Modelling Chemical Vapour Infiltration in C/C composites: numerical tools based on µ-CT images

ISBN 978-3-00-032049-1International audienceIn the production of high-quality Ceramic-Matrix Composites, matrix preparation is often made by Chemical Vapor Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modeling tools.In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools.The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, surface and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modeling step.The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program.Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed

Carbon Emissions From Low-Order Streams in a Tropical, High-Elevation, Peatland Ecosystem Are Mediated by Catchment Morphology

Inland waters emit large amounts of carbon and are key players in the global carbon budget. Particularly high rates of carbon emissions have been reported in streams draining mountains, tropical regions, and peatlands. However, few studies have examined the spatial variability of CO2 concentrations and fluxes occurring within these systems, particularly as a function of catchment morphology. Here we evaluated spatial patterns of CO2 in three tropical, headwater catchments in relation to the river network and stream geomorphology. We measured dissolved carbon dioxide (pCO(2)), aquatic CO2 emissions, discharge, and stream depth and width at high spatial resolutions along multiple stream reaches. Confirming previous studies, we found that tropical headwater streams are an important source of CO2 to the atmosphere. More notably, we found marked, predictable spatial organization in aquatic carbon fluxes as a function of landscape position. For example, pCO(2) was consistently high (>10,000 ppm) at locations close to groundwater sources and just downstream of hydrologically connected wetlands, but consistently low (<1,000 ppm) in high gradient locations or river segments with larger drainage areas. Taken together, our findings suggest that catchment area and stream slope are important drivers of pCO(2) and gas transfer velocity (k) in mountainous streams, and as such they should be considered in catchment-scale assessments of CO2 emissions. Furthermore, our work suggests that accurate estimation of CO2 emissions requires understanding of dynamics across the entire stream network, from the smallest seeps to larger streams

Expanding towards contraction: the alternation of floods and droughts as a fundamental component in river ecology

Climate warming is causing more extreme weather conditions, with both larger and more intense precipitation events as well as extended periods of drought in many regions of the world. The consequence is an alteration of the hydrological regime of streams and rivers, with an increase in the probability of extreme hydrological conditions. Mediterranean-climate regions usually experience extreme hydrological events on a seasonal basis and thus, freshwater Mediterranean ecosystems can be used as natural laboratories for better understanding how climate warming will impact ecosystem structure and functioning elsewhere. In this paper, we revisited and contextualized historical and new datasets collected at Fuirosos, a well-studied Mediterranean intermittent stream naturally experiencing extreme hydrological events, to illustrate how the seasonal alternation of floods and droughts influence hydrology, microbial assemblages, water chemistry, and the potential for biogeochemical processing. Moreover, we revised some of the most influential conceptual and quantitative frameworks in river ecology to assess to what extent they incorporate the occurrence of extreme hydrological events. Based on this exercise, we identified knowledge gaps and challenges to guide future research on freshwater ecosystems under intensification of the hydrological cycle. Ultimately, we aimed to share the lessons learned from ecosystems naturally experiencing extreme hydrological events, which can help to better understand warming-induced impacts on hydrological transport and cycling of matter in fluvial ecosystems

Enhanced stream greenhouse gas emissions at night and during flood events

Headwater streams play a large role in aquatic greenhouse gas emissions. Carbon dioxide (CO2) and dissolved oxygen in streams often undergo changes through diel cycles. However, methane (CH4) and nitrous oxide (N2O) have unknown diel dynamics. Here, we reveal consistent patterns in CO2, CH4, and N2O over diel cycles and during flood events using high-frequency continuous observations in a subtropical headwater stream. Diel cycles were most pronounced during baseflow. Increased nighttime discharge due to higher groundwater inputs enhanced gas transfer velocities and concentrations. Overall nocturnal emissions were 31%, 68%, and 32% greater than daytime for CO2, CH4, and N2O, respectively. Floods dampened diel signals. If both flood events and diel patterns are neglected, estimates of greenhouse gas emissions from headwaters may be greatly underestimated. Overall, CH4 and N2O emissions from headwater streams may be underestimated by similar to 20-40% due to a lack of observations during nighttime, floods, and in warmer climates

