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111.
Lydie Herfort Tawnya D. Peterson Fredrick G. Prahl Lee Ann McCue Joseph A. Needoba Byron C. Crump G. Curtis Roegner Victoria Campbell Peter Zuber 《Estuaries and Coasts》2012,35(3):878-891
The localized impact of blooms of the mixotrophic ciliate Myrionecta rubra in the Columbia River estuary during 2007–2010 was evaluated with biogeochemical, light microscopy, physiological, and molecular data. M. rubra affected surrounding estuarine nutrient cycles, as indicated by high and low concentrations of organic nutrients and inorganic nitrogen, respectively, associated with red waters. M. rubra blooms also altered the energy transfer pattern in patches of the estuarine water that contain the ciliate by creating areas characterized by high primary production and elevated levels of fresh autochthonous particulate organic matter, therefore shifting the trophic status in emergent red water areas of the estuary from net heterotrophy towards autotrophy. The pelagic estuarine bacterial community structure was unaffected by M. rubra abundance, but red waters of the ciliate do offer a possible link between autotrophic and heterotrophic processes since they were associated with elevated dissolved organic matter and showed a tendency for enhanced microbial secondary production. Taken together, these findings suggest that M. rubra red waters are biogeochemical hotspots of the Columbia River estuary. 相似文献
112.
The capacity to detect remnants of fire usage in archaeological sites, along with a better understanding of its use by prehistoric populations, can help us to shed light on hominin cognition, social organization, and technology. The application of phytolith studies to understand fire and its use can be widely applicable since plants typically contain phytoliths that are identifiable to different taxonomic levels. Pinnacle Point 13B (PP13B) is one of several South African Middle Stone Age (MSA) sites that shows an abundant presence of lenses of burnt material and intact hearths. Phytolith analyses at PP13B have been used to identify the types of plants used as fuel in the hearths. The phytoliths overall show high levels of alteration, and varying alteration is used to identify areas with higher alkaline conditions related to dripping water. In some areas of the site, there is excellent preservation of multicellular structures from the epidermal leaves of dicotyledonous plants, suggesting in situ structures with practically no chemical or post‐depositional alteration. A notable pattern is the abundance of dicotyledonous leaves from the rear of the cave, which might indicate specific leaf‐fuels for the fires, short‐term fire activities, or other actions such as cooking. 相似文献
113.
The permeability of lunar soil simulant, JSC-1A, is measured over a range of bulk densities from 1550 to 2000 kg m−3. The corresponding viscous flow permeability is 1 × 10−12 m2 to 6.1 × 10−12 m2 for this bulk density range. Implications of these values on the contamination of regolith by rockets, on barrier/enhancement to bulk flow of ice, and on cratering are discussed. Although the particle size and shape distribution of the JSC-1A are extremely wide, the permeability measurements agree surprisingly well with the Carman-Kozeny equation. The results provide evidence that the Carman-Kozeny model could be applicable to other naturally occurring soils if effective soil properties are considered. 相似文献
114.
We have carried out numerical simulations of three-dimensional nonisothermal flow around an in situ heat-based flow sensor to investigate how formation heterogeneities can affect the interpretation of ground water flow velocities from this instrument. The flow sensor operates by constant heating of a 0.75-m-long, 5-cm-diameter cylindrical probe, which contains 30 thermistors in contact with the formation. The temperature evolution at each thermistor can be inverted to obtain an estimate of the ground water flow velocity vector using the standard interpretive method, which assumes that the formation is homogeneous. Analysis of data from heat-based flow sensors installed in a sand aquifer at the Former Fort Ord Army Base near Monterey, California, suggested an unexpected component of downward flow. The magnitudes of the vertical velocities were expected to be much less than those of the horizontal velocities at this site because the sensors were installed just above a clay aquitard. Numerical simulations were conducted to examine how differences in thermal conductivities may lead to spurious indications of vertical flow velocities. We found that a decrease in the thermal conductivity near the bottom of the sensor can perturb the temperature profiles along the instrument in such a manner that analyses assuming homogeneous thermal conductivity could indicate a vertical flow component even though flow is actually horizontal. This work demonstrates how modeling can be used to simulate instrument response to formation heterogeneity and shows that caution must be used in interpreting data from such devices. 相似文献
115.
