Isotopic studies of leaf water. Part 1: A physically based two-dimensional model for pine needles

Understanding of isotopic variations in leaf water is important for reconstruction of paleoclimate and assessment of global biochemical processes. We report here a study of isotopic distributions within a single needle of two pine species, Pinus resinosa Ait and Pinus strobes L., with the objective of understanding how isotopic compositions of leaf water are controlled by environmental and physiological variables. A 2D model was developed to simulate along-leaf isotopic variations and bulk leaf water isotopic compositions. In addition to variables common to all leaf water isotopic models, this 2D model also takes into account the specific geometry and dimensions of pine needles and the isotopic transport in xylem and mesophyll. The model can successfully simulate oxygen isotopic variations along a single needle and averaged over a leaf (bulk leaf water). The simulations suggest that isotopic composition of the bulk leaf water does not always depend only upon the average transpiration rate, which in turn raises questions about using leaf water isotopic values to estimate transpiration rates. An unsuccessful attempt to simulate along-needle hydrogen isotopic variations suggests that certain unknown biological process(es) may not have been incorporated into our 2D model, and if so, it calls for a reevaluation of all other models for hydrogen isotopic simulations of leaf water since they too lack these processes.Existing leaf water isotopic models are reviewed in this work. In particular, we evaluate the most frequently used model, the stomatal boundary layer model (also referred to as the Craig-Gordon model). We point out that discrepancy between the boundary layer model and the measured bulk leaf water seems to depend upon relative humidity. Using our 2D model, we show that this humidity dependency is a result of an interplay between environmental and physiological conditions: if the transpiration rate of plant leaves decreases with increasing relative humidity, our 2D model can reproduce the pattern of isotopic discrepancy between boundary layer model predictions and observations, enabling us to understand better the reason behind this discrepancy.     

Dissolved metals and associated constituents in abandoned coal-mine discharges,Pennsylvania, USA. Part 1: Constituent quantities and correlations

Complete hydrochemical data are rarely reported for coal-mine discharges (CMD). This report summarizes major and trace-element concentrations and loadings for CMD at 140 abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania. Clean-sampling and low-level analytical methods were used in 1999 to collect data that could be useful to determine potential environmental effects, remediation strategies, and quantities of valuable constituents. A subset of 10 sites was resampled in 2003 to analyze both the CMD and associated ochreous precipitates; the hydrochemical data were similar in 2003 and 1999. In 1999, the flow at the 140 CMD sites ranged from 0.028 to 2210 L s⁻¹, with a median of 18.4 L s⁻¹. The pH ranged from 2.7 to 7.3; concentrations (range in mg/L) of dissolved (0.45-μm pore-size filter) SO₄ (34–2000), Fe (0.046–512), Mn (0.019–74), and Al (0.007–108) varied widely. Predominant metalloid elements were Si (2.7–31.3 mg L⁻¹), B (<1–260 μg L⁻¹), Ge (<0.01–0.57 μg L⁻¹), and As (<0.03–64 μg L⁻¹). The most abundant trace metals, in order of median concentrations (range in μg/L), were Zn (0.6–10,000), Ni (2.6–3200), Co (0.27–3100), Ti (0.65–28), Cu (0.4–190), Cr (<0.5–72), Pb (<0.05–11) and Cd (<0.01–16). Gold was detected at concentrations greater than 0.0005 μg L⁻¹ in 97% of the samples, with a maximum of 0.0175 μg L⁻¹. No samples had detectable concentrations of Hg, Os or Pt, and less than half of the samples had detectable Pd, Ag, Ru, Ta, Nb, Re or Sn. Predominant rare-earth elements, in order of median concentrations (range in μg/L), were Y (0.11–530), Ce (0.01–370), Sc (1.0–36), Nd (0.006–260), La (0.005–140), Gd (0.005–110), Dy (0.002–99) and Sm (<0.005–79). Although dissolved Fe was not correlated with pH, concentrations of Al, Mn, most trace metals, and rare earths were negatively correlated with pH, consistent with solubility or sorption controls. In contrast, As was positively correlated with pH.     

