UV-B protecting compounds in the marine algaPhaeocystis pouchetii from Antarctica

Phaeocystis pouchetii (Hariot) Lagerheim is widely distributed in polar waters, and forms massive near-surface blooms in the marginal ice-edge zone around Antarctica during spring and summer. UV irradiance in the Antarctic marine environment is reportedly as high in October and November as in mid-summer due to stratospheric ozone depletion. Because of the location and timing of theP. pouchetii bloom, this prymnesiophyte will be exposed to high levels of UV-B (280 to 320 nm) radiation. Colourless water-soluble compounds, produced by the colonial stage in the life cycle of this alga, absorb strongly between 250 and 370 nm, with absorbance maxima at 271 and 323 nm. The concentration of these compounds in culturedP. pouchetii depends on the strain, stage in the life cycle, and presence of bacteria. As well as conferring substantial protection to this alga, these substances may also provide UV protection to other organisms present in the water column.     

Gastroschisis and omphalocele: Prenatal diagnosis and perinatal management

Obstetric ultrasonography has made the prenatal diagnosis of gastroschisis and omphalocele more common. We present illustrative cases 2nd review the ultrasonographic features. Because of the increased risk of concomitant abnormalities (including trisomies) with omphalocele, full evaluation is indicated when this diagnosis is suspected. Recent perinatal approaches to delivery have favoured caesarean section. without scientific evidence that outcome is improved. Our experience. as well as a review of the literature, suggests that the outcome for vaginally delivered infants is acceptable. A prospective study of this question is needed.     

The enigma of progress in denitrification research.

Humans have dramatically increased the amount of reactive nitrogen (primarily ammonium, nitrogen oxides, and organically bound N) circulating in the biosphere and atmosphere, creating a wide array of desirable products (e.g., food production) and undesirable consequences (e.g., eutrophication of aquatic ecosystems and air pollution). Only when this reactive N is converted back to the chemically unreactive dinitrogen (N2) form, do these cascading effects of elevated reactive N cease to be of concern. Among the quantitatively most important processes for converting reactive N to N2 gas is the biological process of classical denitrification, in which oxides of nitrogen are used as terminal electron acceptors in anaerobic respiration. This Invited Feature on denitrification includes a series of papers that integrate our current state of knowledge across terrestrial, freshwater, and marine systems on denitrification rates, controlling factors, and methodologies for measuring and modeling denitrification. In this paper, we present an overview of the role of denitrification within the broader N cycle, the environmental and health concerns that have resulted from human alteration of the N cycle, and a brief historical perspective on why denitrification has been so difficult to study. Despite over a century of research on denitrification and numerous recent technological advances, we still lack a comprehensive, quantitative understanding of denitrification rates and controlling factors across ecosystems. Inherent problems of measuring spatially and temporally heterogeneous N2 production under an N2-rich atmosphere account for much of this slow progress, but lack of interdisciplinary communication of research results and methodological developments has also impeded denitrification research. An integrated multidisciplinary approach to denitrification research, from upland terrestrial ecosystems, to small streams, river systems, estuaries, and continental shelf ecosystems, and to the open ocean, may yield new insights into denitrification across landscapes and waterscapes.     

Tsunami generation by submarine landslides: comparison of physical and numerical models

