Short-term biogeochemical influence of a diatom bloom on the nutrient and trace metal concentrations in South San Francisco Bay microcosm experiments

Two laboratory microcosm experiments were conducted to mimic an annual spring diatom bloom in South San Francisco Bay by isolating the phytoplankton community from the benthic grazing pressure to induce a phytoplankton bloom. The purpose of these experiments was to isolate the impact of a spring diatom bloom on the nutrient and trace metal geochemical cycling. Microcosms were created in 2.5 L incubation bottles and subjected to one of 4 treatments (control, copper [Cu] addition, manganese [Mn] addition, and both Cu and Mn addition) to investigate the toxicity of Cu on the resident plankton and the potential antagonistic effects of Mn on reducing Cu toxicity. Dissolved macronutrient (nitrate + nitrite, phosphate, and silicate), and dissolved and particulate trace metal (Cu, Ni, Mn) concentrations were monitored in the grow-out incubations on a daily basis. Chlorophylla concentrations were also monitored over the course of the experiment and used to calculate diatom-specific growth rates. In the experiments containing ambient South San Francisco Bay surface waters, average specific growth rates were on the order of 1.1 d^?1. The induced diatom blooms resulted in significant removal of macronutrients from the microcosms over the course of the experiments. Our research supports previous suggestions that dissolved Ni and Cu concentrations in South San Francisco Bay have a very low biological availability as a result of organic chelation. Ni(EDTA)^2? has been found to be the dominant dissolved Ni species by other researchers and Cu speciation analyses from this study and others indicate that > 99% of the dissolved Cu in South San Francisco Bay is strongly chelated as CuL₁. The free cupric ion concentration was on the order of 10^?12 M. Marked removal of dissolved Mn was observed in the control treatments, well exceeding expected dissolved Mn removal by diatom uptake. Additions of 375 nM Cu resulted in the complete titration of the chelating ligand (L₁) concentrations. The elevated [Cu²⁺] (≈10^?8MM) appeared to have a toxic effect on the diatom community observed in the significant decreases in their specific growth rates (μ=0.4 d^?1). The suppression of dissolved Mn removal from solution was also observed in treatments spiked with high levels of dissolved Cu, providing support that Mn precipitation was due to biologically mediated oxidation not phytoplankton assimilation. The observed geochemical behavior in the concurrent Cu and Mn addition treatments provide evidence in support of Mn alleviation of Cu toxicity. The biological role in the ambient short-term biogeochemical cycling of Cu and Ni in South San Francisco Bay appears to be minimal due to the inert character of the organic ligand-metal complexes. A significant portion of the annual macronutrient and Mn cycling occurs as a result of spring diatom blooms in South San Francisco Bay.     

Understanding ship-grounding impacts on a coral reef: potential effects of anti-foulant paint contamination on coral recruitment

The 184 m cargo ship Bunga Teratai Satu collided with Sudbury Reef, part of the Great Barrier Reef and remained grounded for 12 days. The ship was re-floated only 3 days prior to the November 2000 mass coral spawning. No cargo or fuel was lost but the impact resulted in significant contamination of the reef with anti-foulant paint containing tributyltin (TBT), copper (Cu) and zinc (Zn). Larvae of the reef-building scleractinian coral Acropora microphthalma were exposed to various concentrations of sediment collected from the grounding site in replicated laboratory experiments. Two experiments were performed, both of which used varying ratios of contaminated and control site sediment in seawater as treatments. In the first experiment, the influence of contaminated sediment on larval competency was examined using metamorphosis bioassays. In the second, the effect of contaminated sediment upon larval recruitment on pre-conditioned terracotta tiles was assessed. In both experiments, sediment containing 8.0 mg kg(-1) TBT, 72 mg kg(-1) Cu and 92 mg kg(-1) Zn significantly inhibited larval settlement and metamorphosis. At this level of contamination larvae survived but contracted to a spherical shape and swimming and searching behaviour ceased. At higher contamination levels, 100% mortality was recorded. These results indicate that the contamination of sediment by anti-fouling paint at Sudbury Reef has the potential to significantly reduce coral recruitment in the immediate vicinity of the site and that this contamination may threaten the recovery of the resident coral community unless the paint is removed.     

An integrated model of clastic injectites and basin floor lobe complexes: implications for stratigraphic trap plays

Injectites sourced from base‐of‐slope and basin‐floor parent sandbodies are rarely reported in comparison to submarine slope channel systems. This study utilizes the well‐constrained palaeogeographic and stratigraphic context of three outcrop examples exposed in the Karoo Basin, South Africa, to examine the relationship between abrupt stratigraphic pinchouts in basin‐floor lobe complexes, and the presence, controls, and character of injectite architecture. Injectites in this palaeogeographic setting occur where there is: (i) sealing mudstone both above and below the parent sand to create initial overpressure; (ii) an abrupt pinchout of a basin‐floor lobe complex through steep confinement to promote compaction drive; (iii) clean, proximal sand beds aiding fluidization; and (iv) a sharp contact between parent sand and host lithology generating a source point for hydraulic fracture and resultant injection of sand. In all outcrop cases, dykes are orientated perpendicular to palaeoslope, and the injected sand propagated laterally beneath the parent sand, paralleling the base to extend beyond its pinchout. Understanding the mechanisms that determine and drive injection is important in improving the prediction of the location and character of clastic injectites in the subsurface. Here, we highlight the close association of basin‐floor stratigraphic traps and sub‐seismic clastic injectites, and present a model to explain the presence and morphology of injectites in these locations.     

