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1.
CHRISTIAN HJORT SVEND FUNDER 《Boreas: An International Journal of Quaternary Research》1974,3(1):23-33
The subfossil occurrence of Mytilus edulis in central East Greenland has been C14 -dated to roughly between 8000 B.P. and 5500 B.P.; compared with other areas this is a short period. Its immigration coincides with the final deglaciation of the innermost fjords, and its disappearance is contemporaneous with an increase in cold-climate plants, as shown by pollen spectra. It is suggested that it immigrated from the Svalbard area rather than from southeast Greenland, and that the central East Greenland fjord zone forms an isolated oasis, where more southerly species like Mytilus and Chlamys islandica can or could live, even if this was not possible along the surrounding and more hostile outer coasts. The reason for the absence of Mytilus edalis from the region today is probably not the local climate. 相似文献
2.
The frequency distribution of zinc concentrations in a population of mussels (Mytilus edulis) from the moderately polluted Tyne estuary showed marked positive skewness. A peak was reached between 3 and 4 μmoles per dry gram of whole soft tissue followed by a long tail ending with a single exceptional value of 20.5 μmoles per g. The mean zinc concentration for the population was 5.13±2.66 (standard deviation). The skewness (g1) value was 1.78 (SE+0.14 p?0.001). Within the population, there was a strong positive association between the log mean zinc concentration of a single collection and the log variance of the collection. The significance of this for biomonitoring procedures is discussed. 相似文献
3.
Mussel populations (Mytilus edulis) in the Dutch Wadden Sea (intertidal mussel beds, subtidal beds and culture plots), the culture methods, the extent of mussel culture, and the ecology of the mussel are described. Mussels filter suspended matter from the water column and deposit it as feces and pseudofeces. Mussel beds consume large amounts of phytoplankton and speed up the cycle of production and breakdown of organic matter. There are indications that the consumption of phytoplankton can lead to food shortage for several animal groups. Mussels serve as an important food source for a wide range of organisms (e.g., starfish, eider ducks, and oystercatchers). Because mussel culture increased the mussel biomass in the Dutch Wadden Sea, the impact also increased. The most obvious impact of the culture is the dredging of seed mussels. Overexploitation of intertidal mussel and cockle beds and bad spatfall of both mussels and cockles since 1988 had a negative impact on bird populations. The extent of positive and negative aspects of mussel culture depends on natural and human influences. The negative aspects may (partly) be overcome by appropriate measures. *** DIRECT SUPPORT *** A01BY069 00007 相似文献
4.
Richard F. Modlin 《Estuaries and Coasts》1980,3(1):1-10
Sampling theC. septemspinosa population of the Mystic River Estuary simultaneously in deep water and along the shoreline indicated that this population has two major reproductive periods. Berried females move into the estuary in early spring and late autumn to hatch their eggs. Two-and three-year-old females produce the larvae in the spring and 1.0- to 1.5-year-old females give rise to the larvae in winter. All larvae are carried seaward by the tidal currents and eventually settle as juveniles in the deep water near the mouth of the estuary or on the continental shelf. Juveniles from the spring hatch migrate to the shallow shoreline where they grow, rapidly, 0.15 mg/day. Those that hatch during the late autumn do not migrate shoreward. A model of this life cycle and evidence to support two recruitment mechanisms that involve inshore migration of adults and the offshore drift of the larvae are presented. 相似文献
5.
