Évaluation de l'applicabilité d'une méthode statistique aux variations saisonnières des relations concentration-débit sur un petit cours d'eau

Les paramètres chimiques jouent un rôle important dans l'équilibre des écosystèmes aquatiques. De nombreuses études ont déjà démontré que les caractéristiques chimiques d'un cours d'eau peuvent changer avec les saisons. Cette étude a pour but de revoir les relations débit- concentration sur un petit cours d'eau, dans le contexte des variations entre deux périodes climatiques. Pour ce faire, une analyse de régression entre le débit et six paramètres de qualité de d'eau (sodium, magnésium, conductivité, pH, azote total et le carbone organique dissous) provenant d'un petit bassin versant forestier (ruisseau Catamaran, N.-B., Canada) a été réalisée afin de déterminer la différence entre la saison sans glace et la saison avec glace. Des échantillons mensuels d'eau ont été récoltés sur le ruisseau Catamaran depuis 1990. Les analyses chimiques faites sur ses échantillons ont permis de déterminer les concentrations des paramètre étudiés. La plupart des variables de qualité ont démontré une relation significative avec le débit, sauf l'azote total. Les coefficients de détermination variaient entre 0.752 et 0.898, exception faite du carbone organique dissous dont le r2 était de 0.294. La conductivité était le paramètre dont le débit expliquait le plus la variance. Une étude des rapports des sommes des carrés des résidus a permis de déterminer que seul le pH requiert un modèle différent pour la période sans glace et la saison avec glace. Les variations saisonnières de la relation débit-pH revêt une importance significative pour les ruisseaux comme celui de Catamaran, qui incluent de nombreux habitats pour le saumon de l'Atlantique. Les résultats des analyses de régressions indiquent que lorsque la géochimie est plus complexe, comme c'est le cas pour le pH, il faut diviser les séries temporelles en sous-composantes saisonnières avant de tenter d'établir une relation débit-concentration.The chemical composition of water is of great importance to ecosystem functioning and in habitat management. Many studies have already shown that the chemical characteristics of a stream change with seasons. These variations have a strong impact on the ecosystem, especially on fish populations. The objective of this study is to quantify the relationship between the logarithm of discharge and six water quality parameters (sodium, magnesium, conductivity, pH, dissolved organic carbon and total nitrogen) for a small forested catchment (Catamaran Brook, N.B., Canada) and to verify the importance of seasonality. Monthly water samples have been gathered at Catamaran Brook since 1990. Detailed water chemistry performed on these samples provided a data base for this project. Various linear regression models were tested to verify if regressions were required for the winter season. The criterion used was the ratio of the squared sum of residuals for each data set, which follows a Fisher distribution. Of the six water quality parameters, all except total nitrogen showed a significant relationship with discharge. On an annual basis, the coefficient of determination (r2) varied between 0.752 and 0.898, except for dissolved organic carbon which showed a r2 of 0.294. Of the studied parameters, conductivity was the parameter for which discharge explained the most variance. Ratios of the squared sum of residuals were analyzed to verify the need for different regression models for the ice-covered and ice-free seasons. Only streamwater pH required 2 different models. This is of specific importance and interest because of an important salmon population in Catamaran Brook. Other researchers have shown that salmonids can be negatively impacted by pH depressions during snowmelt events.These results show that most dissolved ions which follow simple geochemical reactions can be modelled year-round with only one linear regression. When the geochemistry is more complex, such as in the case of pH, linear regression models can sometimes be used, provided that the annual time-series is divided into seasons with relatively homogenous hydrological and geochemical functions

Spatial trends of breast and prostate cancers in the United States between 2000 and 2005

