Technetium-99 in the Irish marine environment

Technetium-99 activity concentrations in seawater and biota from Irish coastal waters are presented. Time series measurements of 99Tc in seawater and Fucus vesiculosus from the western Irish Sea show that activity concentrations have increased in line with the increase in discharges of 99Tc from Sellafield. The peak in activity concentrations in both seawater and Fucus vesiculosus occurred in 1997 approximately two years after the peak in 99Tc discharges. The highest activity concentration recorded in Fucus vesiculosus showed a 29-fold increase over the mean concentration for the period 1988-1993. Technetium-99 activity concentrations were measured in fish, lobsters, prawns, mussels and oysters landed at major fishing ports on the east and northeast coasts of Ireland between 1996 and 1998. Concentration factors for 99Tc in the brown seaweed Fucus vesiculosus and certain species of fish, crustaceans and molluscs from the Irish Sea were estimated. In general, these concentration factors were higher than those in the literature which were derived from laboratory studies, but agreed well with values which were based on field studies. The mean committed effective doses to Irish typical and heavy seafood consumers due to 99Tc in the period 1996-1998 were 0.061 and 0.24 microSv, respectively.     

Denitrification as a nitrogen removal mechanism in a Vermont peatland

Atmospheric deposition of nitrogenous compounds to ombrotrophic peatlands (i.e., those that have peat layers higher than their surroundings and receive nutrients and minerals exclusively by precipitation) has the potential to significantly alter ecosystem functioning. This study utilized the acetylene inhibition technique to estimate the relative importance of denitrification in nitrogen removal from a primarily ombrotrophic peatland, in an attempt to estimate the threat of increased nitrogen loadings to these areas. Estimates of mean rates of denitrification ranged from -2.76 to 84.0 ng N(2)O-N cm(-3) h(-1) (equivalent to -150 to 4800 microg N(2)O-N m(-2) h(-1)) using an ex situ core technique and from -8.30 to 5.98 microg N(2)O-N m(-2) h(-1) using an in situ chamber technique. Core rates may have been elevated over natural field levels due to effects of disturbance on substrate availability, and chamber rates may have been low due to diffusional constraints on acetylene and N(2)O. Net nitrification was also measured in an attempt to evaluate this process as a source of nitrate for denitrifiers. The low rates of net nitrification measured, in combination with the low rates of in situ denitrification and the very low amounts of free nitrate measured in this peatland, suggests that inorganic N turnover in this wetland is low. Results showed that nitrate was a limiting factor for denitrification in this peatland, with mean rates from nitrate-amended cores ranging from 13.1 to 260 ng N(2)O-N cm(-3) h(-1), and it is expected that increases in nitrogen loadings will increase denitrification rates in this ecosystem.     

Predicting Invasions of Woody Plants Introduced into North America

Plant species continue to be introduced in North America for various purposes. If the trend continues, it is probable that some will escape cultivation and become invasive in native ecosystems. We present a retrospective analysis of several structural, life history, and biogeographical attributes of woody plants introduced in North America to determine which traits characterize species that have and have not invaded. Predictive models derived from discriminant analysis correctly classified 86.2% of the species in cross-validation, whereas those derived from classification and regression trees classified 76% correctly. From these models we created a hierarchical predictive tree that allows the user to divide species into three categories: admit (low risk of invasiveness), deny admission (high risk of invasiveness), or delay admission for further analyses and/or monitor intensively (risk cannot adequately be assessed based on only the included attributes). We recommend that species that are highly invasive elsewhere not be allowed into the U.S. and that a more conservative introduction policy using a hierarchical predictive method be employed.     

CLIMATE CHANGE AND EXTRATROPICAL STORMINESS IN THE UNITED STATES: AN ASSESSMENT1

ABSTRACT: Climate change due to enrichment of the atmosphere with carbon dioxide is projected to change the circulation of the atmosphere, increase its moisture content, warm the surface layers, and increase precipitation. Extratropical storms are the intermediate agent in mid-latitudes between changes in the circulation of the atmosphere and surface water resources. The climatology of extratropical storms for the period 1885–1996 is presented, and major changes in storminess are detected across much of North America. General Circulation Model (GCM) projections of storm frequency and storm track are found to have little in common with the observed pattern of storms and evidence no systematic changes in response to an enrichment of the atmosphere with carbon dioxide.     

Vegetation changes along the United States east coast following the great storm of march 1962

Regional-scale vegetation changes on Assateague Island following overwash from the Ash Wednesday Storm of 1962 were investigated using historical aerial photography. Grasses and dunes were more abundant in 1974 in areas that were overwashed, whereas areas that were not overwashed have been more extensively colonized by shrubs. The increase in shrubs on Assateague Island is attributed to the absence of a subsequent storm overwash.     

