Fire is an important ecological feature across temperate forests, yet characteristics of the coast redwood fire regime remain uncertain due to generally few fire histories. This study examines legacies of fire in redwood forests in northern California through radiocarbon dating and quantification of soil macro-charcoal, soil carbon and pyrogenic carbon in old growth redwood stands. We sampled soils in the Headwaters Forest Reserve, a protected fragment of old growth redwood in Humboldt County, California. Radiocarbon dates from macro-charcoal indicate fire events occurring a maximum of 6,840 calibrated years BP, predating existing records. Composite 14C dates show increased fire activity within the last 1,000 years in synchrony with existing dendrochronological records. Soil C averaged 928 g/m2, of which a high proportion was pyrogenic C (15-30%). Information from this multi-proxy reconstruction clarifies our understanding of the nature of coast redwood fires, contributing to ongoing discussions of coast redwood fire management.

Mining operations have led to an increase in polycyclic aromatic compound (PAC) concentrations in the Alberta oil sands area. However, the toxicity of most PACs and PAC mixtures is not well characterized. Some PACs and PAC mixtures are known to be mutagenic, though there is limited research on the genotoxicity of PACs from the Alberta oil sands to wildlife. This thesis tested the hypothesis that anthropogenic sources of PACs from the Alberta oil sands are mutagenic to wildlife. The objectives were: 1) to determine whether wildlife with increased exposure to PACs had increased mutations, and 2) to determine whether an anthropogenic source of PACs is mutagenic in a controlled lab setting. For the first objective, we used a single-molecule polymerase chain reaction (SM-PCR) assay to detect microsatellite mutations in river otters with differing liver tissue PAC concentrations in the Athabasca oil sand region (AOSR; Alberta, Canada). For objective two, an in vitro mammalian mutagenicity assay with the FE1 MutaMouse epithelial cell line (FE1) was used to determine the mutagenic potential of a bitumen extraction by-product, tailings pond bitumen. We found that PAC exposure in the AOSR was positively correlated with elevated microsatellite mutations in river otters. From the in vitro study, tailings pond bitumen extracts did not induce lacZ mutations in the FE1 cells. Differences in detection methods between the two assays and PAC profiles between the otter tissue and tailings pond bitumen are suspected reasons for contradictory results. Further investigation of the different sources and PAC profiles within the AOSR environment and wildlife food web will provide insights on what types of PACs are mutagenic. Cytotoxicity, observed following exposure to tailings pond bitumen extracts, also suggests other toxicity pathways should be considered when investigating the toxicity of bitumen from the AOSR. Overall, this thesis provided data on the potential mutagenicity of PACs in the AOSR, which can be used to elucidate potential molecular mechanisms of toxicity in wildlife exposed to oil processing contaminants.

The contribution of energy from biomass sources is projected to increase in Britain to assist in meeting renewable energy targets and reducing anthropogenic CO2 emissions. With increasing concerns over the sustainability of food crop-based biofuels, purpose-grown lignocellulosic biomass crops such as Miscanthus and short rotation coppice (SRC) willow have been promoted as more sustainable feedstocks for the production of heat and electricity as well as for the future production of liquid biofuels. With the introduction of the Energy Crops Scheme, land-use change (LUC) for lignocellulosic biomass crop production has become increasingly common in Britain in recent decades. However, there is limited understanding of the impact this has on soil organic carbon (SOC) stocks and limited predictability concerning the overall trajectory, magnitude and rate of SOC changes under a range of different conditions. Using a chronosequence of 93 biomass crop plantations in England and Wales, mainly of 1 to 14 years age, empirical models were developed to determine the short term trajectory of SOC stocks following LUC from arable and grassland to SRC willow and Miscanthus production. SOC stocks were calculated for each site using a fixed sampling depth of 30 cm and estimated changes were inferred by comparing with typical pre-change SOC stocks. These results indicate that only LUC from arable crops to SRC