Coupling Remote Sensing and Modelling to Monitor the Spatial Distribution and Trends of Surface Temperature and Ice Thickness on Sub-Arctic Lakes

Lake surface temperature (LST), lake ice thickness (LIT), and lake ice phenology (LIP) play significant roles in the diverse regional processes of freshwater in cold regions. They offer direct indications of regional weather and climate conditions, and their interactions with the atmosphere impact climate processes. Furthermore, lake ice is valuable to northern communities, such as those in the Northwest Territories (NWT). Ice roads, including the longest ice road in the NWT, spanning over 80 lakes, are constructed during winter to haul goods to and from industrial establishments (e.g., mines) and for travel within and between communities. A significant challenge to lakes and the ongoing use of ice roads are the changes in LST, LIT and LIP due to climate warming. Knowledge of LST, LIT, and LIP is crucial to understanding how lakes respond to climate change and determining how much weight an ice cover can safely sustain for winter travel on frozen lakes. This knowledge, however, is minimal due to the logistical difficulties in traditionally collecting measurements directly. In recent years, satellite-based observations have gained significant traction for studying lakes. However, multispectral sensors are not equipped to measure ice thickness directly, as it is a subsurface feature, which poses a limitation. Furthermore, other methods, such as one-dimensional thermodynamic lake ice models, which rely on weather station input data, are limited by the sparse availability of weather station and in-situ data, especially at high latitudes. This research adopts a multimodal monitoring approach to address these limitations by combining remote sensing data with spatially distributed modelling to study and monitor the trends and spatial distribution of LST, LIT and LIP. In this study, a retrieval algorithm was applied to the thermal bands of Landsat archives to generate a lake-specific surface temperature dataset (North Slave LST dataset) for 535 lakes in the North Slave Region (NSR), NWT, Canada, from 1984 to 2021. Cloud masks were applied to Landsat images to eliminate cloud cover. In addition, a 100 m inward buffer was used on lakes to prevent pixel mixing with shorelines. A good agreement was observed between in-situ observations and North Slave LST, with a mean bias of 0.12 °C and a root mean squared deviation (RMSD) of 1.7 °C. The North Slave LST dataset contains more available data for warmer months (May to September; 57.3 %) than colder months (October to April). The North Slave LST dataset is available at https://doi.org/10.5683/SP3/J4GMC2 (Attiah et al., 2022). Based on the North Slave LST data, LST trends and spatial distribution across the 535 predominantly small to medium lakes across NSR were studied. LST was analyzed in four distinct periods: open water season (OW), ice cover season (IC), and the transitional months of May (TM) and October (TO). The trend and relationships of LST were analyzed using the Mann-Kendall test and a multilinear regression model. The analysis revealed an overall increase in LST, with average rates (max) of 0.03 °C/year (0.05 °C/year), 0.03 °C/year (0.06 °C/year), and 0.13 °C/year (0.27 °C/year) for OW, TM, and TO, respectively across study lakes. A faster rate of change was observed in October compared to other periods. Using the North Slave LST data generated as input, a comprehensive approach was adopted to simulate the spatial variability of ice thickness on lakes at a high resolution by spatially distributing a one-dimensional thermodynamic lake ice model. The spatial distribution of LIT was modelled for study lakes from 1984 to 2022. The generated LST data, in combination with the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) data, were used as inputs for the model. The model simulates the spatial distribution of daily lake ice thickness on a 50-meter spatial grid as well as the annual freeze-up and break-up dates. Results showed a root mean square deviation of LIT from 2.7 cm to 7 cm compared to in-situ data. Further analysis of ice cover on study lakes from 1984 to 2022 revealed decreasing trends in LIT (-0.26 cm/year to -0.10 cm/year) and ice cover duration (ICD) (-0.40 day/year to -0.15 day/year). Simulated LIT and freeze-up proved sensitive to morphometry (depth), while location properties (latitude/longitude) primarily drove the break-up process. This dissertation provides comprehensive approaches to deriving LST, LIT, and LIP information from small and medium lakes in data-sparse regions. A multimodal approach combining remote sensing and spatially distributed modelling is adopted to address the insufficiency of in-situ data and the sparse distribution of weather station data. The methods utilized can be replicated in other regions, providing a broader understanding of the trends and spatial distribution of LST, LIT, and LIP on sub-arctic lakes with varying physical, geographical, and morphometrical properties

The Design and Synthesis of New Materials using Nucleophilic Aromatic Substitution Reactions

Abstract The overall objective of this research was to synthesize and study the structure-property relationships of novel polycyclic aromatic compounds capable of producing open crystalline networks based on π-stacking interactions in solid state. In this work, we describe a method of producing polycyclic aromatic compounds bearing electron-rich and electron-poor rings in order to promote cofacial π-stacking in the solid state. These compounds were synthesized from easily accessible molecules using nucleophilic aromatic substitution and copper-catalyzed aryl amination. The scope of phenoxazines bearing N-aryl substituents was explored for the synthesis of various polycyclic aromatic compounds. Interesting characteristics such as luminescence and predictable solid-state packing are displayed by electron-deficient phenoxazines. A focus was placed upon tuning the properties of the compounds by attaching phenoxazine units to different molecular architectures with the goal of producing open crystalline networks based on π-stacking interactions. The orange-colored solid compound 30 N-(4-bromophenyl) di-fluoro-di-cyano-phenoxazine was synthesized. Suzuki cross-coupling was used to attach an additional phenyl ring to compound 30 to produce compound 31. Similarly, compound 32 was synthesized by the reaction of 1, 4- benzenediboronic acid with two equivalents of compound 30. The crystal structure of compound 31revealed the presence of π-stacking interactions between the phenoxazine rings. The synthetic approach was extended to the preparation of heteropentacenes such as 52 and 58. Compound 52, which bears long alkyl chains, showed evidence of liquid crystallinity by polarized optical microscopy. However, the N-aryl heteropentacenes also showed limited stability

