Bio-optical Modeling and Remote Sensing of Inland Waters
Abstract Sun-induced chlorophyll- a fluorescence (SICF) is the emission of red light by chlorophy... more Abstract Sun-induced chlorophyll- a fluorescence (SICF) is the emission of red light by chlorophyll- a in the presence of sunlight. In surface waters, chlorophyll- a is present in phytoplankton and SICF is observable in the light leaving the water surface. This allows, in principle, the estimation of phytoplankton absorption from measurements of light leaving water. However, while the concentration of phytoplankton in surface waters is the dominant source of optical variability, phytoplankton physiology and the optical characteristics of water also play a significant role in altering the observed emission. The latter have a particularly strong impact in inland and coastal waters. To examine these interactions and their impact on the observed light field, a four-component bio-optical model was developed to create synthetic datasets of reflectance spectra. These synthetic spectra are used together with field measurements of reflectance to understand the relationships between SICF, phytoplankton abundance, colored dissolved organic matter absorption, and suspended inorganic matter concentration in inland and coastal waters. The retrieval of SICF using hyperspectral data and fluorescence line height algorithms is analyzed by considering the wavebands of past, current, and future ocean color sensors. The use of fluorescence signatures in polarimetric observations and applications to algal bloom detection are also discussed.
Despite decades of research and mitigation efforts, declines in freshwater quality resulting from... more Despite decades of research and mitigation efforts, declines in freshwater quality resulting from anthropogenic nutrient input remain a persistent issue worldwide. Canada has the greatest number of freshwater lakes in the world, yet we have a limited understanding of the magnitude and scale at which most lakes have been affected by human activities, namely Land Use/Land Cover (LULC) alterations. In response, the NSERC Canadian Lake Pulse Network has compiled the first nationwide systematic database of Canadian lake quality metrics by surveying 664 lakes across 12 ecozones over three years. To assess the influence of human impact on water quality and its spatial variation across this lake set, we built models quantifying the association between watershed LULC and physiochemical water parameters. We found that agricultural and urban land use explained the greatest proportion of variation in water quality among LULC categories (R2 = 0.20–0.29), although threshold values of water qualit...
Lakes are highly heterogenous ecosystems inhabited by a rich microbiome whose genomic diversity r... more Lakes are highly heterogenous ecosystems inhabited by a rich microbiome whose genomic diversity remains poorly defined compared to other major biomes. Here, we present a continental-scale study of metagenomes collected across one of the most lake-rich landscapes on Earth. Analysis of 308 Canadian lakes resulted in a metagenome-assembled genome (MAG) catalogue of 1,008 bacterial genomospecies spanning a broad phylogenetic and metabolic diversity. Lake trophic state was a significant determinant of taxonomic and functional turnover of MAG assemblages. We detected a role for resource availability, particularly carbohydrate diversity, in driving biogeographic patterns. Coupling the MAG catalogue with geomatics information on watershed characteristics revealed an influence of soil properties and human land use on MAG assemblages. Agriculture and human population density were particularly influential on MAG functional turnover, signifying a detectable human footprint in lake bacterial com...
Our decreasing ability to fight bacterial infections is a major health concern. It is arising due... more Our decreasing ability to fight bacterial infections is a major health concern. It is arising due to the evolution of antimicrobial resistance (AMR) in response to the mis- and overuse of antibiotics in both human and veterinary medicine. Lakes integrate watershed processes and thus may act as receptors and reservoirs of antibiotic resistance genes (ARGs) introduced into the watershed by human activities. The resistome - the diversity of ARGs – under varying anthropogenic watershed pressures has been previously studied either focused on few select genes or few lakes. Here, we link the resistome of ∼350 lakes sampled across Canada to human watershed activity, trophic status, as well as point sources of ARG pollution. A high percentage of the resistance genes detected was either unimpacted by human activity or highly prevalent in pristine lakes, highlighting the role of AMR in microbial ecology in aquatic systems, as well as a pool of genes available for potential horizontal gene tran...
