bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithospheric structure in northwestern Canada from Lithoprobe seismic refraction and related studies: a synthesis
Authors: Clowes Ron M , Hammer Philip TC , Fernández-Viejo Gabriela , Welford J Kim
Published: October 2005

The SNORCLE refraction  wide-angle reflection (R/WAR) experiment, SNORE'97, included four individual lines along the three transect corridors. A combination of SNORE'97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the Archean Slave craton to the present Pacific basin. Using this model and coincident near-vertical incidence (NVI) reflection data and geological information, an interpreted cross section that exemplifies 4 Ga of lithospheric development is generated. The velocity structural models correlate well with the reflection sections and provide additional structural, compositional, and thermal constraints. Geological structures and some faults are defined in the upper crust. At a larger scale, the seismic data identify a variety of orogenic styles ranging from thin- to thick-skinned accretion in the Cordillera and crustal-scale tectonic wedging associated with both Paleoproterozoic and Mesozoic collisions. Models of Poisson's ratio support the NVI interpretation that a thick wedge of cratonic metasediments underlies the eastern accreted Cordilleran terranes. Despite the variety of ages, orogenic styles, and tectono-magmatic deformations that are spanned by the seismic corridors, the Moho remains remarkably flat and shallow (3336 km) across the majority of the transect. Significant variations only occur at major tectonic boundaries. Laterally variable crustal velocities are consistently slower beneath the Cordillera than beneath the cratonic crust. This is consistent with the high temperatures (800900 °C) required by the slow upper mantle velocities (7.87.9 km/s) observed beneath much of the Cordillera. Heterogeneity of the lithospheric mantle is indicated by wide-angle reflections below the Precambrian domains and the western Cordillera.
Early and Middle Proterozoic evolution of Yukon, Canada
Authors: Thorkelson Derek J , Abbott J Grant , Mortensen James K , Creaser Robert A , Villeneuve Michael E , McNicoll Vicki J , Layer Paul W
Published: October 2005

This paper provides a comprehensive synthesis of virtually all units and events of Early and Middle Proterozoic age in the Yukon, spanning ~1 Ga. Early and Middle Proterozoic time was dominated by a series of extensional-basin-forming events punctuated by orogenesis, magmatism, and hydrothermal activity. Basinal deposits include the Wernecke Supergroup (>1.71 Ga), Pinguicula Group (~1.38 Ga), and Mackenzie Mountains Supergroup (1.000.78 Ga). Igneous rocks include the Bonnet Plume River Intrusions (1.71 Ga), Slab volcanics (≥1.6 Ga), Hart River sills and volcanics (1.38 Ga), and Bear River (Mackenzie) dykes (1.27 Ga). A voluminous hydrothermal event generated the widespread Wernecke breccias at 1.60 Ga. The Racklan orogeny deformed the Wernecke Supergroup prior to emplacement of the Wernecke Breccia. The Corn Creek orogeny deformed Mackenzie Mountains Supergroup and older rocks prior to deposition of the Windermere Supergroup (<0.78 Ga). Long intervals with scanty rock records extended for as much as 300 Ma and appear to represent periods of crustal stability and subaerial conditions. By the time of Windermere rifting (<0.78 Ga), the supracrust of northwestern Laurentia was a mature, largely denuded orogenic belt with a composite sedimentarymetamorphicigneous character. New isotopic data include Nd depleted mantle model ages for the Wernecke Supergroup (2.282.69 Ga) and Wernecke Breccia (2.362.96 Ga), a UPb zircon age for a Hart River sill 1381.9+5.3-3.7 (Ma), detrital UPb zircon ages from the basal Pinguicula Group (18413078 Ma), detrital muscovite ages from the Mackenzie Mountains Supergroup (10372473 Ma), and muscovite 40Ar/39Ar cooling ages from the Wernecke Supergroup (788 ± 8 and 980 ± 4 Ma).
Early Proterozoic orogeny and exhumation of Wernecke Supergroup revealed by vent facies of Wernecke Breccia, Yukon, Canada
Authors: Laughton John R , Thorkelson Derek J , Brideau Marc-André , Hunt Julie A , Marshall Daniel D
Published: October 2005

In the Yukon, the oldest known supracrustal succession, the Wernecke Supergroup, was deposited in a marine basin before 1.71 Ga. The earliest orogenic event to disturb these strata was the Racklan orogeny, which produced folds and fabrics at peak temperatures of 450550 °C. These features and those of the correlative Forward orogeny are recognized at the surface and in the subsurface throughout much of northwestern Canada. Zones of Wernecke Breccia (hydrothermal breccias, 1.60 Ga) were emplaced into the Wernecke Supergroup after Racklan deformation and metamorphism. Two main types of breccia are recognized: grey sodic breccias and colourful potassic breccias. In the Slab Mountain area, a belt of grey breccias contains abundant megaclasts of country rock including blocks of a subaerial lava succession, the Slab volcanics. These grey breccias are interpreted as a vent facies of Wernecke Breccia, and their emplacement into the stratigraphically lowest unit of the Wernecke Supergroup infers that at least 9 km of exhumation occurred in the core of a major Racklan anticline prior to brecciation. The Slab volcanics are preserved only as clasts in Wernecke Breccia and are interpreted as fragments of a former valley-filling basalt succession which overlay deformed and deeply incised strata of the Wernecke Supergroup.
An 1800 km cross section of the lithosphere through the northwestern North American plate: lessons from 4.0 billion years of Earth's history
Authors: Cook Frederick A , Erdmer Philippe
Published: October 2005

