Nitrogen (N) uptake in streams is an important ecosystem service that reduces nutrient loading to downstream ecosystems. Here we synthesize studies that investigated the effects of urban stream ...burial on N-uptake in two metropolitan areas and use simulation modeling to scale our measurements to the broader watershed scale. We report that nitrate travels on average 18 times farther downstream in buried than in open streams before being removed from the water column, indicating that burial substantially reduces N uptake in streams. Simulation modeling suggests that as burial expands throughout a river network, N uptake rates increase in the remaining open reaches which somewhat offsets reduced N uptake in buried reaches. This is particularly true at low levels of stream burial. At higher levels of stream burial, however, open reaches become rare and cumulative N uptake across all open reaches in the watershed rapidly declines. As a result, watershed-scale N export increases slowly at low levels of stream burial, after which increases in export become more pronounced. Stream burial in the lower, more urbanized portions of the watershed had a greater effect on N export than an equivalent amount of stream burial in the upper watershed. We suggest that stream daylighting (i.e., uncovering buried streams) can increase watershed-scale N retention.
Waters impounded behind dams (i.e., reservoirs) are important sources of greenhouses gases (GHGs), especially methane (CH
), but emission estimates are not well constrained due to high spatial and ...temporal variability, limitations in monitoring methods to characterize hot spot and hot moment emissions, and the limited number of studies that investigate diurnal, seasonal, and interannual patterns in emissions. In this study, we investigate the temporal patterns and biophysical drivers of CH
emissions from Acton Lake, a small eutrophic reservoir, using a combination of methods: eddy covariance monitoring, continuous warm-season ebullition measurements, spatial emission surveys, and measurements of key drivers of CH
production and emission. We used an artificial neural network to gap fill the eddy covariance time series and to explore the relative importance of biophysical drivers on the interannual timescale. We combined spatial and temporal monitoring information to estimate annual whole-reservoir emissions. Acton Lake had cumulative areal emission rates of 45.6 ± 8.3 and 51.4 ± 4.3 g CH
m
in 2017 and 2018, respectively, or 109 ± 14 and 123 ± 10 Mg CH
in 2017 and 2018 across the whole 2.4 km
area of the lake. The main difference between years was a period of elevated emissions lasting less than 2 weeks in the spring of 2018, which contributed 17 % of the annual emissions in the shallow region of the reservoir. The spring burst coincided with a phytoplankton bloom, which was likely driven by favorable precipitation and temperature conditions in 2018 compared to 2017. Combining spatially extensive measurements with temporally continuous monitoring enabled us to quantify aspects of the spatial and temporal variability in CH
emission. We found that the relationships between CH
emissions and sediment temperature depended on location within the reservoir, and we observed a clear spatiotemporal offset in maximum CH
emissions as a function of reservoir depth. These findings suggest a strong spatial pattern in CH
biogeochemistry within this relatively small (2.4 km
) reservoir. In addressing the need for a better understanding of GHG emissions from reservoirs, there is a trade-off in intensive measurements of one water body vs. short-term and/or spatially limited measurements in many water bodies. The insights from multi-year, continuous, spatially extensive studies like this one can be used to inform both the study design and emission upscaling from spatially or temporally limited results, specifically the importance of trophic status and intra-reservoir variability in assumptions about upscaling CH
emissions.
Nitrogen (N) retention in streams is an important ecosystem service that may be affected by the widespread burial of streams in stormwater pipes in urban watersheds. We predicted that stream burial ...suppresses the capacity of streams to retain nitrate (NO₃ ⁻) by eliminating primary production, reducing respiration rates and organic matter availability, and increasing specific discharge. We tested these predictions by measuring whole-stream NO₃ ⁻ removal rates using ¹⁵NO₃ ⁻ isotope tracer releases in paired buried and open reaches in three streams in Cincinnati, Ohio (USA) during four seasons. Nitrate uptake lengths were 29 times greater in buried than open reaches, indicating that buried reaches were less effective at retaining NO₃ ⁻ than open reaches. Burial suppressed NO₃ ⁻ retention through a combination of hydrological and biological processes. The channel shape of two of the buried reaches increased specific discharge which enhanced NO₃ ⁻ transport from the channel, highlighting the relationship between urban infrastructure and ecosystem function. Uptake lengths in the buried reaches were further lengthened by low stream biological NO₃ ⁻ demand, as indicated by NO₃ ⁻ uptake velocities 17-fold lower than that of the open reaches. We also observed differences in the periphyton enzyme activity between reaches, indicating that the effects of burial cascade from the microbial to the ecosystem scale. Our results suggest that stream restoration practices involving “daylighting” buried streams have the potential to increase N retention. Further work is needed to elucidate the impacts of stream burial on ecosystem functions at the larger stream network scale.
