Shellfish as the impetus for embayment management     

Sandra L. Macfarlane 《Estuaries and Coasts》1996,19(2):311-319

Concern about declining stocks of municipally managed shellfish species in Orleans, Massachusetts, led to several shellfish enhancement programs. Projects included bottom and raft culture of hatchery-raised seed, hatchery and upweller techniques, transplants of seed and adult shellfish, and other management options. However, deterioration of water quality and habitat prompted the town to initiate a multifaceted program to address the issues causing environmental degradation. A water-quality task force, appointed to determine solutions to the problems, recommended changes in land-use practices. A drainage remediation program was undertaken at five sites, resulting in the reopening of a viable shellfish area for the first time in 12 yr. Issues concerning nutrient enrichment, groundwater flow and depth, flushing characteristics of the embayments, proliferation of private docks and piers in the public tidelands, effect of barrier beach dynamics including erosion control measures, and the number of users and diversity of their activies employed on the waters themselves will be addressed in current municipal planning initiatives.  相似文献   

Crustal attenuation in the Southern Andean retroarc (38°–39°30′ S) determined from tectonic and gravimetric studies: The Lonco-Luán asthenospheric anomaly     

Andrs Folguera  Antonio Introcaso  Mario Gimnez  Francisco Ruiz  Patricia Martinez  Cynthia Tunstall  Ezequiel García Morabito  Víctor A. Ramos 《Tectonophysics》2007,439(1-4):129-147

The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate.  相似文献   

Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)     

Rowe  M. C.; Wolff  J. A.; Gardner  J. N.; Ramos  F. C.; Teasdale  R.; Heikoop  C. E. 《Journal of Petrology》2007,48(11):2063-2091

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO₂)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements  相似文献   

Halogen-bearing minerals in syenites and high-grade marbles of Dronning Maud Land,Antarctica: monitors of fluid compositional changes during late-magmatic fluid-rock interaction processes   总被引：1，自引：0，他引：1  

Markl  Gregor  Piazolo  Sandra 《Contributions to Mineralogy and Petrology》1998,132(3):246-268

Meta-sedimentary rocks including marbles and calcsilicates in Central Dronning Maud Land (CDML) in East Antarctica experienced a Pan-African granulite facies metamorphism with peak metamorphic conditions around 830 ± 20 °C at 6.8 ± 0.5 kbar which was accompanied by the post-kinematic intrusion of huge amounts of syenitic (charnockitic) magmas at 4.5 ± 0.7 kbar. The marbles and calcsilicates may represent meta-evaporites as indicated by the occurrence of metamorphic gypsum/anhydrite and Cl-rich scapolite that formed in the presence of saline fluids with X _NaCl in the range 0.15–0.27. The marbles and calcsilicates bear biotite, tremolite and/or hornblende and humite group minerals (clinohumite, chondrodite and humite) which are inferred to have crystallized at about 650 °C and 4.5 kbar. The syenitic intrusives contain late-magmatic biotite and amphibole (formed between 750 and 800 °C) as well as relictic magmatic fayalite, orthopyroxene and clinopyroxene. Two syenite and two calcsilicate samples contain fluorite. Corona textures in the marbles and calcsilicates suggest very low fluid-rock ratios during the formation of the retrograde (650 °C) assemblages. Biotite in all but two syenite samples crystallized at log(f _{H 2 O}/f _HF) ratios of 2.9 ± 0.4, while in the calcsilicates, both biotite and humite group minerals indicate generally higher log(f _{H 2 O}/f _HF) values of up to 5.2. A few samples, though, overlap with the syenite values. Log(f _{H 2 O}/f _HCl) derived from biotite covers the range 0.5–2.6 in all rock types. Within a single sample, the calculated values for both parameters vary typically by 0.1 to 0.8 log units. Water and halogen acid fugacities calculated from biotite-olivine/orthopyroxene-feldspar-quartz equilibria and the above fugacity ratios are 1510–2790 bars for H₂O, 1.3–5.3 bars for HF and 7–600 bars for HCl. The results are interpreted to reflect the reaction of relatively homogeneous magmatic fluids [in terms of log(f _{H 2 O} /f _HF)] derived from the late-magmatic stages of the syenites with both earlier crystallized, still hotter parts of the syenites and with adjacent country rocks during down-temperature fluid flow. Fluorine is successively removed from the fluid and incorporated into F-bearing minerals (close to the syenite into metamorphic fluorite). In the course of this process log(f _{H 2 O} /f _HF) increases significantly. Chlorine preferably partitions into the fluid and hence log(f _{H 2 O} /f _HCl) does not change markedly during fluid-rock interaction. Received: 28 November 1997 / Accepted: 27 April 1998  相似文献   

