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61.
62.
Physiochemical controls on the carbonate geochemistry of large river systems are important regulators of carbon exchange between terrestrial and marine reservoirs on human time scales. Although many studies have focused on large-scale river carbon fluxes, there are few investigations of mechanistic aspects of carbonate mass balance and transport at the catchment scale. We determined elemental and carbonate geochemistry and mass balances for net carbonate dissolution fluxes from the forested, mid-latitude Huron River watershed, established on carbonate-rich unconfined glacial drift aquifers. Shallow groundwaters are near equilibrium with respect to calcite at pCO2 values up to 25 times atmospheric values. Surface waters are largely groundwater fed and exhibit chemical evolution due to CO2 degassing, carbonate precipitation in lakes and wetlands, and anthropogenic introduction of road salts (NaCl and CaCl2). Because the source groundwater Mg2+/HCO3 ? ratio is fairly constant, this parameter permits mass balances to be made between carbonate dissolution and back precipitation after groundwater discharge. Typically, precipitation does not occur until IAP/K calcite values exceed 10 times supersaturation. Stream chemistry changes little thereafter even though streams remain highly supersaturated for calcite. Our data taken together with historical United States Geological Survey (USGS) data show that alkalinity losses to carbonate precipitation are most significant during periods of lowest discharge. Thus, on an annual basis, the large carbon flux from carbonate dissolution in soil zones is only decreased by a relatively small amount by the back precipitation of calcium carbonate. 相似文献
63.
Kathryn Besio 《Area》2003,35(1):24-33
This paper examines the transcultural relations between researchers and research subjects in a postcolonial research setting. I draw from my experience doing dissertation research in northern Pakistan to discuss how my research subjects' effectively constructed me as a sahib, or what I saw as a colonial subject position. I examine the ways that my research subjects and I co-constructed, although unequally, my position and location as a researcher. The asymmetries of power relations in research are exacerbated by postcolonial relations in this contact zone. The contribution of those I researched is significant towards understanding our locations as postcolonial subjects in this research setting, and the location from which I produced the research. While it was difficult to do research as anyone other than a sahib during my research, the stories I tell and metaphors I employ in this paper attempt to destabilize my location as a colonial sahib, an authority. The scatological references that run throughout this paper are an attempt to write against the inherently colonial epistemologies that underpin geographic research more generally. 相似文献
64.
Kathryn L. Linge 《Geostandards and Geoanalytical Research》2008,32(4):453-468
This review describes developments in trace element determination using inductively coupled plasma‐atomic emission spectrometry (ICP‐AES) and inductively coupled plasma‐mass spectrometry (ICP‐MS) that were reported in 2006 and 2007. It focuses on the application of ICP techniques to geological and environmental samples; fundamental studies in ICP‐MS and ICP‐AES instrumentation have largely been ignored. New advances in ICP‐MS and ICP‐AES were incremental over this period, partly because both techniques are now well‐established. A continuing shift towards the hyphenation of low‐flow separation techniques has sparked activity in the development of appropriate low‐flow interfaces, and papers discussing interference removal also contribute significantly to the volume of research for both ICP‐AES and ICP‐MS. Whereas the majority of new ICP publications concerned advances in ICP‐MS analysis rather than ICP‐AES, development for ICP‐AES still occurs in almost all areas, particularly in sample introduction and hyphenated techniques. 相似文献
65.
Kathryn E. Collins Catherine M. Febria Helen J. Warburton Hayley S. Devlin Kristy L. Hogsden Brandon C. Goeller 《新西兰海洋与淡水研究杂志》2019,53(2):182-200
Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species. 相似文献
66.
