Postdoctoral Fellowships - University of Ottawa
Environmental factors influencing microcystin congeners in freshwaters
Environmental factors influencing microcystin congeners in freshwaters
Cyanobacterial blooms increasingly impair freshwater lakes, with the potential for a parallel increase in neuro- and hepatotoxins produced by these organisms. This is problematic given that wildlife, livestock and even human fatalities have been linked to cyanotoxin exposure.
During my postdoctoral fellowship at University of Ottawa (F. Pick Lab), I examined how environmental factors influenced cyanotoxin composition (i.e., different microcystin congeners) in freshwater lakes. With respect to the microcystins, little is known about the occurrence of specific congeners in the environment, yet these vary widely in their persistence, mammalian toxicity and potential bioamplification up the food chain. To examine the occurrence of different congeners in response to environmental change, we conducted a regional study (Great Lakes basin) to identify the climatic and nutrient optima of the most commonly measured microcystin congeners (MC-LR, MC-LA, MC-RR and MC-YR). We showed that the more commonly studied MC-LR dominated under calm, warm and nutrient rich conditions, whereas the more recently identified and increasingly common MC-LA was associated with relatively windier, wetter, and nutrient poor conditions. We complemented this study with a synthesis of the literature to examine the variability of microcystin congener composition across the globe. We detected large differences with respect to which congener was most often reported or detected between North America and Europe. The environment-congener associations likely vary among regions, lake types and time of sampling, and more work is needed to identify the patterns and drivers of microcystin congeners composition. Ultimately, the environmental fate of the different microcystin congeners will likely affect the degree of cyanotoxin bioaccumulation in aquatic and terrestrial ecosystems. |
Postdoctoral Fellowships - University of Montreal
Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor
Scientists, governments and non-governmental organizations are increasingly moving towards the collection of large, open-access data. In aquatic sciences, this effort is expanding the scope of questions that can be performed to further our knowledge of the global drivers of water quality. Cyanotoxin concentration is one variable that has received considerable attention, and although strong local-scale models have been described in the literature, modelling cyanotoxin concentrations across broader spatial scales has been more difficult. Commonly used statistical frameworks have not fully captured the complex response of toxic algal blooms to global change, limiting our ability to predict and mitigate the impairment of freshwaters by toxic algae. Here, we advance our understanding of drivers of cyanotoxins by applying a hierarchical “hurdle” model. In particular, we tested the importance of multi-scale interactions among environmental features in driving microcystin concentrations above the limit of detection. We then used boosted regression trees [BRTs] to identify environmental thresholds associated with severe impairment by microcystins. Accounting for numerous non-detections, spatial heterogeneity and cross-scale interactions substantially improved continental-scale predictions of bloom toxicity. Our model accounted for 55% of the variance in the probability of detecting microcystins across the United States, and 26% of the variability in microcystin concentrations once detected. BRTs further showed that although both local and regional drivers were associated with microcystin concentrations at low to intermediate provisional guidelines, only local drivers came into play when predicting higher limits. Identifying the interaction between local and regional processes is key to understanding the heterogeneous responses of microcystins to environmental change.
Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor
Scientists, governments and non-governmental organizations are increasingly moving towards the collection of large, open-access data. In aquatic sciences, this effort is expanding the scope of questions that can be performed to further our knowledge of the global drivers of water quality. Cyanotoxin concentration is one variable that has received considerable attention, and although strong local-scale models have been described in the literature, modelling cyanotoxin concentrations across broader spatial scales has been more difficult. Commonly used statistical frameworks have not fully captured the complex response of toxic algal blooms to global change, limiting our ability to predict and mitigate the impairment of freshwaters by toxic algae. Here, we advance our understanding of drivers of cyanotoxins by applying a hierarchical “hurdle” model. In particular, we tested the importance of multi-scale interactions among environmental features in driving microcystin concentrations above the limit of detection. We then used boosted regression trees [BRTs] to identify environmental thresholds associated with severe impairment by microcystins. Accounting for numerous non-detections, spatial heterogeneity and cross-scale interactions substantially improved continental-scale predictions of bloom toxicity. Our model accounted for 55% of the variance in the probability of detecting microcystins across the United States, and 26% of the variability in microcystin concentrations once detected. BRTs further showed that although both local and regional drivers were associated with microcystin concentrations at low to intermediate provisional guidelines, only local drivers came into play when predicting higher limits. Identifying the interaction between local and regional processes is key to understanding the heterogeneous responses of microcystins to environmental change.
PhD - McGill University
Historical and contemporary drivers of cyanobacterial dynamics: regional and global perspectives
Numerous authors are reporting that anthropogenic changes to the environment (i.e., cultural eutrophication and climate warming) have provided opportune conditions for a global dominance of phytoplankton communities by cyanobacteria. Yet, to date there has been no quantitative synthesis to support this claim and we have very little empirical evidence of synergistic relationships among the environmental drivers that could be responsible for an expansion of cyanobacteria through time.
