Mountain lakes are especially vulnerable to climate change, but are also increasingly exposed to ... more Mountain lakes are especially vulnerable to climate change, but are also increasingly exposed to local anthropogenic development through winter and summer tourism. In this study, we aimed to tease apart the influence of tourism from that of climate in a mountain lake located within one of the largest French ski resorts, by combining paleolimnological and present ecological data. The reconstructed long-term ecological dynamics highlighted an increase in lake biological production from the end of the Little Ice Age up to the 1950s, suggesting a historical dominance of climate control. Afterward, a major drop in pelagic production occurred at the same time as the watershed erosion increased and peaked in the 1990s, concomitant with massive digging for the ski resort expansion. The benthic invertebrates collapsed in the 1980s, concomitantly with the onset of massive salmonid stocking and recent warming. Stable isotope analyses identified benthic invertebrates as the major salmonid diet resource and suggested a possible direct impact of salmonid stocking on benthic invertebrates. However, habitat use may differ among salmonid species as suggested by the way fish DNA was preserved in surficial sediment. The high abundances of macrozooplankton further confirmed the limited reliance of salmonids on pelagic resources. The variable thermal tolerance of benthic invertebrates suggested that the recent warming may mostly affect littoral habitats. Our results indicate that winter and summer tourism may differently affect the biodiversity of mountain lakes and could collectively interfere with the ecological impacts of recent warming, making local management of primary importance to preserve their ecological integrity.
<p>Here we present a series of connected efforts aiming at ... more <p>Here we present a series of connected efforts aiming at curating sediment cores and their related data. Far to be isolated, these efforts were conducted within national structured projects and led to the development of digital solutions and good practices in-line with international standards and practices.</p><p>Our efforts aimed at ensuring FAIR-compatible practices (Plomp, 2020; Wilkinson et al., 2016) throughout the life cycle of sediment cores, from fieldwork to published data. We adopted a step-by-step, bottom-up strategy to formalize a dataflow, mirroring our workflow. We hence created a fieldwork mobile application (CoreBook) to gather information during coring operations and inject them toward the French national virtual core repository “Cyber-Carothèque Nationale” (CCN). At this stage, the allocation of an international persistent unique identifier was crucial and we naturally chose the IGSN.</p><p>Beyond the traceability of samples, the curation of analysis data remains challenging. Most international repository (e.g. NOAA palaeo-data, PANGAEA) have taken the problem from the top by offering facilities to display published dataset with persistant unique identifier (DOI). Yet, those data are only a fraction of the gross amount of acquired data. Moreover, those repositories have very low requirements when it comes to the preservation and display of metadata, in particular analytical parameters, but also fieldwork data which are essential for data reusability. Finally, these repositories do not permit to get a synoptic view on the several strata of analyses that have been conducted on the same core through different research programs and publications. A partial solution is proposed by the eLTER metadata standard DEIMS, which offers a discovery interface of rich metadata. In order to bridge the gap between generalist data repositories and samples display systems (such as CCN, but also IMLGS, to cite an international system), we developed a data repository and visualizer dedicated to the re-use of lake sediment cores, samples and sampling locations (ROZA Retro-Observatory of the Zone Atelier). This system is still a prototype but opens yet interesting perspectives.</p><p>Finally, the digital evolution of science allows the worldwide diffusion of data processing freewares. In that framework, we developed “Serac” an open-source R package to establish radionuclide-based age models following the most common sedimentation hypotheses (serac,). By implementing within this R package the input of a rich metadata file that gathers links to IGSN and other quality metadata, we are linking fieldwork metadata, the physical storage of the core and the analytical metadata. Indeed, Serac also stores data processing procedure in a standardized way.. We hence think that the development of such softwares could help in the spreading of good practices in data curation and favour the use of unique identifiers.</p><p>By tackling all aspects of data creation and curation throughout a lake sediment core life cycle, we are now able to propose a theoretical model of data curation for this particular type of sample that could serve as the sole for further developments of integrated data curation systems.</p>
Environmental monitoring is a key component of understanding and managing ecosystems. Given that ... more Environmental monitoring is a key component of understanding and managing ecosystems. Given that most monitoring efforts are still expensive and time-consuming, it is essential that monitoring programs are designed to be efficient and effective. In many situations, the expensive part of monitoring is not sample collection, but instead sample processing, which leads to only a subset of the samples being processed. For example, sediment or ice cores can be quickly obtained in the field, but they require weeks or months of processing in a laboratory setting. Standard sub-sampling approaches often involve equally-spaced sampling. We use simulations to show how many samples, and which types of sampling approaches, are the most effective in detecting ecosystem change. We test these ideas with a case study of Cladocera community assemblage reconstructed from a sediment core. We demonstrate that standard approaches to sample processing are less efficient than an iterative approach. For our ...
