Physiological responses of transplants of the freshwater angiosperm Vallisneria americana along a salinity gradient in the Caloosahatchee Estuary (Southwestern Florida)

Fluctuations in freshwater input may affect the physiology and survival of submerged aquatic vegetation (SAV) occurring in oligoaline to mesohaline estuarine regions. Controls on the distribution of the freshwater angiosperm Vallisneria americana, were investigated by transplanting ramets. Pots (3.8-1) containing ramets were distributed among four sites (upstream site [least saline], donor site, near downstream site, and far downstream site [most saline]) in the Caloosahatchee Estuary (Southwest Florida) during wet (May–August) and dry (October–February) seasons. During 2–4 mo of each season, physiological indicators were monitored, including photosynthesis, glutamine synthetase activity, and protein content in shoots, and carbohydrates and total nitrogen and carbon in shoot and subterranean tissues. Where the physical environment (light or salinity) was suboptimal, all physiological indices, except photosynthetic rate, showed similar stress responses, which ranged from a slow decline to a rapid drop in physiological function. Levels of soluble carbohydrates decreased in response to unfavorable conditions more rapidly than did insoluble carbohydrates. Shoot protein of V. americana declined prior to transplant death, suggesting that measuring protein content may provide a rapid assessment of physiological health. V. americana transplants at the low-salinity upstream site died during both wet and dry season experiments, likely in response to light limitation and/or partial burial by sediments. At the far downstream site, death occurred within 2–4 wk, and was attributable to elevated salinities (>ca. 15‰). Comparison of physiological responses with salinity and light regimes at the donor and near downstream sites suggest that light may ameliorate salinity stress. This study demonstrates that V. americana, nominally classed as a freshwater macrophyte, is capable of a remarkable degree of halotolerance.     

Evaluation of a digital echo sounder system for detection of submersed aquatic vegetation

A technique is presented for rapid detection of submersed aquatic vegetation (SAV) using a high-frequency, high-resolution digital echo sounder linked with global positioning system equipment. The acoustic reflectivity of SAV allows for detection and explicit meaqsurement of canopy geometry using a digital signal processing algorithm described here. Comparing output data from this system with physical measurements shows good detection and measurement performance over a wide range of conditions for freshwater tape grass (Vallisneria americana) and seagrasses (Thalassia testudinum, Halodule wrightii, andSyringodium filiforme) in a sandy-bottom, south Florida estuary. The range of environmental conditions for which the system can be used is defined. Based on these measured performance data and a review of existing literature, this system appears to fill a gap in the inventory of established methods for measuring the distribution and abundance of submersed macrophytes.     

Penglai Zircon Megacrysts: A Potential New Working Reference Material for Microbeam Determination of Hf–O Isotopes and U–Pb Age

We introduce a potential new working reference material – natural zircon megacrysts from an Early Pliocene alkaline basalt (from Penglai, northern Hainan Island, southern China) – for the microbeam determination of O and Hf isotopes, and U–Pb age dating. The Penglai zircon megacrysts were found to be fairly homogeneous in Hf and O isotopes based on large numbers of measurements by LA-multiple collector (MC)-ICP-MS and SIMS, respectively. Precise determinations of O isotopes by isotope ratio mass spectrometry (IRMS) and Hf isotopes by solution MC-ICP-MS were in good agreement with the statistical mean of microbeam measurements. The mean δ¹⁸O value of 5.31 ± 0.10‰ (2s) by IRMS and the mean ¹⁷⁶Hf/¹⁷⁷Hf value of 0.282906 ± 0.0000010 (2s) by solution MC-ICP-MS are the best reference values for the Penglai zircons. SIMS and isotope dilution-TIMS measurements yielded consistent ²⁰⁶Pb/²³⁸U ages within analytical uncertainties, and the preferred ²⁰⁶Pb/²³⁸U age was found to be 4.4 ± 0.1 Ma (95% confidence interval). The young age and variably high common Pb content make the Penglai zircons unsuitable as a primary U–Pb age reference material for calibration of unknown samples by microbeam analysis; however, they can be used as a secondary working reference material for quality control of U–Pb age determination for young (particularly < 10 Ma) zircon samples.     

Mass transfer to bean leaves

A vapour of radio-lead (²¹²Pb) has been used to measure the Sherwood number, Sh, of model leaves at various angles of incidence,, to the airstream in a wind tunnel. The results for=0 are compared with Pohlhausen's formula and the results for 0, with Powell's experiments. The local values of Sh on the upwind and downwind sides of discs have been obtained. For leaves in the canopy, Sh was found to be about 25% greater than would be predicted by applying Pohlhausen's equation without correction for orientation.     

