Jean Claude Druart - Academia.edu (original) (raw)
Papers by Jean Claude Druart
Quaternaire, 1994
Analyse d'image à l'ordinateur, étude du sédiment en lame mince, algologie et palynologie... more Analyse d'image à l'ordinateur, étude du sédiment en lame mince, algologie et palynologie sont associées pour interpréter une séquence carbonatée microlaminée courte de 80 cm. Les variations du niveau du lac de Paladru et l'évolution du climat autour de l'an mil peuvent être appréhendées avec un degré de résolution du temps abaissé à la décennie; l'année peut parfois être proposée pour des événements remarquables ponctuels. La notion d'»optimum climatique» en sera ainsi précisée et discutée. L'approche méthodologique est ici privilégiée à la problématique de type climatique.
Cryptogamie Algologie, 1993
Au cours de l'etude du phytoplancton d'un lac de barrage dans le Morvan, les auteurs ont ... more Au cours de l'etude du phytoplancton d'un lac de barrage dans le Morvan, les auteurs ont rencontre la diatomee, Achnanthes catenata Bily et Marvan, espece encore jamais signalee en France
Hydroécologie Appliquée, 1999
J.-F Fruget et ai et de la dynamique de leurs peuplements impliquent une continuité d'observation... more J.-F Fruget et ai et de la dynamique de leurs peuplements impliquent une continuité d'observation et de récolte de données que seules permettent des études à long terme, nécessitant la mise en place de véritables observatoires écologiques du milieu naturel. Mots-clés-Suivi à long terme, fleuve aménagé, Rhône, physico-chimie, periphyton, phytoplancton, macrophytes, invertébrés benthiques, ichtyofaune.
Annales de Limnologie - International Journal of Limnology, 2001
One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, whi... more One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, which leads to high concentrations of atrazine in continental water systems. Periphytic algae play a basic part in aquatic ecosystems and some of them, diatoms, are highly sensitive to environmental changes. Analyses of diatoms can thus indicate the impact of a herbicide on aquatic systems. We compared the effects of two herbicides (atrazine and nicosulfuron) on an aquatic ecosystem in 1998. This study was conducted in 15 identical ponds, each containing a holder for installing artificial substrates. The periphytic diatoms were analysed for cell density, biomass, species diversity and morphology. The general specific diversity was poor, and the diatom community was essentially dominated by Achnanthidium minutissimum. The first results showed a strong similarity between the different categories of mesocosms. Chlorophyll a concentration only seems to be affected by high herbicide concentrations. Effets de deux herbicides (atrazine et nicosulfuron) sur les diatomées du periphyton : approche expérimentale en mésocosmes aquatiques lentiques Mots-clés : Ecotoxicologie, herbicides, mésocosmes aquatiques, periphyton.
Limnology and Oceanography, 2002
The implementation of a conservation program since the early 1980s resulted in a reduction in pho... more The implementation of a conservation program since the early 1980s resulted in a reduction in phosphorus concentrations in Lake Geneva. However, in the 1990s, phytoplankton biomass increased again, almost reaching the high values recorded during the period of greatest P loading. The structural changes in the phytoplankton of Lake Geneva over the past 25 yr have been analyzed using a recently developed statistical method based on hierarchical clustering and Bayesian probabilities. This method has been used to identify phytoplankton assemblages and to map annual and interannual successional patterns simultaneously. Characteristic species were identified for each cluster after calculation of their relative species fidelity and specificity indices. Six distinct phytoplankton assemblages were identified, and although the way species are organized into communities remains unclear, the seasonal patterns of succession are consistent with the C-S-R adaptive strategies and are characteristic of temperate lakes. This pattern broadly recurred over the years, but was markedly influenced by both human activity and regional climatic changes: The warmer winters and springs recorded in Europe since 1988 led to an earlier clear-water phase. In the 1990s, the earlier and deeper depletion of dissolved inorganic phosphorus led to colonization in the summer by large species tolerant of low light levels and that could develop deeper in the water column, where phosphorus was still abundant. Their size made them less vulnerable to grazing losses, which favors their accumulation and lead to an unexpected high biomass in recent years.