Freshwater lakes are experiencing rapid changes under accelerated anthropogenic stress and a warm... more Freshwater lakes are experiencing rapid changes under accelerated anthropogenic stress and a warming climate. Microorganisms underpin aquatic food webs, yet little is known about how freshwater microbial communities are responding to human impact.
Lakes play a pivotal role in ecological and biogeochemical processes and have been described as "... more Lakes play a pivotal role in ecological and biogeochemical processes and have been described as "sentinels" of environmental change. Assessing "lake health" across large geographic scales is critical to predict the stability of their ecosystem services and their vulnerability to anthropogenic disturbances. The LakePulse research network is tasked with the assessment of lake health across gradients of land use on a continental scale. Bacterial communities are an integral and rapidly responding component of lake ecosystems, yet large-scale responses to anthropogenic activity remain elusive. Here, we assess the ecological impact of land use on bacterial communities from over 200 lakes covering more than 660,000 km 2 across Eastern Canada. In addition to community variation between ecozones, land use across Eastern Canada also appeared to alter diversity, community composition, and network structure. Specifically, increasing anthropogenic impact within the watershed lowered diversity. Likewise, community composition was significantly correlated with agriculture and urban development within a watershed. Interaction networks showed decreasing complexity and fewer keystone taxa in impacted lakes. Moreover, we identified potential indicator taxa of high or low lake water quality. Together, these findings point to detectable bacterial community changes of largely unknown consequences induced by human activity within lake watersheds.
• About 90% of Canada's municipal drinking water supplies are from surface waters. • An academic-... more • About 90% of Canada's municipal drinking water supplies are from surface waters. • An academic-government group is providing the first national review of lake health. • Over 100 variables were sampled at about 680 lakes across Canada. • Topics range from greenhouse gases to emerging contaminants to invasive pathogens. • The impacts of land-use and climate changes on lake health are also studied.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers,... more Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers, and symbionts. Yet, a comprehensive view of protist diversity in freshwaters has been challenged by the immense environmental heterogeneity among lakes worldwide. We assessed protist diversity in the surface waters of 366 freshwater lakes across a north temperate to subarctic extent covering nearly 8.4 million km2 of Canada. Sampled lakes represented broad gradients in size, trophic state, and watershed land use. Hypereutrophic lakes contained the least diverse and most distinct protist communities relative to nutrient-poor lakes. Greater taxonomic variation among eutrophic lakes was mainly a product of heterotroph and mixotroph diversity, whereas phototroph assemblages were more similar under high- nutrient conditions. Overall, local physicochemical factors, particularly ion and nutrient concentrations, elicited the strongest responses in community structure, far outweighing the effect...
The Arctic ice scape is composed by a mosaic of ridges, hummocks, melt ponds, leads, and snow. Un... more The Arctic ice scape is composed by a mosaic of ridges, hummocks, melt ponds, leads, and snow. Under such heterogeneous surfaces, drifting phytoplankton communities are experiencing a wide range of irradiance conditions and intensities that cannot be sampled representatively using single-location measurements. Combining experimentally derived photosynthetic parameters with transmittance measurements acquired at spatial scales ranging from hundreds of meters (using a remotely operated vehicle, ROV) to thousands of meters (using a surface and underice trawl, SUIT), we assessed the sensitivity of water column primary production estimates to multiscale underice light measurements. Daily primary production calculated from transmittance from both the ROV and the SUIT ranged between 0.004 and 939 mgC•m -2 •day -1 . Upscaling these estimates at larger spatial scales using satellite-derived sea ice concentration reduced the variability by 22% (0.004-731 mgC•m -2 •day -1 ). The relative error in primary production estimates was two times lower when combining remote sensing and in situ data compared to ROV-based estimates alone. These results suggest that spatially extensive in situ measurements must be combined with large-footprint sea ice coverage sampling (e.g., remote sensing, aerial imagery) to accurately estimate primary production in ice-covered waters. Also, the results indicated a decreasing error of primary production estimates with increasing sample size and the spatial scale at which in situ measurements are performed. Conversely, existing estimates of spatially integrated phytoplankton primary production in ice-covered waters derived from single-location light measurements may be associated with large statistical errors. Considering these implications is important for modeling scenarios and interpretation of existing measurements in a changing Arctic ecosystem.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2018
