Assessment of recharge to groundwater systems in the arid southwestern part of Northern Territory, Australia, using chlorine-36

 The sustainability of community water supplies drawn from shallow aquifers in the arid southwest of the Northern Territory has been evaluated using the radioactive isotope chlorine-36 (³⁶Cl). These aquifers include fractured sandstones of the Ngalia Basin, fractured metamorphic rocks and Cainozoic sands and gravels. ³⁶Cl/Cl ratios for these shallow, regional groundwaters exhibit a bimodal distribution with peaks at 205 (±7) and 170 (±7)×10^–15. The higher ratio probably represents modern (Holocene) recharge, diluted with windblown salts from local playa lakes, and occurs mostly around the margin of the basin. The lower ratio corresponds to a ³⁶Cl "age", or mean residence time, of 80–100 ka, implying that the last major recharge occurred during the last interglacial interval (Oxygen Isotope Stage 5). These values are mainly observed in the interior of the Ngalia Basin. Lower values of the ³⁶Cl/Cl ratio measured near playa lakes are affected by addition of chloride from remobilised salts. Finite carbon-14 (¹⁴C) data for the groundwaters are at variance with the ³⁶Cl results, but a depth profile suggests low recharge, allowing diffusion of recent atmospheric carbon to the water table. The ³⁶Cl results have important implications for groundwater management in this region, with substantial recharge only occurring during favourable, wet, interglacial climatic regimes; most community water supplies are dependent on these "old" waters. Received, September 1997 · Revised, August 1998, March 1999 · Accepted, March 1999     

Observations of atmospheric gravity waves by radio interferometry: are results biased by the observational technique?

In this paper we present a quantitative comparison between a large data base of medium-scale atmospheric gravity waves (AGWs) observed by radio interferometry of transionospheric radio sources and the results of a numerical simulation of the observed effects. The simulation includes: (i) the propagation and dissipation of AGWs up to ionospheric heights and (ii) the calculation of the subsequent slant TEC perturbations integrated along the path to the radio sources. We show that the observed azimuthal distribution of AGWs can be deeply biased. Predicted results are found to be consistent with previous extensive observations using radio beacons aboard geostationary satellites. These observations are rediscussed in view of the present predictions.     

Natural acid rock drainage associated with black shale in the Yukon Territory,Canada

Investigated herein are water and sediment geochemistry, and metal attenuation processes associated with natural acid rock drainage originating from black shale formations in the Macmillan Pass area, Clear Lake prospect and Engineer Creek by the Dempster Highway in the Yukon Territory, Canada. The most metalliferous water having pH 3.0, 150 mg/L Zn, 39 mg/L Ni, 2.8 mg/L Cu and 9.1 mg/L As was found in a tributary stream of Engineer Creek with no known mineral deposits occurring in the vicinity. For all three study areas, the water and sediment geochemistry is significantly affected by the local lithology and prevailing metal attenuation processes. Despite their anomalous acidity and metal contents, the natural acid streams contribute only a small fraction of the contaminant loadings to the major water courses because of their low flows. Dilution, neutralization, sorption and co-precipitation are identified as the major mechanisms attenuating aqueous transport of potentially deleterious metals. However, microbial mediation in metal attenuation is also evident in low-flow systems. The wide variation of water and sediment geochemistry along a flow path renders the establishment of background metal values difficult. In assessing environmental impacts, it may be more practical to consider metal loadings on a watershed scale than to rely on a comparison with operationally defined background concentrations.     

Stratigraphy and magnetic polarity of the high terrace remnants in the upper Ohio and Monongahela Rivers in West Virginia, Pennsylvania, and Ohio

A synthesis of previous work and new data on the stratigraphy of high terraces of the Ohio and Monongahela Rivers upstream from Parkersburg, West Virginia, indicates a correspondence between terrace histories in the ancient Teays and Pittsburgh drainage basins. Four terraces are identified in each. Sediments of the lower three alluvial and slackwater terraces, correlated with Illinoian, early Wisconsin, and late Wisconsin glacial deposits, have been traced along the modern Ohio River through the former divide between the Teays and Pittsburgh basins. Sediments in the fourth terrace, the highest well-defined terrace in each basin, were deposited in two ice-dammed lakes, separated by a divide near New Martinsville, West Virginia. Some deposits of the highest slackwater terrace in both the Teays and Pittsburgh basins have reversed remanent magnetic polarity. This, and the stratigraphic succession in the two basins, suggests that both were ponded during the same glaciation. Reversed polarity in these terrace sediments restricts the age of the first ice-damming event for which stratigraphic evidence is well-preserved to a pre-Illinoian, early Pleistocene glaciation prior to 788,000 yr ago. In contrast, slackwater sediments in the Monongahela River valley, upstream from an outwash gravel dam at the Allegheny-Monongahela confluence, have normal remanent magnetic polarity, corroborating correlation with an Illinoian ponding event.     

Partitioning of strontium between calcite,dolomite and liquids: An experimental study under higher temperature diagenetic conditions,and a model for the prediction of mineral pairs for geothermometry

The partitioning of Sr between calcite, dolomite and liquids is essentially independent of temperature between 150° and 350° C. The partition coefficients corrected for number of cation sites are b _calc=0.096 and b _dol= 0.048 for 1 mol cations/6 mol H₂O liquid. Upon dilution the partition coefficients increase, but their ratio stays constant at about 2∶1. This ratio is due to the fact that calcite has twice as many Ca-sites for Sr-substitution as dolomite. The 2∶1 relationship is also observed in natural calcite and dolomite which have undergone diagenesis. The temperature independence of partitioning is caused by the relatively small thermal expansion of calcite and dolomite. Thermal expansion between 25° and 400° C was found to follow the equations V _calc=7.0·10⁻⁴ T(°C)+36.95 and V _dol=6.9·10⁻⁴ T(°C)+32.24, V: cm³/mol. Therefore calcite and dolomite cannot serve as a temperature indicator. To have an ideal geothermometer a mineral pair with high and low thermal expansion is required. Literature date demonstrate that wurtzite, sphalerite, and galena are such minerals.     