The Lithoprobe Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) study across northwestern North America, in combination with related crustal studies, has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high-resolution geophysical data (seismic reflection, refraction, electromagnetic, potential fields) and detailed bedrock geology. The cross section offers one of the longest "continuous" profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships. The primary conclusion of the study is that, during all major orogenic episodes recorded from Archean to present in that part of Earth's lithosphere, the crust, and perhaps much of the mantle, was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis. The observed subsurface geometries of relict subduction zones, accretion boundaries, and magmatic arcs all lead to the inference that the crust includes a dominant proportion of reworked material. A similar conclusion appears applicable for the origin of subcrustal lithosphere in the region, i.e., that much of the lithosphere, whether Archean in the Slave Province or Proterozoic in the Cordillera, is old and thus that the amount of "new" lithosphere added to the plate during orogenesis is surprisingly small. A corollary is that many accreted rocks at surface that record orogenic complexity are detached from their originally underlying lithosphere and were emplaced upon unrelated crust and mantle during deformation.
Crustal structure and lithology of the northern Canadian Cordillera: alternative interpretations of SNORCLE seismic reflection lines 2a and 2b
Authors: Evenchick Carol A , Gabrielse Hubert , Snyder David
Published: October 2005

Seismic reflectors at shallow crustal levels recorded in SNORCLE (Slave  Northern Cordillera Lithospheric Evolution) lines 2a and 2b in the northern Canadian Cordillera can be reconciled with many stratigraphic and structural elements known from geological mapping. Clearly evident examples are the crustal penetrating, Northern Rocky Mountain Trench (NRMT) Fault, the several kilometres thin slices of Slide Mountain (Sylvester Allochthon) and Cache Creek terranes, and the northward dipping Hotailuh Fault. Interpretations of lithological successions and structures at deeper crustal levels are more speculative. Of fundamental significance is a southwesterly tapering wedge of continental crust overlain in its distal part by the allochthonous terrane Stikinia and, northeast of Thibert Fault, by a thick, probably structurally thickened sequence of sedimentary rocks and the extensive granitic Cassiar batholith. The top of the wedge is interpreted to be a tectonic accretion surface resulting from collision of Stikinia with Cache Creek Terrane and Ancestral North America. The mid-crust accretion surface has an apparent southwest dip, whereas the surface expression of accretion is recorded in part by detached, northeast-dipping faults, such as the King Salmon and Hotailuh faults. East of the NRMT, the lithology of more than 20 km of the middle and lower crust is either layered crystalline basement, Mesoproterozoic and Neoproterozoic sedimentary strata, or a combination of the two. West of the trench this zone of continental crust tapers westward; crystalline basement probably predominates in both zones. In the western part of line 2a, the allochthonous terrane Stikinia occupies the full crust thickness.
Evolution of the early Paleozoic Cordilleran margin of Laurentia: tectonic and eustatic events interpreted from sequence stratigraphy and conodont community patterns
Authors: Zhang Shunxin , Pyle Leanne J , Barnes Christopher R
Published: October 2005

Several field seasons in the Canadian Cordillera have allowed the measurement, description and sampling of over 20 000 m of lower Paleozoic strata from 26 stratigraphic sections across four platform-to-basin transects, with the recovery of over 100 000 conodonts from more than 1200 45 kg samples. This work was part of the Lithoprobe Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) project but is also being extended through a Pan-Lithoprobe project to understand the tectonic and eustatic response of much of the Laurentian plate through the early Paleozoic. Based on the abundant field data, the complex stratigraphic framework is interpreted in terms of sequence stratigraphy and a derived relative sea-level curve. Using detailed conodont taxonomic and biostratigraphic results, cluster analysis of conodont distributional data identified an evolving series of conodont communities through space and time. These communities were partitioned across the platform-to-basin gradient and provide an additional sensitive indicator of relative sea-level change. These two independent approaches generated comparable eustatic curves for this Cordilleran Laurentian margin during much of the early Paleozoic and identified some global eustatic events noted by earlier workers. This part of Laurentia was not a simple passive margin during the early Paleozoic, but rather was affected by four main tectonic events complicated by six principal eustatic changes. Some success was achieved in filtering the global and regional tectoniceustatic effects and in proposing causes for some of the events.
Contrasting seismic characteristics of three major faults in northwestern Canada
Authors: Snyder David B , Roberts Brian J , Gordey Steven P
Published: October 2005