A parameterization of radiative fluxes suitable for use in a statistical-dynamical model     

S. H. Franchito  V. Brahmananda Rao  R. Ramos da Silva 《Meteorology and Atmospheric Physics》1998,69(1-2):23-38

Summary A parameterization of shortwave and longwave radiation fluxes derived from detailed radiative transfer models is included in a global primitive equation statistical-dynamical model (SDM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the shortwave and longwave radiation fluxes matches well with the observations. The SDM variables such as surface and 500 hPa temperatures, zonal winds at 250 hPa and 750 hPa, vertical velocity at 500 hPa and precipitation are also in good agreement with the observations. A comparison between the results obtained with the present SDM and those with the previous version of the model indicates that the model results improved when the parameterization of the radiative fluxes based on detailed radiative transfer models are included into the SDM.The SDM is used to investigate its response to the greenhouse effect. Sensitivity experiments regarding the doubling of CO₂ and the changing of the cloud amount and height are performed. In the case 2×CO₂ the model results are consistent with those obtained from GCMs, showing a warming of the climate system. An enhancement of the greenhouse effect is also noted when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions. This suggests that the greenhouse effect overcomes the albedo effect in the polar latitudes and the opposite occurs in other regions. In all the experiments the changes in the surface temperature are larger near poles, mainly in the Southern Hemisphere.With 8 Figures  相似文献   

Collapse of primordial clouds — I     

Sandra R. Oliveira  Oswaldo D. Miranda  & José C. N. de Araujo  Reuven Opher 《Monthly notices of the Royal Astronomical Society》1998,301(1):101-114

  相似文献   

Mortality by cause of death in Colombia: a local analysis using spatial econometrics     

Spijker  Jeroen  Recaño  Joaquín  Martínez  Sandra  Carioli  Alessandra 《Journal of Geographical Systems》2021,23(2):161-207

Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very...  相似文献   

Trends and correlations in annual extreme precipitation indices for mainland Portugal, 1941–2007     

M. Isabel P. de Lima  Fátima Espírito Santo  Alexandre M. Ramos  Ricardo M. Trigo 《Theoretical and Applied Climatology》2015,119(1-2):55-75

  相似文献   

Compressed sensing for next generation instruments     

A. Asensio Ramos 《Astronomische Nachrichten》2010,331(6):652-654

This document discusses the possibility of using compressed sensing techniques for measuring 2D spectro‐polarimetric information using only one etalon and a broad prefilter. Instead of using an etalon and an extremely narrow prefilter (with all the subsequent problems of alignment), the idea is to use multiplexing techniques to include in the observations all the secondary peaks of the etalon. The reconstruction of the signal is done under the assumption that it can be efficiently reproduced in an orthogonal basis set (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Are assemblages of the fireworm Hermodice carunculata enhanced in sediments beneath offshore fish cages?     

Rodrigo Rier  Oscar P&#;rez  Myriam Rodr&#;guez  Eva Ramos  &#;scar Monterroso 《海洋学报(英文版)》2014,33(4):108-111

Abundances of the fireworm Hermodice carunculata were counted through a monitoring assessment study of fish cages in Barranco Hondo（NE Tenerife）. Seven campaigns were conducted from November 2007 to June 2010 and temporal variations were found, as well as differences among sampling stations. The polychaete H. carunculata obtained its highest abundance in sediments beneath fish cages throughout the study period. Thus, the assemblages of this omnivorous species were favoured by the presence of fish cages.  相似文献