Physical and chemical processes promoting dominance of the toxic cyanobacterium Cylindrospermopsis raciborskii

The freshwater cyanobacterium, Cylindrospermopsis raciborskii (Wo?oszyńska) Seenayya and Subba Raju is a common species in lakes and reservoirs globally. In some areas of the world it can produce cyto- and hepatotoxins (cylindrospermopsins, saxitoxins), making blooms of this species a serious health concern for humans. In the last 10-15 years, there has been a considerable body of research conducted on the ecology, physiology and toxin production of this species and this paper reviews these studies with a focus on the cylindrospermopsin (CYN)-producing strains. C. raciborskii has low light requirements, close to neutral buoyancy, and a wide temperature tolerance, giving it the capacity to grow in many lentic waterbodies. It also has a flexible strategy with respect to nitrogen (N) utilisation; being able to switch between utilising fixed and atmospheric N as sources of N fluctuate. Additionally this species has a high phosphate (DIP) affinity and storage capacity. Like many cyanobacteria, it also has the capacity to use dissolved organic phosphorus (DOP). Changes in nutrient concentrations, light levels and temperature have also been found to affect production of the toxin CYN by this species. However, optimal toxin production does not necessarily occur when growth rates are optimal. Additionally, different strains of C. raciborskii vary in their cell quota of CYN, making it difficult to predict toxin concentrations, based on C. raciborskii cell densities. In summary, the ecological flexibility of this organism means that controlling blooms of C. raciborskii is a difficult undertaking. However, improved understanding of factors promoting the species and toxin production by genetically capable strains will lead to improved predictive models of blooms.     

Deglaciation of the western margin of the Barents Sea Ice Sheet — A swath bathymetric and sub-bottom seismic study from the Kveithola Trough

Kveithola Trough, an E–W trending glacial trough in the NW Barents Sea, was surveyed for the first time during the EGLACOM cruise of R/V OGS-Explora in summer 2008. Swath bathymetry shows that the seafloor is characterized by E–W trending mega-scale glacial lineations (MSGL) that record a fast flowing ice stream draining the Svalbard/Barents Sea Ice Sheet (SBIS) during the Last Glacial Maximum (LGM). MSGL are overprinted by transverse sediment ridges about 15 km apart which give rise to a staircase axial profile of the trough. Such transverse ridges are interpreted to be grounding-zone wedges (GZWs) formed by deposition of subglacial till during episodic ice stream retreat. Sub-bottom (CHIRP) and multi-channel reflection seismic data show that the present-day morphology is largely inherited from the palaeo-seafloor topography at the time of deposition of the transverse ridges, overlain by a draping glaciomarine unit which in places is over 15 m thick. Our data allow the reconstruction of depositional processes which accompanied deglaciation of the Spitsbergen Bank area. The sedimentary drape deposited on top of the GZWs is suggested to have accumulated at a very high rate, (on average in the order of 1–1.5 m ka^?1) and therefore may potentially preserve a high-resolution palaeoclimatic record of deglaciation and post-glacial conditions in this sector of the Barents Sea.     

Hydrogeological study of the intensely exploited aquifer of the Santa Croce leather-producing district, Tuscany (central Italy)

A hydrogeological study was undertaken to define the groundwater circulation in the Santa Croce area (Tuscany, central Italy) where the existing multilayered aquifer has long been intensively exploited. Investigations carried out on about 150 wells revealed the existence of a deep piezometric depression (to 20?m below sea level) which drains groundwater from the entire surrounding area. Samples from about 70 water points, collected twice in 2007, were analysed for major elements and stable isotope composition. Three major groups of waters, which mix in the study area, have been distinguished: (1) waters of the Ca?CMg?CHCO₃ type mainly flowing along the Arno River Plain; (2) waters of the Na?CK?CCl/Ca?CMg?CHCO₃?CSO_4, type with SO₄ content up to 275?mg/L, inflowing from the Pisane Hills; (3) relatively high-salinity waters mainly of the Na?CHCO₃ type which, with Cl concentrations up to 750?mg/L, likely arise from a normal fault located at the foot of the northern hills. The characteristics of the different components are greatly affected by significant modifying processes such as cation exchange and sulfate reduction. The achieved conceptual model suggests the southern hills as the main recharging area of the aquifer system from which water circulation, characterized by pathways of different length and depth, develops.     

Geodynamic evolution of ophiolites from Albania and Greece (Dinaric-Hellenic belt): one, two, or more oceanic basins?

All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) sub-ophiolite mélange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic back-arc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.     

