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Measuring (Subglacial) Bedform Orientation, Length, and Longitudinal Asymmetry – Method Assessment

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-03-20
Abstract: 

Geospatial analysis software provides a range of tools that can be used to measure landform morphometry. Often, a metric can be computed with different techniques that may give different results. This study is an assessment of 5 different methods for measuring longitudinal, or streamlined, subglacial bedform morphometry: orientation, length and longitudinal asymmetry, all of which require defining a longitudinal axis. The methods use the standard deviational ellipse (not previously applied in this context), the longest straight line fitting inside the bedform footprint (2 approaches), the minimum-size footprint-bounding rectangle, and Euler’s approximation. We assess how well these methods replicate morphometric data derived from a manually mapped (visually interpreted) longitudinal axis, which, though subjective, is the most typically used reference. A dataset of 100 subglacial bedforms covering the size and shape range of those in the Puget Lowland, Washington, USA is used. For bedforms with elongation > 5, deviations from the reference values are negligible for all methods but Euler’s approximation (length). For bedforms with elongation < 5, most methods had small mean absolute error (MAE) and median absolute deviation (MAD) for all morphometrics and thus can be confidently used to characterize the central tendencies of their distributions. However, some methods are better than others. The least precise methods are the ones based on the longest straight line and Euler’s approximation; using these for statistical dispersion analysis is discouraged. Because the standard deviational ellipse method is relatively shape invariant and closely replicates the reference values, it is the recommended method. Speculatively, this study may also apply to negative-relief, and fluvial and aeolian bedforms.

Document type: 
Article
File(s): 

Between A Rock and A Soft Place: Using Optical Ages to Date Ancient Clam Gardens on the Pacific Northwest

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-02-09
Abstract: 

Rock-walled archaeological features are notoriously hard to date, largely because of the absence of suitable organic material for radiocarbon dating. This study demonstrates the efficacy of dating clam garden wall construction using optical dating, and uses optical ages to determine how sedimentation rates in the intertidal zone are affected by clam garden construction. Clam gardens are rock-walled, intertidal terraces that were constructed and maintained by coastal First Nation peoples to increase bivalve habitat and productivity. These features are evidence of ancient shellfish mariculture on the Pacific Northwest and, based on radiocarbon dating, date to at least the late Holocene. Optical dating exploits the luminescence signals of quartz or feldspar minerals to determine the last time the minerals were exposed to sunlight (i.e., their burial age), and thus does not require the presence of organic material. Optical ages were obtained from three clam garden sites on northern Quadra Island, British Columbia, and their reliability was assessed by comparing them to radiocarbon ages derived from shells underneath the clam garden walls, as well as below the terrace sediments. Our optical and radiocarbon ages suggest that construction of these clam garden walls commenced between ~1000 and ~1700 years ago, and our optical ages suggest that construction of the walls was likely incremental and increased sedimentation rates in the intertidal zone by up to fourfold. Results of this study show that when site characteristics are not amenable to radiocarbon dating, optical dating may be the only viable geochronometer. Furthermore, dating rock-walled marine management features and their geomorphic impact can lead to significant advances in our understanding of the intimate relationships that Indigenous peoples worldwide developed with their seascapes.

Document type: 
Article
File(s): 

Spatial Relationships between Small-Holder Farms Coupled With Livestock Management Practices Are Correlated With the Distribution of Antibiotic Resistant Bacteria in Northern Tanzania

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-06-12
Abstract: 

We examined the spatial distribution of antibiotic-resistant coliform bacteria amongst livestock from three distinct cultural groups, where group-level differences in practices (e.g., antibiotic use) may influence the magnitude of antibiotic resistance, while livestock interactions (e.g., mixing herds, shared markets) between these locations may reduce heterogeneity in the distribution of antibiotic resistant bacteria. Data was collected as part of a larger study of antibiotic-resistance in northern Tanzania. Simple regression and generalized linear regression were used to assess livestock management and care practices in relation to the prevalence of multidrug-resistant (MDR) coliform bacteria. Simple and multivariable logistic regression were then used to identify how different management practices affected the odds of households being found within MDR “hotspots.” Households that had a higher median neighbourhood value within a 3000 m radius showed a significant positive correlation with livestock MDR prevalence (β = 4.33, 95% CI: 2.41–6.32). Households were more likely to be found within hotspots if they had taken measures to avoid disease (Adjusted Odds Ratio (AOR) 1.53, CI: 1.08—2.18), and if they reported traveling less than a day to reach the market (AOR 2.66, CI: 1.18—6.01). Hotspot membership was less likely when a greater number of livestock were kept at home (AOR 0.81, CI: 0.69–0.95), if livestock were vaccinated (AOR 0.32, CI: 0.21—0.51), or if distance to nearest village was greater (AOR 0.46, CI: 0.36–0.59). The probability of MDR increases when herds are mixed, consistent with evidence for passive transmission of resistant bacteria between animals. Reduced MDR with vaccination is consistent with many studies showing reduced antibiotic use with less disease burden. The neighbourhood effect has implications for design of intervention studies.

