Library

Notes: The loss of acrolein by volatilization and degradation from a large tank of water is described. The standard analytical method for carbonyl compounds, a colorimetric reaction with dinitrophenylhydrazine did not distinguish acrolein from a relatively non-volatile and non-toxic reaction product. In a modification of the method to correct the error, acrolein was separated from reaction products by scrubbing with air. Although acrolein is sufficiently volatile to use air-scrubbing to separate it from reaction products, its loss by evaporation from an open tank was much less than its loss by reaction in the local irrigation water. In other waters differences in chemical properties could affect the loss of acrolein by reaction, and greater turbulence is expected to increase loss by volatilization.Perte d'acroléine à partir de l'eau par volatilisation et dégradation.Les auteurs décrivent la perte d'acroléine par volatilisation et degradation k partir d'un grand reservoir d'eau. La methode analytique standard pour les composes carbonyl. une reaction colorimétrique avec la dinitrophenylhydrazine. n'a pas permis de distinguer l'acroléine d'autres produits relativement non volatils et non toxiques, apparaissant au cours de la reaction. Dans une modification de la méthode en vue de corriger l'erreur. l'acroléinc a été séparée des autres products de la reaction au moyen d'un entrainement par fair. Bien que l'acroléne soit suffisamment volatile pour que Ton puisse utiliser l'air pour la séparer des autres produits de la reaction, la perte par évaporation à partir d'un réservoir ouvert s'est avérée beaucoup moindre que la perte par reaction dans l'eau d'irrigation apportée localement. Dans d'autres CAS, des differences dans les proprióteschimiques peuvent affecter la perte d'acroléine au cours de la reaction de la faut s'attendre à un accroissement de la perte par volatilisation dans le cas d'une turbulence plus grande.Verlust von Acrolein durch Verfükhtigung und Abbau in WasserEs wird der Verlust an Acrotein aus einem grossen Wassertank durch Verdampfung und Abbau beschrieben. Die analytische Standardmethode für Carbonylverbindungen mit Dinitrophenylhydrazin, lässt keine Unterscheidung zwischen Acrolein und einem verhältnismässig wenig flüchtigen und un-giftigen Reaktionsprodukt zu. Um die Fehlermöglichkeit Zu eliminieren. wurde die Methode abgeándert, indem das Acrolein von den Reaktionsprodukten durch “Auswaschen” mit Luft abgetrennt wurde, Obgleich die Flüchugkeit von Acrolein genúgend gross ist. um es durch “Auswaschen” mit Luft von Umsetzungsprodukten abzutrennen. ist der durch seine Verdampfung aus einem offenen Tank verursachte Verlusl viel geringer als der durch Umsetzung im lokalw Beregnun-swasser bedingte. In anderen Wassern könnten Unterschiede in den chemischen Eigenschaften den Verlust von Acrolein durch Umsetzung beeinflussen und es ist zu erwarten. dass grössere Turbulenz die Abnahmc durch Verflüchligung erhöht.

Notes: Fluorescence characteristics and growth of seedling snow gum (Eucalyptus pauciflora Sieb. ex Spreng.) during autumn and winter were related to variation in radiation and temperature regime in a fragmented forest. Seedlings were planted in four treatments along transects perpendicular to tree island edges to characterize plant responses to microclimates ranging from those of cleared areas to those beneath forest canopies. Three-dimensional mapping of seedling leaf display, in combination with information retrieved from hemispherical photographs about shading from overstory canopies, were used to calculate the intercepted amounts of direct radiation energy for unit area of leaves on clear days (IDRE). IDRE was highest on the outside, most variable at the edges and lowest well inside the tree islands. Minimum temperature decreased with increasing view of the sky. Photoinhibition, measured as decrease in Fv/Fm, was correlated with spatial and seasonal differences in weekly minimum temperature and IDRE. Seedlings in the open and under the most canopy cover, with low variability in IDRE in a scale of weeks, exhibited less variability in photoinhibition than those growing along forest edges. Seedlings in the open tended to be most photoinhibited and grew the most. The combination of increased IDRE with reduced minimum temperatures resulted in persistent and strong photoinhibition as the season progressed. Results are discussed in relation to the potential for seedling establishment following forest fragmentation.

Notes: Abstract Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO2 concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO2, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO2. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= ρ cw for CO2, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux ρ′ c w′. Thus, when the net flux of CO2 is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., ρ′ c w′ = −ρ c w. Corrections for the mean convective flux are particularly significant for CO2 because ρ cw and ρ′ c w′ are often of similar magnitude. The correct measurement of the net CO2 flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.

Notes: Abstract Similarity of transport of water vapour and sensible heat was investigated within an advective inversion layer by measuring eddy fluxes together with gradients of temperature and humidity. The experimental site was a field of rice, grown under flood irrigation, which was situated in a semi-arid region. The fetch was about 300 m and local stabilities (z/L) over the rice ranged from 0 to 0.1. Results were expressed as the ratio of eddy transfer coefficients for sensible heat (K H) and water vapour (K w). Near neutral stability, K H/KW approached 1, but the ratio decreased to about 0.65 with increasing stability. Existing theory predicts the result qualitatively but accounts for only about one fifth of the decrease in K H/KW with stability.

Notes: Abstract Terms in the heat and vapour flux equations, appropriate to the atmospheric surface layer with horizontal heterogeneity in one direction, have been evaluated empirically. The experimental site was a flooded rice field, which was bounded to windward by a semi-arid region. Local conditions over the rice were always stable, but the vertical fluxes of heat and water vapour were large. All terms in the flux equations were either measured directly, or, if sufficiently small, estimated, except the term containing fluctuating pressure, which was obtained by difference. The relative magnitudes of the major terms (production and pressure covariance) were similar to those reported previously for horizontally homogeneous flow with similar stabilities. Current parameterizations of the pressure covariance terms sometimes gave values which differed by factors of five or ten from the experimental results, and the interrelationships depended upon the stability.

Notes: Abstract An anemometer based upon measurement of the tangential windspeed around a sphere with hot-film probes is described. The anemometer determined the windspeed with a root-mean-square (rms) error of 5%, and the direction with an rms error of 5.6 °. A comparison between omnidirectional and sonic anemometers in the field gave practically identical results for the vertical sensible heat flux using eddy correlation procedures. Other turbulence statistics are also reported. The new instrument should be useful for measurements in canopies, where turbulence intensities are often large.