Impact of nitrogenous fertilizers on carbonate dissolution in small agricultural catchments: Implications for weathering CO2 uptake at regional and global scales

The goal of this study was to highlight the occurrence of an additional proton-promoted weathering pathway of carbonate rocks in agricultural areas where N-fertilizers are extensively spread, and to estimate its consequences on riverine alkalinity and uptake of CO2 by weathering. We surveyed 25 small streams in the calcareous molassic Gascogne area located in the Garonne river basin (south-western France) that drain cultivated or forested catchments for their major element compositions during different hydrologic periods. Among these catchments, the Hay and the Montousse´, two experimental catchments, were monitored on a weekly basis. Studies in the literature from other small carbonate catchments in Europe were dissected in the same way. In areas of intensive agriculture, the molar ratio (Ca + Mg)/HCO3 in surface waters is significantly higher (0.7 on average) than in areas of low anthropogenic pressure (0.5). This corresponds to a decrease in riverine alkalinity, which can reach 80% during storm events. This relative loss of alkalinity correlates well with the NO3 content in surface waters. In cultivated areas, the contribution of atmospheric/soil CO2 to the total riverine alkalinity (CO2 ATM-SOIL/HCO3) is less than 50% (expected value for carbonate basins), and it decreases when the nitrate concentration increases. This loss of alkalinity can be attributed to the substitution of carbonic acid (natural weathering pathway) by protons produced by nitrification of Nfertilizers (anthropogenic weathering pathway) occurring in soils during carbonate dissolution. As a consequence of these processes, the alkalinity over the last 30 years shows a decreasing trend in the Save river (one of the main Garonne river tributaries, draining an agricultural catchment), while the nitrate and calcium plus magnesium contents are increasing. We estimated that the contribution of atmospheric/soil CO2 to riverine alkalinity decreased by about 7–17% on average for all the studied catchments. Using these values, the deficit of CO2 uptake can be estimated as up to 0.22–0.53 and 12–29 Tg1 yr1 CO2 on a country scale (France) and a global scale, respectively. These losses represent up to 5.7–13.4% and only 1.6–3.8% of the total CO2 flux naturally consumed by carbonate dissolution, for France and on a global scale, respectively. Nevertheless, this loss of alkalinity relative to the Ca + Mg content relates to carbonate weathering by protons from N-fertilizers nitrification, which is a net source of CO2 for the atmosphere. This anthropogenic CO2 source is not negligible since it could reach 6–15% of CO2 uptake by natural silicate weathering and could consequently partly counterbalance this natural CO2 sink

Back-propagation of constraints from consumer to producer

International audienceIn the context of intelligent instrument network, i.e. intelligent sensors and actuators, Producer-Consumer pattern facilitates design and intelligent instrument networking. The connection between producer and consumer can be checked (i.e. type of data) and filtered (condition of exchange). We propose to extend the producer-consumer approach to allow the consumer to define and change constraint parameters: frequency of refreshment and maximum of tolerance. We consider especially interval confidence model of data and refreshment capability. A prototype is presented to illustrate and validate the approach on the OSGI platfor

Alternative methodology for linear polarization resistance assessment of reinforced concrete structure

International audienceFor reinforced concrete structures, several corrosion detection methods exist: concrete resistivity, half-cell potential or linear polarization resistance (LPR) measurement. The LPR value can be linked to the corrosion rate thanks the Stern-Geary equation if strong hypotheses are made. Existing commercial devices use a guard ring to canalize the current on specific steel rebar area and assume that the steel rebar is uniformly polarized. However, recent works reveal that the top part of the steel rebar, right under the counter electrode, is the most polarized point. The particular point is referred as the point of interest (PI). This works belongs to the DIAMOND project which aims to produce a new corrosion rate measurement device. Comsol® software was used to model the influence of concrete cover, resistivity and injected current on the current density at the PI. Moreover, a significant influence of the steel rebars diameter was also demonstrated. Two types of abacus are built. The first one links to polarization measured on the surface to the polarization on the rebar at the PI. The second links the ratio between the current density at the PI and the density of injected current to concrete cover and steel rebar diameter. The Stern-Geary equation can now be used at the PI without using the approximation of a uniformly polarized rebar. The corrosion state of reinforced concrete structure can be controlled more precisely. The methodology is then applied on two concrete slabs in which three metal bars are embedded at different concrete covers. The first slab is prepared with ordinary concrete while the second contain chloride to artificially activate the corrosion process. The results reveal that the rebars embedded on the first slab are not corroding (icorr ≤0.2 μΑ/cm2) while the second rebar are corroding (icorr>0.2 μΑ/cm2)