Diel variations of inherent optical properties (absorption coefficient, attenuation coefficient a... more Diel variations of inherent optical properties (absorption coefficient, attenuation coefficient and volume scattering function at 124 °) of four species of phytoplankton were measured in the laboratory and were simulated using a homogeneous spherical model, a coated spherical model and a homogeneous hexahedral model. The required inputs to run each optical model were acquired from the measurements; the real and imaginary parts of the refractive index were determined from the intracellular carbon and absorption coefficient, and particle size distributions from the Coulter counter. We conducted a sensitivity analysis on the inherent optical properties in response to changes in the slope of Junge distributions that were used to represent non-phytoplankton particles of radii less than 1.12 μm (the minimum size of the Coulter counter), realistic maximum and minimum values of the refractive indices used for the shell and core, shell thickness, cell radius and the number of cells. We found that the shell's refractive index is the most important factor influencing the backscattering ratio. We found that the coated spherical model reproduced the observed optical properties best for all species possessing a shell. The hexahedral and homogenous spherical models give relatively good results for the absorption and attenuation coefficients; but underestimated the volume scattering function at 124 °. Correlations between the measured backscattering cross sections and carbon are significant only for E. huxleyi and D. tertiolecta. In situ measurements will be necessary to determine if our models can reproduce the diel variations of backscattering that are observed in the ocean.
In vivo pigment fluorescence methods allow simple real‐time detection and quantification of fresh... more In vivo pigment fluorescence methods allow simple real‐time detection and quantification of freshwater algae and cyanobacteria. Available models are still limited to high‐cost fluorometers, validated for single instruments or individual water bodies, preventing data comparison between multiple instruments, and thus, restricting their use in large‐scale monitoring programs. Moreover, few models include corrections for optical interference (water turbidity and colored dissolved organic matter, CDOM). In this study, we developed simple models to predict phytoplankton and cyanobacterial chlorophyll a (Chl a) concentrations based on Chl a and C‐phycocyanin in vivo fluorescence, using multiple low‐cost handheld fluorometers. We aimed to: (1) fit models to mixed cyanobacterial and microalgal cultures; (2) cross‐calibrate nine fluorometers of the same brand and series; (3) correct the CDOM and turbidity effects; and (4) test the algorithms’ performance with natural samples. We achieved comparable results between nine instruments after the cross‐calibration, allowing their simultaneous use. We obtained algorithms for total and cyanobacterial Chl a estimation. We developed parametric corrections to remove CDOM and turbidity interferences in the algorithms. Five sampling sites (from a lake, a stream, and an estuary) were used to test the algorithms using eight cross‐calibrated fluorometers. The models showed their best performance after CDOM and turbidity corrections (total Chl a: R2 = 0.99, RMSE = 7.8 μg Chl a L−1; cyanobacterial Chl a: R2 = 0.98, RMSE = 9.8 μg Chl a L−1). In summary, our models can quantify total phytoplankton and cyanobacterial Chl a in real time with multiple low‐cost fluorometers, allowing its implementation in large‐scale monitoring programs.
Adoption of microalgae-sourced products depends on the economic feasibility. In the case of fatty... more Adoption of microalgae-sourced products depends on the economic feasibility. In the case of fatty acids, it is crucial to obtain high lipid yield, especially in the form of storage lipids (TAGs). However, the production of these lipids often comes into competition with the microalgae biomass, resulting in a decrease in growth. A microalgae culture integration project was conducted in an industrial park in Canada in order to cultivate microalgae from park's wastewaters and then obtain products from the biomass. Different deficiencies and stresses were tested to evaluate what condition allowed the induction of the highest lipids accumulation without compromising the growth of microalgae. The results showed that the medium controlled to pH 7.0 allowed reaching the largest amount of extracted lipids (28 ± 4.3%). Companies involved in this project could be able to make significant savings by the reduced wastewater treatment costs and by not adding expensive nutrients in culture.