willow demonstrated an overall increase in SOC stocks, by an estimated 15.3 ± 2.2 t C ha-1 (± 95% confidence intervals) after 14 years and 68.8 ± 49.4 t C ha-1 after 22 years. LUC from arable crops to Miscanthus and from both arable crops and grassland to SRC willow and Miscanthus demonstrated no overall net effect on SOC stocks. Soil texture and climate data were measured for each site and multivariable models were created to assess the influence of different environmental conditions on SOC trajectory. In most cases the addition of these explanatory variables improved the model fit, and the models provide some preliminary estimates of more region-specific changes in SOC following LUC. Since LUC to biomass crops often causes a loss of SOC, at least in the short term, the potential for pyrogenic carbon (PyC) to ameliorate this effect was investigated. Studies indicate that PyC can interact with and stabilise native SOC, a process termed negative priming, although the potential for PyC to reduce LUC-induced losses of SOC by negative priming has not yet been assessed. Although negative priming has been observed in many studies, most of these are long term incubation experiments which do not account for the impact of environmental weathering of PyC on interactions with native SOC. Here the aim was to assess the impact of environmentally weathered PyC on native SOC mineralisation at different points in LUC from arable crops to SRC willow. Soil was sampled to a 5 cm depth from multiple recently established SRC willow plantations approximately 2 years after amendment with PyC. Cumulative CO2 flux was measured weekly from incubated soil and soil-surface CO2 flux was also measured in the field. The results demonstrate a PyC-induced increase in CO2 flux for the surface 5 cm of soil. However, no net effect on soil-surface CO2 flux was observed in the field. Although the mechanisms for these contrasting effects remain unclear, they do not suggest that PyC can reduce LUC-induced SOC losses through negative priming.

No description available.

Les silices pyrogéniques sont très utilisées comme charge pour les polysiloxanes mais elles sont l’un des principaux constituants des superisolants thermiques. Cependant, l’échelle nanométrique de ces silices et leur chimie de surface (groupes silanol) est également responsable de leur aptitude à adsorber la vapeur d’eau, ce qui a pour conséquence d’altérer leurs propriétés d’isolant thermique au cours du temps, notamment lors de leur stockage dans des conditions non contrôlées. Malgré son importance industrielle ce phénomène n’a fait l’objet dans la littérature que d’une seule étude assez limitée.En effet, initialement la surface de ces silices ne sont que partiellement hydroxylées et la présence de ponts siloxanes tendus, susceptibles de réagir avec l’eau va mener à une évolution de leurs propriétés de surface en présence d’humidité.Une première étude a porté sur les silices N20, T30 et T40 (Wacker Chemie AG) sont obtenues par combustion de SiCl4 dans un mélange air/H2, de surfaces spécifiques égales respectivement à 200, 300 et 400 m2/g. Elles ont été vieillies à température constante 22,5 ± 0,1 °C, dans une enceinte fermée, sous humidité relative (HR) contrôlée : 62, 75, 84, 92 et 100%.L'adsorption d'eau a été suivie par gravimétrie. La masse d’eau adsorbée, par unité de surface augmente à la fois avec HR et la surface spécifique. Cette augmentation qui peut atteindre près de 60% de la masse initiale pour une HR de 100%, est liée à l’augmentation de l’hydrophilie de la surface de la silice liée à la formation de nouveaux groupes silanol. Nous avons démontré que cette augmentation suit une cinétique du 1er ordre et que la constante cinétique passe par un maximum pour une RH égale à 84%.L’augmentation du nombre de silanol superficiels a été confirmée par leur dosage chimique. Leur densité superficielle augmente d’environ 50%, passant de 2,4 SiOH/nm2 à 3,6 SiOH/nm2 pour l’HR égale à 100%.La spectroscopie IR atteste clairement d’une diminution nette des silanol isolés au profit de silanol fortement liés par pont hydrogène. Les spectroscopies RMN du proton et du silicium confirment l’augmentation de la densité locale en groupes silanols.L’évolution des propriétés superficielles des silices vieillies environ 1000 h a été suivie par chromatographie inverse à dilution infinie (CGI-DI) et concentration finie (CGI-CF).La CGI-DI pratiquée avec des sondes alcanes linéaires et cycliques démontre que le vieillissement n’affecte que très faiblement tant la composante dispersive de l’énergie de