bluuebunny/crossref_metadata_2025 huggingface dataset:
Protective refuges for seeded juvenile scallops (Placopecten magellanicus) from sea star (Asterias spp.) and crab (Cancer irroratus and Carcinus maenas) predation
Authors: Wong Melisa C , Barbeau Myriam A , Hennigar Allan W , Robinson Shawn MC
Published: September 2005

We examined two methods to provide refuge for seeded juvenile sea scallops (Placopecten magellanicus) from sea star (Asterias spp.) and crab (Cancer irroratus and Carcinus maenas) predation by considering (i) initial density of seeded scallops and (ii) presence of an alternative prey species (blue mussel (Mytilus edulis)). In the seeding density experiment, underwater plots were seeded with different densities of scallops (1, 6, and 69·m2). In the alternative prey experiment, plots were seeded with one density of scallops (5·m2) and different densities of mussels (0, 5, and 30·m2). Animal densities were monitored over time, and predation rate was estimated using tethered scallops. In the seeding density experiment, scallop density in plots initially seeded with 6 scallops·m2 decreased at the slowest rate. Estimated predation rate of scallops in all plots tended to increase with prey density. In the alternative prey experiment, mussel density decreased immediately after seeding, while scallop density decreased after approximately 1 week. Estimated predation rate of scallops decreased with increasing mussel density. Also, sea stars aggregated in plots containing scallops and mussels. In both experiments, 17%58% of seeded scallops were lost to dispersal, and final scallop density was approximately 1·m2, independent of treatment.
An ecosystem-based hypothesis for climatic effects on surplus production in California sardine (Sardinops sagax) and environmentally dependent surplus production models
Authors: Jacobson Larry D , Bograd Steven J , Parrish Richard H , Mendelssohn Roy , Schwing Franklin B
Published: September 2005

We used environmentally dependent surplus production (EDSP) models to test hypotheses linking changes in habitat area, carrying capacity and surplus production in California sardine (Sardinops sagax). Habitat area (with mean sea surface temperatures of 1416 °C) was centered off Oregon, Washington, and British Columbia during JulyDecember and off southern and central California during JanuaryJune. Habitat area increased during El Niño and decreased during La Niña events. EDSP models fit better than a conventional Fox surplus production model without environmental data. Our estimated fishing mortality rate at maximum sustained yield FMSY = 0.099·year1 was consistent with other estimates. Maximum sustained yield (MSY) and stock biomass for MSY (BMSY) depend on habitat area and environmental conditions. Negative surplus production occurred when biomass was high and habitat area declined abruptly. Managers might monitor habitat area to anticipate changes in the California sardine stock and changes in the California Current ecosystem. Periods of high productivity appear easier to identify than periods of negative productivity. Models that incorporate environmental effects on both recruitment and survival and mortality of adult fish appear useful in studying climatic effects on fishery surplus production.
Methyl mercury concentrations in macroinvertebrates and fish from burned and undisturbed lakes on the Boreal Plain
Authors: Allen Erik W , Prepas Ellie E , Gabos Stephan , Strachan William MJ , Zhang Weiping
Published: September 2005

Methyl mercury (MeHg) concentrations in macroinvertebrates and fish were compared among five lakes in burned catchments and five reference lakes on the western Canadian Boreal Plain to determine the influence of forest fire on MeHg bioaccumulation. Two years after fire, MeHg concentrations in five of six aquatic taxa were similar in burned and reference lakes. Among a larger set of 12 lakes, MeHg concentrations in biota were negatively correlated with lake water pH, trophic status, and hardness, reflecting a pre-existing gradient in water chemistry. Biomagnification of MeHg (as determined by regression of MeHg concentration on baseline-adjusted δ15N) was negatively correlated with lake water chlorophyll a concentration. A subsequent logging experiment interrupted by fire provided an opportunity to compare pre- and post-fire MeHg concentrations in aquatic biota. Three months after fire, biota MeHg concentrations had decreased by 32%50%, and lake water ammonium concentrations had increased 11-fold relative to the previous year. In this nutrient-rich setting, fire may lower MeHg concentrations in aquatic biota over the short-term by inducing an increase in lake productivity that dilutes MeHg at the base of the food web.
Effects of turbidity on the reactive distance, search time, and foraging success of juvenile Atlantic cod (Gadus morhua)
Authors: Meager Justin J , Solbakken Turid , Utne-Palm Anne C , Oen Tina
Published: September 2005

We investigated the effects of turbidity on the foraging behaviour of juvenile Atlantic cod (Gadus morhua) on mysid prey (Praunus neglectus) in the laboratory. The influence of turbidity on vision and chemoreception was examined by measuring reactive distances and search times to visual, chemical, and visualchemical prey cues over turbidity levels ranging from 0.4 to 17·m1(beam attenuation·m1). We also compared foraging rates of juvenile cod on mysids in highly turbid water and clear water under well lit and totally dark conditions. Juvenile cod using chemical cues were able to locate mysids from significantly longer distances than when only visual cues were available. Turbidity did not affect reactive distance to chemical cues, and had only a weak negative effect on reactive distance to visual and visualchemical cues. Search time was variable, but tended to increase with turbidity. Turbidity did not affect predation rates on free-ranging mysids, but predation rates were significantly lower in dark conditions than in well lit conditions. We suggest that juvenile cod use chemoreception in conjunction with vision (at close ranges) to locate prey in highly turbid water.
Genetic and demographic implications of aquaculture in white sturgeon (Acipenser transmontanus) conservation
Authors: Jager Henriette I
Published: September 2005