The Impact of Massive Stars on their Surrounding Interstellar Medium

In this paper, I present a brief overview of the observational evidence for the interaction between the winds of hot stars and their surrounding interstellar medium (ISM). As the star evolves, it will impinge on the gas in different ways depending on the nature of its wind and on the physical state of the interstellar gas. The three main evolutionary phases of massive stars, the main sequence O phase, the intermediate red supergiant or luminous blue variable phase and finally the Wolf-Rayet phase are discussed. The study of the ISM in the vicinity of hot stars is shown to be a powerful tool to study the history of the gas and gain more insight into the evolution of the star. This revised version was published online in July 2006 with corrections to the Cover Date.     

Beta diversity of tropical marine benthic assemblages in the Spermonde Archipelago, Indonesia

In order to preserve diversity it is essential to understand how assemblages change across space. Despite this fact, we still know very little about how marine diversity is spatially distributed, especially among lesser‐studied invertebrate taxa. In the present study beta‐diversity patterns of sea urchins, sponges, mushroom corals and larger foraminifera were assessed in the Spermonde Archipelago (Indonesia). Using ordinations we showed that the inshore zone (<5 km offshore), midshore zone (5 < x < 30 km offshore) and distance offshore zone (>30 km offshore) all contained distinct assemblages of sponges and corals, while only foraminifera assemblages from the inshore (<5 km offshore) zone were distinct. There was a significant spatial pattern of community similarity for all taxa surveyed, but this pattern proved to be wholly related to environmental variables for sponges and foraminifera, and primarily for mushroom corals and sea urchins. The lack of a pure spatial component suggests that these taxa may not be dispersal limited within the spatial scales of this study (c. 1600 km²). The analyses of the corals and foraminifera were additionally tested at two spatial scales of sampling. Both taxa were primarily associated with local‐scale environmental variables at the local scale and larger‐scale variables at the larger scale. Mean inter‐plot similarity was also higher and variation lower at the larger scale. The results suggest that substantial variation in similarity can be predicted using simple locally assessed environmental variables combined with remotely sensed parameters.     

Effects of artificial openings of intermittently opening estuaries on macroinvertebrate assemblages of the entrance barrier

Intermittently opening estuaries are artificially opened to manage flood risk, water quality, recreational amenity, and fisheries; however, the ecological impacts of this management technique are incompletely understood. During 2001 and 2004, this study assessed the impacts of artificial openings on the macroinvertebrates of entrance barriers of intermittently opening estuaries in New South Wales (Australia). In 2001 macroinvertebrates were sampled once before artificial opening and 9 and 25 d after re-formation of the entrance barrier. A multiple before–after-control-impact analysis found that, although entrance barriers were destroyed by the artificial openings and then re-formed naturally by wave action, significant interactions for taxonomic richness, density of the amphipod Paracalliope australis (Gammaridae) and density of the gastropod mollusc Aschoris victoriae (Hydrobiidae) meant that the effects of this disturbance could not be distinguished from the natural variations that occurred in unopened estuaries. Multivariate analyses found that assemblages at both opened and unopened estuaries changed from before to after the openings, and the magnitude of the dissimilarity between times varied between estuaries. In 2004, macroinvertebrates were sampled on three randomly selected days within each of three periods (before, 3 d and 42 d after) at one opened and three unopened estuaries. Asymmetrical analysis of this modified before–after-control-impact study found that the change in taxonomic richness at the opened estuary from before to after opening did not differ from temporal changes that occurred in unopened estuaries. Short-term variation (i.e. between days) in total density of macroinvertebrates and density of P. australis in the re-formed entrance barrier of the opened estuary also did not differ from the variation in the control estuaries. Additionally, assemblage structure was not significantly changed by the opening and assemblages at two control estuaries were also unchanged over the same time. Individual taxa and assemblages of macroinvertebrates in entrance barriers of these intermittently open estuarine systems appear to be resilient to the habitat disturbance caused by artificial openings.     

Erosion and Flooding—Threats to Coastal Infrastructure in the Arctic: A Case Study from Herschel Island,Yukon Territory,Canada

Arctic coastal infrastructure and cultural and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this paper are to provide such a tool by assessing potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site. This study focused on Simpson Point and the adjacent coastal sections because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost path analysis based on a high-resolution light detection and ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from ?5.5 to 2.7 m·a^?1 (mean ?0.6 m·a^?1). Mean coastal retreat decreased from ?0.6 m·a^?1 to ?0.5 m·a^?1, for 1952–1970 and 1970–2000, respectively, and increased to ?1.3 m·a^?1 in the period 2000–2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion. This study demonstrates that transgressive forcing may provide ample sediment for the expansion of depositional landforms, while growing more susceptible to overwash and flooding.     

Chlorine and fluorine in tholeiitic and alkaline lavas of Etna (Sicily)

Chlorine and fluorine were measured from whole-rock samples from tholeiites (150,000 years old) to present-day hawaiites. The overall range of F content is from 240 to 985 ppm, with a slight decrease of F/Th and F/Cl ratios, from tholeiites to hawaiites. Chlorine is positively correlated with Th (Cl/Th=100) as well as K₂O and P₂O₅, as the differentiation progresses, and, increases from 220 ppm in tholeiites to 2410 ppm in mugearites. Data obtained from present-day hawaiites indicate that Cl lost by degassing during eruption is limited. However, Cl contents of some whole-rock samples are inconsistent with previous results published for melt inclusions of phenocrysts from the same historic hawaiite samples and suggesting outgassing of Cl prior to the eruption. This implies that apparent correlation between Cl and Th can be considered as the result of superimposition of several petrogenetic processes. Results point out the richness of Etnean tholeiites in chlorine compared to M.A.R. basalts. Such a character could have been inherited from the mantle source or during the mantle source melting.