Fan‐shaped polycrystalline staurolite porphyroblasts, 3–4 cm in length and 0.5 cm in width, occur together with centimetre‐sized euhedral prismatic staurolite porphyroblasts in pelitic schists of the Littleton Formation on the western overturned limb of the Bolton syncline in eastern Connecticut. The fans consist of intergrown planar splays of [001] elongated prisms, which are crudely radial from a single apex. The apical angles of the radial groupings range up to 70°. The orientations of the individual staurolite prisms are related by a rigid rotation about an axis perpendicular to the fan plane. The zone axes [001] always lie in the plane of the fan. Although the angle between the [100] zone axes of the individual prisms is uniform in each fan, it ranges from +30° to ?30° in different fans. Internally, the fans display: (i) remnants of a passively captured Si foliation defined by disc‐shaped quartz blebs (type 1 inclusions) and layers of very fine carbonaceous material and tabular ilmenite platelets; (ii) bent staurolite blades and undulose extinction along low‐angle (010) subgrain boundaries near the apex of the fans; (iii) wedge‐shaped dilatational zones containing equigranular inclusion‐free quartz, mica and staurolite, and (iv) growth‐related quartz inclusion trails roughly perpendicular to a crystal face (type 2 inclusions). The Si inclusion trails are typically perpendicular to the fan surface, radiate parallel to the blades, and show little to no curvature except at the very edge of the fans where they abruptly curve through nearly 90° into parallelism with an external Se foliation. Careful examination of the three‐dimensional geometry of fans based on U‐stage measurements, serial sections and two‐circle optical goniometric measurements permits a detailed reconstruction of their sequential development. The origin of a fan involves limited intracrystalline deformation and brittle crack dilation, spalling, rotation, and growth of small marginal fragments and of new staurolite along wedge‐shaped zones along the Si inclusion surfaces. Fans preferentially develop in porphyroblasts in which Si is subparallel to the 010 cleavage. These internal features reflect the rotation and deformation of a brittle porphyroblast relative to syn‐growth shear stresses. 相似文献
6.
Simultaneous changes in the representation of wetland and dry land taxa are a common feature of mid and late Holocene pollen diagrams from the coastal wetlands of North‐West Europe. Distinguishing both the areas affected and between natural and anthropogenic causes can be problematic. High temporal resolution, improved taxonomic procedures and multivariate statistics have been applied to two Thames estuary sites, along with simulation models, to resolve these issues. Large Poaceae pollen grains appear to be derived from wild grasses rather than cereals, while modelling indicates that even extensive clearance in dry land areas produces relatively minor changes in pollen assemblages where fen carr is the in situ vegetation. It is concluded that rapid/abrupt simultaneous pollen stratigraphic events in coastal wetlands are likely to have been caused by wetland vegetation changes alone. Simultaneous events, dating from c. 2150–1300 cal a BC, can be distinguished at 12 Thames estuary pollen sites. During this interval inter‐tidal environments expanded creating areas attractive to human populations for pasturage. This exploitation is likely to have led to further changes in wetland vegetation and increased clearance activity on adjacent dry land areas. In such circumstances disentangling the processes causing vegetation change is challenging, although considerably aided by the techniques adopted in this paper. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
7.
Eric Rochard Mario Lepage Pierre Dumont Serge Tremblay Christine Gazeau 《Estuaries and Coasts》2001,24(1):108-115
The European sturgeon (Acipenser sturio) is an endangered diadromous fish species that spawns in the rivers in late spring and early summer. The juveniles spend
their first years in the brackish waters (5‰ to 25‰) of the estuary zone before moving out to sea. This study describes the
downstream migration pattern of juvenile sturgeon, belonging to the 1994 cohort, the only one born naturally in the Gironde
basin, France since the end of the 1980s. During October 1994 to December 1996 the inland section of the Gironde estuary was
sampled monthly by trawl (n=818 tows) and all European sturgeon caught (n=381) were marked and released. The first sturgeon
of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. During their second fall of
life, juveniles gradually acclimatized, and spread over a wide range of salinity conditions. A first incursion into marine
water was also observed (at least for a few fish) by the end of the second winter. During this second period, sturgeon showed
preference for two particular zones situated at 18 and 38 km, respectively, from the mouth of the estuary. These zones, belonging
to two different salinity sectors of the estuary, did not appear to be any different to their neighbors with regards to depth
and type of substrate. There were no significant size differences among estuarine zones. Seasonal movements of sturgeon seem
to be motivated by a search for warmer temperatures. After a period of early acclimatization of 15 months, juvenile European
sturgeon appear to be highly tolerant of salinity variations. 相似文献
8.
Larry N. Smith 《Quaternary Research》2006,66(2):311-322
Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2-> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200-1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050-1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon. 相似文献
9.
Yves de Lafontaine 《Estuaries and Coasts》1990,13(1):43-50
The species composition and relative abundance of ichthyoplankton were investigated during summer 1986 at four stations along the salinity gradient in the Manicouagan River estuary, a tributary of the lower St. Lawrence estuary. Physical characteristics of water masses indicated the presence of a strong saline front (>10‰ per km) delineating the freshwater and marine section of the Manicouagan estuary. The estuary supports a depauperate ichthyoplankton community, including four species of pelagic fish eggs and eight species of fish larvae. Species richness increased with salinity. The ichthyoplankton fauna can be divided into two distinct groups: freshwater and marine. These two groups result initially from spawning preferences exhibited by the different species abundance of freshwater larvae was maximal at the head of the estuary and marine larvae were most abundant at the most saline station. The length frequency distribution suggests that marine larvae are not effectively retained within the estuary. The Manicouagan estuary cannot be considered as a major spawning site nor an important nursery zone for any fish found in this area. 相似文献
10.
