The Effect of an Infaunal Suspension Feeding Bivalve Mercenaria mercenaria (L.) on Benthic Recruitment*     

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   

San Pedro Shelf California: testing the Pearson-Rosenberg model (PRM)     

Don MaurerGeorge Robertson  Thomas Gerlinger 《Marine environmental research》1993,35(4)

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   

Hydraulic redistribution by deeply rooted grasses and its ecohydrologic implications in the southern Great Plains of North America     

Erik Oerter  Eric Slessarev  Ate Visser  Kyungjin Min  Megan Kan  Karis J. McFarlane  Malay C. Saha  Asmeret Asefaw Berhe  Jennifer Pett-Ridge  Erin Nuccio 《水文研究》2021,35(9):e14366

Perennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ²H and δ¹⁸O) and ³H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow-rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow-rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow-rooted species in inter-cropping arrangements.  相似文献   

Comparison of streamflow recession between plantations and native forests in small catchments in Central-Southern Chile     

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   

Electrical interferences observed in the Cassini CIRS spectrometer     

Cheong Chan  Shane Albright  Nicolas Gorius  John Brasunas  Don Jennings  F. Michael Flasar  Ronald Carlson  Ever Guandique  Conor Nixon 《Experimental Astronomy》2015,39(2):367-386

  相似文献   

Enriched crustal and mantle components and the role of the lithosphere in generating Paleoproterozoic dyke swarms of the Ungava Peninsula,Canada     

Charles Maurice  Don Francis 《Lithos》2010,114(1-2):95-108

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 εNd_2.0 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 εNd_2.0 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 εNd_2.0 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, εNd_2.0 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 εNd_2.0 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 (T_DM 4.3–3.1 Ga), whereas dykes without this component occur in an isotopically juvenile terrane (T_DM < 3.1 Ga). The lack of a crustal component and the positive εNd_2.0 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   

Spitzer space telescope observations of SGR and AXP environments     

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   

气象因素对飞行安全高度的影响          下载免费PDF全文

白建忠  窦金锋 《气象》1995,21(9):7-10

通过分析气象因素对气压式高度表测量高度的影响，求出了高度误差极值，说明了我国安全高度按高于航线两侧２５ｋｍ范围内的最大标高４００ｍ或６００ｍ存在一定误差，提出了４条预防措施。  相似文献   

The relationship between the hawaiites and basalts of the itcha Volcanic Complex,central British Columbia     

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   

Forum The observational side of volcanology     

Don Swanson 《Bulletin of Volcanology》1994,56(2):133

American Scientist , I think. One panel shows an Einstein-like figure in an easy chair with a pencil and pad of paper; this panel is labeled Big Science. The other panel shows the headquarters of a high-tech company and is labeled Little Science. Think about it. Science builds on testable ideas, often qualitative in nature, that commonly arise from observations of natural phenomena. Technology confirms or denies those ideas and helps to quantify them. Both are important, and there is considerable feedback, but fundamentally the ideas drive the technology. Hence the cartoonist had it right, despite society’s common perception of what is big and what is little. Big bucks do not equal big science. Volcanology is a science, the study of volcanoes. Ideas are key to our understanding of how and why volcanoes erupt. Many of these ideas are formulated from direct observations of volcanoes and their products before, during, and after eruptions. Observational volcanology may seem old-fashioned today but remains one of the most stimulating endeavors I know. If not big science, at least it is moderate science. And rather simple, too. All you need are your eyes, ears, nose, and brain, together with suitable equipment for the situation (often only a hammer or spade). In many instances simple observations and related measurements provide fundamental information about how volcanoes work. I described three such instances in Chapter 21 of USGS Bulletin 1966 and elaborated there my feelings about the importance of field observations for monitoring volcanoes and the concept of keeping monitoring, i.e., repeated direct observation, as simple as practical. I am disheartened by the recent deaths of volcanologists in the field but encouraged by the general understanding that the volcanologic community has shown. No one wants the death rate to continue unchecked, but no one is seriously suggesting cutting back on field observations by volcanologists either. The best way to reduce fatalities is to understand the volcano better. The best way to understand the volcano better involves field observations as well as electronic sensors. Meanwhile, it is well to remember that volcanology is the study of volcanoes, and that purely scientific, curiosity-driven motives are as justified as those designed purely to mitigate risks, and I think more valuable in the end. Curiosity leads to understanding, and understanding is the paramount goal of the science as well as the soundest basis for reducing risk. Volcanologists who are curious will get themselves into trouble and sometimes die because of it. It is often stated that we must weigh the potential benefits and risks before doing something that may be perceived as risky. Of course we must, but it is mathematically impossible to solve one equation with two unknowns, and generally the potential benefits and risks are both unknowns. In the end it comes down to common sense, which varies among individuals and in any case is far from foolproof. Let is be no other way, and let us praise the curious as we mourn the dead.  相似文献