Sulphur uptake by salt grasses,mangroves, and seagrasses in anaerobic sediments

Stable sulfur isotope analyses show that rooted estuarine plants growing in anoxic sediments incorporate substantial amounts of ³⁴S-depleted sulfides, or oxidation products thereof. In roots, this incorporation predominates over sulfate uptake from interstitial porewater. Either the plants incorporate normally toxic sulfides, or they are creating and using a specialized nutrient pool of oxidized sulfides at the root-sediment interface.     

Solubility of rhodochrosite (MnCO3) in water and seawater

The solubility product of rhodochrosite (MnCO₃) was measured in seawater, deionized water and dilute NaCl solutions. The solubility product extrapolated to infinite dilution at 25.0 C was (2.60 ± 0.07)× 10^?11. The stoichiometric solubility product measured in seawater of 34.27%. salinity was (3.24 ± 0.23) × 10^?9 at 25.0 C and (2.28 ± 0.24) × 10^?9 at 3.3 C. The stoichiometric solubility product is in good agreement with the value calculated from an ion association model. The enthalpy of the reaction is in fair agreement with the estimated value.     

Geochemistry and Rb-sr geochronology of associated proterozoic peralkaline and subalkaline anorogenic granites from Labrador

Anorogenic granites of middle to late Proterozoic age in the Davis Inlet — Flowers Bay area of Labrador are subdivided on the basis of petrology and geochemistry into three coeval suites. Two of these are high-temperature anhydrous hypersolvus granites: a peralkaline aegirine-sodic-calcic to sodic amphibole-bearing suite and a non-alkaline fayalite-pyroxene-bearing suite. The third is a group of non-alkaline subsolvus hornblende-biotite-bearing granites. Associated with the hypersolvus peralkaline suite is a group of genetically related syenites and quartz syenites. The granites cut ca. 3,000 Ma old Archaean gneisses as well as Elsonian layered basic intrusions of the Nain Complex. One of these, a crudely layered mass which ranges in composition from gabbro to diorite and monzonite, appears to be related to the syenites. The peralkaline granites and some of the syenites are extremely enriched in the high field-strength elements such as Y, Zr, Nd, as well as Rb, Ga and Zn, and have low abundances of Ba, Sr and most of the transition elements. In contrast, the non-alkaline hypersolvus and subsolvus granites do not show the same degree of enrichment. Concentration of the highly charged cations in the peralkaline suite is believed to be the result of halogen-rich fluid activity during fractionation of the magma. The sodic evolution trend in the peralkaline suite is reflected mineralogically by the development of aegirine and aegirine-hedenbergite solid solutions, and by a spectacular amphibole compositional range from katophorite through winchite, richterite, riebeckite to arfvedsonite and ferro eckermannite. Accessory phases which are ubiquitous in these rocks include aenigmatite, astrophyllite, fluorite, monazite and zircon. The non-alkaline hypersolvus granites typically contain iron-rich phases such as fayalite, eulite, ferrosilite-hedenbergite, and annite rich biotite. In the subsolvus granites, amphiboles range in composition from edenite through common hornblende to actinolite and also coexist with annite-rich biotite.Whole-rock and mineral isotopic data for the different suites yield isochrons that are within error of ca. 1,260 Ma, but they have variable initial ⁸⁷Sr/⁸⁶Sr ratios. The initial ⁸⁷Sr/⁸⁶Sr of the syenites and peralkaline granites (0.7076±11) is significantly lower than the initial ⁸⁷Sr/⁸⁶Sr of the subsolvus granites (0.7138±22). These isotopic data provide further confirmation of the importance of a late Elsonian alkaline event in Labrador which can be correlated with Gardar igneous activity in south Greenland. The petrogenesis of the peralkaline suite is interpreted to reflect the effects of fractionation of anhydrous phases from mantle derived basic magma which was contaminated during ascent by radiogenic partial melts of crustal derivation. The non-alkaline hypersolvus and subsolvus granites are interpreted as crustal melts which formed under conditions of variable in response to the same thermal event, and which subsequently experienced feldspar fractionation during crystallization.     

X-Ray Fluorescence Determination of Trace Elements in 6 B.C.S. and 5 P.R.E. Reference Materials

The concentrations of 20 trace elements in 6 British Chemical Standards (BCS) reference materials and 5 European Federation of Refractories Producers (PRE) reference materials have been determined by X-ray fluorescence spectrometry.     

Surface study of HF- and HFH2SO4-treated feldspar using Auger electron spectroscopy

Auger electron spectroscopy has been used to study K-feldspar that has been reacted with both aqueous 10% HF and a 50% mixture of a 10% HF/0.1 N H₂SO₄ solution. In the feldspar/HF system, the resulting feldspar surface was shown to have been fluorinated; depth profiling, using argon ion sputtering, showed the fluorination to have occurred substantially into the mineral bulk. In the feldspar/ $\text{HF}\text{H}{}_2\text{SO}{}_4$ system, the resulting surface contained both fluorine and sulfur. The fluorination had again penetrated into the bulk, but the sulfur could be removed with mild argon ion sputtering. The $\text{Al}\text{F}$ signal ratio was much lower on the feldspar surface treated with the 10% HF/0.1 N H₂SO₄ solution than the feldspar surface treated with the weaker 10% HF acid solution.     

