechnology can be fully realized.     

A Review on Effect-Dose-Sensitivity Models for Aquatic Ecosystems.

Effect-dose-sensitivity (EDS) models for entire ecosystems, like lakes and defined coastal areas, ought to play a paramount role for environmental sciences and management. The aim of EDS-models is to provide quantitative predictions relating operationally defined ecological effect parameters to compatible dose and sensitivity parameters. Empirically validated EDS-models provide a tool to simulate ecosystem effects of practically feasible remedial measures. The main objective of this paper is to give a compilation of existing EDS-models for aquatic ecosystems. The aim is not to repeat derivations and equations but to present some basic components of EDS-models, their presuppositions and applicability. Since, at present, there exist EDS-models for mercury, radiocesium and phosphorus in lakes and nutrients (N and P) in coastal areas, this compilation can be rather short. To the best of the authors knowledge, there exist no EDS-models (that meet the criteria given in this work) for other types of ecosystems (like forests, agricultural land, urban areas, etc.) or for other types of contaminants (like metals, acidifying substances, halogenated toxins, etc.). Another aim is to clarify the difference between traditional mass-balance models (i.e., dynamic models) and ecometric (i.e., statistical/empirical models) EDS-models, and to give examples of EDS-models based on both these modelling approaches, and techniques (dimensionless moderators) to link these two ways of modelling. The paper also gives examples of the practical use of EDS-models. A new ecometric EDS-model for nutrients in coastal areas, where the oxygen concentration of the bottom water is used as an effect parameter, is presented. The idea with this part is also to give the steps in the ecometric derivation of EDS-models.