This study uses a genetic individual-based model of white sturgeon (Acipenser transmontanus) populations in a river to examine the genetic and demographic trade-offs associated with operating a conservation hatchery. Simulation experiments evaluated three management practices: (i) setting quotas to equalize family contributions in an effort to prevent genetic swamping, (ii) an adaptive management scheme that interrupts stocking when introgression exceeds a specified threshold, and (iii) alternative broodstock selection strategies that influence domestication. The first set of simulations, designed to evaluate equalizing the genetic contribution of families, did not show the genetic benefits expected. The second set of simulations showed that simulated adaptive management was not successful in controlling introgression over the long term, especially with uncertain feedback. The third set of simulations compared the effects of three alternative broodstock selection strategies on domestication for hypothetical traits controlling early density-dependent survival. Simulated aquaculture selected for a density-tolerant phenotype when broodstock were taken from a genetically connected population. Using broodstock from an isolated population (i.e., above an upstream barrier or in a different watershed) was more effective at preventing domestication than using wild broodstock from a connected population.
Covariation between grey seal (Halichoerus grypus) abundance and natural mortality of cod (Gadus morhua) in the southern Gulf of St. Lawrence
Authors: Chouinard G A , Swain D P , Hammill M O , Poirier G A
Published: September 2005

More than 10 years after the collapse of Atlantic cod (Gadus morhua) fisheries in Canada, the role of increased seal populations in the decline and lack of recovery of the stocks continues to be discussed. Using removals and abundance indices from synthetic populations, we found that sequential population analysis can uncover trends in natural mortality. We used this approach to examine variation in natural mortality (M) of southern Gulf of St. Lawrence cod. M increased from the late 1970s to the mid-1990s but declined slightly recently. Results were consistent with previous work indicating that M increased in the 1980s. Changes in estimated M for this cod stock matched fluctuations in grey seal (Halichoerus grypus) abundance. The increase in grey seal abundance from the late 1970s to the mid-1990s corresponded with the increase in estimated M of cod over this time period. The correspondence between seal abundance and M of cod supports the hypothesis that seal predation may be a cause of increased M. However, the diet information available suggests that seals consume mainly juvenile cod, whereas our evidence for an increase in M is for larger cod (ages 3 years and older).
Grey gurnard (Eutrigla gurnadus) in the North Sea: an emerging key predator?
Authors: Floeter Jens , Kempf Alexander , Vinther Morten , Schrum Corinna , Temming Axel
Published: September 2005

Grey gurnard (Eutrigla gurnadus) is a widely distributed demersal species in the North Sea that has been ranked frequently among the 10 dominant species. Since the late 1980s, grey gurnard catch rates in the international bottom trawl surveys showed a pronounced increase and it was included as an "other predator" in the North Sea multispecies virtual population analysis (MSVPA) in 1997. The MSVPA results estimated grey gurnard to be responsible for approximately 60% of the total predation mortality on age-0 Atlantic cod (Gadus morhua). Long-term MSVPA predictions led to the extinction of North Sea cod. As a possible technical reason, the Holling type II functional response implemented in the model was discussed. In the current analysis, it was demonstrated that the Holling type II functional response was not responsible for the extinction of cod in the model, which was rather a true effect of high grey gurnard predation. Further, it was shown that grey gurnard predation had a significant top-down effect on whiting (Merlangius merlangus) and potentially also on cod recruitment, which was linked to the spatial distribution of the three species. Eventually, the implications of the results for North Sea cod stock recovery plans were discussed.
Distributionabundance relationships for North Sea Atlantic cod (Gadus morhua): observation versus theory
Authors: Blanchard Julia L , Mills Craig , Jennings Simon , Fox Clive J , Rackham Brian D , Eastwood Paul D , O'Brien Carl M
Published: September 2005

Density-dependent habitat selection has implications for fisheries management and for the recovery of depleted fish populations. According to ideal free distribution theory, populations contract into areas of highest habitat suitability as their abundance decreases. This can increase their vulnerability to fishing and predation. We detected density-dependent habitat selection by juvenile Atlantic cod (Gadus morhua) (ages 1 and 2) in the North Sea and compared the observed distributionabundance relationships with those predicted from a model based on ideal free distribution theory and knowledge of optimal temperatures for growth, where temperature was used as a measure of suitability. As predicted by the model, in years when stock size was low, the catches were largely confined to regions with near-optimal bottom temperatures. Conversely, when population size was high, catches were spread across a larger area including regions with suboptimal temperatures. The spatial extent of optimal habitat appears to have decreased from 1977 to 2002, reflecting a gradual warming of the North Sea. The combined negative effects of increased temperature on recruitment rates and the reduced availability of optimal habitat may have increased the vulnerability of the cod population to fishing mortality.
Foraging behavior, morphology, and life history variation determine the ontogeny of piscivory in two closely related predators
Authors: Graeb Brian DS , Galarowicz Tracy , Wahl David H , Dettmers John M , Simpson Mathew J
Published: September 2005

