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

Ace Project As A Project Management Tool

The primary challenge of project management is to achieve the project goals and objectives while adhering to project constraints - usually scope, quality, time and budget. The secondary challenge is to optimize the allocation and integration of resources necessary to meet pre-defined objectives. Project management software provides an active learning component to the study of project management principles. Prior literature indicates that active learning contributes to student success when students are actively engaged both inside and outside the classroom

A Search for Nitrogen Enriched Quasars in the Sloan Digital Sky Survey Early Data Release

A search for nitrogen-rich quasars in the Sloan Digital Sky Survey Early Data Release (SDSS EDR) catalog has yielded 16 candidates, including five with very prominent emission, but no cases with nitrogen emission as strong as in Q0353-383. The quasar Q0353-383 has long been known to have extremely strong nitrogen intercombination lines at lambda 1486 and lambda 1750 Angstroms, implying an anomalously high nitrogen abundance of about 15 times solar. It is still the only one of its kind known. A preliminary search through the EDR using the observed property of the weak C IV emission seen in Q0353-383 resulted in a sample of 23 objects with unusual emission or absorption-line properties, including one very luminous redshift 2.5 star-forming galaxy. We present descriptions, preliminary emission-line measurements, and spectra for all the objects discussed here.Comment: 20 pages, 5 figures, submitted to AJ; final refereed versio

The Galaxy Populations of X-Ray Detected, Poor Groups

(Abridged) We determine the quantitative morphology and star formation properties of galaxies in six nearby X-ray detected, poor groups using multi-object spectroscopy and wide-field R imaging. We measure structural parameters for each galaxy by fitting a PSF-convolved, two component model to their surface brightness profiles. To compare directly the samples, we fade, smooth, and rebin each galaxy image so that we effectively observe each galaxy at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We compare results for the groups to a sample of field galaxies. We find that: 1) Galaxies spanning a wide range in morphological type and luminosity are well-fit by a de Vaucouleurs bulge with exponential disk profile. 2) Morphologically classifying these nearby group galaxies by their bulge fraction (B/T) is fairly robust on average, even when their redshift has increased by up to a factor of four and the effective resolution of the images is degraded by up to a factor of five. 3) The fraction of bulge-dominated systems in these groups is higher than in the field (~50% vs. ~20%). 4) The fraction of bulge-dominated systems in groups decreases with increasing radius, similar to the morphology-radius (~density) relation observed in galaxy clusters. 5) Current star formation in group galaxies is correlated with significant morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group galaxies that are most disk-dominated (B/T<0.2) are less star forming and asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12 figures); Figs 1 & 2 also available at http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g

The Magnitude-Size Relation of Galaxies out to z ~ 1

As part of the Deep Extragalactic Evolutionary Probe (DEEP) survey, a sample of 190 field galaxies (I_{814} <= 23.5) in the ``Groth Survey Strip'' has been used to analyze the magnitude-size relation over the range 0.1 < z < 1.1. The survey is statistically complete to this magnitude limit. All galaxies have photometric structural parameters, including bulge fractions (B/T), from Hubble Space Telescope images, and spectroscopic redshifts from the Keck Telescope. The analysis includes a determination of the survey selection function in the magnitude-size plane as a function of redshift, which mainly drops faint galaxies at large distances. Our results suggest that selection effects play a very important role. A first analysis treats disk-dominated galaxies with B/T < 0.5. If selection effects are ignored, the mean disk surface brightness (averaged over all galaxies) increases by ~1.3 mag from z = 0.1 to 0.9. However, most of this change is plausibly due to comparing low luminosity galaxies in nearby redshift bins to high luminosity galaxies in distant bins. If this effect is allowed for, no discernible evolution remains in the disk surface brightness of bright (M_B < -19) disk-dominated galaxies. A second analysis treats all galaxies by substituting half-light radius for disk scale length, with similar conclusions. Indeed, at all redshifts, the bulk of galaxies is consistent with the magnitude-size envelope of local galaxies, i.e., with little or no evolution in surface brightness. In the two highest redshift bins (z > 0.7), a handful of luminous, high surface brightness galaxies appears that occupies a region of the magnitude-size plane rarely populated by local galaxies. Their wide range of colors and bulge fractions points to a variety of possible origins.Comment: 19 pages, 12 figures. Accepted for publication in the Astrophysical Journa

The Tully-Fisher relation of distant cluster galaxies

We have measured maximum rotation velocities (Vrot) for a sample of 111 emission-line galaxies with 0.1 < z < 1, observed in the fields of 6 clusters. From these data we construct 'matched' samples of 58 field and 22 cluster galaxies, covering similar ranges in redshift (0.25 < z < 1.0) and luminosity (M_B < -19.5 mag), and selected in a homogeneous manner. We find the distributions of M_B, Vrot, and scalelength, to be very similar for the two samples. However, using the Tully-Fisher relation (TFR) we find that cluster galaxies are systematically offset with respect to the field sample by -0.7+-0.2 mag. This offset is significant at 3 sigma and persists when we account for an evolution of the field TFR with redshift. Extensive tests are performed to investigate potential differences between the measured emission lines and derived rotation curves of the cluster and field samples. However, no such differences which could affect the derived Vrot values and account for the offset are found. The most likely explanation for the TFR offset is that giant spiral galaxies in distant clusters are on average brighter, for a given rotation velocity, than those in the field. We discuss the potential mechanisms responsible for this, and consider alternative explanations.Comment: 19 pages, 13 figures, accepted by MNRA

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