Mating strategies and mating success of fallow (Dama dama) bucks in a non-lekking population

The rutting behaviour of bucks in an enclosed population was investigated between 1988 and 1990. A substantial proportion of the matings were observed. After preliminary observations in the 1987 rut we categorised bucks into one of four rutting strategies based mainly on their degree of territoriality. We investigate the effects of age, dominance and mating strategy on mating success. Territories were aggregated in an area of oak woods and mating success was highly skewed. Bucks of between 5 and 7 years old achieved the majority (over 90%) of observed matings. Mating success was highly correlated with dominance but only weakly related to fighting success. The possession of a territory was crucial to achieving high reproductive success, with a 38-fold difference between the most and least successful strategies. Bucks pursuing the different strategies also differed in the time they commenced groaning, timing of matings, mating interference and the locations where they achieved their matings. Although high-ranking males devoted considerable effort to obtaining and defending a territory only 36% of each buck's matings were achieved on his territory and males tended to abandon these sites when the tendency of females to visit them decreased.     

Testosterone: from initiating change to modulating social organisation in domestic fowl (Gallus gallus domesticus)

Testosterone (T) concentrations in many species are sensitive to seasonal changes and to changes in social conditions. However, the effect of the natural or endogenous T increase in the juvenile on their social behaviour is not well understood. In this study, T and behaviour were measured from the pro-social juvenile to the adult stage in semi-feral domestic fowl. During the pro-social phase T levels and the distance chicks maintained between each other, i.e. inter-individual distance (IID) were low. Then, as T increased, a corresponding increase in IID occurred and continued in males until dispersal to individual adult male territories. In the new and initially stable adult social structure, T declined and IID remained high, indicating a new behavioural mechanism was in place. Males first mated as T levels were declining. They were then challenged; then T increased, and then IID increased again. Adult male T levels fluctuate, being low or declining in a socially stable environment and increasing following a challenge, suggesting a regulatory or modulating role for T. The results are consistent with T having an endogenous role: in the juvenile, driving behavioural change towards adulthood, and in adulthood, a modulating role regulating social organisation.     

Statistical properties of concentration fluctuations in two merging plumes

The statistics of the fluctuating concentration field within a plume is important in the analysis of atmospheric dispersion of toxic, inflammable and odorous gases. Previous work has tended to focus on concentration fluctuations in single plumes released in the surface layer or at ground level and there is a general lack of information about the mixing of two adjacent plumes and how the statistical properties of the concentration fluctuations are modified in these circumstances. In this work, data from wind tunnel experiments are used to analyse the variance, skewness, kurtosis, intermittency, probability density function and power spectrum of the concentration field during the mixing of two identical plumes and results are compared with those obtained for an equivalent single plume. The normalised variance, skewness and kurtosis on the centre-lines of the combined plume increase with distance downwind of the stack and, in the two-source configuration, takes lower values than those found in the single plumes. The results reflect the merging process at short range, which is least protracted for cases in which the sources are in-line or up to 30 \(^{\circ }\) off-line. At angles of 45 \(^{\circ }\) and more, the plumes are effectively side-by-side during the merging process and the interaction between the vortex pairs in each plume is strong. Vertical asymmetry is observed between the upper and the lower parts of the plumes, with the upper part having greater intermittency (i.e. the probability that no plume material is present) and a more pronounced tail to the concentration probability distribution. This asymmetry tends to diminish at greater distances from the source but occurs in both buoyant and neutral plumes and is believed to be associated with the ‘bending-over’ of the emission in the cross-flow and the vortex pair that this generates. The results allowed us to identify three phases in plume development. The first, very near the stack, is dominated by turbulence generated within the plume and characterised by concentration spectra with distinct peaks corresponding to scales comparable with those of the counter-rotating vortex pair. A second phase follows at somewhat greater distances downwind, in which there are significant contributions to the concentration fluctuations from both the turbulence internal to the plume and the external turbulence. The third phase is one in which the concentration fluctuations appear to be controlled by the external turbulence present in the ambient flow.     

Sexual size dimorphism in fallow deer (Dama dama): do larger, heavier males gain greater mating success?

Sexual size dimorphism may evolve as a result of both natural and sexual selection. In polygynous mammals, the main factor resulting in the evolution of large body size in males is the advantage conferred during competition for mates. In this study, we examined whether sexual selection acts on body size in mature fallow bucks (Dama dama) by examining how the following traits are inter-related: age, body (skeletal) size, body mass, prerut dominance rank, rut dominance rank and mating success. This is the first study to examine how all these factors are together related to the mating success of a large sexually dimorphic and polygynous mammal. We found that male mating success was directly related to body size, but not to body mass. However body mass was related to prerut dominance rank which was in turn strongly related to rut dominance rank, and thus there was an indirect relationship between mating success and body mass. Rut dominance rank was the variable most strongly related to mating success. Mating success among mature males was unrelated to age. We conclude that larger mature fallow bucks have advantages over other males when competing for matings, and sexual selection therefore continues to act on sexual size dimorphism in this species. Heavier fallow bucks also have advantages, but these are mediated through the dominance ranks attained by males before the rut.