Tidal modulation of infragravity waves via nonlinear energy losses in the surfzone

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L05601, doi:10.1029/2005GL025514.The strong tidal modulation of infragravity (200 to 20 s period) waves observed on the southern California shelf is shown to be the result of nonlinear transfers of energy from these low-frequency long waves to higher-frequency motions. The energy loss occurs in the surfzone, and is stronger as waves propagate over the convex low-tide beach profile than over the concave high-tide profile, resulting in a tidal modulation of seaward-radiated infragravity energy. Although previous studies have attributed infragravity energy losses in the surfzone to bottom drag and turbulence, theoretical estimates using both observations and numerical simulations suggest nonlinear transfers dominate. The observed beach profiles and energy transfers are similar along several km of the southern California coast, providing a mechanism for the tidal modulation of infragravity waves observed in bottom-pressure and seismic records on the continental shelf and in the deep ocean.Support was provided by ONR and NSF

Reflection and tunneling of ocean waves observed at a submarine canyon

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 32 (2005): L10602, doi:10.1029/2005GL022834.Ocean surface gravity waves with periods between 20 and 200 s were observed to reflect from a steep-walled submarine canyon. Observations of pressure and velocity on each side of the canyon were decomposed into incident waves arriving from distant sources, waves reflected by the canyon, and waves transmitted across the canyon. The observed reflection is consistent with longwave theory, and distinguishes between cases of normal and oblique angles of incidence. As much as 60% of the energy of waves approaching the canyon normal to its axis was reflected, except for waves twice as long as the canyon width, which were transmitted across with no reflection. Although waves approaching the canyon at oblique angles cannot propagate over the canyon, total reflection was observed only at frequencies higher than 20 mHz, with lower frequency energy partially transmitted across, analogous to the quantum tunneling of a free particle through a classically impenetrable barrier.Funding was provided by the Office of Naval Research and the National Science Foundation

Refraction and reflection of infragravity waves near submarine canyons

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C10009, doi:10.1029/2007JC004227.The propagation of infragravity waves (ocean surface waves with periods from 20 to 200 s) over complex inner shelf (water depths from about 3 to 50 m) bathymetry is investigated with field observations from the southern California coast. A wave-ray-path-based model is used to describe radiation from adjacent beaches, refraction over slopes (smooth changes in bathymetry), and partial reflection from submarine canyons (sharp changes in bathymetry). In both the field observations and the model simulations the importance of the canyons depends on the directional spectrum of the infragravity wave field radiating from the shoreline and on the distance from the canyons. Averaged over the wide range of conditions observed, a refraction-only model has reduced skill near the abrupt bathymetry, whereas a combined refraction and reflection model accurately describes the distribution of infragravity wave energy on the inner shelf, including the localized effects of steep-walled submarine canyons.Funding was provided by the Office of Naval Research and the National Science Foundation

Red squirrel demography and behaviour in a managed interior Douglas-fir forest of British Columbia

I examined the affect of logging intensity and pattern on the North American red squirrel (Tamiasciurus hudsonicus) by measuring density and demography from zero to four years after logging, and by measuring territory size, habitat use, and behaviour of individual animals from three to five years after logging. This study was done in an interior Douglas-fir forest (IDF) near Kamloops, British Columbia, Canada. Patterns of tree removal ranged from small patch cuts (<1.6 ha) to individual tree selection (diameter-limit logging) and intensity of tree removal ranged from 20-50% by volume. From two to four years after logging, red squirrel abundance declined in a 1:1 relationship with the volume of conifer tree removal. Absolute variation in squirrel abundance was highest in the uniform tree removal treatments and lowest in unharvested habitat. Red squirrel recruitment, survival, body weight, and reproduction was unrelated to pattern or intensity of tree removal. In general, these results are consistent with the predictions of the ideal free distribution model of habitat selection. I conclude that logging intensity had the greatest effect on red squirrels, but that uniform tree removal logging may result in poor quality habitat during years of conifer cone crop failure. From three to five years after logging, red squirrel territory size was best explained by the density of Douglas-fir trees larger than 30 cm diameter-at-breast-height (DBH). Similarly, red squirrels prefered conifer trees larger than 15 cm DBH, with the strongest preference for trees between 30 and 44 cm DBH. Despite large differences in conifer tree density on individual territories, red squirrel activity budgets did not change. Further, red squirrels avoided canopy openings created by logging, but this did not affect their use of forest edge compared to interior forest habitat. I suggest that variation in conifer seed production may explain the relationship between Douglas-fir density and red squirrel territory size, habitat selection, and behaviour. I conclude that logging did not have a biologically meaningful effect on red squirrels, either overtime or across the range of habitats I sampled. However, diameter-limit logging may create poor habitat for red squirrels during years when little or no conifer seed is produced, or when logging dilutes conifer trees further than those sampled in this study. Individual tree selection treatments will likely not remain poor habitat for more than five years if greater than 50, 30 cm DBH Douglas fir trees are retained.Forestry, Faculty ofGraduat

Monitoring Cumulative Effects of Human Activity on Alberta’s (Canada) Biodiversity

Due to its significant natural resource wealth, the province of Alberta in western Canada has experienced rapid expansion of related industrial activities (forestry, agriculture, and oil and gas exploration and development), as well as associated population growth, over recent decades. The resulting rate of conversion of natural ecosystems to support these activities led to increasing concerns regarding their cumulative effects on Alberta's biodiversity. As a result, in 2007, the Alberta Biodiversity Monitoring Institute (ABMI) was formally established to monitor the status and trends of Alberta's species, their habitats, as well as human footprint (HF). The ABMI is a not-for-profit scientific organization that operates at arm's length from government and industry. The goal of the ABMI is to provide relevant scientific information on the state of Alberta's biodiversity to support natural resource and land-use decision making in the province. To meet this goal, the ABMI employs a systematic grid of 1,656 site locations across the province, spaced 20 km apart, to collect biodiversity information on terrestrial and wetland sites. At each location, data and field samples are collected for a wide range of plant and animal species through on-the-ground measurements, and also using motion-sensitive camera traps and acoustic technology. Since 2007, over 480,000 specimens-data on over 3000 species have been collected and processed, many of which represent new scientific records for the province, sometimes new records for Canada, and even records new to science. Annually, a percentage of the total sites is surveyed, with the sites revisited approximately every 7 years to measure trend in species abundance. In addition to field surveys, Alberta's land cover and human footprint is monitored using remote sensing technology at two spatial scales. To report on patterns and trend in human footprint, the ABMI classifies human footprint into 115 feature types, which are then rolled up into the categories of energy, forestry, agriculture, residential and industrial, human-created water bodies, and transportation. The ABMI's accumulated biodiversity and HF database supports the creation of predictive species models that provide information on spatial distribution, habitat associations, responses to HF, and predicted relative abundance for over 800 species, including mammals, birds, soil mites, vascular plants, mosses (bryophytes), and lichens. The scale and depth of the ABMI's monitoring program and biodiversity data make it a unique program nationally, and a leader internationally. In addition to ongoing protocol development and data analysis, the ABMI is committed to deriving value from its data and information for a wide range of Alberta stakeholders through concerted knowledge translation and stakeholder engagement efforts.peerReviewe