Role of the floodplain lakes in the methylmercury distribution and exchanges with the Amazon River, Brazil

Seasonal variability of dissolved and particulate methylmercury(F-MeHg, P-MeHg) concentrations was studied in the waters of the Amazon River and its associated Curuai floodplain during hydrological year 2005–2006, to understand the MeHg exchanges between these aquatic systems. In the oxic white water lakes, with neutral pH, high F-MeHg and P-MeHg concentrations were measured during the rising water stage(0.70 ± 0.37 pmol/L, n = 26) and flood peak(14.19 ± 9.32 pmol/g, n = 7) respectively, when the Amazon River water discharge into the lakes was at its maximum. The lowest mean values were reported during the dry season(0.18 ± 0.07 pmol/L F-MeHg, n = 10 and 1.35 ± 1.24 pmol/g P-MeHg, n = 8), when water and suspended sediments were outflowing from the lakes into the River. In these lakes,the MeHg concentrations were associated to the aluminium and organic carbon/nitrogen changes. In the black water lakes, with acidic pH and reducing conditions, elevated MeHg concentrations were recorded(0.58 ± 0.32 pmol/L F-MeHg, n = 16 and 19.82 ± 15.13 pmol/g PMeHg, n = 6), and correlated with the organic carbon and manganese concentrations. Elevated values of MeHg partition coefficient(4.87 Kd 5.08 log(L/kg) indicate that MeHg is mainly transported associated with the particulate phase. The P-MeHg enrichment detected in all lakes suggests autochthonous MeHg inputs from the sediments into the water column. The MeHg mass balance showed that the Curuai floodplain is not the source of P-MeHg for the Amazon River.     

Follow-up to environmental impact assessment: Learning from the Canadian Government experience

The environmental impact assessment procedure for Canadian federal government projects is briefly described. In the non-legislated Canadian system, follow-up to assessments is one of the major means of encouraging and improving the implementation of environmental impact assessment and the quality of environmental work done around development projects. The results of a study on the status of follow-up in the Canadian Government are presented. Factors that limit and that are conducive to follow-up are discussed. The effectiveness of follow-up depends as much on the circumstances surrounding a project and the concerned parties as on the follow-up techniques used; both of these aspects can be addressed in the planning and management of follow-up and of environmental impact assessment overall. Areas for improving the management of follow-up are identified and discussed: planning of follow-up activities, coordination of concerned parties, generation of clear understandings, information management, resource allocation, and maintenance of credibility. A method for planning follow-up activities for specific projects is presented.     

Dose-time-response functions for toxic chemicals

In many situations, the effect of a toxic chemical on a biological system depends on both the intensity and the duration of exposure. The dependence on the time dimension can be the expression of a range of processes including the physical accumulation of toxic chemicals or their metabolites and the functional accumulation of damage. Measures and functions that have been used to describe this dependence are reviewed.Some of these functions are compared through a case study of the neurotoxicity of methylmercury. Use is made of data that indicates a dependency between the blood concentration at which monkeys were exposed and the length of time before damage was detected. Several exposure functions are fitted to these data and their appropriateness is compared. Using the most appropriate function, an exposure-response relationship is developed using probit analysis. An alternative data analysis procedure is also investigated. The apparent threshold after a 100 day exposure is estimated to be greater by a factor of 3–5 compared to the threshold for chronic exposure. Applying this factor to man, the blood concentration threshold for chronic exposure is estimated to be 40–170 ppb, a finding consistent with recent reports of neurological damage in humans exposed below the generally accepted threshold.     

Determination of biomass burning emission factors: Methods and results

Biomass burning, in a broad sense, encompasses different burning practices, including open and confined burnings, and different types of vegetation. Emission factors of gaseous or particulate trace compounds are directly dependent both on the fuel type and the combustion process. Emission factors are generally calculated by stoichiometric considerations using the carbon mass balance method, applied either to combustion chamber experiments or to field experiments based on ground-level measurements or aircraft sampling in smoke plumes. There have been a number of experimental studies in the last 10 years to investigate wildfires in tropical, temperate, or boreal regions. This article presents an overview of measurement methods and experimental data on emission factors of reactive or radiatively active trace compounds, including trace gases and particles. It focuses on fires in tropical regions, that is, forest and savanna fires, agricultural burns, charcoal production, use of fuelwood, and charcoal combustion.     