The ontogeny of piscivory is an important process during the early life history of many fishes, and why ontogenetic patterns of closely related species vary is unclear. We experimentally evaluated the importance of several factors that can determine the switch to piscivory in two predators with different dietary ontogenies: walleye (Sander vitreus), a specialist piscivore, and yellow perch (Perca flavescens), a dietary generalist. We conducted growth and prey selection experiments across several sizes of both predators using fish, zooplankton, and benthic invertebrates as prey. Walleye exhibited piscivorous feeding behavior throughout all size classes (2080 mm), whereas yellow perch were generalist predators, showing negative to neutral selection for fish prey and lower growth than walleye when feeding on fish. Walleye foraged more efficiently than yellow perch on all prey types, in part because gape widths of walleye increased more quickly with size. Bioenergetic model simulations showed that walleye grew slower than yellow perch when the proportion of fish was low in diets, but walleye growth was faster than yellow perch on a diet dominated by fish. Feeding behavior, morphology, and life history patterns likely work in combination, allowing walleye to switch to piscivory earlier than yellow perch.
Persistent organic pollutants in river food webs: influence of trophic position and degree of heterotrophy
Authors: Berglund Olof , Nyström Per , Larsson Per
Published: September 2005

We investigated how the degree of autotrophy/heterotrophy and organism trophic position influenced the bioaccumulation of polychlorinated biphenyls (PCBs) in 10 benthic river food webs consisting of terrestrial detritus, periphyton, invertebrates, and age-0 brown trout (Salmo trutta) in southern Sweden. Concentrations of PCBs increased with trophic position, estimated from δ15N and δ13C, on a dry weight basis (ng·g1 dry weight) but not on a lipid weight basis (ng·g1 lipid). PCB biomagnification factors between the first and second trophic levels (invertebrates/ periphyton and invertebrates/detritus) ranged between 0.3 and 2.3 and between the second and third levels (trout/invertebrates) between 0.3 and 2.0 on a lipid weight basis. The mean proportion of carbon ultimately derived from terrestrial sources, α, was 0.82 ± 0.19 for invertebrates and 0.67 ± 0.28 for trout. Contrary to our hypothesis, PCB concentrations in trout were positively related to α (r2 = 0.580.77, p < 0.05). As α and the periphyton density (g C·m2) in the rivers was positively related (r2 = 0.88, p < 0.01), we propose that this relationship was due to an increased retention and exposure of PCBs to trout in rivers with low grazing pressure and high periphyton density.
Periphyton response to long-term nutrient enrichment in a shaded headwater stream
Authors: Greenwood Jennifer L , Rosemond Amy D
Published: September 2005

We maintained elevated but moderate concentrations of nitrogen and phosphorus continuously for 2 years in a heavily shaded headwater stream and compared effects on stream periphyton with a reference stream. Both streams were sampled for 1 year before treatment. Some measures of periphyton biomass (ash-free dry mass and chlorophyll a) responded positively to enrichment. Increased chlorophyll a was likely a result of higher chlorophyll per cell, as total algal biovolume did not change with enrichment. These differences were greatest during high-light months (November-May), when cellular growth rates (a proxy for production) were also highest with enrichment. Algal assemblages were dominated by diatoms and remained similar between the treatment and reference streams throughout the enrichment period. Although nutrients stimulated algal growth rates, the long-term effects of nutrient addition on periphyton biomass were small in magnitude compared with other published values and were potentially suppressed by light availability and invertebrate consumption. These and other factors may have also been important in limiting the algal species pool and thus a taxonomic response to enrichment. Our results indicate that in headwater streams with intact tree canopies, chronic nutrient enrichment at moderate concentrations may have little detectable effect on benthic algal composition or periphyton biomass. Although nutrients stimulated algal growth rates, the long-term effects of nutrient addition on periphyton biomass were small in magnitude compared with other published values and were potentially suppressed by light availability and invertebrate consumption. These and other factors may have also been important in limiting the algal species pool and thus a taxonomic response to enrichment. Our results indicate that in headwater streams with intact tree canopies, chronic nutrient enrichment at moderate concentrations may have little detectable effect on benthic algal composition or periphyton biomass.
The influence of habitat complexity on littoral invertebrate distributions: patterns differ in shallow prairie lakes with and without fish
Authors: Rennie Michael D , Jackson Leland J
Published: September 2005

