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81.
Don Maurer 《Marine Ecology》1983,4(3):263-274
Abstract. Animal-animal interactions are recognized as critical in benthic invertebrate recruitment. The hypothesis tested was that benthic recruitment is more successful in low densities of infaunal suspension feeders than in high densities. Densities of young hard clams Mercenaria mercenaria (L.) ranging from 82.5 to 330m-2 were placed in defaunated boxes of sand. The mean number of species, mean number of individuals, mean wet weight biomass, mean species richness and mean dominance index per sample were calculated per density of hard clams from May to October. The experiment did not support the hypothesis. It was concluded that feeding behaviour of dense populations of M. mercenaria did not preclude successful recruitment of other benthic species. 相似文献
82.
Based on quarterly sampling (n = 260) over four years (1985–1989) from California's San Pedro Shelf, the Pearson-Rosenberg Model (PRM) or organic enrichment was tested for the Orange County ocean outfall. The null hypothesis was that test species, abundance, and biomass curves (SAB) from the shelf closely resemble those from the model. Principal areas of agreement between test curves and model curves include increased abundance and biomass approaching an ocean outfall. Major departures from the PRM include: (1) no sharp decline in SAB curves to azoic conditions, (2) displacement of SAB curves away from the outfall, and (3) opportunistic species did not exclude or eliminate rare species. Moreover, the role of local dominant species (bivalve—Parvilucina tenuisculpta, ostracod—Euphilomedes carcharodonta polychaetous annelid—Capitella capitata) can greatly influence SAB curves within the model. Bioenhancement should not necessarily be viewed as a diagnostic feature of a polluted site. Since the PRM was originally developed for semi-enclosed, low energy depositional habitats with long residence times (fjords, sea lochs), open ocean, high energy, erosional habitats (coast and shelf) may not be the most appropriate sites to apply this model. Uncritical application of the PRM to the Orange County ocean outfall may lead to unnecessary and costly decisions. 相似文献
83.
Two silver (migratory) male freshwater eels, Anguilla dieffenbachii, were caught in a commercial trawl net in the South Taranaki Bight in April 2014. The capture date and the relatively small eye size indicated that both eels had probably only recently entered the sea. This is the first record of male A. dieffenbachii caught at sea, en route to the presumed spawning area in the South Fiji Basin. 相似文献
84.
Francisco Balocchi Neftali Flores José Luis Arumí Andrés Iroumé Don A. White Richard P. Silberstein Pablo Ramírez de Arellano 《水文研究》2021,35(6):e14182
In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long-term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient (α) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient (α) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south-central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ (p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference (p < 0.05) between these and Eucalyptus plantations. The recession constant is a well-established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate. 相似文献
85.
86.
Paleoproterozoic mafic dyke swarms (2.5–2.0 Ga) of the Ungava Peninsula can be divided in three chemical groups. The main group has a wide range of Fe (10–18 wt.% Fe2O3) and Ti (0.8–2.0 wt.% TiO2) contents, and the most magnesian samples have compositions consistent with melting of a fertile lherzolitic mantle at ~ 1.5 GPa. Dykes of a low-LREE (light rare earth element) subgroup (La/Yb ≤ 4) display decreasing Zr/Nb with increasing La/Yb ratios and positive εNd2.0 Ga values (+ 3.9 to + 0.2) that trend from primitive mantle towards the composition of Paleoproterozoic alkaline rocks. In contrast, dykes of a high-LREE subgroup (La/Yb ≥4) display increasing Zr/Nb ratios and negative εNd2.0 Ga values (? 2.3 to ? 6.4) that trend towards the composition of Archean crust. A low Fe–Ti group has low Fe (< 11 wt.% Fe2O3), Ti (< 0.8 wt.% TiO2), high field strength elements (HFSE; < 6 ppm Nb) and heavy rare earth elements (HREE; < 2 ppm Yb) contents, but are enriched in large ion lithophile elements (LILE; K/Ti = 0.7–3) and LREE (La/Yb > 4). These dykes are interpreted as melts of a depleted harzburgitic mantle that has experienced metasomatic enrichment. A positive correlation of Zr/Nb ratio and La/Yb ratio, negative εNd2.0 Ga values (? 14 to ? 6), and the presence of inherited Archean zircons further suggest the incorporation of a crustal component. A high Fe–Ti group has high Fe (> 14 wt.% Fe2O3) and Ti (> 1.4 wt.% TiO2) contents, along with higher Na contents relative to the main group dykes. Dykes of a high-Al subgroup (> 12 wt.% Al2O3) share Fe contents, εNd2.0 Ga values (? 2.3 to ? 3.4), La/Yb and Th/Nb ratios with Archean ferropicrites, and may represent evolved ferropicrite melts. A low-Al subgroup (< 12 wt.% Al2O3) has relatively lower Yb contents (< 2 ppm) and fractionated HREE patterns that indicate the presence of garnet in their melting residue. A comparison with ~ 5 GPa experimentally-derived melts suggests that these dykes may be derived from garnet-bearing pyroxenite or peridotite. The εNd2.0 Ga values (? 0.3 to ? 2.0) of these dykes lie between the compositions of Archean granitoids and Paleoproterozoic alkaline rocks, signifying their petrogenesis involved both crustal and mantle components.Paleoproterozoic dykes containing a crustal component occur within, or close to, an isotopically enriched Archean terrane (TDM 4.3–3.1 Ga), whereas dykes without this component occur in an isotopically juvenile terrane (TDM < 3.1 Ga). The lack of a crustal component and the positive εNd2.0 Ga values of dykes intruding the latter suggest that the crust they intruded was either too cold to be assimilated, or that its lower crust and/or lithosphere were Paleoproterozoic in age. In contrast, the ubiquitous presence of a crustal component and the diversity of mantle sources for dykes intruding the enriched terrane (lherzolite, harzburgite, pyroxenite) suggest a warmer crust with underlying heterogeneous lithospheric mantle. 相似文献
87.