The Lithoprobe Slave  Northern Cordillera Lithospheric Evolution (SNORCLE) profiles crossed three major tectonic zones of the northwestern Canadian Shield and northern Canadian Cordillera that are diverse in age and in depth of penetration. The oldest (26302590 Ma), the Yellowknife River fault zone, formed as a strike-slip fault in a tensional strain regime. Reflector attenuation or truncations align vertically beneath the fault trace through much of the crust, implying a near-vertical fault plane. The youngest (6010 Ma), the Tintina fault zone, produced cumulative dextral strike-slip displacements of 425 km, perhaps 800 km. Tomographic velocity and ray-trace models of reflection data indicate that several fault splays form a tectonic zone 30 km wide at the surface, but truncations of deeper crustal reflections suggest that the zone thins in the mid-crust and widens near the Moho. This apparent variable width versus depth of the Tintina fault is atypical of major strike-slip faults worldwide. The Teslin fault was an active terrane boundary during accretion of terranes onto North America. Observed reflection geometries indicate that the juxtapositions of highly contrasting metamorphic grades across the Teslin fault are confined to the upper crust along SNORCLE line 3, implying that the fault soles eastward into a mid-crustal detachment at the interpreted top of North American crust. The limited depth extent of the Teslin fault zone is similar to some models of the San Andreas fault and may result from their similar histories as convergent margin structures.
Constraints on the composition of the crust and uppermost mantle in northwestern Canada: Vp/Vs variations along Lithoprobe's SNorCLE transect
Authors: Fernández-Viejo Gabriela , Clowes Ron M , Welford J Kim
Published: October 2005

Shear-wave seismic data recorded along four profiles during the SNoRE 97 (1997 Slave  Northern Cordillera Refraction Experiment) refraction  wide-angle reflection experiment in northwestern Canada are analyzed to provide S-wave velocity (Vs) models. These are combined with previous P-wave velocity (Vp) models to produce cross sections of the ratio Vp/Vs for the crust and upper mantle. The Vp/Vs values are related to rock types through comparisons with published laboratory data. The Slave craton has low Vp/Vs values of 1.681.72, indicating a predominantly silicic crustal composition. Higher values (1.78) for the Great Bear and eastern Hottah domains of the Wopmay orogen imply a more mafic than average crustal composition. In the western Hottah and Fort Simpson arc, values of Vp/Vs drop to ∼1.69. These low values continue westward for 700 km into the Foreland and Omineca belts of the Cordillera, providing support for the interpretation from coincident seismic reflection studies that much of the crust from east of the Cordilleran deformation front to the Stikinia terrane of the Intermontane Belt consists of quartzose metasedimentary rocks. Stikinia shows values of 1.781.73, consistent with its derivation as a volcanic arc terrane. Upper mantle velocity and ratio values beneath the Slave craton indicate an ultramafic peridotitic composition. In the Wopmay orogen, the presence of low Vp/Vs ratios beneath the Hottah  Fort Simpson transition indicates the presence of pyroxenite in the upper mantle. Across the northern Cordillera, low Vp values and a moderate-to-high ratio in the uppermost mantle are consistent with the region's high heat flow and the possible presence of partial melt.
Influence of acidic to basic water pH and natural organic matter on aluminum accumulation by gills of rainbow trout (Oncorhynchus mykiss)
Authors: Winter Anna R , Nichols Joel W , Playle Richard C
Published: October 2005

Juvenile rainbow trout (Oncorhynchus mykiss) (∼0.6 g) were exposed to 3 µmol Al·L1in ion-poor water adjusted to pH 410 in the absence or presence of natural organic matter (NOM). Aluminum accumulation by trout gills was highest at pH 68, there was moderate Al accumulation by trout gills at pH 5 and 9, and trout at pH 4 and 10 did not accumulate any Al on their gills. NOM at 5 mg C·L1eliminated Al accumulation by trout gills at all water pHs. These results are explained by NOM complexing Al and keeping Al in solution but off the gills, by H+competition with Al3+at low pH, by poor binding of the Al(OH)4anion to negatively charged gills at high pH, and by polymerization and precipitation of Al onto the gills at intermediate water pH, especially if water pH in the gill micro environment is considered. Increased fish mortality at pH 10 in the presence of NOM is explained by the indirect effect of NOM tying up the limited amount of Ca in the ion-poor water.
The importance of microzooplankton versus phytoplankton to copepod populations during late winter and early spring in Lake Michigan
Authors: Bundy Marie H , Vanderploeg Henry A , Lavrentyev Peter J , Kovalcik Paul A
Published: October 2005

Feeding rates of the calanoid copepod Leptodiaptomus sicilis on natural assemblages of phytoplankton and microzooplankton were evaluated during late winter and early spring in Lake Michigan. Microzooplankton were the preferred food source for this copepod, and larger size fractions of phytoplankton were preferred to smaller size fractions. Ingestion rates of total chlorophyll a ranged from 2 to 14 ng·copepod1·day1, while ingestion rates of micro zoo plank ton biomass ranged from 0.04 to 0.15 µg C·copepod1·day1. In these experiments, microzooplankton carbon accounted for 22%74% of the total carbon ingested. Clearance rates of microzooplankton carbon were positively related to the larger size fractions of chlorophyll a and to total suspended solids. Measured ingestion rates of microzooplankton and phyto plankton carbon suggest that calanoid copepod populations have the potential to control microzooplankton production in late winter and early spring, and even with an abundance of phytoplankton carbon, food availability may limit the reproduction of L. sicilis. Because microzooplankton contribute significantly to the diet of these copepods, stimulation of the microbial food web by terrigenous inputs of nutrients and carbon may be transmitted to higher trophic levels (i.e., mesozooplankton and their predators) through heterotrophic flagellates and protozoans.
Food web alterations that promote native species: the recovery of cisco (Coregonus artedi) populations through management of native piscivores
Authors: Krueger Damon M , Hrabik Thomas R
Published: October 2005