Ditching and Ditch-Plugging in New England Salt Marshes: Effects on Hydrology, Elevation, and Soil Characteristics

Anthropogenic activities in New England salt marshes have altered hydrologic flows in various ways, but unintended consequences from some types of habitat modifications have received little attention. Specifically, ditches have existed on salt marshes for decades, but the effects of these hydrologic alterations are only poorly understood. Ditch-plugging is a more recent methodology used for salt marsh habitat enhancement and mosquito control, but the long-term effects from this management practice are also unclear. The interactions involving marsh surface elevation, soil characteristics, and hydrologic regimes result in feedbacks that regulate the salt marsh self-maintenance process, and these interactions vary with hydrologic modification. Using natural tidal creeks and pools as controls, we examined the effects of ditching and plugging, respectively, on hydrology, surface elevations, and soils. Results showed the most apparent effects of altered hydrology from ditching are prolonged pore-water retention in the rooting zone and significantly lower soil bulk density and mineral content when compared with natural creek habitat. From a management perspective, the important question is whether the combined alterations to physical and biological processes will hinder the marsh’s ability to keep pace with increasing rates of sea level rise, especially in more heavily ditched marshes. In contrast, ditch-plugging results in the decoupling of feedback processes that promote salt marsh self-maintenance and in doing so, threatens marsh stability and resilience to climate change. High surface water levels, permanently saturated soils, marsh subsidence, and significantly lower bulk density, carbon storage, soil strength, and redox levels associated with hydrologic alterations from ditch-plugging all support this conclusion.     

The Taraklı Flysch in the Boyali area (Sakarya Terrane,northern Turkey): Implications for the tectonic history of the IntraPontide suture zone

In the Boyal? area, northern Turkey, the tectonic units of the ?stanbul–Zonguldak Terrane and the IntraPontide suture zone are thrust over the deposits at the top of the Sakarya Terrane, known as Tarakl? Flysch. It consists of Early Maastrichtian–Middle Paleocene turbidite and mass-gravity deposits, whose source mainly corresponds to the ?stanbul–Zonguldak Terrane, and, with a lesser extent, to the IntraPontide suture zone. These deposits were sedimented in a foredeep basin developed during the convergence between Sakarya and Eurasian continental microplates. In the Late Paleocene–Early Eocene time span, the Tarakl? Flysch was deformed (D1 phase) during the closure of the foredeep basin. In the Miocene time, the strike-slip tectonics (D2 phase) related to the North-Anatolian fault produced further deformations of the Tarakl? Flysch.     

Laboratory Investigation on High Values of Restitution Coefficients

Restitution coefficients are used to quantify the energy dissipation upon impact when predicting rock fall events. These coefficients can be determined in situ or in the laboratory. In any case, the usual values for the normal restitution coefficient k _n are below unity. Values greater than one are quite rare, seen as unusual and barely explained. Previous experimental research conducted in Australia has shown consistent and systematic values of the normal restitution coefficient greater than one. This was tentatively explained by a combination of parameters such as low impacting angle, rotational energy and block angularity. The study presented in this paper aims at (1) identifying the critical parameters conducting to high k _n values and (2) at explaining the associated motion mechanisms. The objective was reached with values of k _n up to almost 2. In addition, the study has confirmed the significance of low impacting angle, rotational energy and block shape in this context.     

Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

Matrix glass and melt inclusions in phenocrysts from pantellerite lavas of the Boseti volcanic complex, Ethiopia, record extreme fractionation of peralkaline silicic magma, with Al₂O₃ contents as low as 2.3?wt.%, FeO* contents up to 17?wt.% and SiO₂ contents ~65?wt.%. The new data, and published data for natural and experimental glasses, suggest that the effective minimum composition for peralkaline silicic magmas has ~5?wt.% Al₂O₃, 13?wt.% FeO* and 66?±?2?wt.% SiO₂. The dominant fractionating assemblage is alkali feldspar?+?fayalite?+?hedenbergite?+?oxides?±?quartz. Feldspar – melt relationships indicate that the feldspar is close to the minimum on the albite-orthoclase solid solution loop through the entire crystallization history. There is petrographic, mineralogical and geochemical evidence that magma mixing may have been a common process in the Boseti rhyolites.     

Salt Marsh Fucoid Algae: Overlooked Ecosystem Engineers of North Temperate Salt Marshes

Salt marsh fucoid algae are a conspicuous component of north temperate marshes, yet comparatively little research has been conducted to examine their ecological effects. We examined the influence of salt marsh fucoids on physical conditions and the biotic community in a manipulative experiment conducted in a southern Maine back-barrier salt marsh. The biomass of salt marsh fucoids was higher than that of aboveground Spartina alterniflora in the zone where we conducted the experiment. Average daytime temperatures at the sediment surface were significantly reduced by the presence of salt marsh fucoids. Density and biomass of standing-dead S. alterniflora was significantly higher when salt marsh fucoids were removed. In contrast, the abundance of various species of epifauna and infauna were significantly enhanced by the presence of salt marsh fucoids. A regional survey indicated that results from the study site may be conservative because the biomass of salt marsh fucoids was lowest among other back-barrier marshes. Salt marsh fucoids are little studied ecosystem engineers whose presence affects the microclimate and biotic community, especially the animals that constitute the basal components of the salt marsh trophic relay.