Apatite incorporates variable and significant amounts of halogens (mainly F and Cl) in its crystal structure, which can be used to determine the initial F and Cl concentrations of magmas. The amount ...of chlorine in the apatite lattice also exerts an important compositional control on the degree of fission‐track annealing. Chlorine measurements in apatite have conventionally required electron probe microanalysis (EPMA). Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) is increasingly used in apatite fission‐track dating to determine U concentrations and also in simultaneous U‐Pb dating and trace element measurements of apatite. Apatite Cl measurements by ICP‐MS would remove the need for EPMA but the high (12.97 eV) first ionisation potential makes analysis challenging. Apatite Cl data were acquired using two analytical set‐ups: a Resonetics M‐50 193 nm ArF Excimer laser coupled to an Agilent 7700× quadrupole ICP‐MS (using a 26 μm spot with an 8 Hz repetition rate) and a Photon Machines Analyte Excite 193 nm ArF Excimer laser coupled to a Thermo Scientific iCAP Qc (using a 30 μm spot with a 4 Hz repetition rate). Chlorine concentrations were determined by LA‐ICP‐MS (1140 analyses in total) for nineteen apatite occurrences, and there is a comprehensive EPMA Cl and F data set for 13 of the apatite samples. The apatite sample suite includes different compositions representative of the range likely to be encountered in natural apatites, along with extreme variants including two end‐member chlorapatites. Between twenty‐six and thirty‐nine isotopes were determined in each apatite sample corresponding to a typical analytical protocol for integrated apatite fission track (U and Cl contents) and U‐Pb dating, along with REE and trace element measurements. 35Cl backgrounds (present mainly in the argon gas) were ~ 45–65 kcps in the first set‐up and ~ 4 kcps in the second set‐up. 35Cl background‐corrected signals ranged from ~ 0 cps in end‐member fluorapatite to up to ~ 90 kcps in end‐member chlorapatite. Use of a collision cell in both analytical set‐ups decreased the low mass sensitivity by approximately an order of magnitude without improving the 35Cl signal‐to‐background ratio. A minor Ca isotope was used as the internal standard to correct for drift in instrument sensitivity and variations in ablation volume during sessions. The 35Cl/43Ca values for each apatite (10–20 analyses each) when plotted against the EPMA Cl concentrations yield excellently constrained calibration relationships, demonstrating the suitability of the analytical protocol and that routine apatite Cl measurements by ICP‐MS are achievable.
L'apatite contient des quantités variables et significatives d'halogènes (notamment F et Cl) dans sa structure cristalline qui peuvent être utilisées pour déterminer la concentration initiale en F et Cl des magmas. La quantité de chlore dans le réseau de l'apatite exerce également un contrôle compositionnel important sur le degré de recuit des traces de fission. Les mesures du chlore dans l'apatite ont conventionnellement nécessité la microanalyse par sonde électronique (EPMA). La spectrométrie de masse à source plasma couplée à l'ablation laser (LA‐ICP‐MS) est de plus en plus utilisé dans la datation sur traces de fission de l'apatite pour déterminer les concentrations en U et aussi pour la datation simultanées U‐Pb et les mesures des éléments traces de l'apatite. Les mesures du Cl dans l'apatite par ICP‐MS élimineraient la nécessité d'utiliser l'EPMA mais le fait que le premier potentiel d'ionisation (12.97 eV) soit haut rend l'analyse difficile. Les données du Cl dans l'apatite ont été acquises au moyen de deux systèmes analytiques: un laser ArF excimer 193 nm Resonetics M‐50 couplé à un ICP‐MS quadripôle Agilent 7700× (utilisant un spot de 26 µm avec un taux de répétition de 8 Hz) et un laser ArF excimer 193 nm Photon Machines Analyte Excite couplé à un Thermo Scientific iCAP Qc (en utilisant un spot 30 µm avec un taux de répétition de 4 Hz). Les concentrations en chlore ont été déterminées par LA‐ICP‐MS (1140 analyses au total) pour dix‐neuf occurrences d'apatite, et il y a une complète base de données EPMA pour le Cl et le F pour treize des échantillons d'apatite. La suite comprend différents échantillons d'apatite représentant la gamme de compositions susceptible d'être rencontré dans les apatites naturelles, ainsi que des variantes extrêmes dont deux endmembers chlorapatites. Entre vingt‐six et trente‐neuf isotopes ont été déterminés dans chaque échantillon d'apatite ce qui correspond à un protocole classique d'analyse intégrée des traces de fission (teneurs en U et Cl) et datation U‐Pb sur apatite, avec les mesures des REE et des éléments traces. Les bruits de fond du 35Cl (surtout