We evaluated the effects of fisheries management on food webs in three northern Wisconsin lakes with exotic rainbow smelt (Osmerus mordax). In two of the lakes, restrictions on fishing reduced mortality rates on adult walleye (Sander vitreus) during the study period. In these lakes, walleye populations increased concurrently with a decline in rainbow smelt populations. As rainbow smelt populations declined in both lakes, native cisco (Coregonus artedi) populations increased. Our analysis of walleye diets illustrated that walleye fed selectively on rainbow smelt but did not feed on cisco during the summer months. When entered into bioenergetics simulations, this information demonstrates that walleye predation alone was enough to cause the observed rainbow smelt declines in our study lakes. Our results indicate that increased walleye density allows for a parallel increase in cisco density. Based on our results, fishery regulations to restore walleye to high densities in lakes invaded by rainbow smelt may restore native planktivores that have co-evolved traits.
A comparison of population structure in black rockfish (Sebastes melanops) as determined with otolith microchemistry and microsatellite DNA
Authors: Miller J A , Banks M A , Gomez-Uchida D , Shanks A L
Published: October 2005

The black rockfish (Sebastes melanops) is a long-lived (≤50 years) viviparous species with an extended pelagic larval period (35 months) and a broad continental distribution. Prolonged larval periods have been assumed to lead to widespread dispersal resulting in minimal population structure. We tested this assumption by comparing otolith microchemistry and microsatellite DNA of adult black rockfish from four locations in Oregon and Washington. We observed significant differences among locations in element-to-Ca ratios (Mg:Ca, Mn:Ca, Zn:Ca, Sr:Ca, and Ba:Ca) at the otolith edge, which represented the last year of life. Discriminant function analysis, based on otolith element-to-Ca ratios classified, on average, 64% of the fish to collection location, suggesting that the majority of individuals from these locations did not mix. Using microsatellite DNA, we observed significant genetic differences among adults collected 340460 km apart (FST = 0.018 ± 0.004). Using five and seven loci, 63% and 75% of the fish, respectively, were correctly assigned to collection location. These two techniques provided corroborative and complementary information on the population structure of S. melanops.
Spatial variability in rockfish (Sebastes spp.) recruitment events in the California Current System
Authors: Field John C , Ralston Stephen
Published: October 2005

A general assumption regarding spatial patterns of recruitment variability is that species with similar early life history characteristics tend to covary in reproductive success over scales of 5001000 km. These assumptions are based on evaluation of recruitments from independent stocks, as few studies have assessed synchrony in recruitment within broadly dispersed stocks over finer spatial scales. We used data on age composition and landings to generate regional time series of recruitment deviations for three species of rockfish in the California Current System (Sebastes goodei, Sebastes entomelas, and Sebastes flavidus). We then used correlation analysis, principal components analysis, and other methods to evaluate the degree of synchrony among recruitment events in these regions. Results show that 51%72% of the year-to-year variability in recruitment is shared coastwide within these species, while a lesser but significant fraction of the variability is associated with finer scale geographic features.
Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates?
Authors: Winder Monika , Schindler Daniel E , Moore Jonathan W , Johnson Susan P , Palen Wendy J
Published: October 2005

In coastal areas of the Pacific Northwest bears (Ursus spp.) prey heavily on spawning Pacific salmon (Oncorhynchus spp.) and selectively kill energy-rich individuals that are the most recent arrivals on spawning grounds. Pacific salmon eventually die in spawning habitats anyway, albeit with considerably lower energetic content. We investigated whether foraging activities of bears facilitate growth of stream invertebrates by increasing the duration of salmon carcass availability and the nutritional value of carcasses for scavengers. Our survey in southwest Alaska showed that carcasses are highly colonized by caddisfly (Trichoptera) larvae. Caddisflies show a strong preference for bear-killed over senescent carcasses, which may be a result of extended temporal availability, improved accessibility of consumable tissue, and higher energetic content of bear-killed fish. Isotope analyses further indicate uptake of marine-derived nutrients in caddisflies during the salmon run, which, however, does not extend into subsequent generations. Thus, species with life histories linked to the annual marine derived nutrient pulse gain the biggest advantage from the salmon resource subsidy. A long-term survey in several creeks in this region showed that bear predation intensity varied greatly among creeks and years, therefore indirect effects of bear predation on aquatic scavengers are likely highly patchy in time and space.
RNA/DNA ratio and total length of yellow perch (Perca flavescens) in managed and natural wetlands of a large fluvial lake
Authors: Tardif D , Glémet H , Brodeur P , Mingelbier M
Published: October 2005