Harmful Algae, 2005
Lac du Bourget, in the Alps, is the largest natural French lake. Following major restoration prog... more Lac du Bourget, in the Alps, is the largest natural French lake. Following major restoration programmes during the 1970s and early 1980s, involving massive efforts to reduce nutrient loads and pollution in the lake, the water quality has improved over the past two decades. This can be inferred from the increase in the nitrate:phosphate ratio, the intensification of the "clear-water phase" (i.e. the increase in the water column transparency in spring), and the reduction in the total phosphorus and chlorophyll a concentrations. However, blooms of the filamentous, phycoerythrin-rich, non-nitrogen fixing and hepatotoxic cyanobacterium Planktothrix rubescens have occurred since 1996 and have been maintained subsequently, at least during summer and autumn periods. Nutrients (especially phosphorus) are usually thought to be one of the most important factors responsible for cyanobacterial blooms, and so the question is asked if this bloom is a paradoxical outcome of the restoration programs? Using a large set of data taken from surveys of Lac du Bourget, from the literature, and from recent laboratory experiments, and also using field data for the neighboring Lake Geneva, we propose a realistic scenario to account for the population dynamics of the cyanobacterium and the occurrence and maintenance of the bloom in Lac du Bourget. The characteristics of the lake (high water column stability, deepening of the nutrient-depleted layer during the last decade, a long water residence time), local conditions (the nutrient load and charge) and global changes (global warming) all had to be taken into account to explain this bloom. We suggest that the success of P. rubescens in Lac du Bourget is probably due to increased transparency and a longer stratified period following (1) the restriction of other phytoplankton species following reduced phosphorus, which has allowed P. rubescens to make use of organic phosphorus to improve its competitiveness; (2) warmer than average winter/spring periods allowing an earlier water stratification and in fine a competitive advantage to P. rubescens; (3) lower than average surface irradiance, which has also given the low-light preferring P. rubescens an advantage. Finally,
Quaternaire, 2007
Les variations paléoenvironnementales de 1000 avant à 1000 après J.C. et la question des « optima... more Les variations paléoenvironnementales de 1000 avant à 1000 après J.C. et la question des « optima » climatiques de l'Antiquité tardive et du Moyen Âge sur le piémont des Alpes du nord à Colletière,
Annales de Limnologie - International Journal of Limnology, 2002
Journal of …, 2010
This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids... more This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids, diatoms and organic matter analysis, and deals with the ability of paleolimnological approach to define an ecological reference state for the lake in the sense of the European Framework Directive. The study at low resolution of subfossil chironomids in a 4-m-long core shows the remarkable stability over the last 2.5 kyrs of the profundal community dominated by a Micropsectra-association until the beginning of the twentieth century, when oxyphilous taxa disappeared. Focusing on this key recent period, a high resolution and multiproxy study of two short cores
Swiss Journal of Hydrology, 1988
Abstract Two new species of the genus Cyclotella are presented which have been discovered during... more Abstract Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.
Journal of Applied Phycology, 2002
A diatom intercomparison exercise on sampling, slide preparation, countsand identification has be... more A diatom intercomparison exercise on sampling, slide preparation, countsand identification has been carried out in September 1999 with 24French-speaking diatomists on the River Loup (Alpes Maritimes, France). Fewoperators strictly respected the standard, especially for the number ofindividuals to be counted. It has however been demonstrated this had a very lowimpact on the index value and that old counts can be used for indexcalculation,if there are at least 300 frustules or valves. Counts higher than 400 did notlead to a better precision. The total variability largely depended on theoperator and was distributed unevenly between sampling, which appears to be acritical stage, slide preparation and counting. For those who strictlyrespectedthe standard procedure, the natural variability can be estimated to about oneunit value of the Biological Diatom Index. This intra-operator variability canbe considered as very low, as the IBD scale is from 0 to 20, and notsignificantin assessing water quality. Despite this, the inter-operator variability isgreater. When comparing operators' results, after excluding those who did notrespect the standard requirements, the main source of variability is due tomisidentifications, especially for small Achnanthes(A. minutissima and A. biasolettiana)and Cocconeis (C. placentula var.placentula, var. euglypta and var.lineata). Intercomparison exercises, internet exchangesforchecking and reference material collections should be encouraged both tosatisfythe internal and external quality controls and to acquaint biologists with theimportance of field and laboratory protocols, as well as to allow progress indiatom identification.
