Bedload sediment transport dynamics in a macrotidal embayment, and implications for export to the southern Great Barrier Reef shelf

Keppel Bay is a macrotidal embayment on a tectonically stable, tropical coast, which links the Fitzroy River with the Great Barrier Reef continental shelf. Estuaries and deltas act as conduits between catchments and inner shelf environments. Therefore, understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral-reefs that are potentially vulnerable to enhanced river sediment loads. Furthermore, the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries, particularly in turbid, episodic systems such as the Fitzroy River and Keppel Bay. Our sedimentological analysis of seabed samples, shear-stress modelling and three-dimensional acoustic imaging reveals that Keppel Bay is a mixed wave- and tide-dominated estuarine system. Areas of sediment starvation and shoreward transport characterise the offshore zone, whereas a complex of both active and relict tidal sand ridges, and associated subaqueous dunes, dominate the relatively protected southern Keppel Bay. Transport within this region is highly dynamic and variable, with ebb-dominated sediment transport through tidal channels into the outer bay where there is a switch to wave-dominated shoreward transport. Ultimately, bedload sediments appear to be reworked back inshore and to the north, and are gradually infilling the bedrock-defined embayment. Our characterisation of the Keppel Bay system provides a detailed example of the physiography of the seaward portion of a tide-dominated system, and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography.     

Environmental factors influencing the biodeposition of the suspension feeding bivalve Dreissena polymorpha (Pallas): Comparison of brackish and freshwater populations

Invasive suspension feeders have been particularly successful in shallow eutrophic estuarine and freshwater ecosystems. The impact of an invasive species is strong under favourable conditions. However, suboptimal feeding conditions may significantly reduce the impact to ambient environment. The invasive bivalve Dreissena polymorpha (Pallas) is able to colonize both fresh and brackish waterbodies. In an in situ experiment the seasonal variability in the biodeposition of D. polymorpha from fresh and brackish water populations was quantified at different temperature, salinity and chlorophyll a (Chl a) regimes. Salinity fluctuations in brackish water areas, temperature and water Chl a content were all important factors in the model of mussels' feeding. The results indicated that D. polymorpha fed significantly more in fresh than in brackish water. Mussels acclimated more easily to acute transfer from brackish to freshwater than vice versa. The biodeposition of zebra mussels increased with temperature and water Chl a content but these effects were less straightforward than that of salinity. The results suggest that the impact of D. polymorpha on recipient ecosystem is more pronounced in fresh than in brackish water environments.     

GLORIA survey of the oceanic-continental transition of the Havre-Taupo back-arc basin

A GLORIA (Geological Long-Range Inclined Asdic) side-scan sonar survey, covering 23,000 km², provides the first complete imagery of an active and contiguous, oceanic to continental back-arc system, namely, the Havre Trough to Taupo Volcanic Zone (TVZ) New Zealand. Havre Trough tectonism and volcanism relates to a series of laterally discontinuous, mutiple spreading rifts which terminate southward at the 3-km-deep Ngatoro Basin. A 45-km sinistral offset attributed toen echelon synthetic shearing separates the basin from the actively spreading TVZ. Sonographs reveal a youthful and complex volcanic seascape with 20 newly discovered seamounts, whereas flanking regions are mantled with a largely featureless mud blanket.     

Stoneley waves,Lopez Island noise,and deep sea noise from 1 to 5 Hz

The Lopez Island OBS Intercomparison Experiment provided a data set of sufficient spatial density to allow study of the propagation of shot-generated Stoneley waves as well as ambient background noise. The Stoneley waves were observed propagating at velocities of 20 to 50 m s^-1, Phase velocities were determined by fitting peaks in the frequency wave number spectrum. Group velocities were calculated by narrowly filtering the data and determining the arrival time of the peak in the frequency packet. Particle displacement plots illustrate the surface wave character of these waves. The analysis of the ambient background noise failed to produce a clearly defined dispersion curve yet it did allow bounds to be placed on the phase velocities (20 to 50 m s^-1). The data were modeled using eleven layers overlying a half-space. The results indicated that the top 7 m of the sediment column at Lopez Island is best approximated by two zones. In the upper zone there is a fairly rapid change of shear velocity with depth. This zone overlies a region in which the shear velocity gradient is much lower. Deep ocean background noise recorded by University of Washington ocean bottom seismometers was also examined. Although insufficient data precluded any velocity analysis, definite similarities exist between these data and noise data observed at Lopez Island.Hawaii Institute of Geophysics Contribution No. 1174.     