surface que leur rugosité à l’échelle moléculaire, autrement dit qu’il ne modifie pas la morphologie de la surface. Notamment la rugosité superficielle des silices T30 et T40 n’est pas affectée.La variation de l’hétérogénéité superficielle avec le vieillissement a été déterminée, en termes de fonctions de distribution des énergies d’adsorption de l’isopropanol, par CGI-CF.Le processus de vieillissement conduit, comme attendu, à une augmentation de la composante de haute énergie liée à l'apparition de nouveaux groupes silanol par ouverture nucléophile des ponts siloxane. Le glissement du maximum de cette composante vers les hautes énergies montre la formation d’un nouveau type de silanol plus interactif par liaison hydrogène.Ces résultats confirment la réactivité des silices de combustion vis-à-vis de l'eau lorsqu’elles sont exposées à une humidité relative élevée. L'eau est chimisorbée sur la surface de la silice par une réaction d'ouverture des ponts siloxane. L'étude de l'influence de la variation de l'humidité relative, montre qu’il existe un seuil (HR50%) au-dessous duquel ces silices restent stables par rapport à la vapeur d'eau. [...] / Pyrogenic silicas , produced by combustion of SiCl4 into a mixture hydrogene/air, are widely used as filler for polysiloxanes, but also as one of the main components of super-thermal insulating. However, the nanoscale of these silicas and surface chemistry (silanol groups) is also responsible for their ability to adsorb water vapour, which alters their insulation and reinforcement properties, especially when stored in uncontrolled conditions. Initially the surface of pyrogenic silicas is partially hydroxylated, silanol groups, but presents also strained siloxane bridges, which can react with adsorbed water, leading to a change in their surface properties when exposed to the atmospheric moisture. Despite its industrial importance, this phenomenon has been rarely studied in the literature, except a single study, which was rather limited.Our study was focused on a set of six pyrogenic silicas, having specific surface areas comprised between 150 to 400 m2 / g. They were aged at constant temperature 22.5 ± 0.1 ° C in a closed chamber under controlled relative humidity (RH): 62, 75, 84, 92 and 100%.The water adsorption was followed gravimetrically. The mass of water adsorbed per unit area increases with both HR and the specific surface area. This increase, which can reach nearly 60% of the initial mass at 100% RH, is induced by the increase of their surface hydrophilicity due to the formation of new silanol groups. But, the study of the influence of the variation in RH, indicates that a threshold exists around HR50%, below which these silicas are stable.Finally, fitting the gravimetric curves, it was evidenced that the water sorption follows a first order kinetics and that the kinetic constant goes through a maximum for an HR equal to 84%. This increase of silanol density was testified by chemical titration. It increases by about 50%, from 2.4 to 3.6 SiOH/nm2 for ageing under 100% RH, but is dependent of the specific surface area and surface roughness. IR spectroscopy clearly indicates a net decrease of isolated silanol band correlated with an increase of H-bounded silanol. Proton and silicon NMR spectroscopies confirm the increase of the local density silanol groups on the aged silca surface.Finally, the evolution of the surface properties of these silica samples, aged during about 1000 h, was followed by inverse gas chromatography in infinite dilution (IGC-ID) and at finite concentration (CGI-FC) conditions.The CGI-ID was performed using linear and cyclic alkane probes. It shows that the ageing process affects only very slightly both the dispersive component of surface energy and the nano-roughness at the molecular level of all studied, indicating that the surface morphology is quite unchanged. Then; the variation of their surface heterogeneities with ageing time, in terms of the distribution functions of the probe adsorption energies, was assessed by CGI-CF, using isopropanol as probe.The aging process leads, as expected, to an increase of the high energy component related to the appearance of new silanol groups by nucleophilic opening of siloxane bridges by water confirming the reactivity of fumed silicas toward water when exposed to a high RH. All our observations, existence of a threshold, maximum for the kinetic constant and decrease of the chemisorbed of water amount with both specific surface area and surface roughness is supported by a model for the ageing process. [...]