Northern lakes are ice-covered for a large part of the year, yet our understanding of microbial d... more Northern lakes are ice-covered for a large part of the year, yet our understanding of microbial diversity and activity during winter lags behind that of the ice-free period. In this study, we investigated under-ice diversity and metabolism of Verrucomicrobia in seasonally ice-covered lakes in temperate and boreal regions of Quebec, Canada using 16S rRNA sequencing, metagenomics and metatranscriptomics. Verrucomicrobia, particularly the V1, V3 and V4 subdivisions, were abundant during ice-covered periods. A diversity of Verrucomicrobia genomes were reconstructed from Quebec lake metagenomes. Several genomes were associated with the ice-covered period and were represented in winter metatranscriptomes, supporting the notion that Verrucomicrobia are metabolically active under ice. Verrucomicrobia transcriptome analysis revealed a range of metabolisms potentially occurring under ice, including carbohydrate degradation, glycolate utilization, scavenging of chlorophyll degradation products...
Diurnal variations of phytoplankton size distributions, chlorophyll, carbon and nitrogen content,... more Diurnal variations of phytoplankton size distributions, chlorophyll, carbon and nitrogen content, in vivo fluorescence and associated optical absorption and scattering properties were observed in the laboratory to help understand in situ and spatial observations. We grew triplicate semi-continuous cultures of T. pseudonana, D. tertiolecta, P. tricornutum and E. huxleyi under a sinusoidal light regime. We observed diurnal variations in the particulate absorption (a), scattering (b), attenuation (c), and backscattering coefficients (b), which correlate with carbon and Chl concentrations. Relative variations from sunrise of bare slightly lower than those of c, suggesting that bdiurnal increases observed in nature are partly caused by phytoplankton. Non-concurrent changes of carbon and Chl-specific backscattering and scattering coefficients and optical cross-sections however indicates that using backscattering to infer scattering or biomass must be done with care.
Bio-optical Modeling and Remote Sensing of Inland Waters
Abstract Sun-induced chlorophyll- a fluorescence (SICF) is the emission of red light by chlorophy... more Abstract Sun-induced chlorophyll- a fluorescence (SICF) is the emission of red light by chlorophyll- a in the presence of sunlight. In surface waters, chlorophyll- a is present in phytoplankton and SICF is observable in the light leaving the water surface. This allows, in principle, the estimation of phytoplankton absorption from measurements of light leaving water. However, while the concentration of phytoplankton in surface waters is the dominant source of optical variability, phytoplankton physiology and the optical characteristics of water also play a significant role in altering the observed emission. The latter have a particularly strong impact in inland and coastal waters. To examine these interactions and their impact on the observed light field, a four-component bio-optical model was developed to create synthetic datasets of reflectance spectra. These synthetic spectra are used together with field measurements of reflectance to understand the relationships between SICF, phytoplankton abundance, colored dissolved organic matter absorption, and suspended inorganic matter concentration in inland and coastal waters. The retrieval of SICF using hyperspectral data and fluorescence line height algorithms is analyzed by considering the wavebands of past, current, and future ocean color sensors. The use of fluorescence signatures in polarimetric observations and applications to algal bloom detection are also discussed.
Despite decades of research and mitigation efforts, declines in freshwater quality resulting from... more Despite decades of research and mitigation efforts, declines in freshwater quality resulting from anthropogenic nutrient input remain a persistent issue worldwide. Canada has the greatest number of freshwater lakes in the world, yet we have a limited understanding of the magnitude and scale at which most lakes have been affected by human activities, namely Land Use/Land Cover (LULC) alterations. In response, the NSERC Canadian Lake Pulse Network has compiled the first nationwide systematic database of Canadian lake quality metrics by surveying 664 lakes across 12 ecozones over three years. To assess the influence of human impact on water quality and its spatial variation across this lake set, we built models quantifying the association between watershed LULC and physiochemical water parameters. We found that agricultural and urban land use explained the greatest proportion of variation in water quality among LULC categories (R2 = 0.20–0.29), although threshold values of water qualit...
