Can the nitrogen and carbon stable isotopes of the pygmy mussel,Xenostrobus securis, indicate catchment disturbance for estuaries in northern New South Wales, Australia?

The nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of the pygmy mussel,Xenostrobus securis, were determined for three estuaries with varying levels of catchment disturbance in northern New South Wales, Australia. The lower Manning River catchment supported the highest human population densities with 3% residential development and some livestock agriculture (41%); the Wallamba River catchment was mostly livestock agriculture (56%) while the Wallingat River catchment was mostly vegetated (79%). Mussels, estuarine particulate organic matter (POM), and livestock and human-derived waste were collected in two stages during the austral summers of 2001–2002 and 2002–2003 for dual carbon-nitrogen stable isotope analysis. The disturbed Manning and Wallamba River catchment mussels were enriched in¹⁵N by an average of 3.2‰ and 1.5‰, respectively, compared to the vegetated Wallingat River mussels. Mussel δ¹³C values ranged from −24.8‰ to −30.3‰ and showed an estuarine gradient becoming enriched with distance downstream within estuaries, but were unable to distinguish patterns in catchment disturbance between estuaries. The δ¹⁵N and δ¹³C values of POM showed a similar pattern to mussels, indicating a direct link between them within each estuary. A multiple regression model of mussel δ¹⁵N using the fractions of land used for livestock agriculture and residential development within 5 km zones from river networks to a distance equivalent to a tidal ellipse from sites explained 67% of the variation in mussel δ¹⁵N with 95% of the differences lying within 1.6‰ of observed values. Increasing fractions of land used for livestock agriculture depleted mussel δ¹⁵N values estimated by the regression equation, indicating the use of cow manure as a nutrient source with a value of 2.0‰. Increasing fractions of land used for residential development enriched estimated mussel δ¹⁵N, indicating the use of human-derived waste with a value of 20.8‰. Pygmy mussels are a useful long-term bio-indicator for the effects of anthropogenic catchment disturbance and nutrient enrichment in estuaries.     

Identifying characteristics of charge transfer transitions in minerals

Criteria used to identify Fe²⁺-Fe³⁺ and Fe²⁺-Ti⁴⁺ intervalence charge transfer absorption bands in electronic spectra are reviewed and compared to the characteristics of unperturbed Fe²⁺ crystal field bands and those that are intensified by interaction with Fe³⁺. Band energy is the least definitive diagnostic criterion. Changes in band intensity with temperature are also of limited value. Large widths are the most reliable characteristic of charge transfer bands. New optical absorption spectra are presented for euclase, as well as 80 K spectra of rockbridgeite, babingtonite and lazulite. Comparison of optical spectra to magnetic susceptibility measurements for rockbridgeite and babingtonite provides support for recent theories regarding the effect of magnetic coupling on the variation of charge transfer intensity with temperature.     

Isotopic evidence for the magmatic and tectonic histories of the Carolina terrane: implications for stratigraphy and terrane affiliation

Establishing the age and crustal nature of exotic terranes and their underlying basements helps to determine their paleogeographic origin and tectonic histories. We present U–Pb ages of zircons and Sm–Nd whole rock isotopic data for volcanic and plutonic rocks of the Carolina terrane, one of several peri-Gondwanan terranes that were accreted to the margins of the circum-Atlantic continents during the Paleozoic. Volcanism in this subduction-related arc culminated in the eruption of the Morrow Mountain rhyolite, at ca. 540 Ma; thus, magmatism in the Carolina terrane ceased at the beginning of the Cambrian. The presence of inherited zircons and non-juvenile depleted mantle model ages of Carolina slate belt rocks favor a basement that is, at least in part, composed of evolved continental crust. Ages of inherited xenocrystic zircons cluster at ca. 1000, 2100 and 2500 Ma. These ages, in addition to volcanism at ca. 618–540 Ma, correlate best with well-known tectonic events in present-day northern South America. Specifically, the Orinoquian-Sunsas, the Trans-Amazonian and the Central Amazonian orogenic zones are likely candidates for potential basement correlatives to the Carolina terrane. Sm–Nd isotopic signatures vary significantly, but permit assimilation of Orinoquian age (1000 Ma) crust by magmas derived from the depleted mantle in a subduction (arc-related) setting. Our findings are also consistent with proposed correlations between the Carolina terrane and Avalonia which is likewise believed to have formed along the northern margin of present-day South America.     

The shape of Fraught – urban – rural – the nation-state: tensions and dynamics

I argue that the tension between cities and nation states go through the countryside, or rural areas, at least in the U.S. Further, cities are decidedly constrained in their abilities to effectuate many of the changes associated with them: addressing climate change, economic inequality and more. What is missing is the way in which rural alienation from economic prosperity plays out politically.     