Relationships between littoral habitat complexity and invertebrate distributions in fishless lakes are not well understood compared with well-documented relationships in lakes with fish. We examined littoral invertebrate distributions over fine-scale gradients of weed-bed habitat complexity and contrasted these patterns in four shallow prairie lakes  two with fish and two without. The above-sediment portion of submerged macrophytes and associated invertebrates was sampled from three littoral microhabitats: weed-bed centres (highly complex), weed-bed edges (moderately complex), and single plants that grew apart from distinct weed beds (least complex). Total invertebrate densities in fishless lakes did not differ between littoral microhabitats, nor were they correlated with macrophyte biomass. In contrast, total invertebrate densities in lakes with fish increased with microhabitat complexity and were positively correlated with macrophyte biomass. Weed-bed complexity also affected littoral invertebrate community structure; in all lakes, the proportion of filter-feeders decreased with increasing microhabitat complexity, but the proportion of predatory invertebrates was greater overall in fishless lakes than in lakes with fish. Our results demonstrate that small-scale variation in littoral microhabitat complexity can lead to specific patterns of invertebrate distribution that systematically differ between lakes with and without fish, and that these systematic differences may be mediated through top-down mechanisms.
Branching complexity and morphological characteristics of coarse woody structure as lacustrine fish habitat
Authors: Newbrey Michael G , Bozek Michael A , Jennings Martin J , Cook James E
Published: September 2005

The objective of this study was to quantify the physical characteristics of coarse woody structure (CWS) as fish habitat in a north temperate lake. Sixteen species of fish were observed in submerged CWS habitat. Branching complexity, distance above the bole, area below the bole, distance to other CWS, and water depth around CWS were significantly related to abundance of schooling cyprinids (Cyprinidae), rock bass (Ambloplites rupestris), smallmouth bass (Micropterus dolomieu), bluegill (Lepomis macrochirus), yellow perch (Perca flavescens), and walleye (Sander vitreus). Branching complexity was the most common characteristic of CWS related to richness, diversity, and total adult abundance of fish taxa, but was not correlated with the total lengths of fish found in submerged trees. Branching-complexity values ranged from 1 (simple) to 500 (moderately complex) in the littoral zone; for comparison, a living riparian conifer had a branching-complexity value of over 1000. Most CWS in the littoral zone was composed of simple trees without branching, but fish tended to inhabit CWS with branching-complexity values greater than 45. This study shows the importance of CWS with fine branching as littoral-zone fish habitat.
Metabolic rates and swimming performance of adult Fraser River sockeye salmon (Oncorhynchus nerka) after a controlled infection withParvicapsula minibicornis
Authors: Wagner G N , Hinch S G , Kuchel L J , Lotto A , Jones S RM , Patterson D A , Macdonald J S , Kraak G Van Der , Shrimpton M , English K K , Larsson S , Cooke S J , Healey M C , Farrell A P
Published: September 2005

Adult sockeye salmon (Oncorhynchus nerka) acquire infections with the myxosporean kidney parasite Parvicapsula minibicornis during their spawning migration in the Fraser River, British Columbia. Controlled infections with this parasite in wild sockeye salmon had no significant impact on plasma ionic status, metabolic rates, and initial maximum prolonged swimming performance (Ucrit) for fish ranked as either strongly, weakly, or noninfected by polymerase chain reaction analysis of kidney tissue. However, strongly infected fish had significantly lower second Ucritand recovery ratio (8%) values, indicating decreased ability to recover from exercise. As the present study shows that the severity of infection is affected by time and temperature, the accumulated thermal units (ATU) of exposure in this study were compared with those experienced by naturally migrating sockeye salmon. A parallel telemetry study revealed that early-timed sockeye experienced significantly more ATU (741.4 ± 29.4 °C) than normally migrating salmon (436.0 ± 20.0 °C) prior to spawning because of a significantly longer holding period in the lake system. The present data are discussed in the context of a threshold of >450 °C ATU for severe infection that would first manifest in early-timed fish in the upper reaches of the Fraser River and certainly on the spawning grounds.
Modelling ice cover, timing of spring stratification, and end-of-season mixing depth in small Precambrian Shield lakes
Authors: Cahill Kendra L , Gunn John M , Futter Martyn N
Published: September 2005

From a 3-year study of 21 northern Ontario lakes, models were developed to determine the duration of ice cover, predict the timing of spring stratification, and predict the end-of-season mixing depth. The model to determine lake freeze and thaw dates was based on the daily variability of water temperature measured with a data logger suspended 1 and 2 m below the surface. The model to predict the duration of time (days) from lake thaw to lake stratification was developed using the mean May air temperature (degrees Celsius), dissolved organic carbon, and lake surface area (r2 = 0.79). The end-of-season mixing depth was best predicted using days to stratification and dissolved organic carbon concentration (r2 = 0.72). By applying a simple climate change scenario model, we were able to show that increased air temperature, rather than increased water clarity, was the most important factor affecting the timing of stratification. In contrast, lake clarity was the most important factor affecting end-of-season mixing depth in small Shield lakes.
Classical individual assignments versus mixture modeling to estimate stock proportions in Atlantic salmon (Salmo salar) catches from DNA microsatellite data
Authors: Koljonen Marja-Liisa , Pella Jerome J , Masuda Michele
Published: September 2005