Composition and petrogenesis of oxide-, apatite-rich gabbronorites associated with Proterozoic anorthosite massifs: examples from the Adirondack Mountains,New York

Mafic dikes and sheets rich in Fe, Ti-oxides and apatite are commonly associated with Proterozoic massif anorthosites and are referred to as oxide-apatite gabbronorites (OAGN). Within the Adirondacks, field evidence indicates that during middle to late stages of anorthositic evolution, these bodies were emplaced as magmas with unspecified liquid-crystal ratios. Sixty whole rock analyses of Adirondack OAGN and related rocks define continuous oxide trends on Harker variation diagrams (SiO₂=37–54%). Similar trends exist for Sr, Y, Nb, Zr, and REE and together suggest a common origin via fractional crystallization. A representative parental magma (plagioclase-rich crystal mush) has been chosen from this suite, and successive daughter magmas have been produced by removal of minerals with compositions corresponding to those determined in actual rocks. Least squares, mass balance calculations of major element trends indicate that removal of intermediate plagioclase (An_40–50) plus lesser amounts of pyroxene account for the compositional variation of this suite and produce very low sums of the squares of the residuals (R² _s>0.25). The extracted mineral phases correspond volumetrically and compositionally to those of the anorthositic suite, and the model succeeds in accounting for the observed OAGN trends. The major element model is utilized to calculate trace elejent concentrations for successive magmas, and these agree closely with observation. We conclude that, beginning with a plagioclase-rich crystal mush, the extraction of intermediate plagioclase (An_40–50) drives residual magmas to increasingly Fe-, Ti-, and P-rich and SiO₂-poor conditions characteristic of Fenner-type fractionation. The crystallization sequence is plagioclaseplagioclase+orthopyroxeneplagioclase+orthopyroxene (pigeonite)+augite. Fe, Ti-oxides begin to crystallize near the end of the sequence and are followed by apatite and fayalitic olivine which appears in place of pigeonite. Augitic pyroxene becomes the dominant ferromagnesian phase in late stages of fractionation. Resultant OAGN magmas are injected into congealed anorthosite by filter pressing of liquid-rich interstitial fractions. Varying compositions of the dikes reflect filter pressing at different stages during fractionation and thereby provide information on the fractionation history of Proterozoic massif anorthosites.     

Sources and sinks of methylgermanium in natural waters

New data have extended our understanding of the distribution and behavior of methylgermanium in the environment. Laboratory attempts to induce aerobic methylation with known biological and abiotic methylating agents were unsuccessful; this confirmed previous field observations of methylgermanium's unreactive behavior. However, biomethylation of inorganic germanium was observed in the anaerobic digestor of a sewage treatment plant, which suggested a terrestrial methanogenic source. Attempts to locate such a source in methanogenic swamps and their drainages reveal very low methylgermanium concentrations typical of other remote, pristine rivers. Polluted rivers have monomethylgermanium (MMGe) and dimethylgermanium (DMGe) concentrations 3–100 times higher than those of pristine rivers, which suggests an anthropogenic source of methylgermanium as a result of the synergistic effects of sewage treatment and coal-ash derived inorganic germanium contamination. A new high-precision profile of MMGe and DMGe in the Sargasso Sea shows conservative behavior with no vertical gradients. However, marine anoxic basins have both inorganic germanium enrichment and methylgermanium depletion, which suggests that of marine anaerobic processes are responsible for demethylating marine organogermanium. These results all suggest that methylgermanium is produced on the continents, is unreactive in the open ocean, and is destroyed in marine anoxic environments. The residence time of organogermanium in the sea, based on a continental source (pristine rivers), is at least 1 Ma, consistent with its unreactive nature, its observed distribution in the ocean, and rates of destruction in anoxic basins.     