The presence of anomalous trace element levels in present day Jamaican soils and the geochemistry of Late-Miocene or Pliocene phosphorites

High levels of Cd and Zn in Jamaican soils observed in geochemical surveys are related to the presence of phosphorites of possible Late-Miocene or Pliocene age. The trace element and REE geochemistry of the phosphorites, together with SEM studies, indicate a guano origin for the phosphorites. No specific host minerals for Cd could be identified in the fossiliferous phosphorite which is characterized by uniquely high levels of Cd, Zn, Ag, Be, U and Y. However, in the soil Cd is present in lithiophorite and a complex history of pedological development is preserved in the aluminous–goethite present in the soil. The unique guano signature is preserved in the soil despite the fact that guanos themselves have either not been observed or have been destroyed by continuing karst and soil development. The phosphorite geochemical signature can be traced in the data of a 1988 island-wide soil geochemical survey, identifying areas where the Palaeo-environment that supported bird ‘rookeries’ existed in the Late-Miocene or Pliocene.     

Comparative analyses of East Texas forest cover maps generated from Landsat and AVHRR data

Comparing satellite data derived map products are affected by differences in data characteristics, image acquisition dates, processing techniques, and classification schemes used for assigning pixels to a thematic class. By comparing two forest maps generated from Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Very High Resolution Radiometer (AVHRR) images acquired on the same day, and processed using identical classification scheme and methods these differences were minimized. The ETM+ derived map had higher classification accuracy values and more precise area estimates than the AVHRR derived map. In the ETM+ derived map, 87 of the 599 verification data were misclassified, whereas in the AVHRR derived map, 155 of the 469 verification data were misclassified. Detailed error analyses by land cover class revealed that a land use based definition of forest accounted for 74% (64 out of 87) and 57% (89 out of 155) of the classification errors in ETM+ and AVHRR derived maps, respectively.     

Monitoring Large-Scale Tests for Nuclear Waste Disposal

Two large-scale “in situ” demonstration experiments and their instrumentation are described. The first test (FEBEX Experiment) involves the hydration of a compacted bentonite barrier under the combined effect of an inner source of heat and an outer water flow from the confining saturated granite rock. In the second case, the progressive de-saturation of Opalinus clay induced by maintained ventilation of an unlined tunnel is analyzed. The paper shows the performance of different sensors (capacitive cells, psychrometers, TDR’s) and a comparison of fill behaviour with modelling results. The long term performance of some instruments could also be evaluated specially in the case of FEBEX test. Capacitive sensors provide relative humidity data during long transient periods characterised by very large variations of suction within the bentonite.     

Observations of a fast burst of the deep western boundary undercurrent and sediment transport in South Wilmington Canyon from DSRVAlvin

On October 3 and 4, 1986, DSRVAlvin dives encountered a strong current at 2,300 m in South Wilmington Canyon. The current, estimated at 1 knot, transported surficial sediment and constructed and modified bedforms. It appears to have been constant in its direction of flow from 30 to 40°. The observed current was probably a burst of fast flow in a region of slow average currents in the Deep Western Boundary Undercurrent. Such episodic events may have a greater influence on the stratigraphic record than the temporally longer more tranquil flow conditions.     

210Pb method for estimating the rate of carbonate sand sedimentation

The plot of²¹⁰Pb activity against depth in carbonate sands on the Virgin Island Bank is a negative asymmetric hyperbolic curve. As depth increases, an initial rapid decrease in²¹⁰Pb activity caused by the decay of unsupported²¹⁰Pb and²²⁶Ra is followed by increasing activity as a result of²¹⁰Pb achieving equilibrium with ingrowing²³⁰Th. As this curve is time dependent, an estimate of the relative ages in carbonate sequences and the rates of net carbonate accumulation can be made. The ease of²¹⁰Pb activity determinations makes this procedure an attractive method in obtaining carbonate sand accumulation rates.     

Waveform Shaping of Sonar Transducers for Improving the Vertical Resolution in Sub-bottom Sediments Profiling

Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst. However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude, Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated by its application to a sediment wedge model.