Influence of uranium (VI) on the metabolic activity of stable multispecies biofilms studied by oxygen microsensors and fluorescence microscopy

The effect of uranium added in ecologically relevant concentrations (1 × 10⁻⁵ and 1 × 10⁻⁶ M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 μm and by confocal laser fluorescence microscopy (CLSM). The microsensor profile measurements in the stable multispecies biofilms exposed to uranium showed that the oxygen concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the oxygen consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61.7 nmol cm⁻³ s⁻¹ in the top layer (0-70 μm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer. Analysis of the amplified 16S rRNA gene fragments showed that the addition of uranium in ecologically relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms and is therefore not responsible for the different oxygen profiles in the biofilms. The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e., the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O₂ depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g., extracellular polymeric substance (EPS) and other organics (e.g., metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium (IV) solids and consequently to a removal of uranium from the aqueous phase.     

Site-specific effects on productivity of an upper trophic-level marine predator: Bottom-up, top-down, and mismatch effects on reproduction in a colonial seabird

We investigated the relative roles of bottom-up and top-down factors in limiting productivity of an upper trophic level marine predator. Our primary working hypothesis was that the reproductive success of black-legged kittiwakes (Rissa tridactyla) a piscivorous, colonial-nesting seabird, was most limited by the abundance, distribution, and species composition of surface-schooling forage fishes. A secondary working hypothesis was that reproductive loss to kittiwake nest predators was greatest during years of reduced prey availability. We report on a broad-scale, integrated study of kittiwakes and their prey in Prince William Sound, Alaska. Our study spanned five breeding seasons (1995–1999) and focused on three colonies that differed in size (ranging from ca. 220 to ca. 7000 breeding pairs) and proximity to each other (50–135 km apart). Kittiwakes in PWS encountered a variety of aquatic habitats, creating a complex foraging environment for breeding birds. We measured kittiwake reproductive success and foraging activities, while simultaneously measuring the abundance of surface schooling forage fishes throughout the foraging range of breeding kittiwakes. The abundance of primary prey species for kittiwakes (Pacific herring Clupea pallasi, Pacific sand lance Ammodytes hexapterus, and capelin Mallotus villosus) varied both annually and regionally, with no one region consistently having the greatest abundance of prey. Likewise, kittiwake reproductive success varied considerably among colonies and years.We found that bottom-up, top-down, timing mismatch, and colony-specific effects were all important to kittiwake productivity. Although bottom-up effects appeared to be strongest, they were not evident in some cases until other effects, such as geographic location (proximity of colony to prey concentrations) and top-down predation, were considered. Important bottom-up effects on kittiwake reproductive success were not only total prey abundance and distribution, but also species, age composition, and chronology of prey occurrence (match/mismatch of timing with critical brood-rearing periods); these effects varied by colony.Top-down effects of predation on kittiwake nest contents (independent of prey abundance) confounded seabird-forage fish relationships. Ultimately, when confounding factors were minimized, non-linear asymptotic relationships were identified between kittiwakes and their prey, with an asymptotic threshold of fish school surface area density of ca. 5 m²/km², beyond which top-down, physiological, or phylogenetic constraints likely restrict further reproductive output. The integrated approach of our investigations provided a more thorough understanding of the mechanisms underlying predator–prey relationships in the complex marine environment. However, such mechanistic theories can only be tested and refined through long-term research and monitoring of much greater duration than the 5-year study reported herein.     

Cadastralizing or coordinating the clam commons: Can competing community and government visions of wild and farmed fisheries be reconciled?

This paper considers socio-political, ecological, and economic dimensions of local efforts to negotiate local control over state-sponsored development of clam aquaculture in one region of British Columbia, Canada. Aquaculture is conceptualized as a type of cadastralization, following James Scott's characterization of state efforts to make the productivity of landscapes more measurable for purposes of rent generation and taxation. The discussion invites a rethinking of community resistance to development as less about the notion of development itself than about the terms under which it occurs, since the community engages in its own form of cadastralization as a negotiating strategy. The concept of cadastralization enriches common property theory approaches to ownership and management by highlighting the key role of technological innovations in allowing global market forces to more easily penetrate local property relationships. At the same time it enables new forms of resistance and assertion of local visions of development.     