Mantle peridotite in newly discovered far-inland subduction complex,southwest Arizona: initial report

The latest Cretaceous to early Palaeogene Orocopia Schist and related units are generally considered a low-angle subduction complex that underlies much of southern California and Arizona. A recently discovered exposure of Orocopia Schist at Cemetery Ridge west of Phoenix, Arizona, lies exceptionally far inland from the continental margin. Unexpectedly, this body of Orocopia Schist contains numerous blocks, as large as ~300 m, of variably serpentinized mantle peridotite. These are unique; elsewhere in the Orocopia and related schists, peridotite is rare and completely serpentinized. Peridotite and metaperidotite at Cemetery Ridge are of three principal types: (1) serpentinite and tremolite serpentinite, derived from dunite; (2) partially serpentinized harzburgite and olivine orthopyroxenite (collectively, harzburgite); and (3) granoblastic or schistose metasomatic rocks, derived from serpentinite, made largely of actinolite, calcic plagioclase, hercynite, and chlorite. In the serpentinite, paucity of relict olivine, relatively abundant magnetite (5%), and elevated Fe³⁺/Fe indicate advanced serpentinization. Harzburgite contains abundant orthopyroxene, only slightly serpentinized, and minor to moderate (1–15%) relict olivine. Mantle tectonite fabric is locally preserved. Several petrographic and geochemical characteristics of the peridotite at Cemetery Ridge are ambiguously similar to either abyssal or mantle-wedge (suprasubduction) peridotites and serpentinites. Least ambiguous are orthopyroxene compositions. Orthopyroxene is distinctively depleted in Al₂O₃, Cr₂O₃, and CaO, indicating mantle-wedge affinities. Initial interpretation of field and petrologic data suggests that the peridotite blocks in the Orocopia Schist subduction complex at Cemetery Ridge may be derived from the leading corner or edge of a mantle wedge, presumably in (pre-San Andreas fault) southwest California. However, derivation from a subducting plate is not precluded.     

Using Audience Physiology to Assess Engaging Conservation Messages and Animal Taxa

Abstract

We used heart rate change as a tool to study how positive and negative wildlife conservation messaging impacts a viewer, and which types of animal images stimulate greatest reaction. We used scenes from five wildlife conservation videos available from environmental organization websites and YouTube, with positive and negative messaging. We found both very positive and very negative messaging in videos may be similarly effective in engaging viewers. A trend in greater changes in heart rate when insects, mammals, and birds appear on the screen suggests generally high human interest in these taxa, potentially due to avoidance and attraction responses. The number of scenes (N?=?54) in which various taxa appear reflects bias toward mammals (65%) and birds (17%) to capture viewers’ attention. Arousal is a primary step in engaging an audience to attend to a message. Physiological research offers innovative new techniques to evaluate public responses to communications about biodiversity conservation.     

Characterization of elemental release during microbe-granite interactions at T = 28 °C

This study used batch reactors to characterize the mechanisms and rates of elemental release (Al, Ca, K, Mg, Na, F, Fe, P, Sr, and Si) during interaction of a single bacterial species (Burkholderia fungorum) with granite at T = 28 °C for 35 days. The objective was to evaluate how actively metabolizing heterotrophic bacteria might influence granite weathering on the continents. We supplied glucose as a C source, either NH₄ or NO₃ as N sources, and either dissolved PO₄ or trace apatite in granite as P sources. Cell growth occurred under all experimental conditions. However, solution pH decreased from ∼7 to 4 in NH₄-bearing reactors, whereas pH remained near-neutral in NO₃-bearing reactors. Measurements of dissolved CO₂ and gluconate together with mass-balances for cell growth suggest that pH lowering in NH₄-bearing reactors resulted from gluconic acid release and H⁺ extrusion during NH₄ uptake. In NO₃-bearing reactors, B. fungormum likely produced gluconic acid and consumed H⁺ simultaneously during NO₃ utilization.Over the entire 35-day period, NH₄-bearing biotic reactors yielded the highest release rates for all elements considered. However, chemical analyses of biomass show that bacteria scavenged Na, P, and Sr during growth. Abiotic control reactors followed different reaction paths and experienced much lower elemental release rates compared to biotic reactors. Because release rates inversely correlate with pH, we conclude that proton-promoted dissolution was the dominant reaction mechanism. Solute speciation modeling indicates that formation of Al-F and Fe-F complexes in biotic reactors may have enhanced mineral solubilities and release rates by lowering Al and Fe activities. Mass-balances further reveal that Ca-bearing trace phases (calcite, fluorite, and fluorapatite) provided most of the dissolved Ca, whereas more abundant phases (plagioclase) contributed negligible amounts. Our findings imply that during the incipient stages of granite weathering, heterotrophic bacteria utilizing glucose and NH₄ only moderately elevate silicate weathering reactions that consume atmospheric CO₂. However, by enhancing the dissolution of non-silicate, Ca-bearing trace minerals, they could contribute to high Ca/Na ratios commonly observed in granitic watersheds.