Nutrient Mass Flux between Florida Bay and the Florida Keys National Marine Sanctuary

There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year^?1 and 63 (±7) ton P year^?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.     

Automated Kerogen Classification in Microscope Images of Dispersed Kerogen Preparation

We develop the classification part of a system that analyses transmitted light microscope images of dispersed kerogen preparation. The system automatically extracts kerogen pieces from the image and labels each piece as either inertinite or vitrinite. The image pre-processing analysis consists of background removal, identification of kerogen material, object segmentation, object extraction (individual images of pieces of kerogen) and feature calculation for each object. An expert palynologist was asked to label the objects into categories inertinite and vitrinite, which provided the ground truth for the classification experiment. Ten state-of-the-art classifiers and classifier ensembles were compared: Naïve Bayes, decision tree, nearest neighbour, the logistic classifier, multilayered perceptron (MLP), support vector machines (SVM), AdaBoost, Bagging, LogitBoost and Random Forest. The logistic classifier was singled out as the most accurate classifier, with an accuracy greater than 90. Using a 10 times 10-fold cross-validation provided within the Weka software, we found that the logistic classifier was significantly better than five classifiers (p<0.05) and indistinguishable from the other four classifiers. The initial set of 32 features was subsequently reduced to 6 features without compromising the classification accuracy. A further evaluation of the system alerted us to the possible sensitivity of the classification to the ground truth that might vary from one human expert to another. The analysis also revealed that the logistic classifier made most of the correct classifications with a high certainty.     

Influence of initial plastic anisotropy of overconsolidated clays on ground behaviour during tunneling

In order to evaluate the influence of the initial plastic anisotropy in the excavation of a tunnel, a “bubble” bounding surface model for structured soils, formulated by Kavvadas and Belokas (Proc. 10th IACMAG Conf., 2001), was implemented in the explicit finite difference code FLAC. Two different initial stress (K ₀) conditions were considered. The size and shape of the initial bounding surfaces were specified to be consistent with the initial stress field. The distorted and rotated shape of the bounding surface, supported by experimental results, defines the anisotropy of shear strength, which is shown to have a significant influence on the displacements. There is also considerable sensitivity of the soil model to the initial stress field.     

Permeability development in vesiculating magmas: implications for fragmentation

 Fragmentation, or the "coming apart" of magma during a plinian eruption, remains one of the least understood processes in volcanology, although assumptions about the timing and mechanisms of fragmentation are key parameters in all existing eruption models. Despite evidence to the contrary, most models assume that fragmentation occurs at a critical vesicularity (volume percent vesicles) of 75–83%. We propose instead that the degree to which magma is fragmented is determined by factors controlling bubble coalescence: magma viscosity, temperature, bubble size distribution, bubble shapes, and time. Bubble coalescence in vesiculating magmas creates permeability which serves to connect the dispersed gas phase. When sufficiently developed, permeability allows subsequent exsolved and expanded gas to escape, thus preserving a sufficiently interconnected region of vesicular magma as a pumice clast, rather than fully fragmenting it to ash. For this reason pumice is likely to preserve information about (a) how permeability develops and (b) the critical permeability needed to insure clast preservation. We present measurements and calculations that constrain the conditions (vesicularity, bubble size distribution, time, pressure difference, viscosity) necessary for adequate permeability to develop. We suggest that magma fragments explosively to ash when and where, in a heterogeneously vesiculating magma, these conditions are not met. Both the development of permeability by bubble wall thinning and rupture and the loss of gas through a permeable network of bubbles require time, consistent with the observation that degree of fragmentation (i.e., amount of ash) increases with increasing eruption rate. Received: 5 July 1995 / Accepted: 27 December 1995     

Testing for quantized redshifts. I. The project

A project intended to examine the long-standing claims that extragalactic redshifts are periodic or quantized was initiated some years ago at the Royal Observatory, Edinburgh. The approach taken is outlined, and the main conclusions to date are summarized. The existence of a galactocentric redshift quantization is confirmed at a high confidence level.     

Gravitational mass of magnetostatic field

Maxwell's displacement current equation is interpreted in the light of recent work to show that static magnetic field in free space should have a colocated and contemporaneous mass that is neither embodied in, nor can be anticipated from, the mass-energy relation. Thus magnetostatic field in the universe represents an invisible mass. Some consequences are discussed.     

