Relation entre la richesse du sol en phosphore et la concentration en phosphore de l'eau de drainage dans deux agro-écosystèmes

Des concentrations en P excédant le seuil d'eutrophisation sont fréquemment mesurées dans l'eau des affluents du fleuve Saint-Laurent au Québec, Canada. Un enrichissement excessif en P des sols agricoles en serait la source. Une norme relative à la saturation en P des sols a été proposée comme critère de risque de contamination en P des eaux de surface. L'objectif de ce travail est d'étudier le lien entre la richesse en P du sol et la teneur en P de l'eau de drainage dans deux agro-écosystèmes du Québec. Le bassin versant de la rivière Boyer (BVB), dominé par des sols en pente, une forte densité animale et des productions fourragères et les Basses Terres de Montréal (BTM), dominées par des sols plats utilisés pour la production intensive de maïs et une faible densité animale sont étudiés. Le degré de saturation en P des sols du BVB est de 8 à 10 % alors que celui des BTM dépasse très souvent 15 %. Le pool du P organique est plus faible dans les sols des BTM que dans le BVB. La concentration moyenne en P de l'eau de drainage est plus élevée dans les sols du BVB (171 µg L-1) que dans ceux des BTM (98 µg L-1). Elle est corrélée à la teneur en P extrait à l'oxalate des sols argileux et à la teneur en P soluble dans l'eau ou à l'index de sorption en P des sols grossiers. Ces relations sont plus étroites pour la couche 0-5 cm de sol que pour les couches plus profondes. Les résultats de cette étude démontrent qu'il est difficile de prédire la concentration en P de l'eau de drainage de sols contrastants. Regrouper les sols selon leur texture améliore la précision de la prédiction de la teneur en P de l'eau de drainage à partir de leurs propriétés.Concentrations of P higher than the recognised threshold for eutrophication are often measured in the tributaries of the St. Lawrence river, Quebec, Canada. An excessive P enrichment of agricultural soils was identified as the potential cause of this phenomenon. This enrichment results in a decrease in the P sorption capacity of soils and an increased risk of P contamination of surface waters. A norm based on soil P saturation degree (DSPS) was proposed as an agro-environmental criterion to reduce this risk. Relationships between DSPS and other soil P attributes and surface runoff P concentration have been reported in the literature but not for tile-drainage water. The objective of this work is to study the relationship between soil P attributes and drainage water P in two agro-ecosystems of Quebec.The Boyer watershed (BW), which is dominated by soils with significant slopes, a high animal density and forage production, and the Montreal lowlands (ML), dominated by flat soils, low animal density and mostly used for corn (Zea mays L.), were studied. The A, B and C horizons from soils from the BW were sampled at three locations in tile-drained fields from farms in surplus or not of manure N in regards to crop needs. Soils were sampled in the ML according to a gradient in clay content with the same procedures. Soils were characterised for their pH, particle size distribution, Mehlich 3-extractable P (Pm3) and Al, water-soluble P (Pw), organic P (Po) and oxalate-extractable P (Pox), Al (Alox) and Fe (Feox) contents. Grab tile-drainage samples were taken in triplicate and characterised for total (TP), particulate (PP) and dissolved reactive P (RP) and unreactive P (UP).The soils of the BW are more acidic and have higher P retention capacities than ML soils. The Pw content of BW soils is lower than in ML ones in spite of comparable Pm3 contents. The DSPS (Pox /Alox + Feox) of BW soils is moderate (8 to 10 %) whereas DSPS in ML soils is often >15 %. The soil P organic pool is much smaller in the ML soils than in those from BW, probably because of more frequent tillage and lower manure C inputs.The average P concentration (TP) in drainage water was higher in soils from the BW (171 µg L-1) than from ML soils (98 µg L-1). The PP was the main P fraction in drainage water from the two ecosystems. The RP was on average 44 % of TP whereas UP was much less. The TP concentration in drainage waters was higher than 0.03 mg L-1 in most cases. The TP concentration was higher in tile-drainage waters from the BW than in the ML even though comparable Pm3 and lower DSPS were found in the BW than in ML soils. These results suggest that other criteria should be included in the prediction of the risk of P contamination of drainage waters. The results of the present study indicate that agricultural practices (crop species, manure inputs, tillage type and frequency) could have a greater influence than soil P status on the TP concentration in tile-drainage waters.A linear correlation analysis between the logarithm of the TP (TP + 0.5) and that of the different soil P attributes indicated that TP was related to the P extracted by oxalate from clay soils and by water in coarse-textured soils. These relationships were closer in the 0-5 cm soil layer than in deeper strata. Multiple regression analysis between the logarithms of drainage water P concentrations and soil attributes revealed that, when soils were grouped by texture, the prediction of TP was much more accurate than when all soils were considered. The present regulatory approach of assessing the risk of water P contamination by using the soil Pm3 and DSPS only was inadequate in the two considered agroecosystems.The results of this study indicate that the prediction of the drainage water P concentration with P attributes from contrasting soils is difficult. Grouping soils by texture improves the prediction of Pt from soil P attributes

Clues to the Origin of the Mass-Metallicity Relation: Dependence on Star Formation Rate and Galaxy Size

We use a sample of 43,690 galaxies selected from the Sloan Digital Sky Survey Data Release 4 to study the systematic effects of specific star formation rate (SSFR) and galaxy size (as measured by the half light radius, r_h) on the mass-metallicity relation. We find that galaxies with high SSFR or large r_h for their stellar mass have systematically lower gas phase-metallicities (by up to 0.2 dex) than galaxies with low SSFR or small r_h. We discuss possible origins for these dependencies, including galactic winds/outflows, abundance gradients, environment and star formation rate efficiencies.Comment: Accepted by ApJ Letter