Polycyclic aromatic hydrocarbon (PAH)-phase associations in Washington coastal sediment

Polycyclic aromatic (PAH) and aliphatic hydrocarbon compositions, organic carbon, nitrogen and lignin contents were determined in whole, unfractionated sediment from the Washington continental shelf and in discrete sediment fractions separated by particle size and density. At least 20 to 25% of perylene and PAH derived from pyrolytic processes and 50% of the retene measured in whole sediment are contained within organic C- and lignin-rich panicles of density ≤ 1.9 g/cc. These particles, which include primarily vascular plant remains and bits of charcoal, comprise less than 1% of the total sediment weight. In contrast, a series of methylated phenanthrene homologs, possibly of fossil origin, are concentrated in some component of the more dense, lithic matrix of the sediment. Equilibrium models of PAH sorption/desorption from aqueous phase onto small particles of high surface area do not appear applicable to the behavior of the major PAH types identified in this aquatic environment.     

Understanding confluence dynamics in the alluvial Ganga–Ramganga valley, India: An integrated approach using geomorphology and hydrology

Confluence dynamics in the Ganga–Ramganga valley in the western Ganga plains of India has been studied through systematic mapping of channel configuration using multi-date remote sensing images and topographic sheets for a period spanning nearly 100 years (1911–2000). The study has been supplemented with a detailed analysis of the channel morphology, hydrology and sediment transport characteristics of the different rivers. Our study indicates that new confluences have been created during this period and that the confluence points have moved both upstream and downstream on a historical time scale. Apart from major avulsions, other processes that have controlled the confluence movements include river capture, cut-offs and aggradation in the confluence area. River capture occurs through lateral bank erosion and migration, encroachment by the master stream and beheading of smaller rivers resulting in upstream movement of the confluence point. Another process which influences the upstream migration of the confluence is an increase in sinuosity of one of the channels near the confluence and then a cut-off. Aggradation in the confluence area and local avulsions of the primary channel in a multi-channel system seem to be the major process controlling the downstream movement of the confluence point. Analysis of channel morphology, hydrology and sediment budget for the study period supports our interpretations.     

Certainty, uncertainty, and the spatiality of disease: a West Nile Virus example

The problem is not uncertainty—proposed here as an inevitable condition—but the chimera of certainty asserted by most contemporary researchers. Problems of data definition, collection, and their use are reviewed in terms of spatial epidemiology and health data with examples drawn from several areas of contemporary health research. The argument is that preconceptions limit data modeled in a manner assuming its completeness. The result, as the West Nile Virus example seeks to demonstrate, may obscure other patterns and limit avenues of research.     

System-wide submerged aquatic vegetation model for Chesapeake Bay

A predictive model of submerged aquatic vegetation (SAV) biomass is coupled to a eutrophication model of Chesapeake Bay. Domain of the model includes the mainstem of the bay as well as tidal portions of major embayments and tributaries. Three SAV communities are modeled: ZOSTERA, RUPPIA, and FRESHWATER. The model successfully computes the spatial distribution and abundance of SAV for the period 1985–1994. Spatial distribution is primarily determined by computed light attenuation. Sensivitity analysis to reductions in nutrient and solids loads indicates nutrient controls will enhance abundance primarily in areas that presently support SAV. Restoration of SAV to areas in which it does not presently exist requires solids controls, alone or in combination with nutrient controls. For regions in which SAV populations exist at the refuge level or greater, improvements in SAV abundance are expected within 2 to 10 years of load reductions. For regions in which no refuge population exists, recovery time is unpredictable and will depend on propagule supply.     

Response of estuarine marsh vegetation to interannual variations in precipitation

The response of deltaic emergent marsh vegetation to increases in precipitation was examined over a 14-mo period at three sites in the lower Nueces Estuary in south Texas. At all three sites, significant changes in plant biomass, percent cover, and allocation of aboveground and belowground tissues were associated with more than double the rainfall in late winter and early spring 1992 compared to the previous year and the 50-yr average for this region. Water column salinities, which ranged from 10‰ to 35‰ at all three sites in 1991, remained below 10‰ through August 1992. Significant changes in marsh vegetative structure included decreases in bare space, increases in the percent cover and aboveground biomass of a relatively less salt tolerant halophytes (Borrichia frutescens), and significant increases in root:shoot ratios inB. frutescens, Batis maritima andSuaeda linearis (inSalicornia virginica root:shoot ratios decreased significantly). Higher precipitation generally led to an overall increase in the biomass of most marsh perennials, but these increases were not statistically significant. For one species,Lycium carolinianum, additional rainfall extended its growing season through August 1992, 2 mo longer than in the previous year. The expansion (+58%) ofB. frutescens at one site was also coincident with the significant loss ofB. maritima, whose cover decreased nearly 20%. In an ecological context, these responses suggest that precipitation events in arid environments may be considered a major physical disturbance that can result in large changes in the composition and relative abundance of emergent vascular plants over a relatively short period. The long-term significance of these changes is unknown and demonstrates the value of ecological studies that are conducted over several years for a more complete understanding of the dynamic processes that regulate marsh productivity.