As Terras Pretas de Índio (TPI), também conhecida por Amazonian Dark Earth, apresentam horizonte A antrópico, elevado pH, nutrientes importantes para o crescimento das plantas, elevado teor de carvão pirogênico e intensa atividade biológica quando comparadas aos seus solos de origem. A comunidade microbiana do solo é essencial para o funcionamento dos ecossistemas, sendo fundamentais em processos de decomposição da matéria orgânica, na disponibilização de nutrientes para as plantas e na ciclagem de nutrientes. Este estudo teve como objetivo acessar as estruturas e composição das comunidades de Bacteria e Archaea em fragmentos de carvão pirogênico (provenientes de TPI), TPI e solo adjacente (ADJ) utilizando as técnicas moleculares. Os solos foram coletados em quatro sítios arqueológicos (Balbina, Barro Branco, Costa do Açutuba e Hatahara), localizados na Amazônia Central. Em geral, as TPIs apresentaram elevados valores de pH, P e Ca corroborando com resultados anteriores em TPIs. As amostras de TPI dos sítios Balbina, Barro Branco e Hatahara apresentaram maior número de cópias do gene 16S rRNA de Bacteria quando comparadas com as amostras de solo ADJ. Os resultados obtidos pelas técnicas de fingerprinting (Terminal Restriction Fragment Length Polymorphism - T-RFLP e Denaturing Gradient Gel Electrophoresis - DGGE) utilizando o gene 16S rRNA de Bacteria e Archaea revelaram que as estruturas das comunidades bacterianas em fragmentos de carvão apresentaram diferenças significativas quando comparados com os solos ADJ. A partir da técnica de pirosequenciamento, os filos Proteobacteria, Actinobacteria e Crenarchaeota apresentaram predominância nos fragmentos de carvão. Observou-se também que em fragmentos de carvão, os microorganismos encontrados podem estar diretamente relacionados aos ciclos do N e C. Além disso, a presença desses micro-organismos em fragmentos de carvão pode favorecer a microbiota do solo e, consequentemente, sua qualidade. Neste sentido, o carvão pode também servir como elemento de recuperação em ambientes degradados, agindo como condicionador do solo sendo esta uma alternativa promissora no manejo de solos agrícolas. / Amazonian Dark Earth (ADE), also known as Terra Preta de Índio, present tropical A horizon, high pH, important nutrients for plant growth, high pyrogenic charcoal levels and intense biological activity when compared to its soil of origin. Soil microbial community is essential for ecosystem function, which is involved in fundamental processes such as the decomposition of organic matter, availability of nutrients to plants and the nutrient cycling. The objective of this study was to assess the structure and composition of bacterial and archaeal communities in fragments of pyrogenic charcoal (from ADE), ADE and adjacent soil (ADJ) using molecular techniques. The soils were collected in four archaeological sites (Balbina, Barro Branco, Costa do Açutuba and Hatahara), located in the central Amazon. In general, ADE presented high values of pH, P and Ca agreeing with previous results in ADE. ADE samples in Balbina, Barro Branco and Hatahara sites presented higher bacterial 16S rRNA gene copy number in comparison with ADJ soil samples. The results obtained with the fingerprinting techniques (Terminal Restriction Length Polymorphism, T-RFLP and Denaturing Gradient Gel Electrophoresis, DGGE) using the bacterial and archaeal 16S rRNA genes revealed that bacterial community structure in charcoal fragments differed significantly when compared to the ADJ soils. Using the pyrosequencing technique, the phyla Proteobacteria, Actinobacteria and Crenarchaeota were predominant in charcoal fragments. It was also observed that microorganisms from charcoal fragments may be directly related to the N and C cycles. Furthermore, the presence of these microorganisms in charcoal fragments may favor the soil microbiota and, consequently, its quality. In this context, pyrogenic charcoal can serve as an element to recover degraded areas acting as soil conditioner and a promising alternative to the management of agricultural soils.