Breaking the Disk/Halo Degeneracy with Gravitational Lensing

The degeneracy between the disk and the dark matter contribution to galaxy rotation curves remains an important uncertainty in our understanding of disk galaxies. Here we discuss a new method for breaking this degeneracy using gravitational lensing by spiral galaxies, and apply this method to the spiral lens B1600+434 as an example. The combined image and lens photometry constraints allow models for B1600+434 with either a nearly singular dark matter halo, or a halo with a sizable core. A maximum disk model is ruled out with high confidence. Further information, such as the circular velocity of this galaxy, will help break the degeneracies. Future studies of spiral galaxy lenses will be able to determine the relative contribution of disk, bulge, and halo to the mass in the inner parts of galaxies.Comment: Replaced with minor revisions, a typo fixed, and reference added; 21 pages, 8 figures, ApJ accepte

Sexually dimorphic gene expression that overlaps maturation of type II pneumonocytes in fetal mouse lungs

BACKGROUND: In human, respiratory distress of the neonates, which occurs in prematurity, is prevalent in male. Late in gestation, maturation of type II pneumonocytes, and consequently the surge of surfactant synthesis are delayed in male fetuses compared with female fetuses. Although the presence of higher levels of androgens in male fetuses is thought to explain this sex difference, the identity of genes involved in lung maturation that are differentially modulated according to fetal sex is unknown. We have studied the sex difference in developing mouse lung by gene profiling during a three-day gestational window preceding and including the emergence of mature PTII cells (the surge of surfactant synthesis in the mouse occurs on GD 17.5). METHODS: Total RNA was extracted from lungs of male and female fetal mice (gestation days 15.5, 16.5, and 17.5), converted to cRNA, labeled with biotin, and hybridized to oligonucleotide microarrays (Affymetrix MOE430A). Analysis of data was performed using MAS5.0, LFCM and Genesis softwares. RESULTS: Many genes involved in lung maturation were expressed with no sex difference. Of the approximative 14 000 transcripts covered by the arrays, only 83 genes presented a sex difference at one or more time points between GDs 15.5 and 17.5. They include genes involved in hormone metabolism and regulation (i.e. steroidogenesis pathways), apoptosis, signal transduction, transcriptional regulation, and lipid metabolism with four apolipoprotein genes. Genes involved in immune functions and other metabolisms also displayed a sex difference. CONCLUSION: Among these sexually dimorphic genes, some may be candidates for a role in lung maturation. Indeed, on GD 17.5, the sex difference in surfactant lipids correlates with the sex difference in pulmonary expression of apolipoprotein genes, which are involved in lipid transport. This suggests a role for these genes in the surge of surfactant synthesis. Our results would help to identify novel genes involved in the physiopathology of the respiratory distress of the neonates

A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey

We compare the structural properties of two classes of galaxies at intermediate redshift: those in dynamically close galaxy pairs, and those which are isolated. Both samples are selected from the CNOC2 Redshift Survey, and have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images were acquired as part of a snapshot survey, and were used to measure bulge fraction and asymmetry for these galaxies. We find that paired and isolated galaxies have identical distributions of bulge fractions. Conversely, we find that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13) than isolated galaxies. Assuming that half of these pairs are unlikely to be close enough to merge, we estimate that 40% +/- 11% of merging galaxies are asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/- 8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We conclude that close to half of the galaxy pairs in our sample are in the process of merging, and that most of these mergers are accompanied by triggered star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages, including 15 figures. For full resolution version, please see http://www.trentu.ca/physics/dpatton/hstpairs

Applying dissipative dynamical systems to pseudorandom number generation: Equidistribution property and statistical independence of bits at distances up to logarithm of mesh size

The behavior of a family of dissipative dynamical systems representing transformations of two-dimensional torus is studied on a discrete lattice and compared with that of conservative hyperbolic automorphisms of the torus. Applying dissipative dynamical systems to generation of pseudorandom numbers is shown to be advantageous and equidistribution of probabilities for the sequences of bits can be achieved. A new algorithm for generating uniform pseudorandom numbers is proposed. The theory of the generator, which includes proofs of periodic properties and of statistical independence of bits at distances up to logarithm of mesh size, is presented. Extensive statistical testing using available test packages demonstrates excellent results, while the speed of the generator is comparable to other modern generators.Comment: 6 pages, 3 figures, 3 table

Bulge mass is king: The dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey

We investigate the origin of galaxy bimodality by quantifying the relative role of intrinsic and environmental drivers to the cessation (or `quenching') of star formation in over half a million local Sloan Digital Sky Survey (SDSS) galaxies. Our sample contains a wide variety of galaxies at z=0.02-0.2, with stellar masses of 8 < log(M*/M_sun) < 12, spanning the entire morphological range from pure disks to spheroids, and over four orders of magnitude in local galaxy density and halo mass. We utilise published star formation rates and add to this recent GIM2D photometric and stellar mass bulge + disk decompositions from our group. We find that the passive fraction of galaxies increases steeply with stellar mass, halo mass, and bulge mass, with a less steep dependence on local galaxy density and bulge-to-total stellar mass ratio (B/T). At fixed internal properties, we find that central and satellite galaxies have different passive fraction relationships. For centrals, we conclude that there is less variation in the passive fraction at a fixed bulge mass, than for any other variable, including total stellar mass, halo mass, and B/T. This implies that the quenching mechanism must be most tightly coupled to the bulge. We argue that radio-mode AGN feedback offers the most plausible explanation of the observed trends.Comment: Accepted to MNRAS. 32 pages, 27 figures. [This version is virtually identical to v1