Birds, seals and the suspension culture of mussels in Bantry Bay, a non-seaduck area in Southwest Ireland

Concerns about the environmental impacts of mariculture have grown in recent years in response to the rapid expansion of the industry. The blue mussel (Mytilus edulis) is the main product of shellfish mariculture in the Northeast Atlantic and Baltic Sea, with approximately one third of the harvest cultured using suspended longlines within sheltered marine areas. The main aim of this study was to examine the interactions, and assess the impacts (if any) of mussel suspension culture on the seabird and seal community, employing a simultaneous study of culture and control sites. The study spanned a 20-month period (from November 2001 to August 2003) and encompassed six sites in Bantry Bay (Southwest Ireland).There was no significant difference in species richness between mussel and control sites. Similarly, species diversity did not significantly differ between the mussel and control sites although control sites were generally more diverse than mussel sites, the latter particularly dominated by large numbers of Laridae.Significantly higher numbers of Phalacrocoracidae, Laridae and Alcidae were recorded in mussel sites than in control sites. However, no significant difference was found between Gaviidae or common seal (Phoca vitulina) numbers in mussel and control sites. Seasonal patterns of abundance were similar in mussel and control sites, with peak numbers of most species groups occurring in spring.Mussel suspension culture does not appear to have an adverse effect on the abundance of seabirds or common seals in this area. The safe perching platforms provided by suspension culture floats, combined with a number of other factors, contribute to an increased abundance of a number of seabird species, particularly Laridae. The possible interactions between vertebrate predators and mussel suspension aquaculture are discussed and possible explanations for the increased seabird abundance observed in these areas are offered.     

Single-crystal X-ray diffraction study of synthetic sodium–hydronium jarosite

Na–H₃O jarosite was synthesized hydrothermally at 413 K for 8 days and investigated using single-crystal X-ray diffraction (XRD) and electron microprobe analysis (EMPA). The chemical composition of the studied crystal is [Na_0.57(3) (H₃O)_0.36 (H₂O)_0.07]^A Fe_2.93(3) (SO₄)₂ (OH)_5.70 (H₂O)_0.30, and Fe deficiency was confirmed by both EMPA and XRD analysis. The single-crystal XRD data were collected at 298 and 102 K, and crystal structures were refined in space group \( R\overline{3}m\). The room-temperature data match structural trends of the jarosite group, which vary linearly with the c axis. The low-temperature structure at 102 K shows an anisotropic decrease in the unit cell parameters, with c and a decreasing by 0.45 and 0.03 %, respectively. Structural changes are mainly confined to the A site environment. Only minor changes occur in FeO₆ and SO₄ polyhedra. The structure responds upon cooling by increasing bond length distortion and by decreasing quadratic elongation of the large AO₁₂ polyhedra. The structural parameters at low temperature follow very similar patterns to structural changes that correspond to compositional variation in the jarosite group, which is characterised by the flexibility of AO₁₂ polyhedra and rigidity of Fe(OH)₄O₂–SO₄ layers. The most flexible areas in the jarosite structure are localized at AO₁₂ edges that are not shared with neighbouring FeO₆ octahedra. Importantly, for the application of XRD in planetary settings, the temperature-related changes in jarosite can mimic compositional change.     

“Of outstanding universal value”: The challenge of scale in applying the World Heritage Convention at national parks in the US

This paper explores the operation of the international World Heritage Convention in the national context of the United States. Although an early advocate of the national park idea and among the earliest proponents of the Convention, the US has shown increasing ambivalence towards the World Heritage Program since the mid-1990s. Through in-depth interviews with expert informants and a questionnaire survey of 406 visitors at four US World Heritage Sites, this study considers whether combining national and international conservation designations provides valuable reinforcement of conservation goals, or leads to unnecessary overlap and even challenges to sovereignty. The majority of my expert informants were supportive of the Convention, related to philosophical and practical benefits that they believed to be associated with the World Heritage label, although most identified few tangible influences of the World Heritage Program itself. Several noted hostility to the Program from a nationalist fringe, which fears international involvement in land use decisions. Such concerns were reflected in questionnaire responses, which revealed some distrust of the Convention and misunderstandings of its operation. I conclude that the scalar mismatch of implementing an international convention at the national scale inevitably involves challenges, but that country-specific factors are important in explaining why the Convention has been particularly controversial in the US. Education is integral to addressing these challenges, as well as reengagement with the Program by both the National Park Service and the federal administration. Intangible values associated with World Heritage mean that the Convention still enjoys considerable support in the US, providing a solid foundation for such a reengagement.