<p>Abstract</p> <p>Background</p> <p>Breast cancer in females and prostate cancer in males are two of the most common cancers in the United States, and the literature suggests that they share similar features. However, it is unknown whether the occurrence of these two cancers at the county level in the United States is correlated. We analyzed Caucasian age-adjusted county level average annual incidence rates for breast and prostate cancers from the National Cancer Institute and State Cancer Registries to determine whether there was a spatial correlation between the two conditions and whether the two cancers had similar spatial patterns.</p> <p>Results</p> <p>There was a significant correlation between breast and prostate cancers by county (r = 0.332, p < 0.001). This relationship was more pronounced when we performed a geographically-weighted regression (GWR) analysis (r = 0.552) adjusting for county unemployment rates. There was variation in the parameter estimates derived with the GWR; however, the majority of the estimates indicted a positive association. The strongest relationship between breast and prostate cancer was in the eastern parts of the Midwest and South, and the Southeastern U.S. We also observed a north-south pattern for both cancers with our cluster analyses. Clusters of counties with high cancer incidence rates were more frequently found in the North and clusters of counties with low incidence rates were predominantly in the South.</p> <p>Conclusion</p> <p>Our analyses suggest breast and prostate cancers cluster spatially. This finding corroborates other studies that have found these two cancers share similar risk factors. The north-south distribution observed for both cancers warrants further research to determine what is driving this spatial pattern.</p

The Review of Economic Performance and Social Progress 2002: Towards a Social Understanding of Productivity

In this chapter, Richard Harris points out that a traditional view has been that there is an inherent conflict between economic efficiency and social equality, a view neatly summarized in the title of Okun's famous book, Equality and Efficiency: The Big Trade-off (1975). This view gained renewed currency in the policy debates of the 1990s, as commentators contrasted the economic performance of Europe and the U.S. in that decade. This view has been challenged both by cross-national empirical studies and by theoretical advances. Recent research seems to suggest that there is no efficiency-equity trade-off and that social policy and greater equality may actually contribute to higher productivity growth. Richard Harris surveys two streams of recent research that point in this direction. The chapter also examines new theoretical literature, especially the new endogenous growth theory that suggests that increases in inequality can hurt growth.Equity, Efficiency, Productivity, Labour Productivity, Labor Productivity, Growth, Income, Inequality, Equality, Social Policy, Education, Health, Welfare, Redistribution, Social Cohesion, Cohesion, Investment, Innovation, Competition, Living Standards

A record of the Surinam cockroach in Vancouver

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Holding solution pH and composition consistently improve vase life of rose, lily and gerbera

We assessed the influence of postharvest pulsing solutions pH and composition on cut flower quality of rose (Rosa hybrida cvs. Avalanche and Black Magic), gerbera (Gerbera jamesonii cv. Beaudine) and lily (Lilium × elegans cv. Fangio) under room (20±2 °C) and cold storage (4±1 °C) conditions. Cut flowers were placed in different acidic (pH, 3.5 - 4) or basic (pH, 7.0 - 7.5) preservative solutions containing water, sugar 5% (flower food), 100 mg/L silver nitrate (AgNO3 act as a bactericide), or a commercial product (2% sugar + bactericide and fungicide). Acidic solutions had higher or similar (never lower) vase life at both room and cold storage conditions and across species. In addition, vase life was 3-4 times longer in cold storage when compared to room conditions. Leaf chlorophyll concentrations for rose and lily were inconsistent or not significant across the species at both conditions (room and cold storage). The commercial preservative solution consistently and significantly had higher vase life than water for all tested cut flower species and under both room and cold storage environments. AgNO3 ranked second in terms of vase life enhancement. Overall, the use of only flower food (sugar) or bactericide (AgNO3) had a positive impact on vase life but only the combined use of a preservative substance (specifically at pH, 3.5 - 4.0) consistently guaranteed a high cut flower quality across flower species

Tool for predicting Caligus rogercresseyi abundance on salt water salmon farms in Chile