Lakes are highly heterogenous ecosystems inhabited by a rich microbiome whose genomic diversity r... more Lakes are highly heterogenous ecosystems inhabited by a rich microbiome whose genomic diversity remains poorly defined compared to other major biomes. Here, we present a continental-scale study of metagenomes collected across one of the most lake-rich landscapes on Earth. Analysis of 308 Canadian lakes resulted in a metagenome-assembled genome (MAG) catalogue of 1,008 bacterial genomospecies spanning a broad phylogenetic and metabolic diversity. Lake trophic state was a significant determinant of taxonomic and functional turnover of MAG assemblages. We detected a role for resource availability, particularly carbohydrate diversity, in driving biogeographic patterns. Coupling the MAG catalogue with geomatics information on watershed characteristics revealed an influence of soil properties and human land use on MAG assemblages. Agriculture and human population density were particularly influential on MAG functional turnover, signifying a detectable human footprint in lake bacterial com...
Our decreasing ability to fight bacterial infections is a major health concern. It is arising due... more Our decreasing ability to fight bacterial infections is a major health concern. It is arising due to the evolution of antimicrobial resistance (AMR) in response to the mis- and overuse of antibiotics in both human and veterinary medicine. Lakes integrate watershed processes and thus may act as receptors and reservoirs of antibiotic resistance genes (ARGs) introduced into the watershed by human activities. The resistome - the diversity of ARGs – under varying anthropogenic watershed pressures has been previously studied either focused on few select genes or few lakes. Here, we link the resistome of ∼350 lakes sampled across Canada to human watershed activity, trophic status, as well as point sources of ARG pollution. A high percentage of the resistance genes detected was either unimpacted by human activity or highly prevalent in pristine lakes, highlighting the role of AMR in microbial ecology in aquatic systems, as well as a pool of genes available for potential horizontal gene tran...
Freshwater lakes are experiencing rapid changes under accelerated anthropogenic stress and a warm... more Freshwater lakes are experiencing rapid changes under accelerated anthropogenic stress and a warming climate. Microorganisms underpin aquatic food webs, yet little is known about how freshwater microbial communities are responding to human impact.
Lakes play a pivotal role in ecological and biogeochemical processes and have been described as "... more Lakes play a pivotal role in ecological and biogeochemical processes and have been described as "sentinels" of environmental change. Assessing "lake health" across large geographic scales is critical to predict the stability of their ecosystem services and their vulnerability to anthropogenic disturbances. The LakePulse research network is tasked with the assessment of lake health across gradients of land use on a continental scale. Bacterial communities are an integral and rapidly responding component of lake ecosystems, yet large-scale responses to anthropogenic activity remain elusive. Here, we assess the ecological impact of land use on bacterial communities from over 200 lakes covering more than 660,000 km 2 across Eastern Canada. In addition to community variation between ecozones, land use across Eastern Canada also appeared to alter diversity, community composition, and network structure. Specifically, increasing anthropogenic impact within the watershed lowered diversity. Likewise, community composition was significantly correlated with agriculture and urban development within a watershed. Interaction networks showed decreasing complexity and fewer keystone taxa in impacted lakes. Moreover, we identified potential indicator taxa of high or low lake water quality. Together, these findings point to detectable bacterial community changes of largely unknown consequences induced by human activity within lake watersheds.
• About 90% of Canada's municipal drinking water supplies are from surface waters. • An academic-... more • About 90% of Canada's municipal drinking water supplies are from surface waters. • An academic-government group is providing the first national review of lake health. • Over 100 variables were sampled at about 680 lakes across Canada. • Topics range from greenhouse gases to emerging contaminants to invasive pathogens. • The impacts of land-use and climate changes on lake health are also studied.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers,... more Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers, and symbionts. Yet, a comprehensive view of protist diversity in freshwaters has been challenged by the immense environmental heterogeneity among lakes worldwide. We assessed protist diversity in the surface waters of 366 freshwater lakes across a north temperate to subarctic extent covering nearly 8.4 million km2 of Canada. Sampled lakes represented broad gradients in size, trophic state, and watershed land use. Hypereutrophic lakes contained the least diverse and most distinct protist communities relative to nutrient-poor lakes. Greater taxonomic variation among eutrophic lakes was mainly a product of heterotroph and mixotroph diversity, whereas phototroph assemblages were more similar under high- nutrient conditions. Overall, local physicochemical factors, particularly ion and nutrient concentrations, elicited the strongest responses in community structure, far outweighing the effect...