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments

Background  

Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.     

Effects of storm-induced salinity changes on submersed aquatic vegetation in Kings Bay, Florida

Hurricanes and other major storms cause acute changes in salinity within Florida's streams and rivers. Winddriven tidal surges that increase salinities may have long-lasting effects on submersed aquatic vegetation (SAV) and the associated fauna. We investigated potential effects of salinity pulses on SAV in Kings Bay, Florida, by subjecting the three most common macrophytes,Vallisneria americana, Myriophyllum spicatum., andHydrilla verticillata, to simulated salinity pulses. In Kings Bay, we documented changes in salinity during three storms in September 2004 and measured biomass and percent cover before and after these storms. During experiments, macrophytes were exposed to salinities of 5‰, 15‰, or 25‰ for 1, 2, or 7 d, with a 28-d recovery period in freshwater. Relative to controls, plants subjected to salinities of 5‰ exhibited few significant decreases in growth and no increase in mortality. All three species exhibited decreased growth in salinities of 15‰ or 25‰.H. verticillata, exhibited 100% mortality at 15‰ and 25‰, irrespective of the duration of exposure.M. spicatum andV. american exhibited increased mortality after 7-d exposures to 15‰ or any exposure to 25‰ Maximum daily salinities in Kings Bay approached or exceeded 15‰ after each of the three storms, with pulses generally lasting less than 2 d. Total aboveground biomass and percent cover of vascular plants, were reduced following the storms.M. spicatum exhibited an 83% decrease in aboveground biomass and an 80% decrease in percent cover.H. verticillata exhibited a 47% and 15% decline in biomass and percent cover, respectively.V. americana, exhibited an 18% increase in aboveground biomass and a 37% increase in percent cover, which suggests greater tolerance of salinity pulses and release from competition with the invasiveH. verticillata andM. spicatum. Our results indicate that rapid, storm-induced pulses of high salinity can have important consequences for submersed aquatic vegetation, restoration efforts, and management of invasive species.     

Statistically downscaled projections of snow/rain partitioning for Alaska

Adaptation planning in Alaska, as in other snowy parts of the world, will require snow projections, yet snow is a challenging variable to measure, simulate and downscale. Here we describe the construction and evaluation of 771‐m‐resolution gridded historical and statistically downscaled projections of snow/rain partitioning for the state of Alaska at decadal temporal resolution. The method developed here uses observational data to describe the relationship between average monthly temperature and the fraction of wet days in that month receiving snow, the snow‐day fraction. Regionally and seasonally specific equations were developed to accommodate variability in synoptic scale climatology of rain and snow events. These equations were then applied to gridded decadal temperature data and projections. The gridded products provide a reasonable characterization of snow‐day fraction throughout the state. However, there are local deviations from the regional relationships, particularly in the topographically complex areas ringing the Gulf of Alaska and Cook Inlet. When applied to questions about changing precipitation regimes in northern, western and south‐eastern Alaska, these data demonstrate the potential for marked changes from snow‐dominated to mixed precipitation regimes and also exhibit a wide range of potential future conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantifying annual groundwater recharge and storage in the central Sierra Nevada using naturally occurring 35S

Identifying aquifer vulnerability to climate change is of vital importance in the Sierra Nevada and other snow‐dominated basins where groundwater systems are essential to water supply and ecosystem health. Quantifying the component of new (current year's) snowmelt in groundwater and surface water is useful in evaluating aquifer vulnerability because significant annual recharge may indicate that streamflow will respond rapidly to annual variability in precipitation, followed by more gradual decreases in recharge as recharge declines over decades. Hydrologic models and field‐based studies have indicated that young (<1 year) water is an important component of streamflow. The goal of this study was to utilize the short‐lived, naturally occurring cosmogenic isotope sulfur‐35 (³⁵S) to quantify new snowmelt contribution to groundwater and surface waters in Sagehen Creek Basin (SCB) and Martis Valley Groundwater Basin (MVGB) located within the Tertiary volcanics of the central Sierra Nevada, CA. Activities of ³⁵S were measured in dissolved sulfate (³⁵SO₄^2?) in SCB and MVGB snowpack, groundwater, springs, and streamflow. The percent of new snowmelt (PNS) in SCB streamflow ranged from 0.2 ± 6.6% during baseflow conditions to 14.0 ± 3.4% during high‐flow periods of snowmelt. Similar to SCB, the PNS in MVGB groundwater and streamflow was typically <30% with the largest fractions occurring in late spring or early summer following peak streamflow. The consistently low PNS suggests that a significant fraction of annual snowmelt in SCB and MVGB recharges groundwater, and groundwater contributions to streamflow in these systems have the potential to mitigate climate change impacts on runoff.     

The planet formation imager

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.