Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.     

The lower crust beneath cratonic north-east Europe: isotopic constraints from garnet granulite xenoliths

Lower crustal garnet-bearing mafic granulite xenoliths from beneath the cratonic areas of NE Europe (NW Russia, Belarus, Finland) have unradiogenic ¹⁴³Nd/¹⁴⁴Nd ratios that differ strongly from those of xenoliths from beneath Phanerozoic regions of the European plate and worldwide, but closely resemble xenoliths from other cratonic regions of the world. Phanerozoic lower crustal xenoliths worldwide also show a very limited range of Pb isotope compositions whereas most cratonic lower crustal xenoliths have more varied but usually unradiogenic Pb isotope compositions, plotting to the left of the Geochron. However, many of the xenoliths from beneath NE Europe plot on the right-hand side of the Geochron and also have more radiogenic ²⁰⁸Pb/²⁰⁴Pb ratios. Thus, the lower crust of NE Europe shows characteristics of both cratonic lower crust (unradiogenic Nd isotopes) and Phanerozoic lower crust (radiogenic Pb isotopes). Its present-day low U/Pb and Th/Pb ratios indicate that it has been depleted in heat-producing elements, but the radiogenic Pb isotope ratios show that this depletion occurred relatively recently.     

Granulite and pyroxenite xenoliths from the Deccan Trap: insight into the nature and composition of the lower lithosphere beneath cratonic India

Granulite and pyroxenite xenoliths in lamprophyre dykes intruded during the waning stage of Deccan Trap volcanism are derived from the lower crust beneath the Dharwar craton of Western India. The xenolith suite consists of plagioclase-poor mafic granulites (55% of the total volume of xenoliths), plagioclase-rich felsic granulites (25%), and ultramafic pyroxenites and websterites (20%) with subordinate wehrlites. Rare spinel peridotite xenoliths are also present, representing mantle lithosphere. The high Mg #, low SiO₂/Al₂O₃ and low Nb/La (<1) ratios suggest that the protoliths of the mafic granulites broadly represent cumulates of sub-alkaline magmas. All of the granulites are peraluminous and light rare-earth element-enriched. The felsic granulites may have resulted from anatexis of the mafic lower crustal rocks; thus, the mafic granulites are enriched in Sr whereas the felsic ones are depleted. Composite xenoliths consisting of mafic granulites traversed by veins of pyroxenite indicate intrusion of the granulitic lower crust by younger pyroxenites. Petrography and geochemistry of the latter (e.g. presence of phlogopite) indicate the metasomatised nature of the deep crust in this region.Thermobarometric estimates from phase equilibria indicate equilibration conditions between 650 and 1200 °C, 0.7-1.2 GPa suggestive of lower crustal environments. These estimates provide a spatial context for the sampled lithologies thereby placing constraints on the interpretation of geophysical data. Integration of xenolith-derived P-T results with Deep Seismic Soundings (DSS) data suggests that the pyroxenites and websterites are transitional between the lower crust and the upper mantle. A three-layer model for the crust in western India, derived from the xenoliths, is consistent with DSS data. The mafic nature of this hybrid lower crust contrasts with the felsic lower crustal composition of the south Indian granulite terrain.     

A simple parameterization of sub-grid scale open water for climate models

The effects of small fractions ( < 30%) of open water covering a grid element are currently neglected even in atmospheric general circulation models (AGCMs) which incorporate complex land surface parameterization schemes. Here, a method for simulating sub-grid scale open water is proposed which permits any existing land surface model to be modified to account for open water. This new parameterization is tested as an addition to an advanced land surface scheme and, as expected, is shown to produce general increases in the surface latent heat flux at the expense of the surface sensible heat flux. Small changes in temperature are associated with this change in the partitioning of available energy which is driven by an increase in the wetness of the grid element. The sensitivity of the land surface to increasing amounts of open water is dependent upon the type of vegetation represented. Dense vegetation (with a high leaf area index) is shown to complicate the apparently simple model sensitivity and indicates that more advanced methods of incorporating open water into AGCMs need to be considered and compared against the parameterization suggested here. However, the sensitivity of one land surface model to incorporating open water is large enough to warrant consideration of its incorporation into climate models.     

Riverine dominance of a nearshore marine demersal food web: evidence from stable isotope and C/N ratio analysis

The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

Sulphur-bearing carbon chains in IRC+10216

We have updated the chemical model of IRC+10216 developed by Millar, Herbst & Bettens to include recent routes to the formation of sulphuretted hydrocarbons. The routes are based on a quantum chemical study of the S+C₂H system. In addition, we have altered the parent species for sulphur to reflect new observational results. We find that the model calculations give excellent agreement with the observed column densities, and discuss the significance of these reactions to the formation of species as yet unobserved and to dark interstellar clouds.     

The population genetic structure of the waratah anemone (Actinia tenebrosa) around New Zealand

The genetic structure of populations is often shaped by the reproductive system and larval properties of the species. The waratah anemone (Actinia tenebrosa) reproduces through both asexual clones, which have very short-distance dispersal, and sexual larvae, which are believed to disperse much greater distances. The impact of this mixed strategy on the New Zealand population structure of Actinia tenebrosa was investigated using microsatellite markers. The analysis incorporated 24 sampling locations from around New Zealand and one Australian location, using four microsatellite markers, n = 420. We observed low connectivity and high genetic differentiation between all locations sampled, with a distinct pattern of isolation by distance. The most distinct grouping of locations sampled was the north-east of the North Island from Cape Reinga to East Cape, which was identified by SAMOVA and STRUCTURE analyses as being moderately diverged from the remainder of the country. A tentative correlation was observed between genetic clustering and biogeographic regionalisation, where the distribution of a number of genetic clusters matched previously defined biogeographic regions. Within each location sampled, large numbers of clones were present and a latitudinal cline was observed in the relative contribution of asexually and sexually generated recruits, with an increase in asexual recruits on the South Island's east coast.     

Two-dimensional models of proto planetary disk chemistry

We have developed a two-dimensional model of a flared protoplanetary disk (PPD) incorporating a self-consistent treatment of gas and dust temperature, and a detailed treatment of the gas-phase chemistry as well as the freeze-out and desorption of material from dust grains. The results show that, in the inner 10 AU of the disk, the gas-phase abundances are dominated by material evaporated from dust grains. The surface layer of the disk shows many of the characteristics of photon-dominated regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

NCCN in TMC-1 and IRC+10216

We employ quantum chemical calculations using the CBS-RAD ('Complete Basis Set – Radicals') technique on the C₂N₂H potential energy surface to show that the reaction of HNC with CN is a viable and plausible route to NCCN in cold astrophysical environments. We use detailed chemical kinetic models to predict the abundance of NCCN in TMC-1 and IRC+10216. Radio-astronomical detection of NCCN is precluded by its lack of a dipole moment. We discuss other prospects for its observation in interstellar and circumstellar environments, by space-borne infrared spectroscopy, indirectly by detection of the NCCNH⁺ ion, or inferentially by detection of its higher-energy, polar isomer CNCN.