présent dans le gaz argon) étaient d'environ 45–65 kcps pour le premier système d'analyse et d'environ 4 kcps pour le second système. Le signal corrigé du bruit de fond pour 35Cl varie de ~ 0 cps dans l'endmember fluorapatite jusqu'à environ 90 kcps pour l'endmember chlorapatite. L'utilisation d'une cellule de collision avec les deux types de systèmes d'analyse a diminué la sensibilité des faibles masses d'environ un ordre de grandeur sans pour autant améliorer le rapport signal‐bruit de fond du 35Cl. Un isotope mineur du Ca a été utilisé comme étalon interne pour corriger la dérive de sensibilité de l'instrument et les variations du volume d'ablation au cours des séances d'analyse. Les valeurs 35Cl/43Ca pour chaque apatite (10–20 analyses chacune) lorsqu'elles sont reportées par rapport aux concentrations en Cl obtenu par EPMA produisent des relations d'étalonnage parfaitement contraintes, ce qui démontre la pertinence du protocole analytique et que les mesures de routine du Cl de l'apatite par ICP‐MS sont réalisables.
Urban streams are degraded by a suite of factors, including burial beneath urban infrastructure, such as roads or parking lots, which eliminates light and reduces direct organic matter inputs to ...streams from riparian zones. These changes to stream metabolism and terrestrial carbon contribution will likely have consequences for organic matter metabolism by microbes and dissolved organic matter (DOM) use patterns in streams. Respiration by heterotrophic biofilms drives the nitrogen and phosphorus cycles, but we lack a clear understanding of how stream burial and seasonality affect microbial carbon use.
We studied seasonal changes (autumn, spring, and summer) in organic matter metabolism by microbial communities in open and buried reaches of three urban streams in Cincinnati, OH. We characterised DOM quality using fluorescence spectroscopy and extracellular enzyme profiles, and we measured the respiration response to carbon supplements in nutrient diffusing substrata (NDS). We hypothesised: (1) that algal production would lead to higher quality DOM in spring compared to other seasons and in open compared to buried reaches, (2) lower reliance of microbial respiration on recalcitrant carbon sources in spring and in open reaches, and (3) that microbial respiration would increase in response to added carbon in autumn and in buried reaches.
Several fluorescence metrics showed higher quality DOM in spring than autumn, but only the metric of recalcitrant humic compounds varied by reach, with more humic DOM in open compared to buried reaches. This likely reflected open reaches as an avenue for direct terrestrial inputs from the riparian zone.
Extracellular enzyme assays showed that microbes in buried reaches allocated more effort to degrade recalcitrant carbon sources, consistent with a lack of labile carbon compounds due to limited photosynthesis. Nitrogen acquisition enzymes were highest in autumn coincident with riparian leaf inputs to the streams. Buried and open reaches both responded more strongly to added carbon in autumn when terrestrial leaf inputs dominated compared to the spring when vernal algal blooms were pronounced.
Our data show that stream burial affects the quality of the DOM pool with consequences for how microbes use those carbon sources, and that heterotrophic respiration increased on carbon‐supplemented NDS in buried and open stream reaches in both seasons. Different carbon quality and use patterns suggest that urban stream infrastructure affects spatiotemporal patterns of bacterial respiration, with likely consequences for nitrogen and/or phosphorus cycling given that carbon use drives other biogeochemical cycles. Management actions that increase light to buried streams could shift the balance between allochthonous and autochthonous DOM in urban streams with consequences for spatiotemporal patterns in bacterial metabolism.
It has been hypothesized that the pathogenesis of diseases induced by cigarette smoking involves oxidative damage by free radicals. However, definitive evidence that smoking causes the oxidative ...modification of target molecules in vivo is lacking. We conducted a study to determine whether the production of F2-isoprostanes, which are novel products of lipid peroxidation, is enhanced in persons who smoke.
We measured the levels of free F2-isoprostanes in plasma, the levels of F2-isoprostanes esterified to plasma lipids, and the urinary excretion of metabolites of F2-isoprostanes in 10 smokers and 10 nonsmokers matched for age and sex. The short-term effects of smoking (three cigarettes smoked over 30 minutes) and the effects of two weeks of abstinence from smoking on levels of F2-isoprostanes in the circulation were also determined in the smokers.