Caligus rogercresseyi is a host-dependent parasite that affects rainbow trout and Atlantic salmon in Chile. Numbers of sea lice on fish increase over time at relatively predictable rates when the environment is conducive to the parasite's survival and fish are not undergoing treatment. We developed a tool for the salmon industry in Chile that predicts the abundance of adult sea lice over time on farms that are relatively isolated. We used data on sea louse abundance collected through the SalmonChile INTESAL sea lice monitoring program to create series of weekly lice counts between lice treatment events on isolated farms. We defined isolated farms as those with no known neighbors within a 10 km seaway distance and no more than two neighbors within a 20 km seaway distance. We defined the time between sea lice treatments as starting the week immediately post treatment and ending the week before a subsequent treatment. Our final dataset of isolated farms consisted of 65 series from 32 farms, between 2009 and 2015. Given an observed abundance at time t = 0, we built a model that predicted 8 consecutive weekly sea louse abundance levels, based on the preceding week's lice prediction. We calibrated the parameters in our model on a randomly selected subset of training data, choosing the parameter combinations that minimized the absolute difference between the predicted and observed sea louse abundance values. We validated the parameters on the remaining, unseen, subset of data. We encoded our model and made it available as a Web-accessible applet for producers. We determined a threshold, based on the upper 97.5% predictive interval, as a guideline for producers using the tool. We hypothesize that if farms exceed this threshold, especially if the sea lice levels are above this threshold 2 and 4 weeks into the model predictions, the sea louse population on the farm is likely influenced by sources other than lice within the farm

Establishment and dynamics of the balsam fir seedling bank in old forests of northeastern Quebec

This study examines balsam fir (Abies balsamea (L.) Mill.) recruitment in old fir stands. Studying the regeneration of these stands is essential to understand the regeneration dynamic of the species in the absence of standdestroying disturbances. The objectives were (1) to obtain substrate-seedling associations for different age-classes and according to the presence or absence of adventitious roots; (2) to evaluate the contribution of the seed rain to seedling recruitment; (3) to re-examine age structures using the most appropriate method that minimizes estimation errors due to the presence of adventitious roots. A total of 90 quadrats (1 m2) were established along transects. In each quadrat, subtrates were characterized (type and topography) and their area was estimated. All balsam fir seedlings (<50 cm tall) present in the quadrats were located, harvested whole (root and shoot), and described (age, height, presence of adventitious roots, etc). Fir seedlings were strongly associated with woody mounds covered with thin mats of mixed mosses and Pleurozium shreberi (Bird.) Mitt. but negatively associated with flat topography particularly dominated by Hylocomium splendens (Hedw.) B.S.G. The presence of adventitious root is related to seedling age more than substrate type or topography. The age structure is in agreement with seed production and disturbance regime

Characterization of an Ionization Readout Tile for nEXO

A new design for the anode of a time projection chamber, consisting of a charge-detecting "tile", is investigated for use in large scale liquid xenon detectors. The tile is produced by depositing 60 orthogonal metal charge-collecting strips, 3~mm wide, on a 10~\si{\cm} $\times$ 10~\si{\cm} fused-silica wafer. These charge tiles may be employed by large detectors, such as the proposed tonne-scale nEXO experiment to search for neutrinoless double-beta decay. Modular by design, an array of tiles can cover a sizable area. The width of each strip is small compared to the size of the tile, so a Frisch grid is not required. A grid-less, tiled anode design is beneficial for an experiment such as nEXO, where a wire tensioning support structure and Frisch grid might contribute radioactive backgrounds and would have to be designed to accommodate cycling to cryogenic temperatures. The segmented anode also reduces some degeneracies in signal reconstruction that arise in large-area crossed-wire time projection chambers. A prototype tile was tested in a cell containing liquid xenon. Very good agreement is achieved between the measured ionization spectrum of a $^{207}$Bi source and simulations that include the microphysics of recombination in xenon and a detailed modeling of the electrostatic field of the detector. An energy resolution $\sigma/E$=5.5\% is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only resolution reported in literature for liquid xenon at 936~V/\si{cm}.Comment: 18 pages, 13 figures, as publishe