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Ammonium excretion by benthic invertebrates and sediment-water nitrogen flux in the Gulf of Mexico near the Mississippi River outflow 总被引：1，自引：0，他引：1
Wayne S. Gardner Elva Escobar Briones Elizabeth Cruz Kaegi Gilbert T. Rowe 《Estuaries and Coasts》1993,16(4):799-808
Benthic macroinvertebrate biomass and ammonium excretion rates were measured at four stations in the Gulf of Mexico near the Mississippi River mouth. Calculated areal excretion rates were then compared to sediment-water nitrogen fluxes measured in benthic bottom lander chambers at similar stations to estimate the potential importance of macroinvertebrate excretion to sediment nitrogen mineralization. Excretion rates for individual crustaceans (amphipods and decapods) was 2–21 nmoles NH4 + (mg dry weight)?1 h?1. The mean excretion rates for the polychaetes, Paraprionaspio pinnata [6–12 nmoles NH4 + (mg dry weight)?1h?1] and Magelona sp. [27–53 nmoles NH4 + (mg dry weight)?1h?1], were comparable or higher than previous measurements for similar size benthic or pelagic invertebrates incubated at the same temperature (22±1°C). Although the relatively high rates of excretion by these selective feeders may have been partially caused by experimental handling effects (e.g., removal from sediment substrates), they probably reflected the availability of nitrogen-rich food supplies in the Mississippi River plume. When the measured weight-specific rates were extrapolated to total areal biomass, areal macroinvertebrate excretion estimates ranged from 7 μmole NH4 + m?2h?1 at a 40-m deep station near the river mouth to 18 μmole NH4 + m?2h?1 at a shallower (28-m deep) station further from the river mouth. The net flux of ammonium and nitrate from the sediments to the water measured in bottom lander chambers in the same region were 15–53 μmole NH4 + m?2h?1 and ?25–21 μmole NO3 ? m?2h?1. These results suggest that excretion of NH4 + by macroinvertebrates could be a potentially important component of benthic nitrogen regeneration in the Mississippi River plume-Gulf shelf region. 相似文献
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A model for adjustment of differential gravity measurements with simultaneous gravimeter calibration
A mathematical model is proposed for adjustment of differential or relative gravity measurements, involving simultaneously
instrumental readings, coefficients of the calibration function, and gravity values of selected base stations. Tests were
performed with LaCoste and Romberg model G gravimeter measurements for a set of base stations located along a north–south
line with 1750 mGal gravity range. This line was linked to nine control stations, where absolute gravity values had been determined
by the free-fall method, with an accuracy better than 10 μGal. The model shows good consistence and stability. Results show
the possibility of improving the calibration functions of gravimeters, as well as a better estimation of the gravity values,
due to the flexibility admitted to the values of the calibration coefficients.
Received: 15 November 1999 / Accepted: 31 October 2000 相似文献
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The influence of upwelling on the distribution of chlorophyll a within the Bay of Concepción, Chile is discussed in light of continuous measurements of surface in vivo chlorophyll fluorescence and temperature taken simultaneously along horizontal transects, and hydrographic stations' data. Results suggest significant temporal variability both in the distribution of in vivo fluorescence, temperature and salinity within the Bay and in the characteristics of the exchange between the Bay and the adjacent shelf waters, induced by variable upwelling. Upwelling is produced by the predominant south-westerly winds during the summer. Significant variations in the wind direction occur with periods from two to seven days. During active upwelling, exchange is characterized by a surface outflow through the mouth of the Bay and an inflow at depth. Low chlorophyll fluorescence is confined to the upwelling areas on the eastern shore either within or outside the Bay; high chlorophyll fluorescence is confined to the central and western Bay. Density data suggest a three-layered circulation pattern at the mouth of the Bay during the upwelling relaxation involving an inflow both at the surface and bottom and outflow at mid-depth. Associated with this exchange is an active high chlorophyll transport from the Bay to the adjacent coastal waters at mid-depth and inflow of low chlorophyll water from the adjacent shelf at the surface and near the bottom. 相似文献
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Jennifer L. Mays Mark Brenner Jason H. Curtis Kathryn V. Curtis David A. Hodell Alex Correa-Metrio Jaime Escobar Andrea L. Dutton Andrew R. Zimmerman Thomas P. Guilderson 《Journal of Paleolimnology》2017,57(4):307-319
Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C3–C4 terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ13C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ13C values in total organic carbon, which reflect times of greater proportions of C4 plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation. 相似文献
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Javier Alcocer Elva G. Escobar Alfonso Lugo Luis A. Oseguera 《International Journal of Salt Lake Research》1999,8(2):113-126
The effects of multiple stressors on the benthic macroinvertebrate community were monitored in Tecuitlapa Norte, a shallow,
perennially-astatic, warm, mesosaline, sodaalkaline lake in Mexico. Physico-chemical and biological variables were determined
monthly for one year. Tecuitlapa Norte displayed a clear seasonal environmental pattern (dry and rainy seasons). The benthic
macroinvertebrate community consisted of five species:Culicoides occidentalis sonorensis Jorgensen,Ephydra hians Say,Stratiomys sp.,Eristalis sp., andLimnophora sp. of which the first two were dominant and the rest scarce.C. occidentalis was the most important species numerically (76 percent of the total), whileE. hians dominated the biomass (73 percent of the total). Primarily salinity and secondarily pH appear to be the most important environmental
factors controlling dominance of benthic organisms in Tecuitlapa Norte. Seasonal abundance dynamics of the dominant organisms
was associated with phases in their reproductive cycles: environmentally-triggered (i.e., temperature rise, water-level descent)
pupation and emergence periods. We concluded that whereas physical and chemical factors (i.e., salinity, pH) exerted the primary
control on benthic macroinvertebrate community composition in Tecuitlapa Norte, another assembly of variables (e.g., water-level,
temperature) influenced species distribution and abundance. 相似文献
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Escobar Sebastian Bi Qilong Fettweis Michael Wongsoredjo Samor Monbaliu Jaak Toorman Erik 《Ocean Dynamics》2023,73(6):333-358
Ocean Dynamics - A dynamic two-dimensional depth-averaged (2DH) parameterization for flocculation of cohesive sediments is proposed based on the kinetic model by Winterwerp (J Hydraul Res... 相似文献
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EVA: GPS-based extended velocity and acceleration determination 总被引：1，自引：0，他引：1
Dagoberto Salazar Manuel Hernandez-Pajares Jose Miguel Juan-Zornoza Jaume Sanz-Subirana Angela Aragon-Angel 《Journal of Geodesy》2011,85(6):329-340
In this work, a new GPS carrier phase-based velocity and acceleration determination method is presented that extends the effective
range of previous techniques. The method is named ‘EVA’, and may find applications in fields such as airborne gravimetry when
rough terrain or water bodies make difficult or impractical to set up nearby GPS reference receivers. The EVA method is similar
to methods such as Kennedy (Precise acceleration determination from carrier phase measurements. In: Proceedings of the 15th
international technical meeting of the satellite division of the Institute of Navigation. ION GPS 2002, Portland pp 962–972,
2002b) since it uses L1 carrier phase observables for velocity and acceleration determination. However, it introduces a wide network
of stations and it is independent of precise clock information because it estimates satellite clock drifts and drift rates
‘on-the-fly’, requiring only orbit data of sufficient quality. Moreover, with EVA the solution rate is only limited by data
rate, and not by the available precise satellite clocks data rate. The results obtained are more robust for long baselines
than the results obtained with the reference Kennedy method. An advantage of being independent of precise clock information
is that, beside IGS Final products, also the Rapid, Ultra-Rapid (observed) and Ultra-Rapid (predicted) products may be used.
Moreover, the EVA technique may also use the undifferenced ionosphere-free carrier phase combination (LC), overcoming baseline
limitations in cases where ionosphere gradients may be an issue and very low biases are required. During the development of
this work, some problems were found in the velocity estimation process of the Kennedy method. The sources of the problems
were identified, and an improved version of the Kennedy method was used for this research work. An experiment was performed
using a light aircraft flying over the Pyrenees, showing that both EVA and the improved Kennedy methods are able to cope with
the dynamics of mountainous flight. A RTK-derived solution was also generated, and when comparing the three methods to a known
zero-velocity reference the results yielded similar performance. The EVA and the improved-Kennedy methods outperformed the
RTK solutions, and the EVA method provided the best results in this experiment. Finally, both the improved version of the
Kennedy method and the EVA method were applied to a network in equatorial South America with baselines of more than 1,770 km,
and during local noon. Under this tough scenario, the EVA method showed a clear advantage for all components of velocity and
acceleration, yielding better and more robust results. 相似文献