Mixture modeling is shown to outperform classical individual assignments for both estimating stock composition and identifying individuals' sources in a case study of an eight-locus DNA microsatellite database from 26 Atlantic salmon (Salmo salar) stocks of the Baltic Sea. Performance of the estimation methods was compared using self-assignment tests applied to each of the baseline samples and using independent repeat samples from two of the baseline stocks. The different theoretical underpinnings, hypothesis testing versus decision theory, of the methods explain their estimation capacities. In addition, actual catch samples from three northern Baltic Sea sites in 2000 were analysed by mixture modeling, and estimated compositions were consistent with previous knowledge. Baltic main basin and Gulf of Finland stocks were each minor components (<1% at any site), and three groups of Gulf of Bothnia stocks, wild (36%43% among sites), Finnish hatchery (15%49%), and Swedish hatchery (11%41%), were each important with the two hatchery contributions trending geographically.
Measurement of Lα/Lι X-ray intensity ratios
Authors: Söğüt Ö , Büyükkasap E , Küçükönder A
Published: September 2005

Lα/Lι X-ray intensity ratios of La2O3, CeO2, Sm, Eu, Ho, Er, YbO2, Hf, Ta, W, Re, Pt, Au, HgO, Tl, Pb, Bi, ThO2, and U have been measured using the 59.5 keV incident photon energy. The LX-rays emitted from the samples were counted using a Si(Li) detector with a resolution 155 eV at 5.96 keV. PACS No.: 32.30.Rj
Surfactant-enhanced electrokinetic remediation of polycyclic aromatic hydrocarbons in heterogeneous subsurface environments
Authors: Saichek Richard E , Reddy Krishna R
Published: September 2005

Polycyclic aromatic hydrocarbon (PAH) contamination exists at numerous sites and poses a substantial risk to public health and the environment. Electrokinetic remediation technology has the potential to treat PAH-contaminated soils, but the effect of soil heterogeneities such as layers, lenses, and mixtures of different soils on the electrokinetic process has not been adequately studied. This study evaluates surfactant-enhanced electrokinetic remediation under heterogeneous soil conditions. A series of bench-scale experiments was conducted using two soils (sand and kaolin) spiked with a representative PAH compound (phenanthrene) in a two-dimensional electrokinetic test apparatus under various layered, lens, or mixed soil configurations. In addition, the homogeneous sand and kaolin soils were each tested alone for comparison purposes. All the experiments employed the same nonionic surfactant (5% Igepal CA-720) flushing solution and a low (0.05) hydraulic gradient. The results showed that the surfactant flushing under the low hydraulic gradient alone was sufficient for complete removal of the contaminant from the homogeneous sand profile, whereas the electroosmotic flow generated by the application of a DC 2.0 V/cm electric potential in a periodic mode considerably enhanced the removal efficiency for the homogeneous and heterogeneous soil profiles containing kaolin. The voltage gradient varied spatially and temporally through the soil profiles and affected the electroosmotic flow and contaminant removal. Key words: clays, electrokinetic remediation, electroosmosis, flushing, heterogeneity, polycyclic aromatic hydrocarbons (PAHs), phenanthrene, soils, sorption, solubilization, surfactants.
Windrow composting of municipal biosolids in a cold climate
Authors: McCartney Daryl , Eftoda Grant
Published: September 2005

This work investigated the technical feasibility of composting digested municipal biosolids using outdoor windrows in an extremely cold climate. Common belief suggested this was not possible because of low ambient temperatures and low biodegradable volatile solids content of the biosolids. Four trials were conducted: (i) batch started in late fall; (ii) batch started in winter; (iii) batch mixed and stored over winter, then started in spring; and (iv) batch mixed with leaves to improve heat generation. All recipes used 2.5 parts wood chips to 1 part biosolids (by volume). All four trials easily met the thermophilic temperatures required by the pathogen reduction criteria. Trial 2 (batch started in winter), however, did not achieve the thermophilic period until the following summer. The results suggest provisions be made for storage of material over winter. This means a 32% increase in area and a doubling of the system-turning capacity are needed. Practical observations included significant heat loss during turning and mixing, snowfall impact on oxygen supply and pile moisture content, wind direction impact on pile temperature profiles, and the impact of large frozen zones that may affect pathogen inactivation efficacy. Key words: municipal sludge, biosolids, windrow composting, pathogens, low temperature, winter.
Polybrominated diphenyl ethers in an advanced wastewater treatment plant. Part 1: Concentrations, patterns, and influence of treatment processes
Authors: Rayne Sierra , Ikonomou Micheal G
Published: September 2005

Concentrations and patterns of the mono- through deca-substituted polybrominated diphenyl ether (PBDE) flame retardants were determined in all major unit operations and processes within a tertiary-level wastewater treatment plant (WWTP) having post-filtration ultraviolet light disinfection. The results show that PBDEs do not appear to be degraded substantially or otherwise removed by wastewater treatment processes such as anaerobic, anoxic, and aerobic biological treatment, anaerobic digestion, dissolved air flotation, or sand–anthracite filtration. An overall removal efficiency of 93% was observed for PBDEs in the WWTP due to sorption onto wastewater sludges, well below that predicted by equilibrium partitioning models. High levels observed in the resulting WWTP biosolids (~2.4 mg·kg–1 dry weight) may contaminate a wider environment through their use as a soil amendment. Lower concentrations of PBDEs contained within high volumes of aqueous WWTP effluent (~26 ng·L–1) may result in a large PBDE flux into receiving waters, posing a potential threat to drinking water supplies and fisheries resources. Key words: polybrominated diphenyl ethers (PBDEs), flame retardants, municipal wastewater treatment, domestic sewage, mass balance, congener patterns.
Three-dimensional ground settlements and stress-transfer mechanisms due to open-face tunnelling
Authors: Ng Charles WW , Lee Gordon TK
Published: September 2005

