Changes in body condition and fatty acid composition of wild Mediterranean horse mackerel (Trachurus mediterraneus, Steindachner, 1868) associated to sea cage fish farms     

Fernandez-Jover D  Jimenez JA  Sanchez-Jerez P  Bayle-Sempere J  Casalduero FG  Lopez FJ  Dempster T 《Marine environmental research》2007,63(1):1-18

Net-cage fish farms attract a great number of wild fishes, altering their behaviour and possibly their physiology. Wild Mediterranean horse mackerel (Trachurus mediterraneus), sampled from populations aggregated around two Mediterranean fish farms and from two natural control populations, were analyzed for differences in body condition, stomach content and fatty acid composition. Pellets used to feed caged fish in both farms were also analyzed to identify their relationship with the fatty acid composition of tissue of wild fish. T. mediterraneus aggregated around the farms throughout the year although large seasonal changes in abundance and biomass occurred. Wild fish aggregated at farms mainly ate food pellets while control fish fed principally on juvenile fish and cephalopods. Wild fish that fed around the cages had a significantly higher body fat content than the control fish (7.30+/-1.8% and 2.36+/-0.7%, respectively). The fatty acid composition also differed between farm-associated and control fish, principally because of the significantly increased levels of linoleic (C18:2omega6) and oleic (C18:1omega9) acids and decreased docosahexaenoic acid (C22:6omega3) in farm-associated fish. The increased condition of wild fish associated with farms could increase the spawning ability of coastal fish populations, if wild fish are protected from fishing while they are present at farms. The fatty acids compositions could also serve as biomarkers to infer the influence of a fish farm on the local fish community, helping to better describe the environmental impact of fish farming.  相似文献   

Input Selection Based on Information Theory for Constructing Predictor Models of Solar and Geomagnetic Activity Indices     

Mohammadmahdi Rezaei Yousefi  Babak Salehi Kasmaei  Abdolhossein Vahabie  Caro Lucas  Babak Nadjar Araabi 《Solar physics》2009,258(2):297-318

Various phenomena with solar origin and their mutual dependence must be studied in order to predict behaviors in solar – terrestrial system. Linear statistical methods prevalent in analyzing natural systems may not be able to detect nonlinear dependencies among solar and geomagnetic processes. When relations, whether linear or nonlinear, between indices and their changes over time are revealed, better predictions can be made through appropriate modeling techniques. Selection of nonredundant input variables to build suitable models for prediction of solar and geomagnetic activity is of utmost importance. Mutual information is a tool that is capable of capturing all dependencies for detecting nonlinear relations and selecting the best subset of input variables by means of an applicable algorithm that maximizes information about the output and minimizes the shared information between inputs. High generalization power and improved interpretability of the selected inputs are the consequences of this analysis.  相似文献   

Hydraulic testing of low-permeability formations: A case study in the granite of Cadalso de los Vidrios, Spain     

Miguel Mejías  Philippe Renard  Damian Glenz   《Engineering Geology》2009,107(3-4):88-97