A numerical model to predict unsteady cavitating flow behaviour in inducer blade cascades

The cavitation behaviour of a four-blade rocket engine turbopump inducer is simulated. A 2D numerical model of unsteady cavitation was applied to a blade cascade drawn fromthe inducer geometry. The physical model is based on a homogeneous approach of cavitation, coupled with a barotropic state law for the liquid/vapour mixture. The numericalresolution uses a pressure-correction method derived from the SIMPLE algorithm and a finite volume discretization. Unsteadybehaviour of sheet cavities attached to the blade suction side depends on the flow rate and cavitation number. Two differentunstable configurations of rotating cavitation, respectively sub-synchronous and super-synchronous, are identified. The mechanisms that are responsible for these unstable behaviours are discussed, and the stress fluctuations induced on the blade by the rotating cavitation are estimated

Absence of Chronic Human Immunodeficiency Virus Infection without Seroconversion in Intravenous Drug Users: A Prospective and Retrospective Study

It has been reported that human immunodeficiency virus type 1 (HIV-1) infection may exist in persons without specific antibodies for years. To measure the frequency of a silent carrier state, a study was conducted in a cohort of 124 intravenous drug users (IVDUs) without anti-HIV-1 antibodies. All the participants had engaged in high-risk behavior for HIV-1 transmission for a number of years until 1987 or later. Samples were analyzed at 6-month intervals for the presence of HIV-1 provirus using DNA amplification and for the appearance of anti-HIV-1 antibodies. HIV-1 provirus and antibodies were undetectable in 122 participants, whereas seroconversion was observed in 2. In one of these, both amplified HIV-1 pol gene segment and anti-HIV-1 antibodies were detected simultaneously, and in the other, provirus was detected 1 month before seroconversion. This study suggests that long-term HIV-1 infection without anti-HIV-1 antibodies is rare and that repeated antibody testing is sufficient to determine the HIV-1 status of a person no longer at high risk for HIV-1 infectio

Symptomatic Primary Infection Due to Human Immunodeficiency Virus Type 1: Review of 31 Cases

In this series of 31 patients with acute infection due to human immunodeficiency virus (HIV) type 1, the male-to-female ratio was 3.4:1 and the mean age was 31.3 years. Sexual transmission accounted for 83.9% of cases; 45.2% of the patients were homosexual and 38.7% were heterosexual. The mean duration of symptoms and signs was 21 days (range, 5-60 days). Fever (87.1%) and skin rash (67.7%) were most commonly reported. Physical examination findings were abnormal for 96% of the patients; the oral cavity (76.7%) and the skin (73.3%) were the most frequently involved sites. Thirteen of 25 patients with sexually acquired infection had genital or oral ulcers, whereas five intravenous drug users had none (P = .052). Thrombocytopenia was the most common hematologic abnormality and was detected in 17 of 23 patients tested. P24 antigenemia, an initially negative screening test for HIV antibody, and a low CD4+ lymphocyte count were noted in 23 of 29, 23 of 30, and 14 of 21 tested patients, respectivel

Nosocomial Outbreak of Multiple Bloodborne Viral Infections

In resource‐limited countries, nosocomial transmission of bloodborne pathogens is a major public health concern. After a major outbreak of human immunodeficiency virus (HIV) infection in ∼400 children in 1998 in Libya, we tested HIV, hepatitis C virus (HCV), and hepatitis B virus (HBV) markers in 148 children and collected epidemiological data in a subgroup of 37 children and 46 parents. HIV infection was detected in all children but one, with HCV or HBV coinfection in 47% and 33%, respectively. Vertical transmission was ruled out by analysis of parents' serology. The children visited the same hospital 1-6 times; at each visit, invasive procedures with potential blood transmission of virus were performed. HIV and HCV genotypic analyses identified a HIV monophyletic group, whereas 4 clusters of HCV sequences were identified. To our knowledge, this is the largest documented outbreak of nosocomial HIV transmissio