Quaternaire, 1994
Analyse d'image à l'ordinateur, étude du sédiment en lame mince, algologie et palynologie... more Analyse d'image à l'ordinateur, étude du sédiment en lame mince, algologie et palynologie sont associées pour interpréter une séquence carbonatée microlaminée courte de 80 cm. Les variations du niveau du lac de Paladru et l'évolution du climat autour de l'an mil peuvent être appréhendées avec un degré de résolution du temps abaissé à la décennie; l'année peut parfois être proposée pour des événements remarquables ponctuels. La notion d'»optimum climatique» en sera ainsi précisée et discutée. L'approche méthodologique est ici privilégiée à la problématique de type climatique.
Cryptogamie Algologie, 1993
Au cours de l'etude du phytoplancton d'un lac de barrage dans le Morvan, les auteurs ont ... more Au cours de l'etude du phytoplancton d'un lac de barrage dans le Morvan, les auteurs ont rencontre la diatomee, Achnanthes catenata Bily et Marvan, espece encore jamais signalee en France
Hydroécologie Appliquée, 1999
J.-F Fruget et ai et de la dynamique de leurs peuplements impliquent une continuité d'observation... more J.-F Fruget et ai et de la dynamique de leurs peuplements impliquent une continuité d'observation et de récolte de données que seules permettent des études à long terme, nécessitant la mise en place de véritables observatoires écologiques du milieu naturel. Mots-clés-Suivi à long terme, fleuve aménagé, Rhône, physico-chimie, periphyton, phytoplancton, macrophytes, invertébrés benthiques, ichtyofaune.
Annales de Limnologie - International Journal of Limnology, 2001
One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, whi... more One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, which leads to high concentrations of atrazine in continental water systems. Periphytic algae play a basic part in aquatic ecosystems and some of them, diatoms, are highly sensitive to environmental changes. Analyses of diatoms can thus indicate the impact of a herbicide on aquatic systems. We compared the effects of two herbicides (atrazine and nicosulfuron) on an aquatic ecosystem in 1998. This study was conducted in 15 identical ponds, each containing a holder for installing artificial substrates. The periphytic diatoms were analysed for cell density, biomass, species diversity and morphology. The general specific diversity was poor, and the diatom community was essentially dominated by Achnanthidium minutissimum. The first results showed a strong similarity between the different categories of mesocosms. Chlorophyll a concentration only seems to be affected by high herbicide concentrations. Effets de deux herbicides (atrazine et nicosulfuron) sur les diatomées du periphyton : approche expérimentale en mésocosmes aquatiques lentiques Mots-clés : Ecotoxicologie, herbicides, mésocosmes aquatiques, periphyton.
Limnology and Oceanography, 2002
The implementation of a conservation program since the early 1980s resulted in a reduction in pho... more The implementation of a conservation program since the early 1980s resulted in a reduction in phosphorus concentrations in Lake Geneva. However, in the 1990s, phytoplankton biomass increased again, almost reaching the high values recorded during the period of greatest P loading. The structural changes in the phytoplankton of Lake Geneva over the past 25 yr have been analyzed using a recently developed statistical method based on hierarchical clustering and Bayesian probabilities. This method has been used to identify phytoplankton assemblages and to map annual and interannual successional patterns simultaneously. Characteristic species were identified for each cluster after calculation of their relative species fidelity and specificity indices. Six distinct phytoplankton assemblages were identified, and although the way species are organized into communities remains unclear, the seasonal patterns of succession are consistent with the C-S-R adaptive strategies and are characteristic of temperate lakes. This pattern broadly recurred over the years, but was markedly influenced by both human activity and regional climatic changes: The warmer winters and springs recorded in Europe since 1988 led to an earlier clear-water phase. In the 1990s, the earlier and deeper depletion of dissolved inorganic phosphorus led to colonization in the summer by large species tolerant of low light levels and that could develop deeper in the water column, where phosphorus was still abundant. Their size made them less vulnerable to grazing losses, which favors their accumulation and lead to an unexpected high biomass in recent years.
