The effect of the Jessica grounding on subtidal invertebrate and plant communities at the Galápagos wreck site     

Marshall PA  Edgar GJ 《Marine pollution bulletin》2003,47(7-8):284-295

Impacts of the grounding of the oil tanker Jessica off San Cristóbal island, Galápagos, included both effects of oil on biota and also mechanical effects associated with a shallow furrow 50 m x 30 m gouged across the rocky seafloor and wreckage strewn over 7500 m(2). The wreckage represented a minor but potentially chronic source of pollution to the surrounding environment through delayed releases of oil, antifouling compounds and other toxic chemicals, and a possible source of exotic marine taxa. Investigation at the wreck site indicated that impacts on subtidal plant and macro-invertebrate communities were largely confined within 100 m of the wreck site itself. Observed population effects included significant increases in cover of opportunistic algae (filamentous green algae, filamentous red algae and Ulva sp.) and the hydroid Ectopleura media adjacent to the wreck, while densities of the green sea urchin Lytechinus semituberculatus significantly decreased from 0.3 m(-2) adjacent to the wreck to 11 m(-2) at 100 m distance.  相似文献   

Effects of the Jessica oil spill on artisanal fisheries in the Galápagos     

Born AF  Espinoza E  Murillo JC  Nicolaides F  Edgar GJ 《Marine pollution bulletin》2003,47(7-8):319-324

In contrast to local perceptions, the impact on the local Galápagos artisanal fishery of the 16 January 2001 grounding of the Jessica and subsequent oil spill was relatively minor. No significant changes in fishing effort, total fishing catches or catch-per-unit effort were detected after the spill based on analyses of fisheries monitoring data. Nevertheless, large boats tended to move away from sites near the path of the spill following the grounding in 2001, with no fishing recorded from the oil-affected regions of Floreana and southern Isabela in February 2001. The total fishing effort of small boats operating from the Jessica-grounding island of San Cristóbal also declined immediately after the spill, probably in part because such boats were used in clean up operations. During 2001, prices paid to fishers remained stable at levels higher than in 2000, with the notable anomaly that prices fell precipitously to 30% of previous levels during a 1-2 week period in early February 2001. Fish exports remained at similar levels for the years 2000 and 2001; however, as in the previous year, little fish product was exported from Galápagos in the month following the spill, with most fish product dried and stored for up to two months prior to transport to the continent.  相似文献   

Setting seagrass depth, coverage, and light targets for the Indian River Lagoon system, Florida     

Joel S. Steward  Robert W. Virnstein  Lori J. Morris  Edgar F. Lowe 《Estuaries and Coasts》2005,28(6):923-935

Seagrass protection and restoration in Florida’s Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs. These programs require, the establishment of management targets indicative of seagrass recovery and health. We used three metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the IRLS’s spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments. Our method consisted of two steps: mapping the union of seagrass coverages from all availabe mapping years (1943, 1986, 1989, 1992, 1994, 1996, and 1999) to delineate wherever seagrass had been mapped and determining the distribution of depth limits based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively.Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using a 10-yr record of light data (1990–1999) and the union coverage depth limit distributions from the most temporally stable seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 ± 17% of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions, is 20 ± 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 ± 13%). Variation in depth limits and light requirements, is probably due to factors other than light that influence the depth limit of seagrasses (e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data sets and can be applied to other estuaries where grass beds are routinely monitored and mapped.  相似文献   

Partial melting of a phlogopite-clinopyroxenite nodule from south-west Uganda: an experimental study bearing on the origin of highly potassic continental rift volcanics   总被引：1，自引：0，他引：1  

F. E. Lloyd  M. Arima  A. D. Edgar 《Contributions to Mineralogy and Petrology》1985,91(4):321-329

Melting experiments on a mantle-derived nodule assemblage consisting of clinopyroxene, phlogopite and minor titanomagnetite, sphene and apatite have been done at 20 and 30 kbar between 1,175 and 1,300° C. The nodule composition was selected on the basis of modal and chemical analyses of 84 mantle derived nodules with metasomatic textures from the Katwe-Kikorongo and Bunyaruguru volcanic fields of south-west Uganda. At 30 kbar, 1,225 and 1,250° C, representing 20–30% partial melting, the compositions of glasses compare favourably to those of the average composition of 26 high potassic mafic lavas from the same region. Glasses produced by sufficiently low degrees of partial melting at 20 kbar could not be analysed. Glass compositions obtained for 20–30% melting at 30 kbar have high K₂O (3.07–5.05 wt.%), low SiO₂ (35.0–39.2 wt.%), high K/K + Na (0.54–0.71), K + Na/Al (0.99–1.08) and Mg/ Mg + Fe_T of 0.59–0.62. These results support the suggestion of Lloyd and Bailey (1975) that the nodules represent the source material for the high K-rich lavas of south-west Uganda. If this conclusion is correct it implies that anomalous mantle source of phlogopite clinopyroxenite composition could produced the Ugandan lavas by relatively higher degrees of partial melting than that normally considered for highly alkaline mafic magmas derived from a pyrolitic mantle source. Higher degrees of melting are considered likely from such a different source region, rich in alkalis, water and radioactive elements. Steeper geotherms and increased fluxing of sub-rift mantle by degassing would also produce higher degrees of partial melting.  相似文献   

