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Modelling the riverine delta Li-7 variability throughout the Amazon Basin
No full textThe present study investigates the processes controlling the elementary and isotopic cycle of the lithium over the Amazon basin. A numerical model is developed to simulate two major processes that have been proposed as key controls of the river lithium isotopic composition: weathering reactions inside the regolith, accounting for secondary phase formation, and interactions between riverine water and secondary phases in floodplain. Both processes generate fractionation of lithium isotopes ("batch" fractionation and "Rayleigh" distillation respectively) that potentially control the riverine isotopic composition of the Amazon and its tributaries. A study of the model parameters shows that two different regimes are impacting the lithium isotopic composition of the rivers within the Amazon catchment. In the South (Madeira and its tributaries), the lithium isotopic signature of river waters can be explained by lithium release and fractionation during weathering reactions in the regolith, followed by "Rayleigh distillation" in the floodplain increasing progressively the lithium isotopic composition, in agreement with a previously published hypothesis. In contrast, the lithium isotopic composition of rivers located in the northern part of the Amazon watershed (Solimoes and tributaries) cannot be simulated by the model assuming the same processes than in the southern part. Model optimization suggests than the nature of the material being eroded and weathered is important. In the North, fresh source rocks of volcanic origin releases large amount of Li and promotes rapid smectite precipitation, allowing the riverine delta Li-7 to rise before flowing through floodplains. This result suggests that the environments able to generate high riverine delta Li-7 (higher than 25 parts per thousand) are complex and not firmly identified yet
Multi-scale analysis of runoff from a statistical perspective in a small Sahelian catchment under semi-arid climate
No full textIn Sahelian and semi-arid regions, understanding the runoff processes and at different spatial scales is critical to assess sources of variation and further improve distributed modelling. In this study, through a multi-scale analysis, runoff measurements on different soil surface features and at different scales of observation were carried over 6 years of monitoring in a typical Sahelian landscape in Burkina Faso. Statistical and dimensional analyses were used to investigate significant differences in runoff response behaviour on plots of 1 m(2), 50 m(2) and 150 m(2), hydrologic units of 6 and 34 ha and the catchment of 37 km(2). Results showed that on both cultivated and bare soils, the runoff excess decreases as the area increases, under similar rainfall pattern and prior antecedent soil moisture conditions. On degraded soils, the processes of runoff generation on the plots of 50 and 150 m(2) are identical and significantly different from those observed on the unit plot (1 m(2)). A minimum plot length of 10 m was found to be sufficient to accurately estimate runoff on degraded soils. On cultivated soils, runoff is significantly different from one site to another because of the spatial variability of hydrodynamic properties of the soil. Such results show that the scale effect on runoff is related to the spatial heterogeneity of soils and is further intensified by the rainfall intensity. Such results highlight the value of quantification of runoff on homogeneous units, hence allowing an innovative approach to the problem of scale transfer
Accumulation of phytate and starch lysophospholipids in rice grains and responses to alterations in P supply or source-sink relations
No full textThe removal of phosphorus (P) from fields in the harvested seeds of staple crops is a major driver of the global P cycle, and consequently, there is interest in breeding grain crops with lower seed P concentrations. While it is expected that a reduction in seed total P would result in lower concentrations of the P-rich anti-nutrient phytate, the potential consequences for starch lysophospholipids (LPLs), which affect rice grain quality and health outcomes in humans, are unknown. We examined the accumulation of phytate and starch LPLs in developing indica (cv. IR64) and japonica (cv. Nipponbare) rice grains as well as the stability of starch LPLs and phytate under varying P supply treatments in hydroponics. Source-sink relationships during grain filling (drought and floret abortion) were also investigated in a pot study. Accumulation of phytate and starch LPLs in seeds continued until 18 days after anthesis (DAA) in cv. Nipponbare and 21 DAA in cv. IR64, which mirrored the accumulation of biomass in seeds. In