Search Results

During the past 1000 years, eruptions of Vesuvius have often been accompanied by large earthquakes in the Apennines 50–60 km to the northeast. Statistical investigations had shown that earthquakes often preceded eruptions, typically by less than a decade, but did not provide a physical explanation for the correlation. Here, we...

Oceanic methane hydrates are mineral deposits formed from a crystalline 'ice' of methane and water in sea-floor sediments (buried to less than about 1 km) in water depths greater than about 500 m; economic hydrate deposits are probably restricted to water depths of between 1.5 km and 4 km. Gas...

To assess the impact of zebra and quagga mussel (Dreissena spp.) infestation on unionids, unionids (Bivalvia: Unionidae) were sampled in the Detroit River in 1982–1983, before mussels invaded the river, and in 1992 and 1994, after mussels invaded the river. Live unionids at four stations along the southeastern shore accounted for...

Field and laboratory tests of a shipborne hydrographic survey system were conducted. The system consists of two 12-channel GPS receivers (one on-board, one fixed on shore), a digital acoustic fathometer, and a digital heave-pitch-roll (HPR) recorder. Laboratory tests of the HPR recorder and fathometer are documented. Results of field tests...

Reanalysis of rock population data at the Mars Viking Lander sites has yielded updated values of rock fractional surface coverage (about 0.16 at both sites, including outcrops) and new estimates of rock burial depths and axial ratios. These data are combined with a finite difference time domain (FDTD) numerical scattering...

Our objective was to synthesize individual components of reproductive ecology into a single estimate of productivity and to assess the relative effects of survival and productivity on population dynamics. We used information on nesting ecology, renesting potential, and duckling survival of northern pintails (Anas acuta) collected on the Yukon-Kuskokwim Delta...

Sequence variation in the control region (D-loop) of the mitochondrial DNA (mtDNA) was examined to assess the genetic distinctiveness of the shortjaw cisco (Coregonus zenithicus). Individuals from within the Great Lakes Basin as well as inland lakes outside the basin were sampled. DNA fragments containing the entire D-loop were amplified...

Studies of the fate of oil released into Prince William Sound, AK, as a result of the 1989 Exxon Valdez oil spill, have led to an unexpected discovery. In addition to oil-like residues attributed to the spill, the ubiquitous presence of flattened tar balls, the carbon isotopic compositions of which...

A claystone and a limestone containing immature Type II-S kerogen were thermally matured in the presence and absence of water, to study the influence of water and clay minerals on the generation of biomarkers. In contrast to hydrous pyrolysis, anhydrous pyrolysis of the claystone did not generate biomarkers, which resulted...

The Antarctic Ice Sheet is today an important part of the global climate engine, and probably has been so for most of its long existence. However, the details of its history are poorly known, despite the measurement and use, over two decades, of low-latitude proxies of ice sheet volume. An...

Neo-Darwinian theory is highly successful at explaining the emergence of adaptive traits over successive generations. However, there are reasons to doubt its efficacy in explaining the observed, impressively detailed adaptive responses of organisms to day-to-day changes in their surroundings. Also, the theory lacks a clear mechanism to account for both...

We extend the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) for solution of the advection-dispersion equation to two dimensions. The method can conserve mass globally and is not limited by restrictions on the size of the grid Peclet or Courant number. Therefore, it is well suited for solution of advection-dominated ground-water...

Experiments with the Rocky 7 rover were performed in the Mojave Desert to better understand how to conduct rover-based, long-distance (kilometers) geological traverses on Mars. The rover was equipped with stereo imaging systems for remote sensing science and hazard avoidance and 57Fe Mössbauer and nuclear magnetic resonance spectrometers for in situ...

Based on usage of the parent compounds and studies of their dissipation in corn fields, atrazine (6-chloro-N-ethyl-N'-(1-methylethyl-1,3,5-triazine-2,4-diamine)), cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropionitrile), and simazine (6-chloro-N,N'diethyl-1,3,5-triazine-2,4-diamine) are thought to be the important contributors of desethylatrazine (6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine) or DEA and desisopropylatrazine(6-chloro-N-ethyl)-1,3,5-triazine-2,4-diamine) or DIA to ground water. Atrazine degrades to both DEA and DIA by dealkylation....

We tested predictions of the California Wildlife Habitat Relationships (CWHR) System in coastal scrub and annual grassland. We detected a total of 28 species of terrestrial vertebrates: 18 mammals, 9 reptiles, and 1 amphibian. The CWHR System prediction omitted 4 of these species: 3 domestic mammals and 1 reptile. For...

Specification of an appropriate model is critical to valid statistical inference. Given the “true model” for the data is unknown, the goal of model selection is to select a plausible approximating model that balances model bias and sampling variance. Model selection based on information criteria such as AIC or its...

Dissolved-solids data collected in the Upper Colorado River Basin upstream from Cameo, Colorado, and in the Gunnison River Basin were analyzed for trends in flow-adjusted dissolved-solids concentrations and loads for water years 1970 to 1993, 1980 to 1993, and 1986 to 1993. Trend results for flow-adjusted...

To assess the extent of sediment contamination in the Upper Mississippi River (UMR) system after the flood of 1993, sediment samples were collected from 24 of the 26 navigational pools in the river and from one site in the Saint Croix River in the summer of 1994. Whole-sediment tests were...

The chemical reactivity of uranium was investigated across estuarine gradients from two of the world’s largest river systems: the Amazon and Mississippi. Concentrations of dissolved (<0.45 μm) uranium (U) were measured in surface waters of the Amazon shelf during rising (March 1990), flood (June 1990) and low (November 1991) discharge...

Reproduction and early life history of ruffe (Gymnocephalus ceriums) was investigated during April to July in 1993 and 1994 in the St. Louis River, a western Lake Superior tributary. This study was conducted to assist fishery managers in determining possible interactions among the early life stages of ruffe and other...

The in situ measurement of water flow and chemical transport through clay pan soils is crucial to understanding potential water contamination from agricultural sources. It is important due to the large areal extent of these soils in agricultural regions of the midwestern United States and because of preferential flow paths...

The age structure of mature lake trout Salvelinus namaycush from the Wisconsin waters of Lake Superior increased following a population recovery that has taken place since the 1960s. As the population aged, it became apparent that scales were unreliable aging structures. Beginning in 1986, we examined both scale and sagittal otolith ages...

Survey for continuous measurement of water temperature, specific conductance, and pH in four low ionic strength streams in the Catskill Mountains of New York was evaluated through a calculation of their bias, precision, and accuracy and by comparison with laboratory measurements of specific conductance and pH on samples collected concurrently....

Knowledge of the spawning cycle and factors affecting fecundity of slimy sculpins (Cottus cognatus) are important in understanding the population dynamics of this species in large lake systems, like Lake Ontario. Fecundity and the spawning cycle of slimy sculpins were described...

ABSTRACT: Spatial and temporal variability in rainfall concentrations of nutrients, major ions, and herbicides was monitored at 7 locations in or near the Conodoguinet Creek watershed in south-central Pennsylvania from 1991.1993. Results were used to (1) compare precipitation quality in forested, agricultural and urban areas, and (2) assess the practicality of...