The Arctic ice scape is composed by a mosaic of ridges, hummocks, melt ponds, leads, and snow. Un... more The Arctic ice scape is composed by a mosaic of ridges, hummocks, melt ponds, leads, and snow. Under such heterogeneous surfaces, drifting phytoplankton communities are experiencing a wide range of irradiance conditions and intensities that cannot be sampled representatively using single-location measurements. Combining experimentally derived photosynthetic parameters with transmittance measurements acquired at spatial scales ranging from hundreds of meters (using a remotely operated vehicle, ROV) to thousands of meters (using a surface and underice trawl, SUIT), we assessed the sensitivity of water column primary production estimates to multiscale underice light measurements. Daily primary production calculated from transmittance from both the ROV and the SUIT ranged between 0.004 and 939 mgC•m -2 •day -1 . Upscaling these estimates at larger spatial scales using satellite-derived sea ice concentration reduced the variability by 22% (0.004-731 mgC•m -2 •day -1 ). The relative error in primary production estimates was two times lower when combining remote sensing and in situ data compared to ROV-based estimates alone. These results suggest that spatially extensive in situ measurements must be combined with large-footprint sea ice coverage sampling (e.g., remote sensing, aerial imagery) to accurately estimate primary production in ice-covered waters. Also, the results indicated a decreasing error of primary production estimates with increasing sample size and the spatial scale at which in situ measurements are performed. Conversely, existing estimates of spatially integrated phytoplankton primary production in ice-covered waters derived from single-location light measurements may be associated with large statistical errors. Considering these implications is important for modeling scenarios and interpretation of existing measurements in a changing Arctic ecosystem.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2018
Diel variations of inherent optical properties (absorption coefficient, attenuation coefficient a... more Diel variations of inherent optical properties (absorption coefficient, attenuation coefficient and volume scattering function at 124 °) of four species of phytoplankton were measured in the laboratory and were simulated using a homogeneous spherical model, a coated spherical model and a homogeneous hexahedral model. The required inputs to run each optical model were acquired from the measurements; the real and imaginary parts of the refractive index were determined from the intracellular carbon and absorption coefficient, and particle size distributions from the Coulter counter. We conducted a sensitivity analysis on the inherent optical properties in response to changes in the slope of Junge distributions that were used to represent non-phytoplankton particles of radii less than 1.12 μm (the minimum size of the Coulter counter), realistic maximum and minimum values of the refractive indices used for the shell and core, shell thickness, cell radius and the number of cells. We found that the shell's refractive index is the most important factor influencing the backscattering ratio. We found that the coated spherical model reproduced the observed optical properties best for all species possessing a shell. The hexahedral and homogenous spherical models give relatively good results for the absorption and attenuation coefficients; but underestimated the volume scattering function at 124 °. Correlations between the measured backscattering cross sections and carbon are significant only for E. huxleyi and D. tertiolecta. In situ measurements will be necessary to determine if our models can reproduce the diel variations of backscattering that are observed in the ocean.