Plasma levels of free and esterified F2-isoprostanes were significantly higher in the smokers (242 +/- 147 and 574 +/- 217 pmol per liter, respectively) than in the nonsmokers (103 +/- 19 and 345 +/- 65 pmol per liter; P = 0.02 for free F2-isoprostanes and P = 0.03 for esterified F2-isoprostanes). Smoking had no short-term effects on the circulating levels of F2-isoprostanes. However, the levels of free and esterified F2-isoprostanes fell significantly after two weeks of abstinence from smoking (250 +/- 156 and 624 +/- 214 pmol per liter, respectively, before the cessation of smoking, as compared with 156 +/- 67 and 469 +/- 108 pmol per liter after two weeks' cessation; P = 0.03 for free F2-isoprostanes and P = 0.02 for esterified F2-isoprostanes).
The increased levels of F2-isoprostanes in the circulation of persons who smoke support the hypothesis that smoking can cause the oxidative modification of important biologic molecules in vivo.
ABSTRACT
In October 2005, the predominately Arab‐immigrant suburbs of Paris, Lyon, Lille and other French cities erupted in riots by socially alienated teenagers, many of them second‐ or ...third‐generation immigrants. For many French observers, it was a painful reminder that France's immigration policy had, quite bluntly, failed. The grand French ideal of égalité, the equality of all citizens of the Republic, itself a by‐product of France's colonial past, demonstrated its incompatibility with twenty‐first century reality.
The French immigration experience is markedly different than those of other European countries, as France's is tainted by colonial history, republican idealism, a rigidly centralized government structure, and deep‐seeded traditions of xenophobia. Indeed, the nineteenth century French policy of the mission civilicatrice (civilizing mission) still influences French policy toward its immigrants today: rather than accept cultural differences, the French government demands that all its citizens adhere to a rigid and exclusive “French” identity.
As such, the children of the generation of immigrants that the French government actively brought to France to fuel its post‐war expansion now find themselves unemployed and socially marginalized. Government social structures meant to ease the disparity between social classes, such as public housing and education, generally do more to aggravate problems than to solve them; public housing is woefully inadequate and the education structure institutionalizes the poor quality of schools in immigrant communities. Despite this generally poor outlook, the French have recently made some progress toward better integration of their immigrant communities, though these efforts are generally met with wide‐spread demagogic and populist opposition.
LES ÉMEUTES D'OCTOBRE EN FRANCE: ÉCHEC DE LA POLITIQUE D'IMMIGRATION OU L'EMPIRE CONTRE‐ATTAQUE?
En octobre 2005, dans les banlieues de Paris, Lyon, Lille et d'autres villes françaises, oú prédominent les immigrés arabes, des émeutes ont éclaté, menées par des adolescents socialement aliénés, dont beaucoup étaient des immigrés de deuxième ou troisième génération. Pour nombre d'observateurs français, ces événements ont douloureusement confirmé que la politique d'immigration de la France était un échec cuisant. Le magnifique idéal français d'égalité de tous les citoyens de la République, lui‐même un sous‐produit du passé colonial de la France, se révélait décidément incompatible avec la réalité du 21e siècle.
En matière d'immigration, l'expérience de la France est sensiblement différente de celle des autres pays européens, la France étant marquée par une histoire coloniale, un idéalisme républicain, une structure gouvernementale rigidement centralisée et une tradition de xénophobie profondément ancrée. D'ailleurs, l'approche française de la mission civilisatrice, qui avait cours au 19e siècle, continue d'influencer la politique de la France à l'égard de ses immigrés: plutôt que d'accepter les différences culturelles, le Gouvernement français exige que tous les citoyens adhèrent à une identité « française » à la fois rigide et exclusive.
Les enfants des immigrés que le Gouvernement français avait fait venir en France pour soutenir son expansion d'après‐guerre se retrouvent maintenant au chômage et socialement marginalisés. Les structures sociales gouvernementales destinées à atténuer les disparités entre classes sociales, notamment le logement social et l'enseignement, font souvent plus pour aggraver les problèmes que pour les résoudre. Les logements sociaux sont cruellement insuffisants et le système d'enseignement institutionnalise la mauvaise qualité des établissements scolaires fréquentés par les communautés d'immigrés. Malgré ces perspectives généralement médiocres, les Français ont fait des progrès dans le sens d'une meilleure intégration de ces communautés, bien que ces efforts se heurtent généralement à une importante opposition teintée de démagogie et de populisme.