A series of three-dimensional, numerical, elastoplastic, coupled-consolidation analyses was conducted to investigate the effects of the stiffness ratio (n = E ′h/E ′v) and the initial coefficient of earth pressure at rest (K0) on ground deformations and stress-transfer mechanisms due to idealized open-face tunnelling (i.e., New Austrian Tunnelling Method or NATM) at a given unsupported length. As n increases, smaller plastic extension strain zones are mobilized at the crown and invert for a given K0, leading to a deeper and narrower transverse surface settlement trough. On the other hand, for a given n, the lower the initial K0 is, the deeper and narrower the computed settlement trough will be. Three-dimensional stress-transfer mechanisms at a tunnel heading are demonstrated through the changes in normal stresses and induced shear stresses around the tunnel. As the tunnel excavation advances, the maximum total normal stress reduction in the lateral direction (Δσxx) and in the vertical direction (Δσzz) occurs at the tunnel heading, whereas the largest total normal stress reduction in the longitudinal direction (Δσyy) takes place at about 0.5D (D = diameter) ahead of the tunnel face. A total stress reduction zone can be identified within 2.0D ahead of the tunnel face, and the stress influence zone diminishes at a distance of about 1.0D beyond the tunnel face. A significant reduction in pore-water pressure, of up to about 75% of its initial value, can be identified around the tunnel heading. Around a tunnel open face, the effective stress coefficient Kxz (= σ′xx/σ′zz) and Kyz (= σ′yy/σ′zz) rise to approximately 1.8 and more than 2.0 at the crown and invert in the initial K0 = 1.0 ground conditions, respectively. On the other hand, Kxz falls to about 50% of the initial K0 value at the springline, and the coefficient at the shoulder and heel drops to between 10% and 20%.Key words: open face, tunnelling, NATM, anisotropy, three-dimensional, stress transfer, ground settlements.
On the evaluation of undrained shear strength and preconsolidation pressure from common field tests in clay
Authors: Larsson Rolf , Åhnberg Helen
Published: September 2005

The undrained shear strength is a key parameter in the estimation of the stability of natural slopes and man-made constructions in soft clay. It is therefore important to develop relevant methods to evaluate the operative strength. Results from an investigation regarding the effect of excavations at slope crests to increase the stability of clay slopes are presented. This study has provided an opportunity to study the effect of overconsolidation on the evaluated parameters from common in situ tests in homogeneous and truly overconsolidated clays. Certain inconsistencies in the commonly used methods of interpretation of field vane tests, cone penetration tests, and dilatometer tests are highlighted, and modified interpretation methods taking the effects of overconsolidation into account are proposed.Key words: clay, overconsolidation, undrained shear strength, cone penetration test, field vane test, dilatometer test.
Solution of the bearing capacity problem by the slip line method
Authors: Cheng Y M , Au S K
Published: September 2005

The authors have derived the bearing capacity factor Nqon sloping ground based on the slip line method and have verified it using finite difference analysis. The bearing capacity factor Nγon sloping ground is obtained by an iterative finite difference solution of the slip line equations, and the results are close to those from laboratory testing. Design figures for Nγon sloping ground are prepared for rapid engineering use. For earthquake loading, the authors have applied the concept of equivalent horizontal acceleration and have derived Nqand Nγbased on slip line analysis.Key words: bearing capacity, slip line, finite difference, sloping ground, earthquake.
Reliability of bored pile foundations considering bias in failure criteria
Authors: Zhang L M , Li D Q , Tang Wilson H
Published: September 2005

The failure of a pile is always defined by a certain failure criterion. Several different failure criteria are commonly used, and the pile capacity values associated with each of these failure criteria can be considerably different. For the sake of international harmonization, it is necessary to calibrate the reliability levels associated with various failure criteria and factors for loads and resistances. This paper aims to evaluate the effects of failure criteria and factors for loads and resistances on the reliability of single bored piles. The bias arising from failure criteria is described by a bias factor, which can easily be accommodated in a reliability analysis. A comprehensive database of static load tests of bored piles is utilized to evaluate the bias associated with several failure criteria. Five limit-state design codes for piles are investigated to illustrate the effect of the bias from failure criteria, the effect of factors for loads and resistances, and their combined effect. The results indicate that the bias from failure criteria has a significant influence on the reliability of piles. Similarly, the use of different factors for loads and resistances in various design codes can also cause considerable differences in the calculated reliability. As a result of these effects, the actual reliability levels of any two design codes, assuming the same nominal target reliability index, can differ considerably.Key words: bored piles, pile capacity, failure criterion, reliability analysis, load factors, resistance factors.
Fire history and forest age distribution of an unmanaged Picea abies dominated landscape
Authors: Wallenius Tuomo H , Pitkänen Aki , Kuuluvainen Timo , Pennanen Juho , Karttunen Hanna
Published: September 2005

