Light Requirements for Growth and Survival of Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) in Pacific Northwest (USA) Estuaries

We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon flux density (PPFD) of about 350–550 μmol quanta m⁻² s⁻¹. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term survival required at least 3 mol quanta m⁻² day⁻¹ on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m⁻² day⁻¹. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta m⁻² day⁻¹ during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m⁻² day⁻¹.     

Validation of a fish farm waste resuspension model by use of a particulate tracer discharged from a point source in a coastal environment

To validate a resuspension model of particulate material (salmonid farm wastes), a UV fluorescent particle tracer was selected with similar settling characteristics. Tracer was introduced to the seabed (water depth ≈30 m) and sediment samples taken on days 0, 3, 10, 17 and 30 to measure the horizontal and vertical distribution of tracer in sediments. A concentric sampling grid was established at radii of 25, 50, 100, 150, 200, 400, 700 and 1, 000 m from the source on transects 30° apart. The bulk of the deployed tracer was initially concentrated in an area 25 m radius from the release point; tracer was observed to steadily decrease to zero over a period of 30 days. In a 200 m region measured from the release point in the direction of the residual current, the redeposition of tracer was low. A Lagrangian particle tracking model was validated using these observed data by varying resuspension model parameters within limits to obtain the best agreement between spatial and temporal distributions. The validated model generally gave good predictions of total mass budgets (±7% of total tracer released), particulary where tracer concentrations were high near the release point. Best fit model parameters (critical erosion shear stress=0.018 N m⁻², erodibility constan=60 g m⁻² d⁻¹) are at the low end of reported parameters for coastal resuspension models. Such a low critical erosion shear stress indicates that the frequency of resuspension and deposition events for freshly deposited material is high.     

D/H ratios of atmospheric H2 in urban air: results using new methods for analysis of nano-molar H2 samples

We present the results of a study of the concentration and D/H ratio of molecular hydrogen from air in the Los Angeles Basin and adjacent San Gabriel Mountains. These data define a mixing relationship in dimensions of D/H ratio vs. 1/(H₂) which constrains the δD_VSMOW of unpolluted winter air in this region to be ca. +100 to +125 ‰ and that of urban H₂ sources to be ca. −270 ‰. This study makes use of a new method for measuring the deuterium content of molecular hydrogen in small samples (∼100 to 500 cc) of air, which we describe in detail. The method consists of an off-line separation of H₂ followed by introduction to the mass spectrometer in a continuous flow of He. Off-line, all components of an atmospheric gas sample, with the exception of He, H₂, and Ne are condensed by exposure to a cold-trap held at 30 Kelvin. This separation is followed by cryo-transfer of non-condensable gases to a small volume molecular sieve finger, with assist from a mercury piston pump. At the mass spectrometer, the sample is put in line with a continuous flow of He where it is focused on to an additional column of molecular sieve before subsequent introduction into the ion source. Analyses of DH/H₂ ratio have accuracy and precision of ±4 to 7 per mil. Comparison of sample peak area to peak areas of standards of known size allows for determination of H₂ concentration with accuracy and precision of ∼±5%, relative. The method reduces sample size and processing time by several orders of magnitude compared to previous methods, allowing for sampling at proportionately higher spatial and temporal resolution.     

Mechanical Behavior of Microbially Induced Calcite Precipitation Cemented Sand

Geotechnical and Geological Engineering - New sustainable ground improvement techniques have been recently required for applications in onshore and offshore geotechnical structures. The...     