Stefanie Wachter Chryssa Kouveliotou Sandeep Patel Don Figer Peter Woods 《Astrophysics and Space Science》2007,308(1-4):67-71
Both Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) are thought to be manifestations of magnetars. However, the specific physical characteristics that differentiate the two classes of objects remain unclear. There is some evidence that the progenitors of these sources and/or the environment in which they form might influence the type of phenomena the resulting magnetar displays. Several of the AXPs appear to be associated with supernova remnants, while embedded clusters of massive stars have been found in the immediate vicinity of some SGRs. Since both AXPs and SGRs are distributed close to the Galactic plane, high extinction makes studies in the optical difficult. We present early results from our Spitzer program aimed at probing the environmental factors that might contribute to the difference in the observed characteristics between AXPs and SGRs. 相似文献
88.
89.
Anne Charland Don Francis John Ludden 《Contributions to Mineralogy and Petrology》1995,121(3):289-302
Volumetrically subordinate alkaline mafic lava flows form a late capping stage over the earlier felsic lavas that form the
shield of the Itcha Volcanic Complex (IVC), of the Anahim Volcanic Belt (AVB) in central British Columbia (B.C.). The mafic
capping stage of the IVC is dominated by hawaiites which are the earliest of the mafic lavas, and are succeeded by alkali
olivine basalts (AOB) and then by basanites. The alkali olivine basalts can be subdivided into high-, intermediate- and low-MgO
AOB groups, all of which share similar HFSE ratios (e.g. Nb/Zr) with the hawaiites. High Al contents and Sr/Zr ratios indicate
that hawaiites and Fe-rich evolved AOB were derived from primitive AOB parental magmas by crystal fractionation of a wehrlitic
assemblage at pressures on the order of 8 to 10 kbar. High Si and low Fe contents indicate that the majority of the evolved
AOB lavas, however, do not represent an intermediate stage in the liquid line of descent to hawaiites, but were most likely
produced by gabbroic fractionation from primitive AOB magmas at relatively low pressures. The parental magmas of the majority
of these lavas were distinct from those of the observed high-MgO basalts, having higher HFSE contents and being more Si-under-saturated.
The high Al, high Sr/Zr signature of high-pressure fractionation of a clinopyroxene-dominated assemblage in the IVC is shared
by hawaiites of other alkaline volcanic suites of the Canadian Cordillera, such as the Edziza Volcanic Complex in northern
B.C. and appears to be a feature of hawaiites in many localities, including Hawaii and Iceland. Viscosities calculated for
both high- and low-pressure crystal fractionation models suggest that aphyric hawaiites are residual liquids escaped from
a wehrlitic crystalline network, at elevated pressures, possibly at the base of the crust.
Editorial responsibility: T.L. Grove 相似文献
90.
In order to determine whether charge transfer during the collision of ice crystals with riming graupel pellets in thunderstorms may be due to the removal of charged growths on the graupel surface, experiments were performed in which an air jet removed forst or pieces of rime from ice surfaces. The results showed that a frost covered or rimed surface charged positively if it was growing by vapour diffusion and negatively if it was evaporating when the air jet fragmented the surface. Other work has shown that similar results are obtained when ice crystals or ice spheres interact with growing or evaporating ice surfaces and so it appears that the charge transfer process is associated with the removal of charged surface features. These results are of relevance to our understanding of the processes of thunderstorm electrification. 相似文献