In a long-term, spatially comprehensive beam trawl survey of the Navesink River-Sandy Hook Bay estuary, the blue crabCallinectes sapidus was one of the most abundant species. Seasonal changes in abundance were evident, with low abundances in summer followed
by peak abundances in the fall, after juveniles recruited to the estuary. We saw no long-term trends in abundance during the
5 yr study. Location in the navesink River or Sandy Hook Bay explained most of the variance in abundance within any one survey.
In diet analyses, we found evidence of cannibalism in all seasons, but in the size range of crabs caught in this study (10–180
mm), we did not find a relationship between cannibalism and juvenile crab abundance. Within surveys, crabs divided into 20
mm size categories showed no sizerelated differences in location within the estuary or among 7 habitat types examined (algae
bed, amphipod bed, beach, channel, marsh edge, mid-depth, and sandbar). Channels and sandbars tended to exhibit lower crab
abundance than other habitats. Shallow habitats with and without cover were equally preferred by juvenile blue crabs, implying
that the presence of structure was not critical. Spatial models of crab abundance (<- 80 mm carapace width) to environmental
data were fit from several seasons of intensive sampling in the Navesink River-Sandy Hook Bay estuary between summer 1996
and spring 1998. These models indicated that fine-grained sediments, tmmperature, depth, and salinity were good indicators
of crab abundance in spring, summer, and fall. Using these spatial models and environmental data collected in subsequent seasons
(summer 1998−fall 1999), we were able to predict blue crab abundance in the river as evidenced by significant correlations
between predicted and observed abundances. For the size range of crabs examined here, physical conditions may be as important
as structural habitat types or cannibalism in determining habitat use in northerly estuaries. 相似文献
Relations are established between the Delaunay variables defined over a phase space E in four dimensions and the Lissajous variables defined over a four-dimensional phase space F when the latter is mapped onto E by a parabolic canonical transformation. 相似文献
We have discovered two FUN inclusions, CG-14 and TE, among a group of five forsterite-rich inclusions in Allende, two of which are described for the first time herein. All five consist of euhedral forsterite and spinel crystals poikilitically enclosed by fassaite. Forsterite and spinel are usually segregated from one another, sometimes into a spinel-rich mantle and a forsterite-rich core. Some inclusions contain vesicles, indicating that they were once molten. The crystallization sequence inferred from textures is: spinel, forsterite, fassaite and, finally, Mg-rich melilite. One concentrically-zoned inclusion contains melilite in its mantle whose composition lies on the opposite side of the liquidus minimum in the melilite binary from that in its core. This suggests that segregation of forsterite from spinel in all of these inclusions could be due to volatilization of MgO and SiO2 relative to Al2O3 and CaO from the outsides of droplets. CG-14 is relatively uniformly enriched in refractory elements relative to Cl chondrites by a factor similar to that for Ca-, Al-rich coarse-grained inclusions except for Ca, Al and Hf which are unusually low. No Ce anomaly such as found in FUN inclusions Cl and HAL is present in CG-14. Whole-rock samples of CG-14 and TE are more strongly mass-fractionated in oxygen relative to “normal” Allende inclusions than the FUN inclusion EK 1-4-1 and less so than Cl. Relative to bulk Allende, both inclusions have strongly massfractionated magnesium and silicon and 25Mg excesses or deficits of 24Mg or 26Mg. CG-14 has a 29Si excess or a deficit of 28Si or 30Si. Volatilization loss cannot be responsible for the magnesium and silicon isotope fractionations, as this would require prohibitively large mass loss from these magnesium-rich inclusions. The remarkable similarity in textures between FUN and non-FUN inclusions implies similar thermal histories, arguing against different rates of evaporative loss of major elements. Sputtering alone may be insufficient to account for the magnitude and direction of oxygen isotope fractionation in FUN inclusions. 相似文献
