SPRING ICE-JAM FLOODING OF THE PEACE-ATHABASCA DELTA: EVIDENCE OF A CLIMATIC OSCILLATION

A historic record of spring ice-jam floods of the Peace-Athabasca Delta was analyzed for the years 1826–1995. The temporal pattern of flooding is non-random. The likelihood of a flood following a flood, or a non-flood following a non-flood, is greater than expected by chance. Probability analysis of flood occurrence reveals that the period 1860–1880 was a time of unusually few floods, and the period 1915–1950 was a time of unusually frequent floods. The long-term flood frequency is 1 flood in 6.25 years. Changes in flood frequency over the record reveal a pattern of oscillation described by a sine-based model that is correlated with the long-term (Gleissberg) cycle of solar activity. Monte Carlo simulation was used to test a Bennett Dam Model and a Cyclic Model. The Bennett Dam Model is unlikely to have generated the observed flood history (p=0.04). The observed flood history shows a better fit to the Cyclic Model (p=0.65). No correlations between floods and ENSO cold or warm events was detected. The most recent wet period began about 1900 and ended in the early 1960's prior to completion of the W. A. C. Bennett Dam in British Columbia. As independent corroboration of climatically-driven changes in flood frequency we present three additional lines of evidence. The pattern of annual muskrat returns (95 year record) reveals both 10 year cycles and long-term patterns that agree well with the observed flood cycle. The annual area burned in Wood Buffalo National Park is inversely related to flood occurrence. Incised channels and dendritic drainage patterns in the bed of Lake Mamawi provide probable evidence of a previous dry period in the delta. Climatic change or oscillation likely underlies the drying trend observed in recent decades in the Peace-Athabasca Delta.     

NATIVENESS,INVASIVENESS, AND NATION IN AUSTRALIAN PLANTS*

ABSTRACT. The conceptualization of alien invasive species conflates two axes of variability that have become unhelpfully blurred. The nativeness/alienness axis refers to the presumed belonging of a species in ecological or social space. Invasiveness refers to the behavior of the species in question, particularly in relation to other species. The overlay of nation introduces further variability. Teasing these axes apart is important for more effective environmental management. We examine these concepts using two influential forms of ecological knowledge: the biogeographical and ecological literature and the vernacular experiences of suburban backyarders. Three case studies, the invasive native Pittosporum undulatum and two invasive exotics, Lantana camara and Cinnamomum camphora, illustrate the complex and contingent nature of human interactions with such species and the potential for human interactions to increase and/or reduce the propagation of plant species.     

ANISOTROPIC TRAVELTIME TOMOGRAPHY

Velocity estimation technique using seismic data is often based on time/distance equations which are independent of direction, and even though we now know that many rocks are quite anisotropic, useful results have been obtained over the years from these isotropic estimates. Nevertheless, if velocities are significantly direction-dependent, then the isotropic assumption may lead to serious structural interpretation errors. Additionally, information on angle-dependence may lead to a better understanding of the lithology of the rocks under measurement. VSP and cross-well data may each lack the necessary aperture to estimate more than two velocity parameters for each wave type, and if the data straddle a symmetry axis, then these may be usefully chosen to be the direct velocities (from time-and-distance measurements along the axis) and NMO velocities (from differential time-offset measurements). These sets of two parameters define ellipses, and provide intermediate models for the variation of velocity with angle which can later be assembled and translated into estimates of the elastic moduli of the rocks under scrutiny. If the aperture of the measurements is large enough e.g. we have access to both VSP and cross-well data, we divide the procedure into two independent steps, first fitting best ellipses around one symmetry axis and then fitting another set around the orthogonal axis. These sets of four elliptical parameters are then combined into a new, double elliptical approximation. This approximation keeps the useful properties of elliptical anisotropy, in particular the simple relation between group and phase velocities which simplifies the route from the traveltimes measurements to the elastic constants of the medium. The inversion proposed in this paper is a simple extension of well-known isotropic schemes and it is conceptually identical for all wave types. Examples are shown to illustrate the application of the technique to cross-well synthetic and field P-wave data. The examples demonstrate three important points: (a) When velocity anisotropy is estimated by iterative techniques such as conjugate gradients, early termination of the iterations may produce artificial anisotropy. (b) Different components of the velocity are subject to different type of artifacts because of differences in ray coverage, (c) Even though most rocks do not have elliptical dispersion relations, our elliptical schemes represent a useful intermediate step in the full characterization of the elastic properties.     

CRYPTOFAUNAL COMMUNITIES OF CORAL REEFS

INTRODUCTION Cryptofaunal communities consist of the animals and plants living within dead coral.As a very large part of a coral reef is composed of dead coral,the biomasses of crypto-faunal communities on a reef must be significant.And as many of the cryptofaunal animalsreproduce at regular intervals,rates of turnover of the community are also high and thusare major contributors to the productivity of coral reefs.Grassle(1973)collected a 4.7     

AUSTRALIAN BACKYARD GARDENS AND THE JOURNEY OF MIGRATION*

ABSTRACT. Gardens have been an important site of environmental engagement in Australia since the British colonization. They are places where immigrant people and plants have carried on traditions from their homelands and have worked out an accommodation with new social and biophysical environments. We examined the backyard gardens of three contemporary migrant groups—Macedonian, Vietnamese, and British born—in suburban Australia and a group of first‐generation Australians with both parents born overseas. In Macedonian backyards, emphasis was strong on the production of vegetables; in Vietnamese backyards, on herbs and fruit. British backyards were more diverse, some focusing on non‐native ornamental flowers and others favoring native plants. The cohesiveness of the respective groups was partly an artifact of our sampling strategy. The Macedonian and Vietnamese migrants shared an affinity for productive, humanized landscapes that reflected their rural, subsistence backgrounds and crossed over into their attitudes toward the broader environment and national parks. The rural and village backgrounds help explain why intensive backyard food production has broken down among the next generation in (sub)urban Australia, becoming part of heritage rather than everyday practice.     

Microbiological effects on slope stability: an experimental analysis

A natural, pure quartz sand has been seeded with the bacterium Pseudomonas atlantica and the fungus Penicillium chrysogenum, and angles of avalanche and repose have been measured under water using a laboratory clinometer. The lowest angles of avalanche occur in freshly packed clean sediment (control), with the seeded sediments having higher values. Among the latter, the lowest angles of repose occur in the bacterial seeded sediments, and the highest in the fungal seeded sediments. The largest differences between the angle of avalanche and angle of repose occur in the bacterial seeded and media control sediments. The smallest differences occur in the fungal seeded sediment. In most cases the second angle of avalanche is lower than the first angle of avalanche, whilst the second angle of repose is higher than the first angle of repose. The bacteria bind particles together with their extracellular polymeric material, while the fungus binds particles by holding them together with a network of hyphal filaments. In the bacterial seeded sediment growth is uniform over the sediment surface. In the fungal seeded sediment growth occurs as discrete colonies separated by bare sediment, and the fungal hyphae penetrate the sediment to a significant depth. On avalanching, the fungal colonies move down the slope with the hyphal filaments trailing behind them in the sediment. Overall, both the bacterium and the fungus increase slope stability. However, the fungal colonies maintain slope stability after avalanching more effectively than does the uniform bacterial growth. The results are discussed in relation to the wide range of biological effects that stabilize flat sediments and to laboratory and field studies on the stability of sediment slopes.