In recent years, the study of low-permeability geological formations has undergone considerable development. This is mainly due to the use of natural geological barriers to confine waste disposals, preventing leaking water from bringing contaminants into contact with the biosphere and the groundwater resources.In that context, the Spanish Geological Survey (IGME, Spanish acronym), supported by the National Radioactive Waste Management Agency (ENRESA, Spanish acronym) and with the technical advice of the Swedish Nuclear Fuel and Waste Management Company (SKB) designed and built a Mobile Hydrogeological Unit (UMH, Spanish acronym) for low-permeability formations characterization, which has been operational since 1997 and has been used for different purposes. Among other possibilities, the UMH allows conducting: constant transient-state flow-rate injection tests, constant-head transient-state injection tests, pseudo-stationary state injection tests, pressure fall-off tests, slug tests and pulse tests.The main objectives of this article are to describe the hydraulic characterization methodology used by IGME to carry out hydraulic tests in low permeability environment, to compare different testing methods and to summarize the results that have been obtained when characterizing the leucogranites of Cadalso de los Vidrios in Spain.The study area presents an increasing interest for granite production inside the Community of Madrid. The petrological and structural characteristics of the granite rocks and the core-samples extracted from a 200 m deep borehole investigation are described. The packer tests are conducted with the Mobile Hydrogeological Unit.The tests are interpreted with the help of analytical solutions. The main software used is Hytool, an open source matlab toolbox that provides a library of analytical solutions and a set of routines to facilitate hydraulic tests interpretation.The results allow the elaboration of a comparative analysis of the applied hydraulic tests and to define the hydraulic conductivity optimum application interval most suited for each of the used methods.Hydraulic conductivity values obtained varies from 3.20·10^− 7 m/s, for the upper weathered layer, to 2.80·10^− 12 m/s, for the test section from 97.36 to 116.15 m depth.Finally, the hydraulic conductivity values obtained in this area are compared with other case studies of granite formations around the world.  相似文献   

Analysis of limestone micromechanical properties by optical microscopy     

Lucas R.D. Jensen  Henrik Friis  Erling Fundal  Per Møller  Mads Jespersen 《Engineering Geology》2010,110(3-4):43-50

Four dense Scandinavian limestones were analyzed to determine their mechanical properties. The generation of dust (? 10 μm) and fines (? 90 μm) during a closed circuit vertical roller mill comminution process was correlated with the calcite crystal size distributions of each limestone. Thin sections were analyzed and by means of stereology the calcite crystal size distributions for each limestone was measured. The dust generation of limestones is governed by a surface abrasive mechanism (R² = 0.99) and the production of fines is governed by the mechanical strength of limestones (R² = 0.99). The overall limestone degradation mechanism is predominantly controlled by the calcite cleavage planes which reduce the power consumption during the comminution process. This study is the first step in determining the influence of limestone texture on the wear rates in heterogenous raw mixes used in closed circuit comminution equipment.  相似文献   

Property matters: Agricultural restructuring and changing landlord-tenant relationships in England     

Brian Ilbery  Damian Maye  Lewis Holloway 《Geoforum》2010,41(3):423-434

Little research has been conducted on the restructuring activities of tenant farmers in response to changing tenancy legislation and recent CAP reforms. This paper examines the geography of farm tenancy agreements in England since 1995 and presents some findings from postal and telephone surveys on the possible future business trajectories of tenant farmers and the changing nature of landlord-tenant relationships. A clear north-south divide is identified in terms of farm tenancy agreements and a complex array of different tenancy agreements is demonstrated. The relationships between landlords and tenants are changing and the increasing variety of agreements provides evidence of a more fluid (post-feudal) system of agricultural leases. Nevertheless, high levels of uncertainty and negativity characterise tenant farmers’ views on the impacts of CAP reforms. Crucially, the very identity of a tenant farmer is changing, towards an owner-occupier who rents additional land, and there is an urgent need for more detailed research on the ‘consequential geographies’ of farm property rights and the changing nature of landlord-tenant relationships.  相似文献   

“It’s a gestalt experience”: Landscape values and development pressure in Hawke’s Bay, New Zealand     

Damian Collins  Robin Kearns 《Geoforum》2010,41(3):435-446

Demand for both primary residences and second homes in high-amenity areas has led to escalating property values and widespread development pressure in coastal New Zealand. We focus on a major development proposal at Ocean Beach, a greenfield coastal site in the Hawke’s Bay region, and seek to explain the opposition it has provoked. In so doing, we address three questions: first, what landscape values are articulated within the planning process; second, what is the anticipated impact of 1000 new dwellings on those values; and third, how does place attachment figure in the ensuing debates. We address these questions though a thematic analysis of data derived from official reports and proposals, planning submissions, and key informant interviews. We find Ocean Beach to be a place that offers a quintessential coastal experience, often linked to youthful memories. Additionally, the site is valued for its accessibility and wilderness qualities - perceptions heightened by awareness that areas of undeveloped coastline relatively close to population centres are increasingly scarce. We contend that such sites are doubly valuable: in a formal sense, as natural landscapes whose processes and forms receive regulatory protection; and in an informal sense, as sites that generate human meaning, including emotions such as nostalgia, freedom and belonging.  相似文献   