Methanotrophic biomass and community structure were assessed for a soil column enriched with natural gas. An increase in microbial biomass, based on phospholipid ester-linked fatty acids (PLFA), was apparent for the natural gas-enriched column relative to a control column and untreated surface soil. Following GC-MS analyses of the derivatized monounsaturated fatty acids, the major component (22% of the PLFA) of the natural gas-enriched column was identified as 18·1Δ 10c. This relatively novel fatty acid has only been previously reported as a major component in methanotrophs. Its presence in the soil, together with other supportive evidence, implies that this microbial metabolic group makes a large contribution to the column flora. Other microbial groups were also recognized and differences compared between the soils analysed. A recently developed HPLC method for the separation and characterisation of archaebacterial phospholipid-derived signature di- and tetra-ether lipids was used to examine methane-producing digesters. With this technique, methanogenic biomasses of approximately 1011 bacteria per g dry weight of digestor material were determined. Differences between ratios of diether to tetraether phospholipids were apparent for the digestors analysed, though the causes are at this stage unknown. Taken together, these two methods can be used to estimate methanotrophic and methanogenic contributions in both model systems and environmental samples. 相似文献
When the National Weather Service (NWS) issues a tornado warning, the alert is rapidly and widely disseminated to individuals in the general area of the warning. Historically, the assumption has been that a false-negative warning perception (i.e., when someone located within a warning polygon does not believe they have received a tornado warning) carries a higher cost than a false-positive warning perception (i.e., when someone located outside the warning area believes they have received a warning). While many studies investigate tornado warning false alarms (i.e., when the NWS issues a tornado warning, but a tornado does not actually occur), less work focuses on studying individuals outside of the warning polygon bounds who believe they received a warning (i.e., false-positive perceptions). This work attempts to quantify the occurrence of false-positive perceptions and possible factors associated with the rate of occurrence. Following two separate storm events, Oklahomans were asked whether they perceived a tornado warning. Their geolocated responses were then compared to issued warning polygons. Individuals closer to tornado warnings or within a different type of warning (e.g., a severe thunderstorm warning) are more likely to report a false-positive perception than those farther away or outside of other hazard warnings. Further work is needed to understand the rate of false-positive perceptions across different hazards and how this may influence warning response and trust in the National Weather Service.
The quality of the groundwater supplying drinking water to the Guadalajara metropolitan area has deteriorated due to both endogenic and exogenic processes. Previous studies of this complex neotectonic volcanic environment suggest that the sources of contamination here are underground fluids derived from an active volcanic center and surface wastewater derived from regional land‐use intensification. This study uses isotopic, gaseous, and chemical signatures to more comprehensively characterize this groundwater flow and its contamination paths. Groundwater is mainly recharged at the La Primavera Caldera to the west and is discharged into the Santiago River to the east. The exception to this trend is the Toluquilla area, where groundwater most likely represents rainfall originating from outside the basin limits. Evaporation affects groundwater in these areas, especially waters that have been affected by recycling below urban areas in the Atejamac area and by intensive agricultural activity in the Toluquilla area. Additionally, we present evidence that groundwater flow through alluvial sediments and tuffs in deeper wells mixes with a lower aquifer unit in basaltic‐andesitic rocks, which are in contact with hydrothermal fluids. Groundwater ages range from postbomb in the western and northwestern regions of the study area (i.e., the Atemajac aquifer unit) to Late Pleistocene in the southern and southeastern regions (i.e., the Toluquilla aquifer unit). Recently recharged water records little mixing and is located mostly in or near the La Primavera volcanic system. As groundwater undergoes gravitational flow towards discharge areas, it mixes with older water components. Chloride and sodium concentrations above natural background levels are primarily related to volcanic activity, nitrate is associated with human activities, and sulfate originates from both anthropogenic sources and water–rock interactions. Nitrate originating from land‐use activities (such as sewers, septic tanks, landfills, and agricultural fields) that is introduced into the deeper part of the groundwater system is expected to travel with the groundwater to the discharge areas because oxidizing conditions will prevent microbial reduction. See Supplementary Information. 相似文献