A case study of using Raman lidar measurements in high-accuracy GPS applications

This paper investigates the impact of rapid small-scale water vapor fluctuations on GPS height determination. Water vapor measurements from a Raman lidar are used for documenting the water vapor heterogeneities and correcting GPS signal propagation delays in clear sky conditions. We use data from four short observing sessions (6 h) during the VAPIC experiment (15 May–15 June 2004). The retrieval of wet delays from our Raman lidar is shown to agree well with radiosonde retrievals (bias and standard deviation (SD) were smaller than 1 and 2.8 mm, respectively) and microwave radiometers (from two different instruments, bias was 6.0/−6.6 mm and SD 1.3/3.8 mm). A standard GPS data analysis is shown to fail in accurately reproducing fast zenith wet delay (ZWD) variations. The ZWD estimates could be improved when mean post-fit phase residuals were removed. Several methodologies for integrating zenith lidar observations into the GPS data processing are also presented. The final method consists in using lidar wet delays for correcting a priori the GPS phase observations and estimating a scale factor for the lidar wet delays jointly with the GPS station position. The estimation of this scale factor allows correcting for a mis-calibration in the lidar data and provides in the same way an estimate of the Raman lidar instrument constant. The agreement of this constant with an independent determination using radiosonde data is at the level of 1–4%. The lidar wet delays were derived by ray-tracing from zenith pointing measurements: further improvement in GPS positioning is expected from slant path lidar measurements that would properly account for water vapor anisotropy.     

Connecting Local to Global: Geographic Information Systems and Ecological Footprints as Tools for Sustainability

Tools that support public engagement with sustainability are essential for local sustainability planning. This research investigates the ability of two geographic information system (GIS)-based tools to promote discussion of sustainability in a suburban context. A local ecological footprint tool and a community environmental atlas (an environmentally themed online mapping system) were created for seven suburban boroughs of Montreal. Variations of both tools have been used to support sustainability efforts, but their use has not been widely evaluated. Working from a public participation GIS (PPGIS) framework that recognizes the powerful influence of data representation, this research uses focus groups to evaluate how well these tools address three criteria that have emerged from the literature on public engagement in sustainability: interdependency across systems, reflexivity about personal and social decision making, and interactions across spatial scales. Whereas the atlas remains advantageous for discussing local spatial specifics, it was found that the ecological footprint helped people see the interconnections among systems, integrate local and global aspects of sustainability, and reflect on the values and assumptions underlying current social and economic structures.     

Carrying capacity of the eastern ecological gradient of Kenya

Kenya's rate of natural population increase exceeds 4.0%/year. At this rate, Kenya's population of 23.5 million will expand to 35 million by the year 2000. Rural migrants are being forced out of the highlands into marginal arid and semiarid regions to the east and south in the eastern ecological gradient including Meru, Kitui, Machakos, and Kajiado districts. The people have become victims of marginalization by which the productivity of a unit of land declines relative to the demands of its occupants. The concept of carrying capacity means the number of people a given area can sustain over the long term. In Maasailand, 3.5 standard stock units (450 kg each) are required per adult equivalent for full subsistence, about 7 cows/person. For the Maasai pastoralists, carrying capacities were examined at 2 levels of subsistence: 100% from the herds and 80% from the herds; 2 technological levels; and population-growth rates of 2%, 2.5%, and 3%/annum. Using the median, 3.5%/year, population-growth scenario these districts will have almost 5 million inhabitants in the year 2000. Poverty at technology level I for 40% of them, or for 2 million people, is implausible. Technology level II implies that current rural-development programs will succeed with technological innovations for farm households, access to credit, and markets for their produce. Level II is likely to prevail toward the end of the century for the majority of farmers. Level III necessitates best agricultural and livestock technology as well as the best management. At most, 25% of the households of the eastern ecological gradient could enter this realm by the year 2000. Current strategies of voluntary family planning, rural development emerging from an antiquated extension system, inability to address inequity in land distribution, and laissez-faire resource management are inadequate to deal with the pace of change.     

The frequency of hail occurrence

Summary Hail occurrence, being a comparatively rare event, is fit well by the Poisson distribution providing the hail storms are independent. When this condition is not met, hail occurrence follows the negative binomial distribution. A test is given which determines whether the Poisson distribution may be used, or whether the negative binomial is necessary. The parameter of the Poisson distribution is always estimated efficiently by the method of moments. The parameters of the negative binomial distribution, however, are only efficiently estimated by the method of moments under certain conditions; when the method of moments fails, the method of maximum likelihood must be employed. A criterion to determine when this method must be used is given together with the method of obtaining the estimates. The methods presented are illustrated by application to several hail records.