Control sample design using a geodemographic discriminator: An application of Super Profiles

 The development and application of an innovative sampling framework for use in a British study of the early detection of gastric cancer are described. The Super Profiles geodemographic discriminator is used in the identification of geographically distinct control and contrast areas from which samples of cancer registry case records may be drawn for comparison with the records of patients participating in the gastric cancer intervention project. Preliminary results of the application of the framework are presented and confirm its effectiveness in satisfactorily reflecting known patterns of variation in cancer occurrence by age, gender and social class. The method works well for cancers with a known and clear social gradient, such as lung and breast cancer, moderately well for gastric cancer and somewhat less well for oesophageal cancer, where the social class gradient is less clear. Received: 1 January 2000 / Accepted: 18 September 2000     

Implementation of microbial processes in the performance assessment of spent nuclear fuel repositories

Present strategies for the long-term disposal of high-level nuclear wastes are based on the construction of repositories hundreds of meters below the earth surface. Although the surrounding host-rocks are relatively isolated from the light at the earth surface they are by no means lifeless. Microorganisms rule the deep part of the biosphere and it is well established that their activity can alter chemical and physical properties of these environments. Microbial processes can directly and indirectly affect radionuclide migration in multiple ways. Within 6th FP IP FUNMIG the interplay between microbial biofilms and radionuclides and the effect of microbially induced redox transformations of Fe on radionuclide mobility have been investigated. For the first time, formation of U(V) as a consequence of microbial U(VI) reduction in a multi-species biofilm was detected in vivo by combining laser fluorescence spectroscopy and confocal laser scanning microscopy. Furthermore, it was demonstrated that addition of U(VI) can lead to increased respiratory activity in a biofilm. Increased respiration in a biofilm can create microenvironments with lower redox potential, and hence induce reduction of radionuclides. Transient mobilization of U was observed in experiments with Fe oxides containing adsorbed U(VI) in which the activity of SO₄-reducing organisms was mimicked by sulfide addition. Faster reaction of sulfide with Fe oxides compared to U(VI) reduction, and decreasing U(VI) adsorption due to the transformation of Fe oxides into FeS can explain the observed intermittent U mobilization. The presented research on microbe-radionuclide interactions performed within FUNMIG addresses only a few aspects of the potential role of microorganisms in the performance assessment of nuclear waste repositories. For this reason, additionally, this article provides a cursory overview of microbial processes which were not studied within the FUNMIG project but are relevant in the context of performance assessment. The following aspects are presented: (a) the occurrence and metabolic activity of microorganisms of several proposed types of host-rocks, (b) the potential importance of microorganisms in the near-field of nuclear waste repositories, (c) indirect effects of microbial processes on radionuclide mobility in the repository far-field, (d) binding of radionuclides to microbial biomass, (e) microbial redox transformations of radionuclides, and (f) the implementation of microbial processes in reactive transport models for radionuclide migration.     

Reviewing the Guayana project: Lifetime migration to and from Bolivar state,Venezuela, 1950–2001

By the mid‐twentieth century the population and economic resources in many developing economies had become concentrated in the capital city. Planned industrial cities became an important mechanism to encourage more balanced urban systems as well as development in peripheralized regions. Venezuela boasts one of the most impressive planned industrial cities, Ciudad Guayana, constructed in 1959 in the resource rich but inaccessible Bolivar state in the southeast. This paper summarizes the lifetime migration to and from Bolivar state for the years 1950, 1971 and 2001. Whereas the majority of lifetime migrants originated from the neighbouring northeast region in 1950 and 1971, by 2001 more migrants arrived from the capital region. For lifetime outmigrants, the destination states became more diverse and less focused on the capital region. Gender ratios of lifetime migrants to and from Bolivar became more equitable as women became more prominent in migration flows. The level of urban primacy in Venezuela declined substantially after 1971 as the country became more internally integrated, although this more equitable distribution of the country's population may not have been solely a result of the creation of the growth pole, but a result of wider economic development.     

How Does the Species Used for Calibration Affect Chlorophyll <Emphasis Type="Italic">a</Emphasis> Measurements by In Situ Fluorometry?

We determined how the species used for calibration affects the accuracy of in situ chlorophyll a (chl a) measurements by fluorometry using single-species cultures and natural phytoplankton populations from Winyah Bay, South Carolina, USA. When a diatom was used for calibration, chl a in a dinoflagellate culture was overestimated by 66 ± 7%, whereas concentrations of a cryptophyte, chlorophyte, and cyanobacterium were underestimated by 16 ± 20%, 40 ± 7%, and 71 ± 33%, respectively. In natural populations, the combination of species-specific and environmentally induced variation in the ratio of fluorescence to chl a (F Chl⁻¹) led to an overestimate by the in situ fluorometer of 40–169% for an April experiment and an underestimate of 4–50% in July. Even when field samples were dominated by diatoms, environmental effects resulted in highly variable predictions of chl a. Thus, while a carefully selected calibration species can improve estimates of in vivo chl a in the laboratory, calibration of in situ fluorometers should be done with natural communities collected from the site of interest.