Levels of organochlorine pesticides in natural water along the Yangtze River,from headstream to estuary,and factors determining these levels 总被引:1,自引:0,他引:1
Chen Liu Guo-Li Yuan Zhong-Fang Yang Tao Yu Xue-Qi Xia Qing-Ye Hou Long Chen 《Environmental Earth Sciences》2011,62(5):953-960
Organochlorine pesticides (OCPs), including hexachlorocyclohexane and dichlorodiphenyltrichloroethane, were monitored in 37
samples of water collected along the Yangtze River, the third longest river in the world (6,300 km). The total concentration
of OCPs (∑OCPs) in the river water ranged from 0.11 to 27.37 ng/L. It was interesting to discover that, except for some sites
near industrial cities, levels of OCPs in the water samples were very similar along the whole river. Significantly, OCPs were
detected in Tuotuo River (the origin of Yangtze River) even though OCPs have never been used in this area because of its 4,540 m
height above sea level. Furthermore, it was found that ∑OCPs was related to temperature and altitude along the river. We assume
OCPs are transported along the Yangtze River, and the factors affecting this process are discussed. 相似文献
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J.R. Stewart S. Aspinall M. Beech P. Fenberg P. Hellyer N. Larkin S.W. Lokier F.G. Marx M. Meyer R. Miller P.S. Rainbow J.D. Taylor J.E. Whittaker K. Al-Mehsin C.J. Strohmenger 《Quaternary Science Reviews》2011,30(25-26):3675-3690
Whale remains (a left and right mandible, scapula, humerus and fragmentary radius and ulna as well as parts of the cranium and rostrum) belonging to a probable humpback whale (Megaptera cf. novaeangliae) were found in the well-described sabkha sequence exposed in the Musaffah Industrial Channel, Abu Dhabi, United Arab Emirates. More precisely, the whale remains were found in a series of sediments representing a range of lagoonal facies. The sediments surrounding the whale bones were age-dated at approximately 5200 14C yrs BP and are therefore interpreted to correspond to the previously documented late Flandrian sea-level peak, preceding a fall in sea-level which culminated in the supratidal sabkha overprint of the carbonates. Associated with the whale remains is an assemblage of molluscs, foraminifera and ostracods. Together with the inferred presence of sea grass and algae, these facies are interpreted to indicate a very shallow subtidal to intertidal lagoonal environment. Cirripede remains found associated with the skeleton were identified as those of the whale barnacle Coronula diadema and hence had their origins with the whale. Significantly, the low species diversity of microfossils suggests that higher salinities existed in the mid-Holocene lagoon than are present in modern counterparts. This is here inferred to be related to the onset of continental aridity in Arabia during the mid-Holocene. 相似文献
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15.
Rats were raised on a variety of isotopically controlled diets comprising 20% C3, C4 or marine protein and C3 and/or C4 non-protein or energy (i.e. sucrose, starch and oil) macronutrients. Compound specific stable carbon isotope (δ13C) analysis was performed on the cholesterol isolated from the diet (n=7 ) and bone (n=15 ) of these animals and the values compared with bulk δ13C measurements of bone collagen and apatite. The dietary signals reflected by these three bone biochemical components were investigated using linear regression analysis. δ13C values of bone cholesterol were shown to reflect whole diet δ13C values, collagen to reflect mainly dietary protein values and apatite to reflect whole diet values. Further correlations between dietary protein-to-energy spacings (Δ13Cprot-engy = δ13Cprotein - δ13Cenergy) and whole diet-to-bone component fractionations (Δ13Cbcomp-wdiet = δ13Cbone component - δ13Cwhole diet) indicates that for hypothetical diets where protein δ13C values are equal to energy values, fractionations between whole diet and bone biochemical fractions are -3.3‰ for cholesterol, +5.4‰ for collagen and +9.5‰ for apatite. Moreover, the narrow range of variation observed in apatite-to-cholesterol spacings (Δ13Capat-bchol) suggests that cholesterol δ13C values can potentially also be used as an independent test for the isotopic integrity of apatite δ13C values. These insights into bone cholesterol, collagen and apatite dietary signals, diet-to-bone fractionations and bone component-to-bone component spacings provide the basis for more accurate interpretations of the dietary behaviour of archaeological populations and food webs when the δ13C analysis of bone is employed. 相似文献
16.