We examined fire history and forest age distribution in an unmanaged, Picea-dominated landscape in the Paanajärvi wilderness, located in northeastern Fennoscandia and northwest Russia. Maximum tree age was determined in 61 systematically located study plots in an area of about 6600 ha. Fire scars were examined in living and dead trees in the study plots and elsewhere in the study area. Charcoal and pollen analyses of peat were performed on samples from two locations. Fires had been rare in the landscape. Nearly half of the dendrochronologically dated fires occurred in a distinct and short period, from 1859 to 1889, in the northeastern part of the area. This nonrandom occurrence of fires, together with the observed signs of past human influence, suggests an anthropogenic origin for the majority of the fires. The fact that 95% of the study area consisted of forests older than 120 years reflects the end of the occurrence of fires in the 1880s. Pollen analysis from the southwestern part of the study area showed that the site had been dominated by Picea at least during the last millennium. Charcoal analysis from the same site indicated that likely more than 1000 years had elapsed since the last fire. In general, the results suggest that the abundance of old forests, with the oldest trees being approximately 300 years of age, belongs to the natural state of a Picea-dominated landscape.
Effect of stand age on fine-root biomass and biomass distribution in three European forest chronosequences
Authors: Claus A , George E
Published: September 2005

Fine-root (<2 mm) biomass and biomass distribution were determined in different age-classes of three European forest chronosequences dominated by Fagus sylvatica L., Picea abies (L.) Karst., and Quercus cerris L., respectively. Root samples were taken with the auger method. There was a clear effect of stand age on standing fine-root biomass, with the highest fine-root biomass in adult but not mature stands. The vertical fine-root biomass distribution showed, at all sites, high densities of roots in the top soil layers and with depth a gradual decrease of fine-root biomass density. The difference in total fine-root biomass between the different age-classes appeared to be due to differences in the top soil layers. Fine-root biomass in the lower soil layers was less variable along the life cycle of the forests. Only in very young stands, specific root length of fine roots was higher than in the other age-classes. The present data together with other published values suggest that fine-root biomass in tree stands develops in three phases: rapid increase after a clear-cut harvest up to a maximum of fine-root biomass; a decrease during maturation of the stand; and a steady-state in mature stands.
Pollen contamination and mating patterns in a Douglas-fir seed orchard as measured by simple sequence repeat markers
Authors: Slavov Gancho T , Howe Glenn T , Adams W Thomas
Published: September 2005

Pollen contamination is detrimental to the genetic quality of seed orchard crops. Highly variable simple sequence repeat (SSR) markers make it possible to accurately measure pollen contamination and characterize patterns of within-orchard mating by directly identifying the male and female parent of each seed produced in the orchard. We used nine SSR markers to measure pollen contamination and characterize mating patterns based on seed samples collected in 3 years (1999, 2000, and 2003) from one block of a nonisolated, open-pollinated, clonal seed orchard of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in western Oregon. Pollen contamination was consistently high across the 3 years (mean = 35.3%, range = 31.0%-41.3%) and appeared to result primarily from cross-pollination among the orchard blocks. Levels of pollen contamination varied substantially among clones and were higher in clones with early female receptivity (mean = 55.5%) than in those with either mid (mean = 36.4%) or late (mean = 28.3%) female receptivity. We detected low rates of self-pollination (mean = 1.8% per clone) and over 10-fold differences in the relative paternal contributions of the clones. There was a clear pattern of positive assortative mating with respect to floral phenology. This study illustrates that SSR markers are powerful tools for characterizing seed lots and improving the design and management of Douglas-fir seed orchards.
Picea abiessite index prediction by environmental factors and understorey vegetation: a two-scale approach based on survey databases
Authors: Seynave Ingrid , Gégout Jean-Claude , Hervé Jean-Christophe , Dhôte Jean-François , Drapier Jacques , Bruno Éric , Dumé Gérard
Published: September 2005

Relationships between site index, environmental variables, and understorey vegetation were examined for Norway spruce (Picea abies (L.) Karst.) in the eastern part of France. The study area concerns all the native range of Norway spruce in France and the northeastern plains. The analysis is based on 2087 plots from the French National Forest Inventory database. The data measured on each plot cover topography, soil, geology, and vegetation. Additional environmental variables were estimated using two methods: climatic data estimated from a climatic model developed by Météo-France (AURELHY), and nutritional variables predicted from vegetation data and species indicator values. General linear model regression was used to predict site index as a function of environmental variables. The best model explains 64% of the site index variance and involves eight variables (elevation, mountain zone, topographic concavity, proportion of plot area occupied by rock outcrop, rock type, soil depth, pH, and C/N ratio). The two main results of this study are (i) the combination of large databases allowed the study of soilsite relationships and construction of a pertinent model, which covers a wide range of ecological conditions, and (ii) vegetation was found to be relevant to separate the effect of acidity from those of nitrogen nutrition on Norway spruce productivity.
Identifying growth releases in dendrochronological studies of forest disturbance
Authors: Fraver Shawn , White Alan S
Published: September 2005

