Measuring acid volatile sulphide in floodplain lake sediments: effect of reaction time, sample size and aeration

For the routine measurement of acid volatile sulphide (AVS) in floodplain lake sediments, an earlier published diffusion method was adapted and optimised. We evaluated the effect of reaction time, sample weight and passive sample aeration on AVS recovery, and determined the method's reproducibility. The optimal reaction time was 4 h. Losses of AVS due to sample aeration did not occur within 15 min of sample-air contact. Relative standard deviation was <2.5% for known sulphide solutions, was between 10% and 15% for AVS concentrations in sediments and <12% for SEM concentrations in sediments, generally. Sediment samples with known SEM and AVS content were used to compare results of the developed method with the purge-and-trap method. There is a good agreement with the purge-and-trap method for SEM concentrations. AVS concentrations measured with the diffusion method are higher than with the purge-and-trap method. We conclude that the adapted diffusion method is well suited for the routine measurement of AVS concentrations in floodplain sediments.     

What attracts juvenile coral reef fish to mangroves: habitat complexity or shade?

The value of mangroves for fish species is usually explained in terms of high food abundance or shelter against predators as a result of high turbidity and structural complexity. In a field experiment, artificial mangrove units (AMUs) were designed as open cages, each of which was provided with a different degree of structural complexity and shade. Fish species that were attracted to the AMUs were identified and counted and the effects of shade and structural complexity, as well as the interaction between the two factors, were tested. Diurnal fish showed a preference for the greatest structured complexity and for a moderate increase in shade. Two nocturnal species common in local mangroves as well as seagrass beds showed statistically significant effects: densities of Haemulon sciurus were positively related to both shade and structural complexity, whereas only shade had a significant positive effect on densities of Ocyurus chrysurus. The experiment indicated that the attractiveness of mangrove vegetation for H. sciurus may be influenced by the structural complexity of the habitat as well as by the degree of shade, and that both factors are equally and separately important. Individuals of O. chrysurus that are attracted to mangroves are more likely to be influenced by the presence of shade than by the degree of structural complexity. The data thus indicated that the positive relationship between fish densities in mangrove habitats and the degree of shade and structural complexity, or both, is species-specific.Communicated by O. Kinne, Oldendorf/Luhe     

Sustained dynamic transience in a Lotka-Volterra competition model system for grassland species

Theoretical approaches, such as the Lotka-Volterra framework, enable predictions about long term species coexistence based on stability criteria, but generally assume temporal constancy of system equations and parameters. In real world systems, temporal variability may interfere with the attainment of stable states. Managed grassland ecosystems in Northwestern Europe experience structural periodic fluctuations in environmental conditions: the seasons. In addition, periodic disturbances such as cutting are very common. Here we show, using a Lotka-Volterra system applied to grassland species with empirically derived parameters, that seasonal variability can result in a time dependent equilibrium and redirection of displacement processes.Parameter estimates differed between species and - in most cases - between the seasons. As a result, five of the fifteen tested species combinations had different outcomes of species interactions between seasons. This indicates that systems remain in dynamic transience over the year as the equilibrium changes and the species composition of the system follows the equilibrium without ever attaining it. The non-attainment of the steady state enables coexistence of species even if there is competitive exclusion in one of the seasons. For three of the fifteen species combinations, cutting frequency affected the long-term coexistence patterns. Cutting resets the biomass of competing species and favours during regrowth those species that have a high growth rate, which can alter species coexistence in comparison to a Lotka-Volterra model without cutting. The Lotka-Volterra framework with seasonally changing empirical parameters predicts coexistence as a possible outcome of systems that in component seasons are characterised by exclusion, and vice versa.     

Comparison of the method of diffusive gels in thin films with conventional extraction techniques for evaluating zinc accumulation in plants and isopods

The measurement of diffusive gels in thin films (DGT) has recently been developed to assess metal bioavailability in soils. The DGT-method is based on diffusion in a porous matrix. To test the predictive capabilities of the method with regard to metal bioavailability, a study was set up with 28 soils having a variety of textures and amounts of zinc salts added. Correlation and regression analyses were performed to compare DGT-extracted zinc levels to zinc concentrations obtained by extraction with 0.01 M CaCl(2) and 0.43 M HNO(3), digestion with aqua regia and the zinc concentration in pore water. The amount of zinc extracted with CaCl(2) correlated well with DGT-extracted zinc levels in all soils spiked with different amounts of ZnCl(2). A similar correlation was not found for zinc concentrations in soil samples collected in the field. Experiments were performed to compare zinc content in organisms and in soils. The organisms tested were plants (grass, lettuce and lupine) and the hard bodied soil dwelling isopod Oniscus asellus. Good correlations were found between zinc accumulation in grass and lettuce and the C(E) (effective concentration) measured by a DGT-device, CaCl(2) extracted zinc and the zinc content in the pore water of all soils. The correlation with C(E) was not significant for lupine, neither for spiked soils, nor for field soils (p< or =0.001). Zinc levels in the isopods were not significantly related to any set of zinc measurements. From a synthesis of all results obtained it is concluded that the DGT-methodology does not have an additional value in predicting bioavailability of zinc in terrestrial ecosystems as compared to conventional extraction methods.     