Document type: 
Article
File(s): 

Short-Term Forecasting of Land Use Change Using Recurrent Neural Network Models

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-09-28
Abstract: 

Land use change (LUC) is a dynamic process that significantly affects the environment, and various approaches have been proposed to analyze and model LUC for sustainable land use management and decision making. Recurrent neural network (RNN) models are part of deep learning (DL) approaches, which have the capability to capture spatial and temporal features from time-series data and sequential data. The main objective of this study was to examine variants of the RNN models by applying and comparing them when forecasting LUC in short time periods. Historical land use data for the City of Surrey, British Columbia, Canada were used to implement the several variants of the RNN models. The land use (LU) data for years 1996, 2001, 2006, and 2011 were used to train the DL models to enable the short-term forecast for the year 2016. For the 2011 to 2016 period, only 4.5% of the land use in the study area had changed. The results indicate that an overall accuracy of 86.9% was achieved, while actual changes in each LU type were forecasted with a relatively lower accuracy. However, only 25% of changed raster cells correctly forecasted the land use change. This research study demonstrates that RNN models provide a suite of valuable tools for short-term LUC forecast that can inform and complement the traditional long-term planning process; however, further additional geospatial data layers and considerations of driving factors of LUC need to be incorporated for model improvements.

Document type: 
Article
File(s): 

Analyzing Performances of Different Atmospheric Correction Techniques for Landsat 8: Application for Coastal Remote Sensing

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-02-25
Abstract: 

Ocean colour (OC) remote sensing is important for monitoring marine ecosystems. However, inverting the OC signal from the top-of-atmosphere (TOA) radiance measured by satellite sensors remains a challenge as the retrieval accuracy is highly dependent on the performance of the atmospheric correction as well as sensor calibration. In this study, the performances of four atmospheric correction (AC) algorithms, the Atmospheric and Radiometric Correction of Satellite Imagery (ARCSI), Atmospheric Correction for OLI ‘lite’ (ACOLITE), Landsat 8 Surface Reflectance (LSR) Climate Data Record (Landsat CDR), herein referred to as LaSRC (Landsat 8 Surface Reflectance Code), and the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System (SeaDAS), implemented for Landsat 8 Operational Land Imager (OLI) data, were evaluated. The OLI-derived remote sensing reflectance (Rrs) products (also known as Level-2 products) were tested against near-simultaneous in-situ data acquired from the OC component of the Aerosol Robotic Network (AERONET-OC). Analyses of the match-ups revealed that generic atmospheric correction methods (i.e., ARCSI and LaSRC), which perform reasonably well over land, provide inaccurate Level-2 products over coastal waters, in particular, in the blue bands. Between water-specific AC methods (i.e., SeaDAS and ACOLITE), SeaDAS was found to perform better over complex waters with root-mean-square error (RMSE) varying from 0.0013 to 0.0005 sr−1 for the 443 and 655 nm channels, respectively. An assessment of the effects of dominant environmental variables revealed AC retrieval errors were influenced by the solar zenith angle and wind speed for ACOLITE and SeaDAS in the 443 and 482 nm channels. Recognizing that the AERONET-OC sites are not representative of inland waters, extensive research and analyses are required to further evaluate the performance of various AC methods for high-resolution imagers like Landsat 8 and Sentinel-2 under a broad range of aquatic/atmospheric conditions.

Document type: 
Article
File(s): 

Epidemiological and Spatial Characteristics of Interpersonal Physical Violence in a Brazilian City: A Comparative Study of Violent Injury Hotspots in Familial Versus Non-Familial Settings, 2012-2014

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-01-07
Abstract: 

This study explores both epidemiological and spatial characteristics of domestic and communityinterpersonal violence. We evaluated three years of violent trauma data in themedium-sized city of Campina Grande in North-Eastern Brazil. 3559 medical and police recordswere analysed and 2563 cases were included to identify socioeconomic and geographicpatterns. The associations between sociodemographic, temporal, and incidentcharacteristics and domestic violence were evaluated using logistic regression. Using GeographicalInformation Systems (GIS), we mapped victims’ household addresses to identifyspatial patterns. We observed a higher incidence of domestic violence among female,divorced, or co-habitant persons when the violent event was perpetrated by males. Therewas only a minor chance of occurrence of domestic violence involving firearms. 8 out of 10victims of domestic violence were women and the female/male ratio was 3.3 times greaterthan that of community violence (violence not occurring in the home). Unmarried coupleswere twice as likely to have a victim in the family unit (OR = 2.03), compared to married couples.Seven geographical hotspots were identified. The greatest density of hotspots wasfound in the East side of the study area and was spatially coincident with the lowest averagefamily income. Aggressor sex, marital status, and mechanism of injury were most associatedwith domestic violence, and low-income neighbourhoods were coincident with bothdomestic and non-domestic violence hotspots. These results provide further evidence thateconomic poverty may play a significant role in interpersonal, and particularly domesticviolence.