Global Methane Budget 2000-2020

Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. CH4 is the second most important human-influenced greenhouse gas in terms of climate forcing after carbon dioxide (CO2), and both emissions and atmospheric concentrations of CH4 have continued to increase since 2007 after a temporary pause. The relative importance of CH4 emissions compared to those of CO2 for temperature change is related to its shorter atmospheric lifetime, stronger radiative effect, and acceleration in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in quantifying the factors responsible for the observed atmospheric growth rate arise from diverse, geographically overlapping CH4 sources and from the uncertain magnitude and temporal change in the destruction of CH4 by short-lived and highly variable hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to improve, synthesise, and update the global CH(4 )budget regularly and to stimulate new research on the methane cycle. Following Saunois et al. (2016, 2020), we present here the third version of the living review paper dedicated to the decadal CH4 budget, integrating results of top-down CH4 emission estimates (based on in situ and Greenhouse Gases Observing SATellite (GOSAT) atmospheric observations and an ensemble of atmospheric inverse-model results) and bottom-up estimates (based on process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). We present a budget for the most recent 2010-2019 calendar decade (the latest period for which full data sets are available), for the previous decade of 2000-2009 and for the year 2020. The revision of the bottom-up budget in this 2025 edition benefits from important progress in estimating inland freshwater emissions, with better counting of emissions from lakes and ponds, reservoirs, and streams and rivers. This budget also reduces double counting across freshwater and wetland emissions and, for the first time, includes an estimate of the potential double counting that may exist (average of 23 Tg CH4 yr(-1)). Bottom-up approaches show that the combined wetland and inland freshwater emissions average 248 [159-369] Tg CH4 yr(-1) for the 2010-2019 decade. Natural fluxes are perturbed by human activities through climate, eutrophication, and land use. In this budget, we also estimate, for the first time, this anthropogenic component contributing to wetland and inland freshwater emissions. Newly available gridded products also allowed us to derive an almost complete latitudinal and regional budget based on bottom-up approaches. For the 2010-2019 decade, global CH4 emissions are estimated by atmospheric inversions (top-down) to be 575 Tg CH4 yr(-1) (range 553-586, corresponding to the minimum and maximum estimates of the model ensemble). Of this amount, 369 Tg CH4 yr(-1) or similar to 65 % is attributed to direct anthropogenic sources in the fossil, agriculture, and waste and anthropogenic biomass burning (range 350-391 Tg CH4 yr(-1) or 63 %-68 %).For the 2000-2009 period, the atmospheric inversions give a slightly lower total emission than for 2010-2019, by 32 Tg CH4 yr(-1) (range 9-40). The 2020 emission rate is the highest of the period and reaches 608 Tg CH4 yr(-1) (range 581-627), which is 12 % higher than the average emissions in the 2000s. Since 2012, global direct anthropogenic CH4 emission trends have been tracking scenarios that assume no or minimal climate mitigation policies proposed by the Intergovernmental Panel on Climate Change (shared socio-economic pathways SSP5 and SSP3). Bottom-up methods suggest 16 % (94 Tg CH4 yr(-1)) larger global emissions (669 Tg CH4 yr(-1), range 512-849) than top-down inversion methods for the 2010-2019 period. The discrepancy between the bottom-up and the top-down budgets has been greatly reduced compared to the previous differences (167 and 156 Tg CH4 yr(-1) in Saunois et al. (2016, 2020) respectively), and for the first time uncertainties in bottom-up and top-down budgets overlap. Although differences have been reduced between inversions and bottom-up, the most important source of uncertainty in the global CH4 budget is still attributable to natural emissions, especially those from wetlands and inland freshwaters. The tropospheric loss of methane, as the main contributor to methane lifetime, has been estimated at 563 [510-663] Tg CH4 yr(-1) based on chemistry-climate models. These values are slightly larger than for 2000-2009 due to the impact of the rise in atmospheric methane and remaining large uncertainty (similar to 25 %). The total sink of CH4 is estimated at 633 [507-796] Tg CH4 yr(-1) by the bottom-up approaches and at 554 [550-567] Tg CH4 yr(-1) by top-down approaches. However, most of the top-down models use the same OH distribution, which introduces less uncertainty to the global budget than is likely justified. For 2010-2019, agriculture and waste contributed an estimated 228 [213-242] Tg CH4 yr(-1) in the top-down budget and 211 [195-231] Tg CH4 yr(-1) in the bottom-up budget. Fossil fuel emissions contributed 115 [100-124] Tg CH4 yr(-1) in the top-down budget and 120 [117-125] Tg CH4 yr(-1) in the bottom-up budget. Biomass and biofuel burning contributed 27 [26-27] Tg CH4 yr(-1) in the top-down budget and 28 [21-39] Tg CH4 yr(-1) in the bottom-up budget. We identify five major priorities for improving the CH4 budget: (i) producing a global, high-resolution map of water-saturated soils and inundated areas emitting CH4 based on a robust classification of different types of emitting ecosystems; (ii) further development of process-based models for inland-water emissions; (iii) intensification of CH4 observations at local (e.g.FLUXNET-CH4 measurements, urban-scale monitoring, satellite imagery with pointing capabilities) to regional scales (surface networks and global remote sensing measurements from satellites) to constrain both bottom-up models and atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) integration of 3D variational inversion systems using isotopic and/or co-emitted species such as ethane as well as information in the bottom-up inventories on anthropogenic super-emitters detected by remote sensing (mainly oil and gas sector but also coal, agriculture, and landfills) to improve source partitioning. The data presented here can be downloaded from 10.18160/GKQ9-2RHT (Martinez et al., 2024)

The North American Greenhouse Gas Budget: Emissions, Removals, and Integration for CO2, CH4, and N2O (2010-2019): Results From the Second REgional Carbon Cycle Assessment and Processes Study (RECCAP2)