Affective Forecasting with a Chance of Collective Action: Women’s Anticipated Affect After Acting Against Sexism and its Relationship to Collective Action Intentions

Confronting sexism elicits social costs like name-calling (Mendes et al., 2018) and anticipating these costs inhibits confrontation (Good et al., 2012). But taking collective action can also improve women’s wellbeing and reduce negative emotion (Foster, 2015). How women anticipate their own emotions in response to social cost may be a predictor of action. However, it is not yet known how women anticipate taking action will make them feel, and how perceived costs relate to these predictions and action intentions. The present thesis integrates two previously distinct literatures, affective forecasting (Gilbert et al., 1998) and collective action motivation to assess the potential link. In Studies 1 and 2, participants imagined engaging in collective action against sexism, and then answered open and closed-ended questions about how taking action would make them feel, and about perceived social costs of taking action. A content analysis of open-text comments provided insight into women’s beliefs about how collective action will make them feel. Parallel mediation models showed that in Study 1 (but not Study 2), higher perceived social cost was associated with more negative affective forecasts, and in turn, lower intentions to engage in collective action. To address questions of causality in Studies 1 and 2, in Studies 3 and 4, participants were asked to create a Tweet about sexism, and then received one of three (fabricated) responses to their Tweet, ostensibly generated by an algorithm that searched Twitter for common responses to Tweets against sexism. The response was either supportive (social benefit), neutral (control), or disparaging (social cost). Participants rated how they thought they would feel if they received that response, both about the fact that they took action, and about the reply they received. Results suggest that the social cost condition, compared to the social benefit condition, increased negative affective forecasts and decreased positive affective forecasts about taking action, and decreased positive affective forecasts about the reply, which in turn, reduced social media action intentions. Future research should consider how to modify affective forecasts to increase women’s confrontation of sexism, and how to maintain its wellbeing benefits in the face of social costs

Anoxia and Re-oxygenation at Colder Temperatures in Goldfish (Carassius auratus): Effects on Oxidative Stress and Metabolites

Under the ice of ponds and lakes, goldfish (Carassius auratus) can survive weeks of anoxia at low temperatures by conserving ATP and by reducing their metabolic rate and relying on liver glycogen stores to meet their ATP demands using glycolysis. The following period of re-oxygenation is also known to be damaging in most vertebrates because it can lead to the generation of reactive oxygen species (ROS) that can cause oxidative damage to lipids, proteins and nucleic acids. Anoxia tolerant vertebrates such as the goldfish and crucian carp (Carassius carassius) accumulate reduced molecules with anoxia, overwhelming the electron transport system, producing ROS, and thus oxidative stress during re-oxygenation. Primary antioxidant defenses and pathways regulating ROS production are thought to minimize oxidative stress. In natural, temperate environments, fishes normally experience anoxia and re-oxygenation at colder temperatures. Yet relatively few studies have directly addressed how important cold-water temperatures are in limiting oxidative damage to goldfish during anoxia and re-oxygenation. In this study, the effects of cold-water acclimation (4°C) on the physiological responses of goldfish to anoxia and re-oxygenation were studied. Goldfish were acclimated to 4 °C or 14°C for 3 months, followed by 96 h or 24 h of anoxia exposure and a 12 h period of re-oxygenation. Tissues (liver, muscle, blood) were collected for analysis of antioxidant enzyme activities, oxidative damage, glycogen stores, and metabolites. Temperature acclimation resulted in 1.5-fold greater superoxide dismutase (SOD) activity and 2.2-fold lower glutathione peroxidase (GPx) activity in the normoxic liver at 4°C. Anoxia exposure resulted in no oxidative damage or changes in antioxidant enzyme activity in the liver or muscle at either temperature. Notably, liver glycogen did not significantly decrease during anoxia at 4°C, but a 70% decrease in liver glycogen was observed following 24 h of anoxia at 14°C and sustained through 12 h of re-oxygenation. Both blood glucose and lactate were elevated following anoxia at both temperatures, consistent with a greater reliance on anaerobic glycolysis. Significant anoxic ethanol accumulation occurred in the blood, which took longer to eliminate at 4°C during subsequent re-oxygenation. These findings support the hypothesis that reduced metabolic rates at cold temperatures reduce energy demands and the accumulation of anaerobic metabolites. In conclusion, oxidative stress in goldfish during re-oxygenation is prevented by mechanisms that do not involve changes in antioxidant enzyme activity, but recovery from anoxia is faster at colder temperatures. The robustness of goldfish to periods of anoxia and re-oxygenation, especially at colder, more environmentally relevant temperatures, represent adaptations that have allowed them to occupy niches that are unsuitable for other freshwater fishes