Percolation-theory and fuzzy rule-based probability estimation of fault leakage at geologic carbon sequestration sites 总被引:1,自引:0,他引:1
Yingqi Zhang Curtis M. Oldenburg Stefan Finsterle 《Environmental Earth Sciences》2010,59(7):1447-1459
Leakage of CO2 and displaced brine from geologic carbon sequestration (GCS) sites into potable groundwater or to the near-surface environment
is a primary concern for safety and effectiveness of GCS. The focus of this study is on the estimation of the probability
of CO2 leakage along conduits such as faults and fractures. This probability is controlled by (1) the probability that the CO2 plume encounters a conductive fault that could serve as a conduit for CO2 to leak through the sealing formation, and (2) the probability that the conductive fault(s) intersected by the CO2 plume are connected to other conductive faults in such a way that a connected flow path is formed to allow CO2 to leak to environmental resources that may be impacted by leakage. This work is designed to fit into the certification framework
for geological CO2 storage, which represents vulnerable resources such as potable groundwater, health and safety, and the near-surface environment
as discrete “compartments.” The method we propose for calculating the probability of the network of conduits intersecting
the CO2 plume and one or more compartments includes four steps: (1) assuming that a random network of conduits follows a power-law
distribution, a critical conduit density is calculated based on percolation theory; for densities sufficiently smaller than
this critical density, the leakage probability is zero; (2) for systems with a conduit density around or above the critical
density, we perform a Monte Carlo simulation, generating realizations of conduit networks to determine the leakage probability
of the CO2 plume (P
leak) for different conduit length distributions, densities and CO2 plume sizes; (3) from the results of Step 2, we construct fuzzy rules to relate P
leak to system characteristics such as system size, CO2 plume size, and parameters describing conduit length distribution and uncertainty; (4) finally, we determine the CO2 leakage probability for a given system using fuzzy rules. The method can be extended to apply to brine leakage risk by using
the size of the pressure perturbation above some cut-off value as the effective plume size. The proposed method provides a
quick way of estimating the probability of CO2 or brine leaking into a compartment for evaluation of GCS leakage risk. In addition, the proposed method incorporates the
uncertainty in the system parameters and provides the uncertainty range of the estimated probability. 相似文献
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119.
Richard W. Battarbee Gavin L. Simpson Helen Bennion Christopher Curtis 《Journal of Paleolimnology》2011,45(4):489-505
This paper has two aims: (1) to show for the first time how a natural typology can be established using palaeoecological methods;
and (2) to show how it can be used in lake restoration studies with respect to the definition of recovery targets for acidified
lakes. By defining the characteristic reference assemblages for low alkalinity site types rather than for a specific site
it allows success to be measured more broadly, unconstrained by the specific composition of the pre-acidification flora. We
analyse statistically the pre-acidification diatom assemblages of sediment cores from 121 low alkalinity lakes in the UK in
order to assess whether a reference typology for such lakes can be defined on the basis of their diatom floras. We use samples
dating to ~1850 AD to represent pre-acidification conditions. The results show that three main clusters can be identified,
two dominated by benthic taxa (Clusters 1 and 3) and one dominated by planktonic taxa (Cluster 2). Cluster 1 is characterised
by taxa such as Brachysira vitrea, Cymbella microcephala and Fragilaria spp., Cluster 2 by Cyclotella comensis, C. radiosa, Asterionella formosa, Aulacoseira subarctica and Achnanthes minutissima and Cluster 3 by Eunotia incisa, Frustulia rhomboides var. saxonica, Fragilaria virescens var. exigua, and Cymbella perpusilla. Although environmental data for 1850 AD are not available it is apparent from the contemporary distribution of the taxa
in the different clusters that Cluster 2 represents the most alkaline pre-acidification conditions. Some sites in this cluster
have been acidified, but some, especially the larger, deeper lakes have been enriched. Cluster 1 includes sites that contain
diatoms with relatively high pH optima (pH 6.4–7.4) whereas Cluster 3 sites contain diatoms with the lowest pre-acidification
pH conditions in the data-set. Sites in this cluster also have the lowest base cation concentrations at the present day and
include the sites in the UK that have been most affected by acid deposition. 相似文献
120.