As Terras Pretas de Índio (TPI), também conhecida por Amazonian Dark Earth, apresentam horizonte A antrópico, elevado pH, nutrientes importantes para o crescimento das plantas, elevado teor de carvão pirogênico e intensa atividade biológica quando comparadas aos seus solos de origem. A comunidade microbiana do solo é essencial para o funcionamento dos ecossistemas, sendo fundamentais em processos de decomposição da matéria orgânica, na disponibilização de nutrientes para as plantas e na ciclagem de nutrientes. Este estudo teve como objetivo acessar as estruturas e composição das comunidades de Bacteria e Archaea em fragmentos de carvão pirogênico (provenientes de TPI), TPI e solo adjacente (ADJ) utilizando as técnicas moleculares. Os solos foram coletados em quatro sítios arqueológicos (Balbina, Barro Branco, Costa do Açutuba e Hatahara), localizados na Amazônia Central. Em geral, as TPIs apresentaram elevados valores de pH, P e Ca corroborando com resultados anteriores em TPIs. As amostras de TPI dos sítios Balbina, Barro Branco e Hatahara apresentaram maior número de cópias do gene 16S rRNA de Bacteria quando comparadas com as amostras de solo ADJ. Os resultados obtidos pelas técnicas de fingerprinting (Terminal Restriction Fragment Length Polymorphism - T-RFLP e Denaturing Gradient Gel Electrophoresis - DGGE) utilizando o gene 16S rRNA de Bacteria e Archaea revelaram que as estruturas das comunidades bacterianas em fragmentos de carvão apresentaram diferenças significativas quando comparados com os solos ADJ. A partir da técnica de pirosequenciamento, os filos Proteobacteria, Actinobacteria e Crenarchaeota apresentaram predominância nos fragmentos de carvão. Observou-se também que em fragmentos de carvão, os microorganismos encontrados podem estar diretamente relacionados aos ciclos do N e C. Além disso, a presença desses micro-organismos em fragmentos de carvão pode favorecer a microbiota do solo e, consequentemente, sua qualidade. Neste sentido, o carvão pode também servir como elemento de recuperação em ambientes degradados, agindo como condicionador do solo sendo esta uma alternativa promissora no manejo de solos agrícolas. / Amazonian Dark Earth (ADE), also known as Terra Preta de Índio, present tropical A horizon, high pH, important nutrients for plant growth, high pyrogenic charcoal levels and intense biological activity when compared to its soil of origin. Soil microbial community is essential for ecosystem function, which is involved in fundamental processes such as the decomposition of organic matter, availability of nutrients to plants and the nutrient cycling. The objective of this study was to assess the structure and composition of bacterial and archaeal communities in fragments of pyrogenic charcoal (from ADE), ADE and adjacent soil (ADJ) using molecular techniques. The soils were collected in four archaeological sites (Balbina, Barro Branco, Costa do Açutuba and Hatahara), located in the central Amazon. In general, ADE presented high values of pH, P and Ca agreeing with previous results in ADE. ADE samples in Balbina, Barro Branco and Hatahara sites presented higher bacterial 16S rRNA gene copy number in comparison with ADJ soil samples. The results obtained with the fingerprinting techniques (Terminal Restriction Length Polymorphism, T-RFLP and Denaturing Gradient Gel Electrophoresis, DGGE) using the bacterial and archaeal 16S rRNA genes revealed that bacterial community structure in charcoal fragments differed significantly when compared to the ADJ soils. Using the pyrosequencing technique, the phyla Proteobacteria, Actinobacteria and Crenarchaeota were predominant in charcoal fragments. It was also observed that microorganisms from charcoal fragments may be directly related to the N and C cycles. Furthermore, the presence of these microorganisms in charcoal fragments may favor the soil microbiota and, consequently, its quality. In this context, pyrogenic charcoal can serve as an element to recover degraded areas acting as soil conditioner and a promising alternative to the management of agricultural soils.