the hydroponic study, permanent withdrawal of P from the nutrient solution at anthesis (until maturity) led to significant reductions in both phytate and starch LPLs with a similar trend observed when P was withdrawn at 8 DAA. In the pot study using soil, alteration of source-sink systems through drought stress during grain filling or floret abortion (manual removal of the top half of each panicle) also led to significant reductions in grain phytate and starch LPLs compared to control plants. These results indicate that in addition to affecting phytate concentrations, reduced P supply to rice plants during grain filling and alteration of source-sink relationships also impacts starch LPL concentrations. Given these complexities, breeding and selection for reduced seed P concentration in rice and other cereals should be undertaken with caution
Global karst springs hydrograph dataset for research and management of the world's fastest-flowing groundwater [Data paper]
No full textKarst aquifers provide drinking water for 10% of the world's population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset's coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations
Divergent roles for macrophage C-type lectin receptors, dectin-1 and mannose receptors, in the intestinal inflammatory response
No full textColonic macrophages are considered to be major effectors of inflammatory bowel diseases (IBDs) and the control of gut inflammation through C-type lectin receptors is an emerging concept. We show that during colitis, the loss of dectin-1 on myeloid cells prevents intestinal inflammation, while the lack of mannose receptor (MR) exacerbates it. A marked increase in dectin-1 expression in dextran sulfate sodium (DSS)-exposed MR-deficient mice supports the critical contribution of dectin-1 to colitis outcome. Dectin-1 is crucial for Ly6C(high)CCR2(high) monocyte population enrichment in the blood and their recruitment to inflamed colon as precursors of inflammatory macrophages. Dectin-1 also promotes inflammasome-dependent interleukin-1 beta (IL-1 beta) secretion through leukotriene B4 production. Interestingly, colonic inflammation is associated with a concomitant overexpression of dectin-1/CCL2/LTA4H and downregulation of MR on macrophages from IBD patients. Thus, MR and dectin-1 on macrophages are important mucosal inflammatory regulators that contribute to the intestinal inflammation
The physical oceanography of the transport of floating marine debris
No full textMarine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales
Prediction of tropical volcanic soil organic carbon stocks by visible-near- and mid-infrared spectroscopy
No full textAssessing soil organic carbon (SOC) stocks is a methodological issue for SOC monitoring at regional scale but crucial for global agendas of SOC sequestration to mitigate climate change and reduce food insecurity. The '4 per mille Initiative: Soils for Food Security and Climate', highlighted agricultural soil as a major lever for climate action and the need to assess SOC stock at different spatial and temporal scale. Infrared spectroscopy appeared as a promising tool to address this methodological issue. This work aimed to evaluate the potential of visible-near-infrared (VNIR) and mid-infrared (MIR) spectroscopic measurement methods to predict SOC stock and its variables (SOC content and bulk density) in tropical volcanic soils of 'La Reunion' island. The diversity of agricultural soils of 'La Reunion' was captured in the sample set (n = 95) with soil orders such as Andosols, Cambisols and Ferralsols. Partial least squares regressions (PLSR) with leave-one-out cross validation were used to build prediction models. With RPD higher than 2, the present study showed good prediction accuracy of models by MIR and VNIR spectroscopy of SOC content, bulk density and SOC stock for measurements in the laboratory or in the field. Accurate and direct SOC stock predictions were achieved on dried and sieved soil samples with MIR spectroscopy (RPD = 2.25; R-cv(2) = 0.80; RMSEcv = 0.69 KgC m(-2)) and VNIR spectroscopy (RPD = 2.74; R-cv(2) = 0.87; RMSEcv = 0.61 KgC m(-2)) but also directly on cores in the field with VNIR spectroscopy (RPD = 3.29; R-cv(2) = 0.91; RMSEcv = 0.51 KgC m(-2)). This unexpected ability to predict directly SOC stocks by infrared spectroscopy can be partly explained by the high SOC content coupled with the large variation of SOC content and bulk density, providing a large range for those variables, and then a higher predictability. Yet these results questioned the underlying drivers of the bulk density and SOC stock, both being largely physical parameters supposed to be hardly predictable by infrared spectroscopy. Analyses of mean spectra and regression coefficients, combined with amorphous product (Alo, Feo, Sio, Alp, Fep) prediction