Stable isotope evidence for regional-scale fluid migration in a Barrovian metamorphic terrane,Vermont, USA

We measured the C- and O-isotopic composition of carbonate minerals in the Waits River Formation, eastern Vermont, to determine the extent of fluid infiltration during regional metamorphism over an approx. 2000 km² area in a deep-seated (>25 km) Barrovian terrane. From a petrologic study of this terrane, Ferry proposed the existence of a large regional metamorphic hydrothermal system with two first-order features: (1) on the scale of the entire terrane fluid flow was focused into the axes of two major antiforms of regional extent; (2) on a smaller scale (about 100 km²) flow was further focused around synmetamorphic granitic plutons that intruded along the axes of the antiforms. We find isotopic evidence for both the regional hydrothermal activity along the antiforms and the more intense fluid flow around synmetamorphic plutons. The evidence for hydrothermal activity around the plutons is large heavy isotope depletions, up to 6–9 in ¹⁸O_carb and ¹³C_carb, in diopside zone rocks adjacent to the plutons. These isotopic shifts are greater than can be explained solely by prograde metamorphic reactions. We find two lines of evidence for the more diffuse regional flow that was focused into axes of the antiforms. First, ¹⁸O_carb and ¹³C_carb, within individual outcrops become increasingly homogeneous with increasing grade towards antiform axes, indicating that the rocks equilibrated with a permeating fluid. Second, there are depletions in ¹⁸O near the margins of the Waits River Formation which can be interpreted as a dispersed, advective infiltration front displaced toward the antiform axes. These fronts were modelled using Eq. 13 of Bickle and Baker and imply time-integrated fluid of 10⁵–10⁶ cm³/cm², which are consistent with values derived by Ferry from measured progress of prograde devolatilization reactions.     

Overconsolidation effects of ground freezing

Temporary ground freezing is a valuable technique for stabilizing soft soils during construction. It imparts large increases in strength and bearing capacity to most soils. However, freezing can cause significant changes in soil structure and density which can lead to adverse settlement during thaw.

Settlement of clay soils after freezing and thawing is the result of the suction forces that draw pore water to the freezing front. These suction forces cause an increase in the effective stress on the clay beneath the freezing front, and thus cause an overconsolidation of the clay. As these suction forces often exceed 1 atm, their direct measurement is not easy.

A technique for indirectly determining the maximum suction occurring during freezing is presented which utilizes the apparent memory that clay soils have for maximum past (preconsolidation) pressures. Suctions as large as 532 kN m⁻² were observed after freezing and thawing a clay soil which was initially consolidated to 128 kN m⁻².

The volume changes resulting from the freezing and thawing of clays were related to the plastic limit and were observed in the laboratory to be as high as 25%. If provisions are not made to account for these volume changes in a ground freezing project, considerable damage to structures can occur from settlement and the resulting stresses.     

Near-surface expression of a young mesothermal gold mineralizing system, Sealy Range, Southern Alps, New Zealand

Carbonate-limonite veins formed in steeply dipping fractures in the upper few hundred metres of basement greywacke in the actively rising Southern Alps of New Zealand. The veins are found commonly in extensional fractures near to, but not in, major faults associated with mountain uplift, and/or sinistral faults which bound mountain ranges. Some of the veins contain sulphides and minor gold deposited as part of incrementally formed fracture fillings. Oxygen isotope ratios of calcite range widely between +6 and +24‰, and calcite δ¹³C_PDB=−5.5 to −11.5‰. The veins formed from isotopically exchanged crustal fluid with a probable meteoric water component. The shallow vein network is the near-surface expression of a tectonically induced hydrothermal system which has deposited gold-bearing veins with a mesothermal style over several vertical kilometres. This vein network has formed in a dilatational zone of the oblique collisional orogen where near-vertical fractures tap deep-sourced fluids. Similar processes acting at the southern end of the Southern Alps in the Miocene resulted in locally rich mesothermal quartz-gold veins. Received: 21 May 1997 / Accepted: 30 June 1998     

Near infrared imaging spectroscopy of Venus with the Anglo-Australian Telescope

We have obtained full-disk spatially resolved spectra of the Venus nightside at near-infrared wavelengths during July 2007 using the Anglo-Australian Telescope and Infrared Imager and Spectrograph 2 (IRIS2). The data have been used to map the intensity and rotational temperature of the O₂(a¹Δ_g) airglow band at . The temperatures agree with those obtained in earlier IRIS2 observations and are significantly higher than expected from the Venus International Reference Atmosphere (VIRA) profile. We also report the detection of the corresponding ν=0-1O₂ airglow band at with a similar spatial distribution to the ν=0-0 band. Observations in the thermal window have been used to image surface topography using two different methods of cloud correction. We have also obtained images that can be used to study cloud motion.     

Some observations on the behaviour of radioiodine vapour in the atmosphere

Summary The diffusion of gaseous radioiodine vapour to surfaces is controlled by boundary layer effects, and diffusion to the walls of a tube is in good agreement with theory. In the presence of condensation nuclei the behaviour of the radioiodine depends on the amount of iodine carrier present. With no carrier the radioiodine appears to undergo adsorption on the nuclei.