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Zusammenfassung Unter der Voraussetzung, daß die Hagelfälle voneinander unabhängig sind, kann das Auftreten dieses verhältnismäßig seltenen Ereignisses gut durch eine Poissonsche Verteilung dargestellt werden; ist dies nicht der Fall, dann folgt es einer negativ binomischen Verteilung. Es wird eine Testmethode mitgeteilt, nach welcher man entscheiden kann, ob die Poissonsche oder die negativ binomische Verteilung zu verwenden ist. Die Parameter der Poissonschen Verteilung können mit der Methode der Momente immer zuverlässig bestimmt werden. Die Parameter der negativ binomischen Verteilung jedoch können mit dieser Methode nur unter bestimmten Umständen ermittelt werden. Falls die Methode der Momente versagt, ist die Methode der größten Wahrscheinlichkeit anzuwenden. Ein Kriterium zur Entscheidung, wann diese Methode angewendet werden muß, sowie eine Methode zur Ermittlung genäherter Werte werden mitgeteilt. Die beschriebenen statistischen Methoden werden durch Anwendung auf einige Hagelbeobachtungsreihen erläutert.

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Résumé En admettant que les chutes de grêle sont indépendantes les unes des autres, on peut convenablement représenter leur apparition par une distribution de fréquences de Poisson. Si cen'est pas le cas, ces chutes obéissent à une distribution binomiale négative. L'auteur propose un test permettant de décider s'il convient d'appliquer la première ou la seconde distribution. On peut toujours déterminer les paramètres de la distribution de Poisson par la méthode des moments; pour la distribution binomiale négative ce n'est possible que sous certaines conditions. Si la méthode des moments échoue, on aura recours à celle de la plus grande probabilité. L'auteur discute un critère pour l'emploi de cette dernière ainsi qu'une méthode pour obtenir des valeurs approchées. Les méthodes statistiques décrites sont illustrées par des applications à quelques séries d'observations de la grèle.

     

Climatological analysis of snowfall thresholds

The climatological analysis for the first occurrence of 24-hour snowfalls of various depths is developed. This gives the probability function of snowfall thresholds which in turn makes any quantiles or probability values readily available. The probability function together with a special convention on years with no threshold value leads also to a definition of mean or expected threshold date. Examples of applications to several thresholds for New England data are presented.

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Zusammenfassung Es wird eine klimatologische Analyse für das erste Auftreten von 24stündigen Schneefällen verschiedener Schneehöhe entwickelt. Dies führt zu der Wahrscheinlichkeitsfunktion von Schneefall-Schwellenwerten, woraus sich beliebige Teilquantile oder Wahrscheinlichkeitswerte gewinnen lassen. Die Wahrscheinlichkeitsfunktion zusammen mit einer Annahme über die Jahre ohne Erreichen des Schwellenwerts führt auch zu einer Definition des mittleren oder zu erwartenden Schwellenwertdatums. Schließlich werden Anwendungsbeispiele für bestimmte Schwellenwerte an Hand von Daten aus Neu-England gegeben.

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Résumé L'auteur développe une analyse climatologique de la première apparition de chutes de neige dans l'intervalle de 24 heures d'épaisseur différente. Celle-ci conduit à la fonction de probabilité des valeurs limites des chutes de neige à partir de laquelle on peut calculer à volonté de quantiles et de valeurs de probabilité. En admettant une convention spéciale concernant les années qui n'atteignent pas de valeurs limites, la fonction de probabilité perment aussi de déterminer la date limite moyenne ou probable. Pour terminer, l'auteur donne quelques exemples d'application pour certaines valeurs limites à partir de données de la Nouvelle Angleterre.

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With 3 Figures

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Presented at the meeting of the Northeast Snow Conference Burlington, Vermont, February 10, 1955.