models, demonstrated that these were detected in the spectra and were the drivers of SOC stock accurate predictions by infrared spectroscopy. Short-range ordered minerals, especially allophanes, appeared as proxy of the bulk density, and amorphous products such as Alp and Fep indicated the presence of organo-mineral complexes involved in SOC storage. Such promising results for SOC stock predictions from near- and mid-infrared volcanic soil spectra, confirmed that VNIR and MIR diffuse reflectance spectroscopy are an appropriate tool, rapid, low cost and non-destructive, to study SOC stocks in tropical volcanic soils. Upscaling of SOC stocks across the agricultural soils of the island is now just a step ahead, following external validation with additional data to validate the robustness of the prediction models
Population genomics of the widespread African savannah trees Afzelia africana and Afzelia quanzensis reveals no significant past fragmentation of their distribution ranges
No full textPremise Few studies have addressed the evolutionary history of tree species from African savannahs. Afzelia contains economically important timber species, including two species widely distributed in African savannahs: A. africana in the Sudanian region and A. quanzensis in the Zambezian region. We aimed to infer whether these species underwent range fragmentation and/or demographic changes, possibly reflecting how savannahs responded to Quaternary climate changes. Methods We characterized the genetic diversity and structure of these species across their distribution ranges using nuclear microsatellites (SSRs) and genotyping-by-sequencing (GBS) markers. Six SSR loci were genotyped in 241 A. africana and 113 A. quanzensis individuals, while 2800 high-quality single nucleotide polymorphisms (SNPs) were identified in 30 A. africana individuals. Results Both species appeared to be mainly outcrossing. The kinship between individuals decayed with the logarithm of the distance at similar rates across species and markers, leading to relatively small Sp statistics (0.0056 for SSR and 0.0054 for SNP in A. africana, 0.0075 for SSR in A. quanzensis). The patterns were consistent with isolation by distance expectations in the absence of large-scale geographic gradients. Bayesian clustering of SSR genotypes did not detect genetic clusters within species. In contrast, SNP data resolved intraspecific genetic clusters in A. africana, illustrating the higher resolving power of GBS. However, these clusters revealed low levels of differentiation and no clear geographical entities, so that they were interpreted as resulting from the isolation by distance pattern rather than from past population fragmentation. Conclusions These results suggest that populations have remained connected throughout the large, continuous savannah landscapes. The absence of clear phylogeographic discontinuities, also found in a few other African savannah trees, indicates that their distribution ranges have not been significantly fragmented during the climatic oscillations of the Pleistocene, in contrast to patterns commonly found in African rainforest trees
Patterns of fish communities and water quality in impounded lakes of China's south-to-north water diversion project
No full textUnderstanding the ecological impacts of large-scale hydraulic projects is critical for maintaining ecosystem health while meeting human water needs. It is, however, currently hindered by a lack of direct evidence on ecological impacts associated with this type of project particularly on water quality and fish communities. Here, we characterized patterns and variations of fish communities and water quality in five impounded lakes of the Chinese South-to-North Water Diversion Project (SNWDP), with the aim of better understanding potential ecological impacts of inter-basin water transfers. We found that 1) the impacts of water transfer on water quality in the impounded lakes was generally characterized by hydrological parameters (e.g. total suspended solids, turbidity, transparency, chlorophyll a, dissolved oxygen, conductivity and total hardness) in an upstream-downstream direction; 2) increased hydrological connectivity may have favored biological invasion (e.g. Tridentiger bifasciatus) and promoted a potential biotic homogenization among the impounded lakes: and 3) there was a pattern of decreased fish abundance and biomass from the upstream to downstream lakes with fish communities strongly driven by changing water quality patterns across the impounded lakes. These findings improve our understanding of ecological impacts of large-scale hydraulic projects and provide a significant basis for water agencies with similar water transfer systems to optimize their water transfer management in order to minimize ecological impacts