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.     

Water quality impacts from mining in the Black Hills,South Dakota,USA

The focus of this research was to determine if abandoned mines constitute a major environmental hazard in the Black Hills. Many abandoned gold mines in the Black Hills contribute acid and heavy metals to streams. In some areas of sulfide mineralization local impacts are severe, but in most areas the impacts are small because most ore deposits consist of small quartz veins with few sulfides. Pegmatite mines appear to have negligible effects on water due to the insoluble nature of pegmatite minerals. Uranium mines in the southern Black Hills contribute some radioactivity to surface water, but the impact is limited because of the dry climate and lack of runoff in that area.     

Evaluating igneous sources of the Taveyannaz formation in the Central Alps by detrital zircon U–Pb age dating and geochemistry

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.     

伊利石结晶度Kübler，Weaver和Weber指数关系式常数的确定与应用

根据衍射峰具有的不同分布特点推导出了14个伊利石结晶度Kübler指数，Weaver指数和Weber指数关系式中常数项C1-C14的数值，提出了PearsonⅦ分布中形态参数μ与C5，C6，C11，C12的4个定量方程。由此，14个伊利石结晶度指数关系式可直接用于实际计算。根据阿尔卑斯复理石伊利石形态特征Sc=0.731，由这些关系式进行近变质带上下界线的转换得出与Kübler指数0.42～0.25。△2θ界线对应的Weaver指数和Weber指数的界线值分别为5.8～17.6和300～179。讨论了在自然干燥状态下直接进行伊蒙混层鉴定的基本原理。     

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...