Accurate accounting of greenhouse-gas (GHG) emissions and removals is central to tracking progress toward climate mitigation and for monitoring potential climate-change feedbacks. GHG budgeting and reporting can follow either the Intergovernmental Panel on Climate Change methodologies for National Greenhouse Gas Inventory (NGHGI) reporting or use atmospheric-based "top-down" (TD) inversions or process-based "bottom-up" (BU) approaches. To help understand and reconcile these approaches, the Second REgional Carbon Cycle Assessment and Processes study (RECCAP2) was established to quantify GHG emissions and removals for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), for ten-land and five-ocean regions for 2010-2019. Here, we present the results for the North American land region (Canada, the United States, Mexico, Central America and the Caribbean). For 2010-2019, the NGHGI reported total net-GHG emissions of 7,270 TgCO(2)-eq yr(-1) compared to TD estimates of 6,132 +/- 1,846 TgCO(2)-eq yr(-1) and BU estimates of 9,060 +/- 898 TgCO(2)-eq yr(-1). Reconciling differences between the NGHGI, TD and BU approaches depended on (a) accounting for lateral fluxes of CO2 along the land-ocean-aquatic continuum (LOAC) and trade, (b) correcting land-use CO2 emissions for the loss-of-additional-sink capacity (LASC), (c) avoiding double counting of inland water CH4 emissions, and (d) adjusting area estimates to match the NGHGI definition of the managed-land proxy. Uncertainties remain from inland-water CO2 evasion, the conversion of nitrogen fertilizers to N2O, and from less-frequent NGHGI reporting from non-Annex-1 countries. The RECCAP2 framework plays a key role in reconciling independent GHG-reporting methodologies to support policy commitments while providing insights into biogeochemical processes and responses to climate change

Irrigation performance and gross water productivity in furrow-irrigated ornamental tree production

In the ornamental plant production region of Girona (Spain), which is one of the largest of its kind in southern Europe, most of the surface is irrigated using wide blocked-end furrows. The objectives of this paper were: (1) to evaluate the irrigation scheduling methods used by ornamental plant producers; (2) to analyse different scenarios in order to assess how they affect irrigation performance; (3) to evaluate the risk of deep percolation; and (4) to calculate gross water productivity. A two-year study in a representative commercial field, planted with Prunus cerasifera ‘Nigra’, was carried out. The irrigation dose applied by the farmers was slightly smaller than the required water dose estimated by the use of two different methods: the first based on soil water content, and the second based on evapotranspiration. Distribution uniformity and application eff iciency were high, with mean values above 87%. Soil water content measurements revealed that even at the end of the furrow, where the infiltrated water depth was greatest, more than 90% of the infiltrated water was retained in the shallowest 40 cm of the soil; accordingly, the risk of water loss due to deep percolation was minimal. Gross water productivity for ornamental tree production was € 11.70 m–3, approximately 20 times higher than that obtained with maize in the same region.En la zona de producción de planta ornamental de Girona (España), que es una de las mayores del sur de Europa, la mayor parte de la superficie es regada por surcos. Los objetivos del presente artículo son: (1) evaluar la programación de riegos que realizan los productores de planta ornamental; (2) analizar diferentes escenarios para ver como afectan la calidad del riego; (3) evaluar el riesgo de percolación profunda; (4) calcular la productividad bruta del agua. Se realizó un estudio de dos años en un campo comercial de Prunus cerasifera ‘Nigra’. La dosis de agua aplicada por los agricultores fue ligeramente inferior a la dosis de riego requerida estimada por dos métodos distintos: el primero basado en el contenido de agua en el suelo y el segundo en la evapotranspiración. La uniformidad de distribución y eficiencia de aplicación fueron altos, con valores medios por encima del 87%. Las medidas de contenido de agua en el suelo revelaron que al final del surco, donde la lámina de agua infiltrada fue mayor, más del 90% del agua infiltrada se retuvo en los primeros 40 cm del suelo; en consecuencia, el riesgo de pérdidas de aguas debido a la percolación profunda fue mínimo. La productividad bruta del agua en la producción de árboles ornamentales fue de 11,70 € m–3, aproximadamente 20 veces mayor que la obtenida en maíz en la misma región

Effect of flushing frequency on emitter clogging in microirrigation with effluents

Flushing is an important maintenance task that removes accumulated particles in microirrigation laterals that can help to reduce clogging problems. The effect of three dripline flushing frequency treatments (no flushing, one flushing at the end of each irrigation period, and a monthly flushing during the irrigation period) was studied in surface and subsurface drip irrigation systems that operated using a wastewater treatment plant effluent for three irrigation periods of 540 h each. The irrigation systems had two different emitters, one pressure compensating and the other not, both molded and welded onto the interior dripline wall, placed in laterals 87 meters long. Dripline flow of the pressure compensating emitter increased 8% over time, while in the nonpressure compensating emitter, dripline flow increased 25% in the surface driplines and decreased 3% in the subsurface driplines by the emitter clogging. Emitter clogging was affected primarily by the interactions between emitter location, emitter type, and flushing frequency treatment. The number of completely clogged emitters was affected by the interaction between irrigation system and emitter type. There was an average of 3.7% less totally clogged emitters in flushed surface driplines with the pressurecompensating emitter as compared to flushed subsurface laterals with the nonpressure compensating emitte