RNA/DNA ratios and total lengths were compared to determine growth patterns of age-0 yellow perch (Perca flavescens) in managed and natural habitats of a large fluvial lake (Lake Saint-Pierre, St. Lawrence River, Quebec, Canada) over seasonal and yearly temporal scales. In 2002, the RNA/DNA ratio responded to degree-days accumulated over periods of 78 days before sampling, while in 2003, no relationship with temperature was established. The growth patterns obtained each year probably reflect indices responding to different limiting variables. In 2002, temperature would have been limiting, whereas in 2003, other factors such as prey availability, food quality, and competition may have influenced growth. In addition, the discrepancy between total length and RNA/DNA ratio observed in 2003 may reflect a differential time of response to limiting variables. These results together show that the two indices reflect growth at different time scales and suggest that their combination can help identify shifts between limiting environmental variables. Also, growth in managed wetlands during springtime was systematically superior to that in the natural environment, supporting the contention that managed wetlands are highly productive habitats. In natural habitats, growth rates were higher on the south shore by summer, which is consistent with the established north-south productivity gradient in Lake Saint-Pierre.
Environmental predictors of benthic consumers and autotrophic communities along a recovery gradient
Authors: Hogsden Kristy L , Vinebrooke Rolf D
Published: October 2005

Ecological theory predicts that biological factors replace abiotic regulation of community structure during recovery from ecosystem stress. We examined relationships between benthic autotroph (epilithic periphyton) and consumer communities, and environmental variables, along a gradient of six recovering acidified lakes to identify the best explanatory variables of community structure. Dissolved organic carbon, pH, and total dissolved phosphorus were important predictors of autotrophic biomass, while total dissolved phosphorus was the only significant factor explaining variation in consumer biomass. Abiotic factors (e.g., dissolved organic carbon, pH) were also significant predictors of autotrophic and consumer community composition. Autotrophic biomass was significantly greater in recovering lakes owing to an increased abundance of attached filamentous green algae. However, consumer biomass did not differ significantly between severely stressed and recovering lakes because of a compensatory shift from numerous small tolerant omnivores to fewer large-bodied sensitive grazers. Lack of a significant relationship between autotrophic and consumer biomass along with stable isotopic evidence of few primary consumers suggested that grazing pressure was weak, especially in the stressed lakes. The persistent importance of abiotic factors to autotrophic and consumer communities suggested that ecosystem recovery remained incomplete in these lakes.
Imbalance of fatty acids in the base of the Baltic Sea food web  a mesocosm study
Authors: Ahlgren Gunnel , Nieuwerburgh Lies Van , Wänstrand Ingrid , Pedersén Marianne , Boberg Merike , Snoeijs Pauli
Published: October 2005

A reproductive disturbance in Baltic Sea Atlantic salmon (Salmo salar), the M74 syndrome, has been reported since early 1970s and has occasionally caused up to 90% mortality for newborn fry. Previous research has revealed that the M74 syndrome may be due to reduced levels of the vitamin thiamin, the carotenoid astaxanthin, and elevated ratios of ω3/ω6 fatty acids in salmon eggs. Using mesocosm experiments, we compared the quantity (µg·L1) and quality (mg·g1 C) of fatty acids in microalgae and copepods in the southern Baltic Sea where the M74 syndrome is common with those in a habitat in the Norwegian Sea where the syndrome has not been observed. Daily additions were made of the nutrients N and P or N, P, and Si, copepods were added after 67 days, and nutrient additions were stopped after 910 days. Flagellates dominated completely in the Baltic Sea, whereas higher phytoplankton diversity was found in the Norwegian Sea. We found elevated ω3/ω6 ratios in phytoplankton and abnormally high docosahexaenoic acid/arachidonic acid ratios (22:6ω3/20:4ω6) in copepods in the Baltic Sea mesocosms compared with those in the Norwegian Sea. Our results suggest that imbalance in fatty acid composition may prevail in the basic food web of the Baltic Sea.
Estimates of egg deposition and effects of lake trout (Salvelinus namaycush) egg predators in three regions of the Great Lakes
Authors: Jonas Jory L , Claramunt Randall M , Fitzsimons John D , Marsden J Ellen , Ellrott Brian J
Published: October 2005

Excessive mortality from spawning through the first year of life is likely responsible for recruitment failures in many lake trout (Salvelinus namaycush) populations. We evaluated relationships between interstitial predator species and lake trout egg deposition in three regions of the Great Lakes. The introduced crayfish Orconectes rusticus dominated the nearshore zone in northern Lake Michigan, whereas other sites in Lake Michigan and Parry Sound were dominated by native Orconectes propinquus. In Lake Champlain, sculpin (Cottus spp.) were the most common interstitial predator, yet densities were comparable with those in Lake Michigan. Predator densities in Lake Michigan (mean ± standard error = 15.5 ± 0.4 predators·m2) were twice those in Lake Champlain or Parry Sound (6 ± 1 predators·m2). Densities of eggs were higher in Lake Champlain (2994.1 ± 398.3 eggs·m2) and Parry Sound (454.7 ± 36.3) than in Lake Michigan (7.5 ± 1.3; Kruskal-Wallis, P ≤ 0.05). Ratios of eggs to predator provide simple measures of the effectiveness of lake trout rehabilitation efforts. The average ratio calculated from 10 successful spawning locations is 190 eggs·predator1·m2. Ratios may help establish target egg densities for restoration efforts and the concentration of spawning adults required to allow survival to the fry stage.
Growth potential and host mortality of the parasitic phase of the sea lamprey (Petromyzon marinus) in Lake Superior
Authors: Jorgensen Jeffrey C , Kitchell James F
Published: October 2005

