Lunar periods as grouping variables for temporally fixed sampling regimes in a tidally dominated estuary

The complex interaction of a daily temporally fixed sampling design with seasonal, tidal, and diurnal cycles can result in serious aliasing and reduced usefulness of estuarine data. The choice of appropriate sampling windows for data grouping and analysis of tidally influenced data is complex and must take into account both solar and lunar influences and their interactions in order to represent actual estuarine conditions. A fixed modulus for grouping or time-series analysis introduces errors. Grouping data by calendar month can be misleading since calendar months may have as many as three or as few as one spring tide. Daily measurements of salinity and water clarity at a fixed time of day were analyzed to illustrate the effects of aliasing. Although the length of synodical (lunar) months is also variable, a seasonally adjusted grouping variable based on solar and synodical month (MO-DAY), created to partially correct for aliasing, was found to be an efficient way to remove short-term cycles for the identification of long-term trends, episodic events, and spatial patterns.     

Seasonal variation in standing crop of the seagrassSyringodium filiforme and associated macrophytes in the Northern Indian River,Florida

Seasonal variation in the standing crop of the seagrassSyringodium filiforme and its associated macrophytes was studied in a northern basin of the Indian River, a large mesohaline lagoon in central Florida, near the northern distributional limit ofS. filiforme. The minimum standing crop occurred from February through April and the maximum in September. Two other seagrasses,Halodule wrightii andHalophila engelmannii, together with a drift algal community, occurred in the study quadrat, but were not major components of the macrophytic system. The formation of sizeable sandy patches within Indian River seagrass beds is partially due to the burrowing activities ofLimulus polyphemus. Thermal stresses associated with the northern geographicalS. filiforme range may contribute to this phenomenon by restricting annual production, hence limiting patch regrowth.     

Contrasting styles of Archaean crustal evolution in parts of southern West Greenland

Aspects of the crustal evolution of three areas in the Archaean block of southern West Greenland are compared and new Rb and Sr isotope data are presented for one of them (inner Godthåbsfjord). It is concluded that major differences resulted from variations in crustal thickness with the early Archaean Amîtsoq gneisses controlling later events.     

Pore pressure diffusion and the mechanism of reservoir-induced seismicity

The study of reservoir-induced seismicity offers a controlled setting to understand the physics of the earthquake process. Data from detailed investigations at reservoirs in South Carolina suggested that the mechanism of transmission of stress to hypocentral locations is by a process of diffusion of pore pressure (Pp). These results were compared with available worldwide data. The seismic hydraulic diffusivity, _s , was estimated from various seismological observations, and was found to be a good estimate of the material hydraulic diffusivity, . Application of these results to a dedicated experiment to understand RIS at Monticello Reservoir, S.C., suggested that the diffusing Pp front plays a dual role in the triggering of seismicity. The spatial and temporal pattern of RIS can be explained by the mechanical effect of diffusion of Pp with a characteristic hydraulic diffusivity within an order of magnitude of 5×10⁴ cm²/s, corresponding to permeability values in the millidarcy range. The triggering of seismicity is due to the combined mechanical effect of Pp in reducing the strength and, possibly, the chemical effect in reducing the coefficient of friction between the clays in the pre-existing fractures and the rocks that enclose these fractures.     

Characterization of grass shrimp (Palaemonetes pugio) embryo toxicity tests using the water soluble fraction of number 2 fuel oil

Toxicity test procedures using grass shrimp Palaemonetes pugio exposed to water soluble fraction (WSF) of Number 2 fuel oil were modified to improve test utility and efficiency. The original test procedure, a 12-day embryo exposure period in glass tubes, was compared with modified 4-day and 12-day tests in plastic tissue culture plates. Comparison of LC₅₀ values, coefficients of variation and time to hatch indicated no significant change in test sensitivity due to the plastic containers. Sensitivity was slightly reduced by shortening the test to a 4-day exposure period initiated 9 days after oviposition. This exposure period encompassed sensitive life stages of the developing organism. Using the 4-day exposure in plastic plates, variability due to different broods and preparations of WSF was characterized.     

Effects of dimilin on the blue crab,Callinectes sapidus,in shallow-water habitats

Diffubenzuron (Dimilin) is used as an insecticide for control of the gypsy moth. Because it is a chitin synthetase inhibitor, it can be a potential threat to other arthropods, including crustaceans. We used a static renewal testing paradigm to determine the LC₅₀ of Dimilin WP-25 to juvenile blue crabs (carapace width: 25–60 mm). Both molt stage of dose frequency effect toxicity. When we exposed the crabs at random molt stages, LC₅₀=3.5 mg l^?1. When crabs were exposed on the day of molt, LC₅₀=300 μg l^?1. If initial exposure occurred on the day of molt and the crabs were subsequently exposed to repeated doses, LC₅₀=18.5 μg l^?1. Effects were age and molt-stage sensitive. We include a review of the data available on Dimilin effects in the marine and estuarine environments.     

FRACTURE CHARACTERIZATION FROM NEAR-OFFSET VSP INVERSION

A global optimization method incorporating a ray-tracing scheme is used to invert observations of shear-wave splitting from two near-offset VSPs recorded at the Conoco Borehole Test Facility, Kay County, Oklahoma. Inversion results suggest that the seismic anisotropy is due to a non-vertical fracture system. This interpretation is constrained by the VSP acquisition geometry for which two sources are employed along near diametrically opposite azimuths about the well heads. A correlation is noted between the time-delay variations between the fast and slow split shear waves and the sandstone formations.     

Ultraviolet Laser Sampling and High Resolution Inductively Coupled Plasma-Mass Spectrometry of NIST and BCR-2G Glass Reference Materials

A Merchantek LUV266 ^TM petrographic ultraviolet (UV) laser microprobe has been used in conjunction with a Finnigan MAT ELEMENT ^TM high resolution ICP double-focusing mass spectrometer (HR-ICP-MS) for solid microsampling and geochemical analysis. This new configuration for laser ablation has the advantage of coupling the high sensitivity and fast scanning technology applied in the ELEMENT with the ablation efficiency of a UV laser. Optimisation of the configuration on the synthetic NIST SRM 612 glass standard reference material using Q-switched UV laser energy of 2 mJ and a 5 Hz repetition rate demonstrates: (1) a linear element response factor throughout the mass spectrum, suggesting limited fractionation during laser ablation; (2) a high sensitivity and very low background noise for most elements of interest; (3) limits of detection ranging from 3 ng g-1 for Sc to 300 pg g-1 for U; (4) a flat topped peak shape suitable for precise isotopic measurements; and (5) a flat bottomed crater geometry which permits progressive ablation for the analysis of thin sections. Average precision and accuracy estimates based on replicate analyses of synthetic NIST standard reference material and USGS BCR-2G glasses are below 10% for most elements.