An idealised two-dimensional laboratory model of tsunamis generated by submarine landslides is described. The experimental configuration corresponds to the benchmark configuration suggested by other researchers in the international tsunami community. It comprises a semi-elliptical rigid landslide with a height to length ratio of 0.052 sliding down a 15° slope. The initial landslide submergence and specific gravity are varied, the second of which primarily determines the initial landslide acceleration. In these experiments the landslide motion is generally well approximated as consisting of two periods of constant acceleration. The first phase of positive acceleration finishes as the landslide reaches the base of the slope, while the second period of a slower deceleration continues until the landslide comes to rest along the horizontal base of the tank. A novel experimental technique, which utilises laser-induced fluorescence (LIF), is employed to measure the free surface displacement over the entire space and time domains. This enables the wave potential energy field to be computed directly and provides a vivid picture of the wave generation and development process. Particle tracking velocimetry provides detailed information on the landslide motion and also some data on the sub-surface velocity field. Experimental runs require multiple repeats (typically 35–50) of the same setup in order to capture the entire wave field with the desired resolution. Thus high level experimental repeatability is required, and this is demonstrated. A range of parameters relevant to hazard management are presented and discussed. Maximum crest and trough amplitudes of the offshore propagating waves are shown to be approximately proportional to the initial landslide acceleration and somewhat less strongly dependent on the initial landslide submergence. The maximum wave run-up experienced at the shoreline is shown to depend almost linearly on the magnitude of a high deceleration that occurs for a short period when the landslide nears the toe of the slope. The initial submergence and initial acceleration do not directly determine the maximum wave run-up, although for these experiments they impact indirectly on the magnitude of the deceleration. The efficiency of the energy transfer from the landslide potential energy to the wave field potential energy reaches values of up to 6% and is found to be strongly dependent on the initial submergence. However because of the link between the landslide mass and its acceleration, this efficiency is almost completely independent of the initial acceleration. The results from a numerical model based on linear, inviscid and irrotational wave theory, and solved with the boundary element method, are compared with the data from the experimental program. The numerical model accurately produces the generated sequence of wave crests and troughs, but slightly overpredicts their phase speed by between 2 and 4%. For all other parameters the numerical model predictions are within 25% of the experimental values, although this includes both under- and overprediction for the range of independent parameters covered.     

Mate replacement in experimentally widowed collared flycatchers (Ficedula albicollis): determinants and outcomes

There is increasing evidence that sexual selection may be intense even in socially monogamous birds, resulting from both mate choice and sperm competition. We studied these two modes of sexual selection experimentally by removing paired male collared flycatchers, Ficedula albicollis, from their mates for 2 days and investigating the factors that influenced the likelihood of a replacement male appearing and how the removals influenced paternity. Replacement males (usually neighbouring males) appeared at 81% (n = 37) of nests where males were removed. The likelihood of this appearance was unaffected by the probable reproductive value of the female's clutch to the replacing male. A replacement was, however, less likely when the original male had a large forehead patch, a trait previously shown to be subject to sexual selection in this population. Experimental removal of males increased the level of sperm competition: 74% of experimental broods were multiply sired, compared to 29% of unmanipulated broods in a previous study. Only two factors predicted how paternity was shared between males: removed males fathered more young if removed closer to laying, and if they had larger forehead patches. The former result is consistent with last-male sperm precedence determining paternity, whereas the latter adds to other evidence that forehead patch size is the target of female preference in this species. Our results suggest that females exert some control over male replacement, and also that they may influence the fertilisation success of males by behavioural means. Received: 15 July 1998 / Received in revised form: 16 March 1999 / Accepted: 28 March 1999     

Manure management effects on grass production, nutritive content, and soil nitrogen for a grass silage-based dairy farm

Legislation in the United States has recently focused on improving water quality by establishing management practices that limit the quantities of nutrients entering the water supply. Timely application and quantification of the amount of manure applied throughout the grass-growing season can reduce the loss of nutrients into ground or surface water while improving the quality and quantity of grass harvested. During the 2001 and 2002 growing seasons, we measured the effects of different manure application rates on grass yields, grass nutritive value, and soil chemistry on a dairy farm. On-farm estimates of manure N were combined with yield estimates and forage quality measures to evaluate the effects of varying levels of manure application. Yield estimates, N content of grass, and the amount of N in soil and manure were monitored at each cutting for plots amended at different manure application rates. There are three major outcomes of this evaluation: (i) new grass seedings were at higher risk of elevated levels of nitrate N in forage; (ii) increased forage nitrate N at harvest was associated with malfermented silage and increased levels of ammonia N, which resulted in less efficient use of metabolizable protein for milk production; and (iii) increased understanding of N cycling between manure, soil, and plant provided an opportunity to reduce purchased fertilizer.