Landlocked Lake Superior sea lampreys (Petromyzon marinus) cause a significant but uncertain amount of mortality on host species. We used a sea lamprey bioenergetics model to examine the scope of host sizes vulnerable to death as a consequence of sea lamprey feeding and incorporated the bimodal lake-ward migration of parasitic sea lampreys. At their peak feeding rate and maximum size (P = 1.0, proportion of maximum consumption), spring migrants were capable of killing lean lake trout (Salvelinus namaycush) hosts ≤ 2.0 kg, which was larger than fall migrants (1.8 kg). Spring migrants feeding on Pacific salmon (coho (Oncorhynchus kisutch), Chinook (Oncorhynchus tshawytscha), and steelhead (Oncorhynchus mykiss)) killed hosts ≤ 2.0 kg, but fall migrants killed hosts as large as 2.8 kg. Although there is no direct empirical evidence, bioenergetics modeling suggests that it is plausible that some of the largest sea lampreys in Lake Superior spent more than one summer as parasites. Two-summer parasites readily attained sizes of sea-run adult anadromous sea lampreys and killed hosts from 3 to >5.5 kg in size. The maximum upper limit number of 2-kg hosts killed by two-summer parasites was nearly twice that of one-summer parasites.
Sea lamprey (Petromyzon marinus) size trends in a salmonid stocking context in Lake Superior
Authors: Jorgensen Jeffrey C , Kitchell James F
Published: October 2005

Fish community objectives for Lake Superior call for restoration such that it resembles its historical species composition, to the extent possible, yet allow for supplementation of naturalized Pacific salmonids (Oncorhynchus spp.). To achieve these goals, managers strive to control the sea lamprey (Petromyzon marinus) to levels that cause insignificant (<5%) mortality to host species. While control efforts have been successful, sea lamprey size has increased during the control period. We analyzed long-term sea lamprey size trends and found a significant increase from 1961 to 2003 (F = 36.76, p < 0.001, R2 = 0.473). A local regression revealed two significant size increase periods. We used Bayesian model averaging to find the relationship between sea lamprey size and the stocking of salmonids (lean lake trout (Salvelinus namaycush) and Pacific salmon). Bayesian model averaging identified 91 models, and several regressors were common features in many of the models. Sea lamprey weight was related to stocked lake trout lagged 3, 9, 11, and 13 years, and stocked Pacific salmon lagged 4 years. If sea lampreys can achieve larger sizes attached to Pacific salmonid hosts, and thus inflict more damage, there may be a trade-off for managers in achieving the fish community objectives for Lake Superior.
Early life history of Lake Michigan alewives (Alosa pseudoharengus) inferred from intra-otolith stable isotope ratios
Authors: Dufour Elise , Patterson William P , Höök Tomas O , Rutherford Edward S
Published: October 2005

We apply a robotic micromilling technique to the sampling of young-of-the-year (YOY) and 1+ otoliths from alewives (Alosa pseudoharengus) captured in different habitat types of Lake Michigan during 20012003. δ18O values of otolith cores of YOY alewives from Muskegon Lake (a sheltered, drowned river mouth lake connected to Lake Michigan), Muskegon Channel (which connects Muskegon Lake to Lake Michigan), and Lake Michigan proper are compared with δ18O values of ambient water from different potential early life habitats. Otolith core δ18O values used in conjunction with δ13C values serve as good discriminators of nursery areas. The majority of YOY alewives captured in Muskegon Lake emerge and grow in this habitat, whereas the majority of YOY alewives captured in Lake Michigan emerge and grow in Lake Michigan. In addition, early-life movements of alewives between the two lakes are documented but limited. Even if drowned river mouth lakes are more favorable for alewife growth and survival, their contribution to the Lake Michigan population could be limited because all of the 1+ alewives were individuals that spent their early life in Lake Michigan. The application of high-resolution isotope analysis of small otoliths of forage fish for fish population dynamics studies appears promising.
Predicting cutthroat trout (Oncorhynchus clarkii) abundance in high-elevation streams: revisiting a model of translocation success
Authors: Young Michael K , Guenther-Gloss Paula M , Ficke Ashley D
Published: October 2005

Assessing viability of stream populations of cutthroat trout (Oncorhynchus clarkii) and identifying streams suitable for establishing populations are priorities in the western United States, and a model was recently developed to predict translocation success (as defined by an index of population size) of two subspecies based on mean July water temperature, pool bankfull width, and deep pools counts. To determine whether the translocation model applied to streams elsewhere with more precise abundance estimates, we examined the relation between electrofishing-based estimates of cutthroat trout abundance and these habitat variables plus occupied stream length. The preferred model was (population size)1/2 = 0.00508(stream length (m)) + 5.148 (N = 31). In contrast, a model based on data from the original translocation model included stream temperature and deep pool counts as variables. Differences in models appear to largely have a methodological rather than biological basis. Additional habitat coupled with increased habitat complexity may account for the form of the abundance  stream length relation in the electrofishing-based model. Model-derived estimates imply that many cutthroat trout populations are below thresholds associated with reduced risk of extinction. We believe that this model can reduce uncertainty about projected population sizes when selecting streams for reintroductions or evaluating unsampled streams.
Hiemenz flow of a micropolar viscoelastic fluid in hydromagnetics
Authors: El-Kabeir S MM
Published: October 2005