Wellbore attributes (i.e., deviation, casings and plugging characteristics) for 85 wells in the St. Lawrence Lowlands basin of southern Quebec were compiled from drilling reports and abandonment programs to provide an overview of the abandoned well characteristics and to establish a diagnosis on the long-term reliability of the completion and abandonment practices carried out by the companies since the beginning of oil and gas exploration. Using these data, the conventional and unconventional wells were divided into four categories: (1) conventional wells drilled before 1950, (2) conventional wells drilled between 1950 and 1970, (3) conventional wells drilled after 1970 and shale gas wells (all drilled after 2000). Very little information was available for wells drilled before 1950. More information was available for the wells drilled from 1950 to 1970 which is considered a transition period between old and modern technology. Conventional and unconventional wells drilled after 1970 were generally well documented and their attributes corresponded to API standards. A decision tree, inspired from the methodology proposed by Watson and Bachu (SPE Drill Complet 24(1):115–126, 2009. https://doi.org/10.2118/106817-PA), was then created to assess the potential of leakage of each of the conventional and unconventional wells using the compiled attributes. The factors defining the probability of well leakage were wellbore deviation, height of cement in casing annuli (partially or fully cemented), type of abandonment plugs (cement or mechanical plugs) and drilling date (before or after 1970). Among the 85 wells assessed by this tree, the probability of leakage was higher than 50% for 55 wells (65% of wells). Wellbore deviation and lack of information on the construction and abandonment methods were respectively the primary and secondary causes of high probability of leakage of these wells. 相似文献
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Peter G. Verity 《Estuaries and Coasts》2002,25(5):961-975
A sampling program was initiated in 1986 in the Skidaway River estuary, a tidally dominated subtropical estuary in the southeastern USA. Hydrography, nutrients, particulate organic matter (POM), and microbial and plankton abundance and composition were measured at weekly intervals at high and low tide on the same day at a single site. Hydrographic and nutrient data during 1986–1996 were given in Verity (2002); particulate organic carbon (POC), nitrogen (PON) and chlorophylla (chla) are presented here; plankton data will be presented elsewhere. Chla was fractionated into <8 μm and >8 μm size classes. All classes of POM exhibited distinct seasonal patterns superimposed upon significant long-term increases during the study period. Total chla, <8 μm chla, and >8 μm chla increased 36%, 61%, and 18%, respectively, however the fraction of total biomass attributable to small phytoplankton (<8 μm) increased 25%. The annual amplitude between minimum and maximum stock sizes increased significantly, meaning that bloom events became larger. POC and PON also increased 16% over the decade and, as observed with patterns in chla, exhibited increases in annual amplitude. The C:N ratio was typically 6.4–6.6 (wt:wt) and did not change significantly, while the annual mean C:Chla ratio decreased 19% from 165 to 140. These characteristics indicated highly labile POM composed of significant amounts of detritus, but which became increasingly autotrophic with time. Averaged over the decade, temperature explained 45–50% of the variance in POM. Nutrients were even better predictors of POM, as 60–75% of the variance in chla, POC, and PON were explained by ambient concentrations of DIN, or PO4. Combined with significant increases in NO3, NH4, PO4, Si(OH)4, and DON during 1986–1996, these data strongly suggest that anthropogenic activities contributed to increased loading of dissolved nutrients, which became incorporated into living and nonliving particulate organic matter. 相似文献
19.
The following equation has been previously developed for the drag coefficient of a sphere. In this work the authors propose a power series expansion for C0 in terms of the Reynolds number: A fifth-order polynomial permits obtaining the drag coefficient and the settling velocity of a sphere, up to a Reynolds number of 3 × 105, with an average relative error of about 2%. 相似文献
20.
1 IntroductionThe Mesozoic-Cenozoic tectonic evolution and ki-netics mechanism of the intracontinental orogen are thekey subjects of continental dynamics (Ma Zongjin andGao Xianglin, 2004) and the key to understanding theregional geological tectonics (Qia… 相似文献