<div>In fire-prone forests, tree taxa and burn temperature are the major controllers of the chemical and physical properties of pyrogenic organic matter (PyOM), the aromatic carbon-rich product of the incomplete combustion of plant biomass, that accumulates in soil in such settings. These controls also dictate how soil microbes can degrade plant C once it enters into soil as previous studies demonstrate that increased fire temperature results in low PyOM degradability but also impacts the decomposition of the original soil. However, we know little about how taxa and temperature of C-inputs impact the production and accumulation of cellular residues from soil microbes, which can be the dominant source of stabilized soil organic matter in many ecosystems. </div><div>This work presents the results of the analysis of soil microbial amino sugars, as proxies for soil microbial necromass, from long-term soil incubation experiments, 180 and 600 days, that were amended with jack pine (JP) and red maple (RM) wood or their PyOM produced at 300°C or 450°C. Both wood taxa amendments resulted in an increase in microbial sugar residues compared to non-amended soils but RM, the taxa with the highest proportion of soluble sugars and low tannin content, exhibited the highest percentage increase. Soils amended with PyOM exhibited lower amino sugar content as compared to their wood but no difference compared to controls (non-amended soils). There was no difference in soil amino sugars observed between the PyOM derived from the two taxa nor between the temperature of pyrolysis, possibly due to only small amounts of bioavailable C and N in the PyOM. Total amino sugar concentrations varied significantly between PyOM and fresh wood treatments, with PyOM treatments yielding 659 – 730 μg/ g soil while wood treatments yielded 757 – 930 μg/ g soil early in incubations. While fungal-derived amino sugars were dominated in all treatments, longer soil incubation time, 600 days vs 180 days, resulted in a proportionately greater decrease bacterial-derived amino sugars. Overall, at 180 days, PyOM treatments exhibited 19-27% of soil N and 4-5% of soil C quantifiable as amino sugars while wood treatments exhibited 27-28% of total soil N and 6-7% of total soil C as amino sugars. This work shows, for the first time, that on a per C or per N basis, PyOM versus fresh wood addition to soils will result in a net depletion of microbial residues. The variable response in amino sugars between treatments and incubation time highlights the importance and dynamic nature of the physicochemical characteristics of organic matter input to soil in controlling the contribution of soil microbial residues to that soil. </div><div><br></div>

Climate change is causing larger wildfires and more extreme precipitation events throughout the world. As these ecological disturbances increasingly coincide, they are altering lateral fluxes of sediment, organic matter, and nutrients. Increased lateral flux of nutrients could exacerbate eutrophication and associated harmful algal blooms, and increased sediment and organic matter flux could degrade the water supply. Here, we report the immediate stream chemistry response of watersheds in central Utah (USA) that were affected by a megafire followed by an extreme precipitation event in 2018. The wildfires burned throughout the summer of 2018 until the remnants of Hurricane Rosa released torrential rain on the still smoldering, 610-km2 burn scar. To assess how these multiple stressors affected lateral material fluxes, we collected daily to hourly water samples at 10 stream locations starting immediately before the storm event until three weeks after it finished. We quantified suspended sediment, solute and nutrient concentrations, water isotopes, and the concentration, optical properties, and reactivity of dissolved organic matter. For all land-use types, the wildfire caused substantial increases in sediment concentration and flux, increasing total suspended sediment by over 20-fold, attributable to the loss of stabilizing vegetation and increased runoff. Unexpectedly, dissolved organic carbon (DOC) was 2.1-fold higher in burned watersheds, despite the decrease in plant and soil organic matter, and this DOC was 1.3-fold more biodegradable and 2.0-fold more photodegradable than in unburned watersheds based on 28-day light and dark incubations. However, nitrogen and phosphorus concentrations were higher in watersheds with high anthropogenic influences, regardless of burn status. Likewise, direct human land use had a greater effect than wildfire on runoff response, with rapid storm water signals in urban and agricultural areas and a slow arrival of storm water in unburned areas without direct human influence. These findings indicate how megafires and intense rainfall fundamentally increase short-term sediment flux and alter organic matter concentration and characteristics, confirming previous research. These fluxes of degradable dissolved and particulate organic matter could exert short-term pressure on ecosystems already fragmented by human infrastructure. However, in contrast with previous research, which overwhelming focuses on burned-unburned comparisons in pristine watersheds, we found that the presence of urban and agricultural activity exerted a much greater influence on nutrient status than the wildfire. This novel finding suggests that reducing nutrient fluxes from urban and agricultural areas could make ecosystems more resilient to megafire and extreme precipitation events. Together with reducing anthropogenic climate change to reduce the frequency and extent of large wildfires, improving nutrient management should be a priority in semi-arid regions such as Utah.