Short-lived radionuclides are measured in surface sediment to provide a geochronology for the pas... more Short-lived radionuclides are measured in surface sediment to provide a geochronology for the past century. Age-depth models can be produced from 210Pbex activity-derived sedimentation rates and confirmed by 137Cs and 241Am activities that are result of fallout from nuclear weapon tests and the Chernobyl accident. Different methods of age depth modelling using such data require expertise in lake sedimentation processes.Here, we present a package, serac, that allows the user to compute an age-depth model, output a graph and an age model as a text file, and provide metadata using the free open-source statistical software R. serac ensures the reproducibility of age-depth or age-mass depth models and allows testing of several 210Pbex models (CFCS, CIC, CRS) and sedimentation hypotheses (changes in the sedimentation rates, instantaneous deposits, varved sedimentation, etc.). Using several case studies, including lakes and lagoon in different environments, we demonstrate the use of the pr...
There are no doubts long-term observatories provide unique insight on ecosystems trajectories. Ca... more There are no doubts long-term observatories provide unique insight on ecosystems trajectories. Can we use earliest data to set restoration goals? We take the example of Lake Geneva, for which descriptions of the ecosystem are available for as soon as the late 19th and early 20th century. Forel writes about how the luxuriant growth of plant communities provided important habitat for aquatic animals, as well as trapping nutrients and affecting water currents. It can be hard to believe Forel is referring to the same lake as present-day Lake Geneva; however, without continuous monitoring, this qualitative description can hardly be compared to recent observations. We resorted to paleolimnology to quantify the changes in plankton communities, as a proxy of general ecological changes, over the past 1,500 years. Our results show that from 563 AD (beginning of the record) to the 20th century, the cladoceran assemblage remained stable, despite important amplitude of climate variability (3°C)....
1. Hysteresis linked to alternative stable states may explain delays in water quality recovery de... more 1. Hysteresis linked to alternative stable states may explain delays in water quality recovery despite reduced nutrient loadings in shallow lakes. Because deep lakes are assumed to be less prone to critical transitions, similar delays are attributed to the confounding effects of additional environmental disturbances, such as climate warming. Herein, we hypothesised that the lack of evidence of nutrient-driven alternative stable states in a deep lake arises from the fact that the nutrient threshold that causes the critical transition is lower than the nutrient threshold in shallow lakes. Thereby, it might have been crossed much earlier in the lake history. 2. To test this hypothesis, we focused on the palaeo-ecological trajectory of Lake Varese, which is a deep, hypereutrophicated peri-alpine lake undergoing restoration. Proxies for drivers of ecological state (i.e. total phosphorus-TP-through diatoms and pigments) and ecological responses (Cladocera), as well as a repeatable analysis, were used to identify transitions and to distinguish hysteretic delays from those of the ecosystems responding to additional constraints over the past century. 3. Our results suggest spatial heterogeneity in the ecological response. The littoral habitats changed abruptly and prematurely for a low TP threshold, causing a shift that met many criteria of a flickering-type critical transition. Soon after the littoral shift, a striking increase in the lake phosphorous concentration was recorded and drove the pelagic assemblage towards a new state. This transition was abrupt, and the pelagic communities exhibited limited evidence of recovery; however, we found no evidence of hysteresis. Therefore, the modern ecological trajectory of the pelagic communities is currently driven by climate warming. 4. This detailed analysis allowed us to go beyond the general pattern that links ecological responses to drivers and suggest that a nonlinear transition following eutrophication can take place in a deep lake synchronously with linear transitions. Instead of triggering a new regime shift, climate warming, to which pelagic habitats are more sensitive than littoral ones, has driven the lake further from its safe operating space.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season throug...
Environmental monitoring is a key component of understanding and managing ecosystems. Given that ... more Environmental monitoring is a key component of understanding and managing ecosystems. Given that most monitoring e orts are still expensive and time-consuming, it is essential that monitoring programs are designed to be e cient and e ective. In many situations, the expensive part of monitoring is not sample collection, but instead sample processing, which leads to only a subset of the samples being processed. For example, sediment or ice cores can be quickly obtained in the field, but they require weeks or months of processing in a laboratory setting. Standard sub-sampling approaches often involve equally-spaced sampling. We use simulations to show how many samples, and which types of sampling approaches, are the most e ective in detecting ecosystem change. We test these ideas with a case study of Cladocera community assemblage reconstructed from a sediment core. We demonstrate that standard approaches to sample processing are less e cient than an iterative approach. For our case study, using an optimal sampling approach would have resulted in savings of 195 person-hours-thousands of dollars in labor costs. We also show that, compared with these standard approaches, fewer samples are typically needed to achieve high statistical power. We explain how our approach can be applied to monitoring programs that rely on video records, eDNA, remote sensing, and other common tools that allow re-sampling.