Harmful Algae, 2005
Lac du Bourget, in the Alps, is the largest natural French lake. Following major restoration prog... more Lac du Bourget, in the Alps, is the largest natural French lake. Following major restoration programmes during the 1970s and early 1980s, involving massive efforts to reduce nutrient loads and pollution in the lake, the water quality has improved over the past two decades. This can be inferred from the increase in the nitrate:phosphate ratio, the intensification of the "clear-water phase" (i.e. the increase in the water column transparency in spring), and the reduction in the total phosphorus and chlorophyll a concentrations. However, blooms of the filamentous, phycoerythrin-rich, non-nitrogen fixing and hepatotoxic cyanobacterium Planktothrix rubescens have occurred since 1996 and have been maintained subsequently, at least during summer and autumn periods. Nutrients (especially phosphorus) are usually thought to be one of the most important factors responsible for cyanobacterial blooms, and so the question is asked if this bloom is a paradoxical outcome of the restoration programs? Using a large set of data taken from surveys of Lac du Bourget, from the literature, and from recent laboratory experiments, and also using field data for the neighboring Lake Geneva, we propose a realistic scenario to account for the population dynamics of the cyanobacterium and the occurrence and maintenance of the bloom in Lac du Bourget. The characteristics of the lake (high water column stability, deepening of the nutrient-depleted layer during the last decade, a long water residence time), local conditions (the nutrient load and charge) and global changes (global warming) all had to be taken into account to explain this bloom. We suggest that the success of P. rubescens in Lac du Bourget is probably due to increased transparency and a longer stratified period following (1) the restriction of other phytoplankton species following reduced phosphorus, which has allowed P. rubescens to make use of organic phosphorus to improve its competitiveness; (2) warmer than average winter/spring periods allowing an earlier water stratification and in fine a competitive advantage to P. rubescens; (3) lower than average surface irradiance, which has also given the low-light preferring P. rubescens an advantage. Finally,
Quaternaire, 2007
Les variations paléoenvironnementales de 1000 avant à 1000 après J.C. et la question des « optima... more Les variations paléoenvironnementales de 1000 avant à 1000 après J.C. et la question des « optima » climatiques de l'Antiquité tardive et du Moyen Âge sur le piémont des Alpes du nord à Colletière,
Annales de Limnologie - International Journal of Limnology, 2002
Journal of …, 2010
This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids... more This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids, diatoms and organic matter analysis, and deals with the ability of paleolimnological approach to define an ecological reference state for the lake in the sense of the European Framework Directive. The study at low resolution of subfossil chironomids in a 4-m-long core shows the remarkable stability over the last 2.5 kyrs of the profundal community dominated by a Micropsectra-association until the beginning of the twentieth century, when oxyphilous taxa disappeared. Focusing on this key recent period, a high resolution and multiproxy study of two short cores
Swiss Journal of Hydrology, 1988
Abstract Two new species of the genus Cyclotella are presented which have been discovered during... more Abstract Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.
Journal of Applied Phycology, 2002
A diatom intercomparison exercise on sampling, slide preparation, countsand identification has be... more A diatom intercomparison exercise on sampling, slide preparation, countsand identification has been carried out in September 1999 with 24French-speaking diatomists on the River Loup (Alpes Maritimes, France). Fewoperators strictly respected the standard, especially for the number ofindividuals to be counted. It has however been demonstrated this had a very lowimpact on the index value and that old counts can be used for indexcalculation,if there are at least 300 frustules or valves. Counts higher than 400 did notlead to a better precision. The total variability largely depended on theoperator and was distributed unevenly between sampling, which appears to be acritical stage, slide preparation and counting. For those who strictlyrespectedthe standard procedure, the natural variability can be estimated to about oneunit value of the Biological Diatom Index. This intra-operator variability canbe considered as very low, as the IBD scale is from 0 to 20, and notsignificantin assessing water quality. Despite this, the inter-operator variability isgreater. When comparing operators' results, after excluding those who did notrespect the standard requirements, the main source of variability is due tomisidentifications, especially for small Achnanthes(A. minutissima and A. biasolettiana)and Cocconeis (C. placentula var.placentula, var. euglypta and var.lineata). Intercomparison exercises, internet exchangesforchecking and reference material collections should be encouraged both tosatisfythe internal and external quality controls and to acquaint biologists with theimportance of field and laboratory protocols, as well as to allow progress indiatom identification.