Dioxin emissions after installation of a polishing wet scrubber in a hazardous waste incineration facility

Dioxin levels measured after wet scrubbing systems have been found to be higher than levels measured before the scrubber. It is believed that there is an adsorption of PCDD/Fs on plastic materials in the scrubber. The PCDD/F levels after a polishing wet scrubber were followed continuously for 18 months using long-time sampling equipment at a hazardous waste incineration facility in Sweden. Each sampling period lasted two weeks. It was found that the levels during and shortly after start-up periods were elevated. The decline was very slowly, which supports a memory effect in the scrubber. Further, a multivariate model showed that the relation between different homologues changed over time, which is in agreement with a desorption model, taking into account the vapour pressures for different congeners.     

Spatial and Temporal Performance of the MiniFACE (Free Air CO2 Enrichment) System on Bog Ecosystems in Northern and Central Europe

The Bog Ecosystem Research Initiative (BERI) projectwas initiated to investigate, at five climaticallydifferent sites across Europe, the effects of elevatedCO₂ and N deposition on the net exchange ofCO₂ and CH₄ between bogs and the atmosphere,and to study the effects of elevated CO₂ and Ndeposition on the plant biodiversity of bogcommunities. A major challenge to investigate theeffects of elevated CO₂ on vegetation andecosystems is to apply elevated CO₂concentrations to growing vegetation without changingthe physical conditions like climate and radiation.Most available CO₂ enrichment methods disturb thenatural conditions to some degree, for instance closedchambers or open top chambers. Free Air CO₂Enrichment (FACE) systems have proven to be suitableto expose plants to elevated CO₂ concentrationswith minimal disturbance of their natural environment.The size and spatial scale of the vegetation studiedwithin the BERI project allowed the use of a modifiedversion of a small FACE system called MiniFACE. Thispaper describes the BERI MiniFACE design as well asits temporal and spatial performance at the five BERIfield locations. The temporal performance of theMiniFACE system largely met the quality criteriadefined by the FACE Protocol. One minute averageCO₂ concentrations measured at the centre of thering stayed within 20% of the pre-set target for morethan 95% of the time. Increased wind speeds werefound to improve the MiniFACE system's temporalperformance. Spatial analyses showed no apparentCO₂ gradients across a ring during a 4 day periodand the mean differences between each sampling pointand the centre of the ring did not exceed 10%.Observations made during a windy day, causing aCO₂ concentration gradient, and observations madeduring a calm day indicated that short term gradientstend to average out over longer periods of time. On aday with unidirectional strong winds, CO₂concentrations at the upwind side of the ring centrewere higher than those made at the centre and at thedownwind side of the ring centre, but the bell-shapeddistribution was found basically the same for thecentre and the four surrounding measurement points,implying that the short term (1 sec) variability ofCO₂ concentrations across the MiniFACE ring isalmost the same at any point in the ring. Based on gasdispersion simulations and measured CO₂concentration profiles, the possible interferencebetween CO₂-enriched and control rings was foundto be negligible beyond a centre-to-centre ringdistance of 6 m.     

The toxicity of copper contaminated soil using a gnotobiotic Soil Multi-species Test System (SMS)

A gnotobiotic multi-species study was designed to consist of a food-web of soil-dwelling animals. The food-web was exposed to five concentrations copper (Cu) spiked soil for three exposure durations i.e. 28, 56 and 84 days. Based on multivariate analysis the food-web was significantly affected by Cu exposure at and above 300 mg Cu kg(-1) soil (lowest tested concentration). The number of animals present in the 2500 mg Cu kg(-1) (highest tested concentration) was at all sampling occasions below the starting point level. Based on analysis of the individual species the lowest 10% effect concentration (EC10) observed was 50 mg Cu kg(-1) soil, for Enchytraeus crypticus. Using the EC10 for the individual species the HC5 (Hazard Concentration at the 5% level) was estimated to be between 25 and 36 mg Cu kg(-1) soil, depending on the exposure duration. A similar experiment but using a reduced design was performed employing soil contaminated with Cu in the field more than 80 years ago. The trend in the field-contaminated soil was similar to that observed for the spiked soil.     

Tipping Points and Climate Change: Metaphor Between Science and the Media

Over the past decade, scientists and journalists have prominently utilized the metaphor of a tipping point for drastic, irreversible and dangerous climate change. This paper shows how the tipping point metaphor became a multi-purpose bridge between science and the news media, describing how its meaning and use developed and diversified in interaction between these two domains. Within the scientific domain, the metaphor developed from a rhetorical device conveying a warning of drastic, irreversible and dangerous climate change to a theoretical concept driving empirical research. The news media soon picked up the tipping point metaphor for abrupt and dangerous climate change, turning it into a common part of the journalistic lexicon. Moreover, both science and the news media developed another, societal use of the tipping point metaphor, calling for radical societal change to avoid climate change catastrophe. The tipping point metaphor is hence not a monolithic notion but a highly versatile concept and expression, allowing it to be used for various communicative purposes by distinct stakeholders in different contexts.