Effects of long-term irrigation with treated wastewater. Part II: Role of organic carbon on Cu,Pb and Cr behaviour     

Lobna Tarchouna Gharbi  Patricia MerdyYves Lucas 《Applied Geochemistry》2010

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 year experiment. In this second part, we focused on Cu, Cr and Pb behaviour in relation with soil organic carbon (SOC). Soil samples were collected every 3 months during 2 years at the depths 0–20, 20–40 and 40–60 cm and were analysed for exchangeable and total metals, organic carbon content, metal sequential extraction and humic substances – Humic Acids (HA), Fulvic Acids (FA) and Non-Humified Fraction (NHF). Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil. Irrigation lowered the HA and NHF fractions of SOC and made the FA fraction more mobile. Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.  相似文献   

Near-infrared imaging polarimetry of young stellar objects in ρ Ophiuchi     

A. F. Beckford  P. W. Lucas  A. C. Chrysostomou  T. M. Gledhill 《Monthly notices of the Royal Astronomical Society》2008,384(3):907-929

The results of a near-infrared ( J H K L _P) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in ρ Ophiuchi are presented. The majority of the sources are unresolved, with K -band polarizations, P _K < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of P _K > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K -band core polarizations >6 per cent are only observed in Class I YSOs.
A 3D Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the ρ Oph YSOs with extended nebulae. A ρ∝ r ^−1.5 power law for the density is applied throughout the envelopes. The large-scale centrosymmetric polarization structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned non-spherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually ≤10 per cent, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes 1.05 μm.  相似文献   

Polymictic pool behaviour in a montane meadow,Sierra Nevada,CA          下载免费PDF全文

Ryan G. Lucas  Francisco Suárez  Scott W. Tyler  Jean E. Moran  Martha H. Conklin 《水文研究》2016,30(18):3274-3288

We observed polymictic behaviour in stream pools in Long Meadow, Sequoia National Park, California—part of the Southern Sierra Critical Zone Observatory. Stream pools stratified thermally during the day time and were isothermal at night—this pattern persists from the middle of summer into the fall. We found that four characteristics typical of a mountain meadow environment—low stream flow, open sky, cold groundwater discharge, and elevated organic carbon concentrations—are particularly conducive to pool stratification. Incoming shortwave radiation was the dominant energy input to heat pool water while nighttime emitted longwave radiation was the major cooling mechanism. Relatively cold groundwater discharge into the pool bottom increased density stratification within the pool. Elevated DOC concentrations increased the capacity of the pool to absorb photosynthetically active radiation and also promoted stratification. Stream velocities in the meadow were generally insufficient to meet threshold Richardson numbers and mix the pools during the daytime; smaller stream cross sectional areas would have potential for destabilizing pools in the daytime. We propose a conceptual model for describing polymictic stream pools and assessing the potential for polymictic pools to occur. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Progressive formation of modern drumlins at Múlajökull,Iceland: stratigraphical and morphological evidence          下载免费PDF全文

Ívar Örn Benediktsson  Sverrir A. Jónsson  Anders Schomacker  Mark D. Johnson  Ólafur Ingólfsson  Lucas Zoet  Neal R. Iverson  Johann Stötter 《Boreas: An International Journal of Quaternary Research》2016,45(4):567-583

The drumlin field at Múlajökull, Iceland, is considered to be an active field in that partly and fully ice‐covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto‐drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto‐drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat.  相似文献