Evidence for Multiple Mechanisms of Crustal Contamination of Magma from Compositionally Zoned Plutons and Associated Ultramafic Intrusions of the Alaska Range

Models of continental crustal magmagenesis commonly invoke theinteraction of mafic mantle-derived magma and continental crustto explain geochemical and petrologic characteristics of crustalvolcanic and plutonic rocks. This interaction and the specificmechanisms of crustal contamination associated with it are poorlyunderstood. An excellent opportunity to study the progressiveeffects of crustal contamination is offered by the compositeplutons of the Alaska Range, a series of nine early Tertiary,multiply intruded, compositionally zoned (Peridotite to granite)plutons. Large initial Sr and Nd isotopic contrasts betweenthe crustal country rock and likely parental magmas allow evaluationof the mechanisms and extents of crustal contamination thataccompanied the crystallization of these ultra-mafic throughgranitic rocks. Three contamination processes are distinguishedin these plutons. The most obvious of these is assimilationof crustal country rock concurrent with magmatic fractionalcrystallization (AFC), as indicated by a general trend towardcrustal-like isotopic signatures with increasing differentiation.Second, many ultramafic and mafic rocks have late-stage phenocrystreaction and orthocumulate textures that suggest interactionwith felsic melt. These rocks also have variable and enrichedisotopic compositions that suggest that this felsic melt wasisotopically enriched and probably derived from crustal countryrock. Partial melt from the flysch country rock may have reactedwith and contaminated these partly crystalline magmas followingthe precipitation and accumulation of the cumulus phenocrystsbut before complete solidification of the magma. This suggeststhat in magmatic mush (especially of ultramafic composition)crystallizing in continental crust, a second distinct processof crustal contamination may be super imposed on AFC or magmamixing involving the main magma body. Finally, nearly all rocks,including mafic and ultramafic rocks, have (⁸⁷Sr/⁸⁶Sr)_i thatare too high, and (T) _Nd that are too low, to represent theexpected isotopic composition of typical depleted mantle. However,gabbro xenoliths with typical depicted-mantle isotopic compositionsare found in the plutons. This situation requires either anadditional enriched mantle component to provide the parentalmagma for these plutons, or some mechanism of crustal contaminationof the parent magma that did not cause significant crystallizationand differentiation of the magma to more felsic compositions.Thermodynamic modeling indicates that assimilation of alkali-andwater-rich partial melt of the metapelite country rock by fractionating,near-liquidus basaltic magma could cause significant contaminationwhile suppressing significant crystallization and differentiation. KEY WORDS: crustal contamination; Alaska Range; isotope geochemistry; zoned plutons; assimilation ^*Corresponding author. e-mail: preiners{at}u.washington.edu; fax: (206) 543-3836.     

Impacts of growth in resource use and human population on the Nechako River: A major tributary of the Fraser River, British Columbia, Canada

Hydroelectric development, forest exploitation, agricultural land use and related human population numbers have increased rapidly during the last 40 years, in the basin of the Nechako River, a major tributary system of the Fraser River. The Kemano project of the Aluminum Company of Canada Ltd. begun in 1950, was the largest industrial scheme in the area. A key feature of the first stage of it was a dam which diverted about 40% of flow of the south branch of the Nechako River, through a tunnel in the mountains, to the Pacific Ocean. In 1987 an agreement for the Kemano Completion Project (KCP), which would have diverted 87% of the flow, was signed. This final phase of the project would have put important fisheries resources of the upper Fraser River at high risk. Mitigation for fisheries protection were inadequate or untested in the system at the time. Potential cumulative impacts of water abstraction, elevated pollution levels, increased water temperature and natural sediment were not addressed. In January 1995 KCP was cancelled but there remain at present no adequate measures to protect the fish and the river ecosystem. These measures are to be negotiated in the future. Future management of the whole Kemano development must provide biologically realistic flow and temperature regimes in the Nechako River, and must deal with cumulative impacts of population and industrial growth. To achieve sustainability of fisheries in the Nechako River and upper Fraser watershed the present approach to the Kemano development must be changed fundamentally. The future of the Kemano development must be set in the context of the whole future of the upper Fraser system. Continued growth and development, as has occurred in the upper Fraser and total basin, can not go on without inimical changes to ecosystem conditions and loss of fisheries resources.