Mountain lakes are especially vulnerable to climate change, but are also increasingly exposed to ... more Mountain lakes are especially vulnerable to climate change, but are also increasingly exposed to local anthropogenic development through winter and summer tourism. In this study, we aimed to tease apart the influence of tourism from that of climate in a mountain lake located within one of the largest French ski resorts, by combining paleolimnological and present ecological data. The reconstructed long-term ecological dynamics highlighted an increase in lake biological production from the end of the Little Ice Age up to the 1950s, suggesting a historical dominance of climate control. Afterward, a major drop in pelagic production occurred at the same time as the watershed erosion increased and peaked in the 1990s, concomitant with massive digging for the ski resort expansion. The benthic invertebrates collapsed in the 1980s, concomitantly with the onset of massive salmonid stocking and recent warming. Stable isotope analyses identified benthic invertebrates as the major salmonid diet resource and suggested a possible direct impact of salmonid stocking on benthic invertebrates. However, habitat use may differ among salmonid species as suggested by the way fish DNA was preserved in surficial sediment. The high abundances of macrozooplankton further confirmed the limited reliance of salmonids on pelagic resources. The variable thermal tolerance of benthic invertebrates suggested that the recent warming may mostly affect littoral habitats. Our results indicate that winter and summer tourism may differently affect the biodiversity of mountain lakes and could collectively interfere with the ecological impacts of recent warming, making local management of primary importance to preserve their ecological integrity.
<p>Here we present a series of connected efforts aiming at ... more <p>Here we present a series of connected efforts aiming at curating sediment cores and their related data. Far to be isolated, these efforts were conducted within national structured projects and led to the development of digital solutions and good practices in-line with international standards and practices.</p><p>Our efforts aimed at ensuring FAIR-compatible practices (Plomp, 2020; Wilkinson et al., 2016) throughout the life cycle of sediment cores, from fieldwork to published data. We adopted a step-by-step, bottom-up strategy to formalize a dataflow, mirroring our workflow. We hence created a fieldwork mobile application (CoreBook) to gather information during coring operations and inject them toward the French national virtual core repository “Cyber-Carothèque Nationale” (CCN). At this stage, the allocation of an international persistent unique identifier was crucial and we naturally chose the IGSN.</p><p>Beyond the traceability of samples, the curation of analysis data remains challenging. Most international repository (e.g. NOAA palaeo-data, PANGAEA) have taken the problem from the top by offering facilities to display published dataset with persistant unique identifier (DOI). Yet, those data are only a fraction of the gross amount of acquired data. Moreover, those repositories have very low requirements when it comes to the preservation and display of metadata, in particular analytical parameters, but also fieldwork data which are essential for data reusability. Finally, these repositories do not permit to get a synoptic view on the several strata of analyses that have been conducted on the same core through different research programs and publications. A partial solution is proposed by the eLTER metadata standard DEIMS, which offers a discovery interface of rich metadata. In order to bridge the gap between generalist data repositories and samples display systems (such as CCN, but also IMLGS, to cite an international system), we developed a data repository and visualizer dedicated to the re-use of lake sediment cores, samples and sampling locations (ROZA Retro-Observatory of the Zone Atelier). This system is still a prototype but opens yet interesting perspectives.</p><p>Finally, the digital evolution of science allows the worldwide diffusion of data processing freewares. In that framework, we developed “Serac” an open-source R package to establish radionuclide-based age models following the most common sedimentation hypotheses (serac,). By implementing within this R package the input of a rich metadata file that gathers links to IGSN and other quality metadata, we are linking fieldwork metadata, the physical storage of the core and the analytical metadata. Indeed, Serac also stores data processing procedure in a standardized way.. We hence think that the development of such softwares could help in the spreading of good practices in data curation and favour the use of unique identifiers.</p><p>By tackling all aspects of data creation and curation throughout a lake sediment core life cycle, we are now able to propose a theoretical model of data curation for this particular type of sample that could serve as the sole for further developments of integrated data curation systems.</p>
Environmental monitoring is a key component of understanding and managing ecosystems. Given that ... more Environmental monitoring is a key component of understanding and managing ecosystems. Given that most monitoring efforts are still expensive and time-consuming, it is essential that monitoring programs are designed to be efficient and effective. In many situations, the expensive part of monitoring is not sample collection, but instead sample processing, which leads to only a subset of the samples being processed. For example, sediment or ice cores can be quickly obtained in the field, but they require weeks or months of processing in a laboratory setting. Standard sub-sampling approaches often involve equally-spaced sampling. We use simulations to show how many samples, and which types of sampling approaches, are the most effective in detecting ecosystem change. We test these ideas with a case study of Cladocera community assemblage reconstructed from a sediment core. We demonstrate that standard approaches to sample processing are less efficient than an iterative approach. For our ...