Document type: 
Article
File(s): 

Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-03-27
Abstract: 

Lake-rich Arctic river deltas are recharged with terrigenous dissolved organic matter (DOM) during the yearly peak water period corresponding with the solstice (24 h day−1 solar irradiance). Bacteria-free DOM collected during peak Mackenzie River discharge was exposed to sunlight for up to 14 days in June 2010. As solar exposure increased, carbon and lignin concentrations declined (10% and 42%, respectively, after 14 days), as did DOM absorptivity (62% after 14 days), aromaticity, and molecular weight. Photochemical changes were on par with those normally observed in Mackenzie Delta lakes over the entire open-water season. When irradiated freshet DOM was provided as a substrate, no significant differences were observed in community-level metabolism among five bacterial communities from representative delta habitats. However, bacterial abundance was significantly greater when nonirradiated (0 day) rather than irradiated DOM (7 or 14 days) was provided, while cell-specific metabolic measures revealed that per-cell bacterial production and growth efficiency were significantly greater when communities were provided irradiated substrate. This complex response to rapid DOM photodegradation may result from the production of inhibitory reactive oxygen species (ROS), along with shifts in bacterial community composition to species that are better able to tolerate ROS, or metabolize the labile photodegraded DOM.

Document type: 
Article

Supplemental information for Jorge M. G. et al., Subjectivity of drumlin manual mapping and inter-mapper differences in derived morphometrics.

Peer reviewed: 
No, item is not peer reviewed.
Date created: 
2017-02-14
Abstract: 

Supplemental data for Jorge M. G. et al, Subjectivity of drumlin manual mapping and inter-mapper differences in derived morphometrics.

S1 Table. Inter-mapper differences – results of the Wilcoxon signed-rank tests and absolute differences in morphometric medians for all pairs of mappers, for footprints from both DTMs (DTM2; DTM11).

S2 Files. The KML-format file contains the location of the mapped drumlins. The shapefile combines all the footprints mapped by the 14 mappers who participated in the study.

Document type: 
Dataset

Calculation of in-situ acoustic sediment attenuation using off-the-shelf ADCPs in low concentration settings

Peer reviewed: 
Yes, item is peer reviewed.
Abstract: 

The use of ‘off-the-shelf’ acoustic Doppler velocity profilers (ADCPs) to estimate suspended sediment concentration and grain size in rivers requires robust methods to estimate sound attenuation by suspended sediment. Theoretical estimates of sediment attenuation require a priori knowledge of the concentration and grain size distribution (GSD), making the method impractical to apply in routine monitoring programs.  In-situ methods use acoustic backscatter profile slope to estimate sediment attenuation, and are a more attractive option.  However, the performance of in-situ sediment attenuation methods has not been extensively compared to theoretical methods.  We used three collocated horizontally mounted ADCPs in the Fraser River at Mission, British Columbia and 298 observations of concentration and GSD along the acoustic beams to calculate theoretical and in-situ sediment attenuation. Conversion of acoustic intensity from counts to decibels is influenced by the instrument noise floor, which affects the backscatter profile shape and therefore in-situ attenuation.  We develop a method that converts counts to decibels to maximize profile length, which is useful in rivers where cross-channel acoustic profile penetration is a fraction of total channel width. Nevertheless, the agreement between theoretical and in-situ attenuation is poor at low concentrations because cross-stream gradients in concentration, sediment size or GSD can develop, which affect the backscatter profiles.  So we establish threshold concentrations below which in-situ attenuation is unreliable in Fraser River. Results call for careful examination of cross-stream changes in suspended sediment characteristics and acoustic profiles across a range of flows before in-situ attenuation methods are applied in river monitoring programs. 

Document type: 
Dataset

They Go the Extra Mile, the Extra Ten Miles...”: Examining Canadian Medical Yourists’ Interactions with Health Care Workers Abroad

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015
Abstract: 

Developing an understanding of medical tourists' interactions with their health care workers while abroad is important for a number of reasons. Social support has been linked to improved health outcomes for patients (Berkman et al., 2000; Lee and Rotheram-Borus, 2001; Uchino, 2004, 2006), while a lack of social support has been found to lead to higher mortality rates (Brummett et al., 2001; Rutledge et al., 2004). While abroad, medical tourists are not in a position to draw on their usual social support networks as they are away from home. It could be the case that workers in medical tourism facilities are aware of this and work to form a supportive and trusting bond with the patients given that they are away from home and unable to draw on their usual support networks. Furthermore, when patients perceive their relationship with their health care workers as positive, they have been shown to have a higher chance of improved health outcomes (Stewart et al., 2000; Arora, 2003; Beach et al., 2006; Street et al., 2009). There is no reason to think this would be any different for medical tourists. The patient-health care worker relationship can have important implications for patient health and therefore we believe that research into this topic using medical tourists' own experiential accounts can help to identify strategies that can be used to secure and improve this relationship.

Document type: 
Book chapter
File(s):