Characterization of microbial communities from coastal waters using microarrays

Molecular methods, including DNA probes, were used to identify and enumerate pathogenic Vibrio species in the Chesapeake Bay; our data indicated that Vibrio vulnificus exhibits seasonal fluctuations in number. Our work included a characterization of total microbial communities from the Bay; development of microarrays that identify and quantify the diversity of those communities; and observation of temporal changes in those communities. To identify members of the microbial community, we amplified the 16S rDNA gene from community DNA isolated from a biofilm sample collected from the Chesapeake Bay in February, 2000. The resultant 75 sequences were 95% or more similar to 7 species including two recently described Shewanella species, baltica and frigidimarina, that have not been previously isolated from the Chesapeake. When the genera of bacteria from biofilm after culturing are compared to those detected by subcloning amplified 16S fragments from community DNA, the cultured sample exhibited a strong bias. In oysters collected in February, the most common bacteria were previously unknown. Based on our 16S findings, we are developing microarrays to detect these and other microbial species in these estuarine communities. The microarrays will detect each species using four distinct loci, with the multiple loci serving as an internal control. The accuracy of the microarray will be measured using sentinel species such as Aeromonas species, Escherichia coli, and Vibrio vulnificus. Using microarrays, it should be possible to determine the annual fluctuations of bacterial species (culturable and non-culturable, pathogenic and non-pathogenic). The data may be applied to understanding patterns of environmental change; assessing the health of the Bay; and evaluating the risk of human illness associated with exposure to and ingestion of water and shellfish.     

Life-history parameters and vertical distribution of Maurolicus muelleri in Masfjorden in summer

Population characteristics, individual life-history variables, feeding and vertical distribution of the mesopelagic fish Müller's pearlside Maurolicus muelleri collected in 1990 in Masfjorden, western Norway, are reported as well as environmental variables from the fjord. Minimum size at maturity was far smaller than reported from previous investigations in the same region. Fecundity was size-dependent and total egg numbers were higher than reported from other investigations of M. muelleri world wide, while the number of maturing eggs was far lower than observed in the same region earlier. Food concentration in the fjord was an order of magnitude lower than previous early summer observations, and several factors indicated that feeding opportunities may have been low for a long period. Daily feeding rate (g prey g^-1 fish) decreased with increasing fish size. These observations fit well with a model of maximizing fitness by means of a flexible size at maturity. Minimum age at maturity seems to be achieved at the expense of fecundity. M. muelleri was concentrated in a 20 to 30 m deep sound scattering layer (SSL). The SSL stayed close to the surface during the night and at 100 to 180 m during the daytime. The vertical position of the SSL varied instantaneously with changes in surface light intensity, remaining at 10^-3 to 10^-4 mol m^-1 s^-1 at the top of the SSL. Stomach fullness was highest during the night; feeding intensity seems to have been peaked at dusk. Cladocerans were the main prey ranked by number, copepods by biomass. Intake of large copepods increased with fish size.     

The modern theory of biological evolution: an expanded synthesis

In 1858, two naturalists, Charles Darwin and Alfred Russel Wallace, independently proposed natural selection as the basic mechanism responsible for the origin of new phenotypic variants and, ultimately, new species. A large body of evidence for this hypothesis was published in Darwins Origin of Species one year later, the appearance of which provoked other leading scientists like August Weismann to adopt and amplify Darwins perspective. Weismanns neo-Darwinian theory of evolution was further elaborated, most notably in a series of books by Theodosius Dobzhansky, Ernst Mayr, Julian Huxley and others. In this article we first summarize the history of life on Earth and provide recent evidence demonstrating that Darwins dilemma (the apparent missing Precambrian record of life) has been resolved. Next, the historical development and structure of the modern synthesis is described within the context of the following topics: paleobiology and rates of evolution, mass extinctions and species selection, macroevolution and punctuated equilibrium, sexual reproduction and recombination, sexual selection and altruism, endosymbiosis and eukaryotic cell evolution, evolutionary developmental biology, phenotypic plasticity, epigenetic inheritance and molecular evolution, experimental bacterial evolution, and computer simulations (in silico evolution of digital organisms). In addition, we discuss the expansion of the modern synthesis, embracing all branches of scientific disciplines. It is concluded that the basic tenets of the synthetic theory have survived, but in modified form. These sub-theories require continued elaboration, particularly in light of molecular biology, to answer open-ended questions concerning the mechanisms of evolution in all five kingdoms of life.Dedicated to Prof. Dr. Dr. hc mult. Ernst Mayr on the occasion of his 100th birthdayThis revised version was published online in March 2004, with corrections to the caption of Figure 6.