Boundary-layer equations are solved for the hydromagnetic problem of two-dimensional Hiemenz flow, for a micropolar, viscoelastic, incompressible, viscous, electrically conducting fluid, impinging perpendicularly onto a plane in the presence of a transverse magnetic field. The governing system of equations is first transformed into a dimensionless form. The resulting equations then are solved by using the RungeKutta numerical integration procedure in conjunction with shooting technique. Numerical solutions are presented for the governing momentum and angular-momentum equations. The proposed approximate solution, although simple, is nevertheless sufficiently accurate for the entire investigated range of values of the Hartman number. The effect of micropolar and viscoelastic parameters on Hiemenz flow in hydromagnetics is discussed.PACS No.: 46.35
Analytical and numerical solutions of generalized Burgers' equation via Buckingham's Pi-theorem
Authors: Hassanien I A , Salama A A , Hosham H A
Published: October 2005

A generalized dimensional analysis performed by using Buckingham's Pi-theorem for the generalized Burgers' equation is presented. The application of the Buckingham Pi-theorem is used to reduce the governing partial differential equation with the boundary and initial conditions to an ordinary differential equation with appropriate corresponding conditions. By using a scaling invariant we simplify the similarity solutions, which are discussed for a specific choice of boundary conditions, and yield analytical solutions, which are in closed form. Also, using extended one-step methods of order five we solve the final ordinary differential equations. This criterion for solvability involves converting the boundary value problem to an initial value problem. PACS Nos.: 02.60.Lj, 47.27.Jv
Radial fall of a test particle onto an evaporating black hole
Authors: Aste Andreas , Trautmann Dirk
Published: October 2005

A test particle falling onto a classical black hole crosses the event horizon and ends up in the singularity within finite eigentime. In the "more realistic" case of a "classical" evaporating black hole, an observer falling onto a black hole observes a sudden evaporation of the hole. This illustrates the fact that the discussion of the classical process, commonly found in the literature, may become obsolete when the black hole has a finite lifetime. The situation is basically the same for more complex cases, for example, where a particle collides with two merging black holes. It should be pointed out that the model used in this paper is mainly of academic interest, since the description of the physics near a black-hole horizon still presents a difficult problem that is not yet fully understood, but our model provides a valuable possibility for students to enter the interesting field of black-hole physics and to perform numerical calculations of their own that are not very involved from the computational point of view.PACS Nos.: 04.25.g, 04.70.s, 04.70.Dy
Improved theoretical prediction for the 2s hyperfine interval in helium ion
Authors: Karshenboim S G , Ivanov V G
Published: October 2005

We consider the uncertainty of theoretical calculations for a specific difference of the hyperfine intervals in the 1s and 2s states in a light hydrogen-like atom. For a number of crucial radiative corrections the result for the hydrogen atom and the helium ion appears as an extrapolation of the numerical data from medium to low Z. An approach to a plausible estimation of the uncertainty is suggested using the example of the difference D21 = 8Ehfs(2s)  Ehfs(1s). PACS Nos.: 12.20.FV, 21.45.+v, 31.30.Jv, 32.10.Fn
Bearing capacity factorNγfor ring footings using the method of characteristics
Authors: Kumar Jyant , Ghosh Priyanka
Published: October 2005

The bearing capacity factor Nγwas determined for both smooth and rough ring footings using the method of stress characteristics. The analysis was based on the assumption that for a rough footing the friction angle (δ) between the footing base and underlying cohesionless material increases gradually from zero along the axis of symmetry to ϕ along the outer edge of the footing. The value of Nγwas found to decrease significantly with an increase in ri/ro, where riand roare the inner and outer radii of the ring, respectively. For larger values of ϕ, the magnitude of Nγfor a rough footing was seen to be significantly higher than that for a smooth footing. The obtained results were compared with those available in the literature.Key words: bearing capacity, failure, foundations, method of characteristics, plasticity.
Radial consolidation of clay using compressibility indices and varying horizontal permeability
Authors: Indraratna Buddhima , Rujikiatkamjorn Cholachat , Sathananthan Iyathurai
Published: October 2005