The heat-capacity of ilmenite and phase equilibria in the system Fe-T-O     

Lawrence M. Anovitz  Allan H. Treiman  Eric J. Essene  Bruce S. Hemingway  Edgar F. Westrum  Victor J. Wall  Ramón Burriel  Steven R. Bohlen 《Geochimica et cosmochimica acta》1985,49(10):2027-2040

Low temperature adiabatic calorimetry and high temperature differential scanning calorimetry have been used to measure the heat-capacity of ilmenite (FeTiO₃) from 5 to 1000 K. These measurements yield S₂₉₈⁰ = 108.9 J/(mol · K). Calculations from published experimental data on the reduction of ilmenite yield Δ₂₉₈⁰(I1) = ?1153.9 kJ/(mol · K). These new data, combined with available experimental and thermodynamic data for other phases, have been used to calculate phase equilibria in the system Fe-Ti-O. Calculations for the subsystem Ti-O show that extremely low values of $\text{?O}{}_2$ are necessary to stabilize TiO, the mineral hongquiite reported from the Tao district in China. This mineral may not be TiO, and it should be re-examined for substitution of other elements such as N or C. Consideration of solid-solution models for phases in the system Fe-Ti-O allows derivation of a new thermometer/oxybarometer for assemblages of ferropseudobrookite-pseudobrookite_ss and hematite-ilmenite_ss. Preliminary application of this new thermometer/oxybarometer to lunar and terrestrial lavas gives reasonable estimates of oxygen fugacities, but generally yields subsolidus temperatures, suggesting re-equilibration of one or more phases during cooling.  相似文献   

Comprehensive chemical analyses of natural cordierites: implications for exchange mechanisms     

Christian Bertoldi  Alexander Proyer  Dieter Garbe-Schnberg  Harald Behrens  Edgar Dachs 《Lithos》2004,78(4):389-409

Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H₂O and CO₂ (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg₋₁ and MnMg₋₁ on the octahedral site, some minor KNa₋₁ on the Ch0 channel site, and Fe³⁺Al₋₁ on the T₁1 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□₋₁Mg₋₁), and of Be and other divalent cations on the tetrahedral T₁1 site (NaBe□₋₁Al₋₁ and Na(Mg,Fe²⁺)□₋₁Al₋₁). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: ^Ch(Na,K)_0–1 ^VI(Mg,Fe²⁺,Mn,Li)₂ ^IVSi₅ ^IVAl₃ ^IV(Al, Be, Mg, Fe²⁺, Fe³⁺)O₁₈ *x^Ch(H₂O, CO₂…). Our results show that the population of (Mg, Fe²⁺) on the T₁1-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M²⁺–Na.  相似文献   

The Helmeth Grits of the Caradoc Range,church stretton; their bearing on part of the Pre-Cambrian succesion of Shropshire     

Edgar Sterling Cobbold  Walter Frederick Whittard 《Proceedings of the Geologists' Association. Geologists' Association》1935,46(3):348-IN13

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SHEBA flux–profile relationships in the stable atmospheric boundary layer     

Andrey A. Grachev  Edgar L Andreas  Christopher W. Fairall  Peter S. Guest  P. Ola G. Persson 《Boundary-Layer Meteorology》2007,124(3):315-333

Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used to examine the profile stability functions of momentum, φ _m , and sensible heat, φ _h , in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φ _m and φ _h in detail and includes ample data for the very stable case. New parameterizations for φ _m (ζ) and φ _h (ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ _m follows a ζ ^1/3 dependence, whereas φ _h initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects of self-correlation, which occur in plots of φ _m and φ _h versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging.  相似文献   

Effect of moisture content on ammonia emissions from broiler litter: A laboratory study   总被引：3，自引：0，他引：3  

Zifei Liu  Lingjuan Wang  David Beasley  Edgar Oviedo 《Journal of Atmospheric Chemistry》2007,58(1):41-53

A dynamic flow-through chamber system was designed to measure ammonia emissions from broiler litter and to investigate the responses of ammonia emissions to litter moisture content under laboratory-controlled conditions. It was observed that ammonia emissions from litter were very sensitive to litter moisture content. As water was added to the litter, the total ammoniac nitrogen content (TAN) in the litter increased, and can potentially increase ammonia emissions. However, measurements of ammonia concentrations in the chamber and total nitrogen losses from litter samples all suggested that water applied to the litter also had an effect of suppressing ammonia emissions for a short time. After enough time (1 to 2 weeks) was allowed, higher moisture content in litter eventually resulted in higher ammonia emissions. It was also noticed that, at very high litter moisture content, even when more time was allowed, ammonia concentrations began to decrease as moisture content further increased.  相似文献   

Pumping of a planetesimal disc by a rapidly migrating planet     

Richard Edgar  Pawel Artymowicz 《Monthly notices of the Royal Astronomical Society》2004,354(3):769-772

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