Information on historical disturbances is vital to our understanding of current forest conditions. Dendro chronological methods provide one means of reconstructing disturbance histories in temperate and boreal forests. In particular, the dates of significant growth releases recorded on surviving trees provide strong inferential evidence of past disturbance events. The most common method of detecting releases (the percent-increase method) expresses the postevent growth increase as a percentage of the preevent rate. Despite its widespread use, the method is known to be overly sensitive at low rates of prior growth and overly stringent at high rates. We present an alternative method that directly follows the percent-increase method, but instead of dividing the postevent growth rate by the preevent rate, we simply subtract the two. If the difference exceeds a predetermined species-specific threshold, the event is considered a release. This absolute-increase method has convenient properties that remedy the shortcomings of the percent-increase method. We tested the validity of the absolute-increase thresholds by binary logistic regressions, and we compared the absolute- and percent-increase methods by various methods. We conclude that for the species evaluated in this study, the absolute-increase method represents an improvement over the standard percent-increase method.
Ectomycorrhizal mushroom distribution by stand age in western hemlock – lodgepole pine forests of northwestern British Columbia
Authors: Kranabetter J M , Friesen J , Gamiet S , Kroeger P
Published: September 2005

Commercial forest rotations are usually shorter than natural disturbance return intervals, which could affect the distribution of ectomycorrhizal fungal (EMF) species dependent on late-seral stands. We examined this potential reduction in species richness by comparing ectomycorrhizal mushroom communities across four age-classes (pole stage, young, mature, and old growth) of western hemlock (Tsuga heterophylla (Raf.) Sarg.) – lodgepole pine (Pinus contorta Dougl. ex Loud.) stands on submesic sites in northwestern British Columbia. Almost 130 species of ectomycorrhizal mushrooms were identified over the 12 sites during the 3-year study period. EMF richness was lowest in pole stands and almost twice as high in the older age-classes. Species composition and abundance were related to stand age, with relatively large differences in communities between the ages of 20 and 120 and relatively smaller differences between 120 and 225 years. Twelve species, including the economically important pine mushroom (Tricholoma magnivelare (Peck) Redhead), were late-seral stand dependent, fruiting in forests that are at least older than 85 years. This distribution of ectomycorrhizal mushrooms across stand ages suggests EMF succession is primarily an accumulation of species and is likely affected by differences in dispersal by ectomycorrhizal fungi, soil properties (increased soil acidity and reduced nitrogen availability), and the rate of stand development. The evidence for EMF species limited to late-seral stands supports the maintenance of some mature forests within these landscapes to conserve EMF richness.
Estimating the mass density of fine roots of trees for minirhizotron-based estimates of productivity
Authors: Bernier Pierre Y , Robitaille Gilles , Rioux Danny
Published: September 2005

Allocation of carbon for the production of fine roots is a significant component of the carbon budget within trees. Transformation of fine-root volumes or lengths as seen with minirhizotrons into fine-root mass per unit of horizontal area requires an estimate of the mass density or specific root length of fine roots for the species of interest. We obtained values of mass density of fine roots using three different sampling strategies on temperate and boreal forested sites. The strategies examined were (1) the use of bulk root samples from soil cores, (2) the use of individual roots from seedlings, and (3) the use of individual roots from soil cores. Our results show that the mass density of fine roots taken from seedlings is strongly dependent on root diameter, as shown by the strong drop in mass density with a decrease in diameter in all species examined. However, the dependency of mass density of individual fine roots extracted from soil cores on root diameter varies with the species mixture. Examination of thin cross-sections of roots using microscopy reveals that the proportion of xylem cell walls as a percentage of total cell walls also decreases strongly as root diameter diminishes for seedling fine roots, but that this relationship is not as clear in fine roots obtained from soil cores. We conclude that using the mass density from core fine roots may yield the best estimate of fine-root productivity when deriving such a value from the analysis of minirhizotron images. We also discuss some of the problems associated with the use of specific root length.
Gradient analysis, the next generation: towards more plant-relevant explanatory variables
Authors: Lookingbill Todd R , Urban Dean L
Published: September 2005

The long history of gradient analysis is anchored in the observation that species turnover can be described along elevation gradients. This model is unsatisfying in that elevation is not directly relevant to plants and the ubiquitous "elevation gradient" is composed of multiple intertwined environmental factors. We offer an approach to landscape-scale vegetation analysis that disentangles the elevation gradient into its constituent parts through focused field sampling and statistical analysis. We illustrate the approach for an old-growth watershed in the Oregon Western Cascades. Our initial model of this system supports the common observation that forest community types are highly associated with specific elevation bands. By replacing elevation and other crude environmental proxy variables with estimates of more direct and resource gradients (radiation, temperature, and soil moisture), we create a vegetative model with stronger explanatory power than the proxy model in both cross-validation analysis and validation using an independent data set. The resulting model is also more biologically interpretable, which provides more meaningful insight into potential forest response to environmental change (e.g., global climate change scenarios). Acquiring a better mechanistic understanding of the relationship between plant communities and environmental predictor variables presents the next great challenge to community ecologists conducting gradient studies at landscape scales.