En Afrique tropicale, là où le paludisme est fortement endémique, la plupart des individus sont semi-immuns et les infections asymptomatiques sont très répandues. Ainsi la détection de parasites dans le sang de malades fébriles n'est pas un critère suffisant pour distinguer le paludisme des autres causes de fièvre. A Dielmo, un village du Sénégal d'environ 500 habitants en 2010, un suivi épidémiologique continu très étroit du paludisme a débuté en 1990. Dans ce village où la transmission est pérenne, la mise en place de moyens de lutte et de prévention contre le paludisme de plus en plus efficaces a profondément transformé l'épidémiologie du paludisme. Dans ce travail, nous analysons l'impact de ces interventions sur les prévalences parasitaires, les densités parasitaires et les critères diagnostiques du paludisme et nous mesurons l'évolution du paludisme clinique à Plasmodium falciparum, P. malariae et P. ovale de juin 1990 à décembre 2010. Les données parasitologiques et cliniques ont été analysées par régression logistique à effet aléatoire pour étudier la relation entre les densités parasitaires et le risque de fièvre. Les prévalences parasitaires des trois espèces plasmodiales ont considérablement diminué lors de l'abandon de la chloroquine en traitement de première ligne et de son remplacement par des combinaisons thérapeutiques, puis sont devenues presque nulles après la mise en place de moustiquaires imprégnées d'insecticides à longue durée d'action. Les seuils pyrogéniques calculés nous ont permis de mesurer la densité d'incidence des accès palustres et d'étudier l'impact des mesures de lutte sur la morbidité palustre dans la population. / In tropical Africa, where malaria is highly endemic, most people are semi-immune and asymptomatic infections are widespread. Thus, the detection of malaria parasites in the blood of febrile patients is not a sufficient criterion for distinguishing malaria from other causes of fever. In Dielmo, a Senegalese village of about 500 inhabitants in 2010, a very closely continuous epidemiological monitoring of malaria began in 1990. In this village where the transmission is perennial, the establishment of more effective means of control and prevention against malaria have profoundly changed the epidemiology of malaria. In this work, we analyze the impact of these interventions on the parasite prevalences, the parasite densities and the malaria diagnostic criteria and we measure the evolution of Plasmodium falciparum, P. malariae and P. ovale clinical malaria from June 1990 to December 2010 in Dielmo. Parasitological and clinical data are analyzed in a random effect logistic regression to investigate the relationship between parasite density and fever risk. The prevalence of the three Plasmodium species decreased dramatically with the abandonment of chloroquine as first line treatment and his replacing with the combination therapies and became almost zero after the introduction of long lasting insecticidal nets. Pyrogenic thresholds calculated enabled us to measure the incidence density of malaria and to study the impact of intervention methods on malaria morbidity in the population.