In my doctoral thesis, I quantified temporal (decadal; 1985-2011 CE to centennial; 1800-2011 CE) cyanobacterial trends, both at the regional (Alberta, Canada) and global scale. Using phytoplankton time series data from five Albertan lakes, I show that the increase in cyanobacterial biomass is greatest under a combination of warmer water temperatures, increased intensity of thermal stratification, and elevated nutrient concentrations. I further show that space for time substitutions are valid for predicting cyanobacterial biomass by comparing empirical models developed from lake surveys to decadal-scale time series. To test whether the response of cyanobacteria in the face of environmental development has changed since the start of Anthropocene (ca. 1850 CE), I then compared models based on different time scales. In extending the timeframe, I found as much as a 70% loss in variance explained with the centennial models. Finally, I quantified the increases in cyanobacterial abundance (rate and magnitude) over the past ~200 years by conducting a synthesis of more than 100 paleolimnological records and ~20 long-term monitoring records. With this dataset, I have shown that in the Northern Hemisphere, the increase in cyanobacteria is related to nutrient concentrations, lake elevation and lake morphometry.
Historical and contemporary drivers of cyanobacterial dynamics: regional and global perspectives
Numerous authors are reporting that anthropogenic changes to the environment (i.e., cultural eutrophication and climate warming) have provided opportune conditions for a global dominance of phytoplankton communities by cyanobacteria. Yet, to date there has been no quantitative synthesis to support this claim and we have very little empirical evidence of synergistic relationships among the environmental drivers that could be responsible for an expansion of cyanobacteria through time.
In my doctoral thesis, I quantified temporal (decadal; 1985-2011 CE to centennial; 1800-2011 CE) cyanobacterial trends, both at the regional (Alberta, Canada) and global scale. Using phytoplankton time series data from five Albertan lakes, I show that the increase in cyanobacterial biomass is greatest under a combination of warmer water temperatures, increased intensity of thermal stratification, and elevated nutrient concentrations. I further show that space for time substitutions are valid for predicting cyanobacterial biomass by comparing empirical models developed from lake surveys to decadal-scale time series. To test whether the response of cyanobacteria in the face of environmental development has changed since the start of Anthropocene (ca. 1850 CE), I then compared models based on different time scales. In extending the timeframe, I found as much as a 70% loss in variance explained with the centennial models. Finally, I quantified the increases in cyanobacterial abundance (rate and magnitude) over the past ~200 years by conducting a synthesis of more than 100 paleolimnological records and ~20 long-term monitoring records. With this dataset, I have shown that in the Northern Hemisphere, the increase in cyanobacteria is related to nutrient concentrations, lake elevation and lake morphometry.
MSc - McGill University
Tracking changes in water quality due to catchment land-use and lake morphometry across spatial and temporal scales
Past studies have shown that diffuse nutrient loading from agricultural activities is an important cause of lake eutrophication. The degree to which this relationship can be scaled-up (e.g. at an inter-regional scale) has not, however, been widely addressed. My thesis objectives were therefore to define the generality and the impact of agriculture land use and lake morphometry on lake water quality. We tested whether agricultural activities explain a significant proportion of the variation in lake water quality at a broad inter-regional scale. The degree to which lake mean depth modulates this response was also assessed. From our meta-analyses of 358 lakes, we noted a significant correlation between total phosphorus concentration and the extent of agricultural catchment development. This relationship was further strengthened by including lake mean depth as a second predictor. We also observed among-study variability in the relationship between these three variables. Thus, although there is a general relationship between total phosphorus concentrations and our two predictors, agriculture catchment development and lake mean depth, regional baseline nutrient differences modify this relationship. To address the issue of lake morphometry more closely, we adopted a spatio-temporal approach to investigate whether the effect of agricultural catchment development on water quality differed between dimictic and polymictic Albertan lakes. We found that the correlation between surface water total phosphorus concentration and the percent of agriculture in a lake’s catchment was strongly modified by lake mixis patterns (which in turn are related to morphometry). Furthermore, with our paleo-indicators of lake water-quality, the chironomid communities, we detected opposing responses between the dimictic and polymictic basins to temporal land-use change. We suggest that external nutrient loading exerts a more notable effect on dimictic lakes, whereas internal loading is more important in polymictic systems.
Tracking changes in water quality due to catchment land-use and lake morphometry across spatial and temporal scales
Past studies have shown that diffuse nutrient loading from agricultural activities is an important cause of lake eutrophication. The degree to which this relationship can be scaled-up (e.g. at an inter-regional scale) has not, however, been widely addressed. My thesis objectives were therefore to define the generality and the impact of agriculture land use and lake morphometry on lake water quality. We tested whether agricultural activities explain a significant proportion of the variation in lake water quality at a broad inter-regional scale. The degree to which lake mean depth modulates this response was also assessed. From our meta-analyses of 358 lakes, we noted a significant correlation between total phosphorus concentration and the extent of agricultural catchment development. This relationship was further strengthened by including lake mean depth as a second predictor. We also observed among-study variability in the relationship between these three variables. Thus, although there is a general relationship between total phosphorus concentrations and our two predictors, agriculture catchment development and lake mean depth, regional baseline nutrient differences modify this relationship. To address the issue of lake morphometry more closely, we adopted a spatio-temporal approach to investigate whether the effect of agricultural catchment development on water quality differed between dimictic and polymictic Albertan lakes. We found that the correlation between surface water total phosphorus concentration and the percent of agriculture in a lake’s catchment was strongly modified by lake mixis patterns (which in turn are related to morphometry). Furthermore, with our paleo-indicators of lake water-quality, the chironomid communities, we detected opposing responses between the dimictic and polymictic basins to temporal land-use change. We suggest that external nutrient loading exerts a more notable effect on dimictic lakes, whereas internal loading is more important in polymictic systems.