LAS REVUELTAS DE OCTUBRE EN FRANCIA: ¿UNA POLÍTICA DE INMIGRACIÓN ERRÓNEA O EL IMPERIO CONTRAATACA?
En octubre de 2005, los barrios donde predomina la inmigración árabe de París, Lyon, Lille y otras ciudades francesas fueron el escenario de revueltas de adolescentes socialmente alienados, muchos de ellos inmigrantes de segunda o tercera generación. Para muchos observadores franceses, fue un doloroso recordatorio de que, con bastante claridad, la política de inmigración de Francia había fracasado. El gran ideal francés de l'égalité, es decir, la igualdad de todos los ciudadanos de la República, consecuencia en sí misma del pasado colonial francés, demostró su incompatibilidad con la realidad del siglo XXI.
La experiencia de la inmigración francesa es muy distinta a la de otros países europeos, ya que Francia está marcada por su historia colonial, el idealismo republicano, una estructura gubernamental estrictamente centralizada y unas tradiciones arraigadas de xenofobia. Ciertamente, la política francesa del siglo XIX de la mission civilisatrice (misión civilizadora) influye aún hoy en la política francesa sobre inmigración: más que aceptar las diferencias culturales, el Gobierno francés exige que todos sus ciudadanos se adhieran a una identidad “francesa” rígida y exclusiva.
Los hijos de la generación de inmigrantes a los que el Gobierno francés alentó activamente a ir a Francia para impulsar la expansión de la postguerra se encuentran ahora sin trabajo y marginados de la sociedad. Las estructuras sociales del Estado, encaminadas a disminuir la disparidad entre clases sociales, tales como la vivienda y la educación públicas, contribuyen generalmente a agravar los problemas más que a solucionarlos: las viviendas públicas son lamentablemente inadecuadas y la estructura educativa institucionaliza la escasa calidad de las escuelas de las comunidades de inmigrantes. A pesar de este panorama en general poco prometedor, los franceses han logrado recientemente algunos progresos hacia una mejor integración de sus comunidades inmigrantes, aunque estos esfuerzos se encuentran a menudo con una oposición demagógica y populista ampliamente extendida.
The bombings in Madrid (2004) and London (2005) and the murder of the Dutch filmmaker Theo van Gogh in 2004 alerted European governments to their susceptibility to terrorism perpetrated by ...unassimilated Muslim immigrants. Whether they had pursued multicultural immigration policies or regulated their immigrant communities closely, European countries began adopting stricter measures in the attempt to contain-if not transform-'radical' Islam. There appears to be a convergence toward a rigid model that includes highly-visible deportations, demonstrations of support for pro-government Muslim leaders, and infiltration of mosques and Muslim communities, as well as sponsoring or endorsing programs to train Euro-friendly imams. This study examines the development and diversity of such policies as they affect imams in various European countries with special reference to immigration policy, domestic surveillance and education programs in France, Britain and the Netherlands.
Oxidative modification of low density lipoprotein (LDL) has been suggested to play a casual role in human atherosclerosis, and prevention of LDL oxidation may be an effective strategy to prevent or ...slow the progression of this disease. It is important, therefore, to identify the factors that determine LDL's susceptibility to oxidation. We have analyzed 62 human LDL samples for content of antioxidants, preformed lipid hydroperoxides, and cholesterol. To investigate their oxidative susceptibility, the LDL samples were exposed to either a metal ion-dependent (Cu2+) or -independent (aqueous peroxyl radicals) oxidizing system; the length of the lag phase of inhibited lipid peroxidation was measured, as well as the rate of lipid peroxidation during the lag and ensuing propagation phases. The susceptibility of LDL to metal ion-dependent oxidation was not related to its susceptibility to metal ion-independent oxidation. A strong predictor of an increased susceptibility of LDL to metal ion-dependent oxidation was a decreased vitamin E-to-cholesterol ratio, in contrast to the vitamin E-to-protein ratio. Elevated levels of performed lipid hydroperoxides in LDL and an increased cholesterol content were also associated with an increased susceptibility of the lipoprotein to Cu2+-induced oxidation. Remarkably, a strong predictor of an increased susceptibility of LDL to metal ion-independent oxidation was an increased, rather than decreased, vitamin E content relative to protein. An increased cholesterol content also was associated with an increased oxidative susceptibility of LDL to aqueous peroxyl radicals, while preformed lipid hydroperoxides showed no significant correlation. Ubiquinol-10, beta-carotene, and lycopene, whether quantitated relative to cholesterol or protein, did not show significant protective effects against both metal ion-dependent and -independent oxidation of LDL
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