Kinetic studies of lead(II) uptake by the seagrass Zostera muelleri in water by radiotracing,atomic absorption spectrometry and electrochemical techniques

Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent.     

Weathering process at the natural fission reactor of Bangombé

 The uranium deposits in the basin of Franceville (Gabon) host the only natural fission reactors known in the world. Unique geological conditions favoured a natural fission reaction 2 Ga ago. This was detected by anomalous isotopic compositions of uranium and rare earth elements (REE), which are produced by the fission reaction. In total, 16 reactor zones were found. Most of them are mined out. The reactor zone of Bangombé, is only 10–11 m below the surface. This site has been influenced by surface weathering processes. Six drill cores have been sampled at the site of the reactor zone of Bangombé during the course of the study and only one drill core (BAX 08) hit the core of the reactor. From these data and previous drilling campaigns, the reactor size is estimated to be 10 cm thick, 2–3 m wide and 4–6 m long. The migration of fission products can be traced by the anomalous isotope ratios of REE because of the fission process. The ¹⁴⁹Sm/¹⁴⁷Sm ratio close to the reactor zone is only 0.28 (normal: 0.92) because of the intense neutron capture of ¹⁴⁹Sm and subsequent transmutation, whereas ¹⁴⁷Sm is enriched by the fission reaction. Similar changes in isotopic patterns are detectable on other REE. The isotope ratios of Sm and Nd of whole rock and fracture samples surrounding the reactor indicate that fission-genic REE migrated only a few decimetres above and mainly below the reactor zone. Organic matter (bitumen) seems to act as a trap for fission-genic REE. Additional REE-patterns show less intense weathering with increasing depth in the log profile and support a simple weathering model. Received: 26 November 1999 · Accepted: 2 May 2000     

Characterization of soil's structural crust by spectral reflectance in the SWIR region (1.2–2.5 μm)

Structural crust is a thin layer formed on the soil surface after a rainstorm. The crust is the result of a physical segregation and rearrangement of soil particles in a way that affects some of the soil properties, such as infiltration, runoff and soil erosion. In practice, there is no rapid, in situ method for monitoring, assessing and mapping crust intensity and quality. In this study, a controlled spectral investigation of the structural crust across the NIR–SWIR spectral region was conducted on three selected Israeli soils, to study the potential of reflectance radiation to detect structural crust in soils. Two major factors served as the driving forces for this study: (1) there is no valid method for in situ assessment of the crust's characteristics in the agriculture field, and (2) the crust might bias thematic remote sensing of soils, because the thin layer of crust blocks photon–matter interaction, which represents the relevant soil body. Through the use of a laboratory rainfall simulator and a sensitive spectrometer, it was revealed that for three selected soils, significant spectral differences occurred between the crust and its bulk soil. The spectral information was found to be related to changes in particle size distribution and texture at the surface of the soil. This conclusion was based on indications of absorption of OH in clay lattice, OH in adsorbed water and CO₃ in carbonates. It was concluded that the structural crust is a phenomenon that should not be ignored by remote-sensing users. In fact, in the field of agriculture, the spectral properties of crust can be used as tools for estimating the crust's intensity.     

Microboudin structures of piemontite along the Sambagawa metamorphic belt, Japan: implications for lateral variation of differential stress during regional metamorphism

Evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains (p) in a quartz matrix in metacherts. It is proposed that p is a practical indicator of relative differential stress. Analysis of 123 metacherts from the 800 km long Sambagawa metamorphic belt, Japan, reveals that p‐values range from < 0.01 to 0.7 in this region. Most samples from Wakayama in the mid‐belt area have p‐values of 0.4–0.6, whereas those from western Shikoku have p‐values of < 0.1. This difference cannot be explained by variations in metamorphic temperature, and is instead attributed to a regional, lateral variation in differential stress during metamorphism.     

Inverted echo sounder measurement of dynamic height through an ENSOcycle in the central equatorial Pacific

A four-year record from an inverted echo sounder deployed near Palmyra Island at 6°N in the central Pacific Ocean is compared with a simultaneous record of subsurface pressure from this island lagoon. A factor m, converting round-trip acoustic travel time to surface dynamic height relative to a deep pressure level, was estimated from the ratio of the spectra of the two records in the energetic synoptic oscillation band. Year-to-year variation in m was not statistically significant. For the overall record, m was found to be -70±8 dynamic m/s, where the error bounds represent a 90% confidence interval. This is consistent with first-baroclinic-mode excitation     

Wooden Panel Deterioration by Tropical Marine Wood Borers

Wood destruction in test panels ofShorea leprosulawas related to the percentage of fouling, types of wood borers and the number of wood borers. The natural durability ofShorea leprosulapanels was estimated to be 4–5 months in Malaysian marine waters. A higher fouling cover resulted in lower rates of wooden panel deterioration. Larger numbers of wood borers brought about greater panel deterioration. Primary wood destruction was caused by bivalve wood borers, mainlyMartesia striata, Lyrodus pedicellatus, Bankia campanellata, Teredo furciferaandTeredo bartschi. Martesia striatawas the important wood destroying agent in the intertidal zone and, together with the shipworms, was also responsible for panel destruction in the subtidal zone.     

A time series analysis of sound propagation in a strongly multipathshallow water environment with an adiabatic normal mode approach

Measured time series were generated by small omnidirectional explosive sources in a shallow water area. A bottom-mounted hydrophone recorded sound signals that propagated over a sloping bottom. The time series in the 250-500 Hz band were analyzed with a broad-band adiabatic normal mode approach. The measured waveforms contain numerous bottom interacting multipaths that are complicated by the subbottom structure that contains high-velocity layers near the water-sediment interface. Several of the details of the geoacoustic structure and the depth of the water column at the receiver are inferred from comparisons of the measured data to simulated time series. The sensitivity of broad-band matched-field ambiguity surfaces in the range-depth plane for a single receiver to selected waveguide parameters is examined. A consistent analysis is made where the simulated time series are compared to the measured time series along with the single-receiver matched-field localization solutions for ranges out to 5 km. In this range interval, it was found that the peak cross-correlation between the measured and simulated time series varied between 0.84 and 0.69. The difference between the GPS range and the range obtained from the matched-field solution varied from 0 to 63 m. The geoacoustic structure obtained in the analysis consists of an 8-m low-velocity sediment layer over an 8-m high-velocity layer followed by a higher velocity, infinite half-space