In vivo pigment fluorescence methods allow simple real‐time detection and quantification of fresh... more In vivo pigment fluorescence methods allow simple real‐time detection and quantification of freshwater algae and cyanobacteria. Available models are still limited to high‐cost fluorometers, validated for single instruments or individual water bodies, preventing data comparison between multiple instruments, and thus, restricting their use in large‐scale monitoring programs. Moreover, few models include corrections for optical interference (water turbidity and colored dissolved organic matter, CDOM). In this study, we developed simple models to predict phytoplankton and cyanobacterial chlorophyll a (Chl a) concentrations based on Chl a and C‐phycocyanin in vivo fluorescence, using multiple low‐cost handheld fluorometers. We aimed to: (1) fit models to mixed cyanobacterial and microalgal cultures; (2) cross‐calibrate nine fluorometers of the same brand and series; (3) correct the CDOM and turbidity effects; and (4) test the algorithms’ performance with natural samples. We achieved comparable results between nine instruments after the cross‐calibration, allowing their simultaneous use. We obtained algorithms for total and cyanobacterial Chl a estimation. We developed parametric corrections to remove CDOM and turbidity interferences in the algorithms. Five sampling sites (from a lake, a stream, and an estuary) were used to test the algorithms using eight cross‐calibrated fluorometers. The models showed their best performance after CDOM and turbidity corrections (total Chl a: R2 = 0.99, RMSE = 7.8 μg Chl a L−1; cyanobacterial Chl a: R2 = 0.98, RMSE = 9.8 μg Chl a L−1). In summary, our models can quantify total phytoplankton and cyanobacterial Chl a in real time with multiple low‐cost fluorometers, allowing its implementation in large‐scale monitoring programs.
Adoption of microalgae-sourced products depends on the economic feasibility. In the case of fatty... more Adoption of microalgae-sourced products depends on the economic feasibility. In the case of fatty acids, it is crucial to obtain high lipid yield, especially in the form of storage lipids (TAGs). However, the production of these lipids often comes into competition with the microalgae biomass, resulting in a decrease in growth. A microalgae culture integration project was conducted in an industrial park in Canada in order to cultivate microalgae from park's wastewaters and then obtain products from the biomass. Different deficiencies and stresses were tested to evaluate what condition allowed the induction of the highest lipids accumulation without compromising the growth of microalgae. The results showed that the medium controlled to pH 7.0 allowed reaching the largest amount of extracted lipids (28 ± 4.3%). Companies involved in this project could be able to make significant savings by the reduced wastewater treatment costs and by not adding expensive nutrients in culture.
Northern lakes are ice-covered for a large part of the year, yet our understanding of microbial d... more Northern lakes are ice-covered for a large part of the year, yet our understanding of microbial diversity and activity during winter lags behind that of the ice-free period. In this study, we investigated under-ice diversity and metabolism of Verrucomicrobia in seasonally ice-covered lakes in temperate and boreal regions of Quebec, Canada using 16S rRNA sequencing, metagenomics and metatranscriptomics. Verrucomicrobia, particularly the V1, V3 and V4 subdivisions, were abundant during ice-covered periods. A diversity of Verrucomicrobia genomes were reconstructed from Quebec lake metagenomes. Several genomes were associated with the ice-covered period and were represented in winter metatranscriptomes, supporting the notion that Verrucomicrobia are metabolically active under ice. Verrucomicrobia transcriptome analysis revealed a range of metabolisms potentially occurring under ice, including carbohydrate degradation, glycolate utilization, scavenging of chlorophyll degradation products...
Diurnal variations of phytoplankton size distributions, chlorophyll, carbon and nitrogen content,... more Diurnal variations of phytoplankton size distributions, chlorophyll, carbon and nitrogen content, in vivo fluorescence and associated optical absorption and scattering properties were observed in the laboratory to help understand in situ and spatial observations. We grew triplicate semi-continuous cultures of T. pseudonana, D. tertiolecta, P. tricornutum and E. huxleyi under a sinusoidal light regime. We observed diurnal variations in the particulate absorption (a), scattering (b), attenuation (c), and backscattering coefficients (b), which correlate with carbon and Chl concentrations. Relative variations from sunrise of bare slightly lower than those of c, suggesting that bdiurnal increases observed in nature are partly caused by phytoplankton. Non-concurrent changes of carbon and Chl-specific backscattering and scattering coefficients and optical cross-sections however indicates that using backscattering to infer scattering or biomass must be done with care.
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Papers by Yannick Huot