Short-lived radionuclides are measured in surface sediment to provide a geochronology for the pas... more Short-lived radionuclides are measured in surface sediment to provide a geochronology for the past century. Age-depth models can be produced from 210Pbex activity-derived sedimentation rates and confirmed by 137Cs and 241Am activities that are result of fallout from nuclear weapon tests and the Chernobyl accident. Different methods of age depth modelling using such data require expertise in lake sedimentation processes.Here, we present a package, serac, that allows the user to compute an age-depth model, output a graph and an age model as a text file, and provide metadata using the free open-source statistical software R. serac ensures the reproducibility of age-depth or age-mass depth models and allows testing of several 210Pbex models (CFCS, CIC, CRS) and sedimentation hypotheses (changes in the sedimentation rates, instantaneous deposits, varved sedimentation, etc.). Using several case studies, including lakes and lagoon in different environments, we demonstrate the use of the pr...
There are no doubts long-term observatories provide unique insight on ecosystems trajectories. Ca... more There are no doubts long-term observatories provide unique insight on ecosystems trajectories. Can we use earliest data to set restoration goals? We take the example of Lake Geneva, for which descriptions of the ecosystem are available for as soon as the late 19th and early 20th century. Forel writes about how the luxuriant growth of plant communities provided important habitat for aquatic animals, as well as trapping nutrients and affecting water currents. It can be hard to believe Forel is referring to the same lake as present-day Lake Geneva; however, without continuous monitoring, this qualitative description can hardly be compared to recent observations. We resorted to paleolimnology to quantify the changes in plankton communities, as a proxy of general ecological changes, over the past 1,500 years. Our results show that from 563 AD (beginning of the record) to the 20th century, the cladoceran assemblage remained stable, despite important amplitude of climate variability (3°C)....
1. Hysteresis linked to alternative stable states may explain delays in water quality recovery de... more 1. Hysteresis linked to alternative stable states may explain delays in water quality recovery despite reduced nutrient loadings in shallow lakes. Because deep lakes are assumed to be less prone to critical transitions, similar delays are attributed to the confounding effects of additional environmental disturbances, such as climate warming. Herein, we hypothesised that the lack of evidence of nutrient-driven alternative stable states in a deep lake arises from the fact that the nutrient threshold that causes the critical transition is lower than the nutrient threshold in shallow lakes. Thereby, it might have been crossed much earlier in the lake history. 2. To test this hypothesis, we focused on the palaeo-ecological trajectory of Lake Varese, which is a deep, hypereutrophicated peri-alpine lake undergoing restoration. Proxies for drivers of ecological state (i.e. total phosphorus-TP-through diatoms and pigments) and ecological responses (Cladocera), as well as a repeatable analysis, were used to identify transitions and to distinguish hysteretic delays from those of the ecosystems responding to additional constraints over the past century. 3. Our results suggest spatial heterogeneity in the ecological response. The littoral habitats changed abruptly and prematurely for a low TP threshold, causing a shift that met many criteria of a flickering-type critical transition. Soon after the littoral shift, a striking increase in the lake phosphorous concentration was recorded and drove the pelagic assemblage towards a new state. This transition was abrupt, and the pelagic communities exhibited limited evidence of recovery; however, we found no evidence of hysteresis. Therefore, the modern ecological trajectory of the pelagic communities is currently driven by climate warming. 4. This detailed analysis allowed us to go beyond the general pattern that links ecological responses to drivers and suggest that a nonlinear transition following eutrophication can take place in a deep lake synchronously with linear transitions. Instead of triggering a new regime shift, climate warming, to which pelagic habitats are more sensitive than littoral ones, has driven the lake further from its safe operating space.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season throug...
Environmental monitoring is a key component of understanding and managing ecosystems. Given that ... more Environmental monitoring is a key component of understanding and managing ecosystems. Given that most monitoring e orts are still expensive and time-consuming, it is essential that monitoring programs are designed to be e cient and e ective. In many situations, the expensive part of monitoring is not sample collection, but instead sample processing, which leads to only a subset of the samples being processed. For example, sediment or ice cores can be quickly obtained in the field, but they require weeks or months of processing in a laboratory setting. Standard sub-sampling approaches often involve equally-spaced sampling. We use simulations to show how many samples, and which types of sampling approaches, are the most e ective in detecting ecosystem change. We test these ideas with a case study of Cladocera community assemblage reconstructed from a sediment core. We demonstrate that standard approaches to sample processing are less e cient than an iterative approach. For our case study, using an optimal sampling approach would have resulted in savings of 195 person-hours-thousands of dollars in labor costs. We also show that, compared with these standard approaches, fewer samples are typically needed to achieve high statistical power. We explain how our approach can be applied to monitoring programs that rely on video records, eDNA, remote sensing, and other common tools that allow re-sampling.
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Papers by Rosalie Bruel