A system of vertical drains, with surcharge load to accelerate consolidation by shortening the drainage path, is one of the most popular methods of soft ground improvement. The conventional radial consolidation theory (including smear and well resistance) has been commonly used to predict the behaviour of vertical drains in soft clay. Its mathematical formulation is based on the small strain theory; and for a given stress range, a constant volume compressibility (mv) and a constant coefficient of horizontal permeability (kh) are assumed. However, the value of mvvaries along the consolidation curve over a wide range of applied pressure (Δp). In the same manner, khalso changes with the void ratio (e). In this paper, the writers have replaced mvwith the compressibility indices (Ccand Cr), which define the slopes of the e  log σ′ relationship. Moreover, the variation of the horizontal permeability coefficient (kh) with the void ratio (e) during consolidation is represented by the e  log khrelationship that has a slope of Ck. In contrast to the conventional analysis, the current study highlights the influence of the Cc/Ck(or Cr/Ck) ratio and the preloading increment ratio (Δp/σi) on the consolidation process. The analytical predictions are compared with the experimental results when a large-scale consolidation chamber was used, and these predictions show good agreement with the measured data. Finally, an embankment case history taken from Muar Plains, Malaysia, is analysed on the basis of the current solution and compared with field measurements.Key words: compressibility, embankments, permeability, soft soils, soil consolidation, vertical drains.
Consolidation properties of a dewatered municipal sewage sludge
Authors: O'Kelly Brendan C
Published: October 2005

The consolidation properties of a dewatered municipal sewage sludge were studied using the oedometer, hydraulic consolidation cell, and triaxial apparatus. Bioactive and stabilized test specimens of dried-compacted material and slurry material at different states of biodegradation (LOI = 5570%, where LOI is the loss on ignition) were consolidated under applied stresses of 3400 kPa. The rate of biogas production and the resulting pore pressure response of the unsaturated material were also studied for different specimen drainage conditions. The sludge material largely consisted of organic clay-sized particles, and although highly compressible, the material was practically impermeable (k = 1091011 m/s for slurry material, where k is the coefficient of permeability). Primary consolidation generally constituted only a small part of the overall deformation response for moderately degraded material (LOI [Formula: see text] 70%). Secondary compression was dominant, and for the bioactive material, included a significant contribution as a result of ongoing degradation of the organic solids. The contribution of primary consolidation to the overall deformation response increased for higher levels of treatment (LOI [Formula: see text] 55%) and the coefficient of secondary compression (Csec) values reduced; for example, Csec = 0.100.24 (σa = 35150 kPa, where σa is the applied stress) for moderately degraded material and Csec [Formula: see text] 0.09 (σa = 300 kPa) for strongly degraded material. Biogas evolved from the material at a steady rate of up to 0.33 m3 gas/day/tonne for moderately degraded slurry, which caused the pore pressure to steadily increase to up to 40 kPa/day when the biogas remained trapped within the specimens.Key words: sewage sludge, consolidation, biodegrade, biogas.
Shaking table tests and stability analysis of steep nailed slopes
Authors: Hong Yung-Shan , Chen Rong-Her , Wu Cho-Sen , Chen Jian-Ren
Published: October 2005

Shaking table tests were performed on five model slopes to examine the effects of the angle and length of the nails and the frequency of excitation on the seismic resistance and failure mechanism of the slopes. Seismic excitation was also applied to slopes at various angles. Experimental results showed that nails markedly improved the seismic resistance of all model steep slopes. Additionally, nailed slopes exhibit characteristics of ductility under strong excitation. The angle of the nails influences the deformation of the slope but only slightly affects seismic resistance. An increase in the length of the nails increased the seismic resistance of the slope and reduced the displacement of the facing only when subjected to strong excitation. The slope at an angle of 90° to the horizontal has a markedly lower seismic resistance than that at 80°. The rocking of the model slope was strong for the slope with inclined nails and the slope at 90° to the horizontal. The failure surface of the soil mass is approximately a bilinear surface; the pullout of nails from the lower rows of nails caused total slope failure. The seismic resistance of a nailed slope is categorized viz. response of the models by three stages: stable, seismic resistance, and incipient collapse phases. Critical seismic acceleration coefficients of all models are evaluated and compared with values predicted by a developed pseudo-static, limit-equilibrium-based slope stability approach, which postulates a two-wedge failure mechanism.Key words: shaking table test, steep nailed slope, seismic resistance, pseudo-static approach.
Characteristics of wall deflections and ground surface settlements in Shanghai
Authors: Wang Zhong W , Ng Charles WW , Liu Guo B
Published: October 2005

The characteristics of wall deflections and surface ground settlements at six deep multi-strutted excavations in Shanghai soft soils were studied and compared with those of similar case histories reported worldwide, particularly in Taipei and Singapore. The measured wall deflections at the six metro stations of the Pearl II Circle Line show a typical bulging profile (or deep-seated shape) at the end of the excavation. The ratio between the measured maximum wall deflection and the depth of the excavation (δhm/H) in Shanghai was <0.007, which was similar to the ratio measured in Taipei, but it was substantially smaller than the Peck bounding limit of 0.01. At each station, the measured maximum displacement was <0.45% of the final excavation depth. Because of the large aspect ratios of the underground excavations, no significant three-dimensional effects or corner effects were observed. The measured maximum settlements of the six metro excavations fell within zone I of the Peck classical normalized settlement-distance chart. These small measured settlements were consistent with the small measured wall deflections. The observed relatively small maximum wall deflections can likely be attributed to the use of prestressed struts, the constant adjustment of the stresses to about 0.7 times the total vertical stress during the excavation, and the short horizontal span of the excavation.Key words: multi-strutted excavations, soft clay, Shanghai, metro stations, horizontal deflection, settlement.