A two-dimensional (2D) finite element analytical model is developed to analyze the seismic response of rigid highway bridge abutments, retaining and founded on dry sand. A well verified finite element code named FLEX is used for this purpose. The proposed model has the following characteristics: (1) The soil (dry sand in this study) is modeled by a 2D finite element grid; (2) The bridge abutment is molded as a rigid substructure; (3) The strength and deformation of the soil are modeled using the viscous cap constitutive model. This model consists of a failure surface and hardening cap together with an associated flow rule. The cap surface is activated for the soil under the wall to represent compaction during wall rocking. In addition, viscoelastic behavior is provided for representing the hysteretic-like damping of soil during dynamic loading; (4) Interface elements are used between the wall and the soil (at the backface of the wall and under its base) to allow for sliding and for debonding/recontact behavior; (5) The finite element grid is truncated by using an absorbing boundary approximation. Using this boundary at both sides of the grid simulates the horizontal radiation of energy scattered from the wall and the excavation. Shear beams are placed adjacent to the lateral boundaries from each side which give the far-field ground motion, for comparison with those computed adjacent to the boundaries. The analytical model is verified comparing predictions to results from dynamic centrifuge tests, with satisfactory agreement. The proposed model is used to study the dynamic response of an 8.0 m high and 3.0 m wide rigid bridge abutment (proportioned using the traditional approach to design) for different sinusoidal and earthquake acceleration input motions. The results from the analysis show that outward tilting of rigid bridge abutments is the dominant mode of response during dynamic shaking and that these abutments end up with a permanent outward tilt at the end of shaking. The results from all the analyzed cases of the 8.0 m high gravity retaining wall together with those from the analysis of the tilting wall centrifuge tests are discussed and used for proposing a practical method for evaluating the seismic response of rigid abutments during earthquakes. 相似文献
67.
Alluvial rivers are composed of self-formed channels which are sensitive to disturbances in their flow and sediment-supply regimes. Regime changes commonly occur over decadal and longer timescales and can be caused by anthropogenic alterations such as dam construction and removal. Advances in numerical modeling have increased our ability to explore geomorphic adjustments over long timescales; however, many models designed to be run for decades or longer assume that banks are immovable or that channel width is constant. Since river channels often respond to disturbance by adjusting their geometry, this is a significant shortcoming. To investigate the impact of long-term sediment supply alterations on channel geometry and stability, we have adapted MAST-1D, a reach-scale bed evolution model, to incorporate functions for bank erosion, vegetation encroachment, and local avulsions. The model is designed for medium-large, coarse multithreaded rivers and can be run over long (decades–centuries) timescales. Bank erosion is a function of the mobility and transport capacity for structurally-important grains which protect the bank toe. Vegetation growth is proportional to point bar width and occurs during conditions of low shear stress. Local avulsions occur when aggradation causes channel depth to drop below a threshold. We apply the model to the Elwha River in Washington, USA with the goal of investigating if and when the river recovers from dam emplacement and removal. The Elwha was dammed for nearly 100 years, and then two dams were removed, releasing a large pulse of sediment. We have modeled the set of reaches between the two dams. Our simulations suggest that channel response to dam emplacement occurs gradually over several decades but that the channel recovers to near pre-dam conditions within about a decade following the removal. The dams leave a lasting legacy on the floodplain, which does not completely recover, even after two centuries. © 2019 John Wiley & Sons, Ltd. 相似文献
68.
Understanding the extent to which local factors, including bedrock and structure, govern catchment denudation in mountainous environments as opposed to broader climate or tectonic patterns provides insight into how landscapes evolve as sediment is generated and transported through them, and whether they have approached steady-state equilibrium. We measured beryllium-10 (10Be) concentrations in 21 sediment samples from glaciated footwall and hanging wall catchments, including a set of nested catchments, and 12 bedrock samples in the Puga and Tso Morari half-grabens located in the high-elevation, arid Zanskar region of northern India. In the Puga half-graben where catchments are underlain by quartzo-feldspathic gneissic bedrock, bedrock along catchment divides is eroding very slowly, about 5 m/Ma, due to extreme aridity and 10Be concentrations in catchment sediments are the highest (~60–90 × 105 atoms/g SiO2) as colluvium accumulates on hillslopes, decoupled from their ephemeral streams. At Puga, 10Be concentrations and the average erosion rates of a set of six nested catchments demonstrate that catchment denudation is transport-limited as sediment stagnates on lower slopes before reaching the catchment outlet. In the Tso Morari half-graben, gneissic bedrock is also eroding very slowly but 10Be concentrations in sediments in catchments underlain by low grade meta-sedimentary rocks, are significantly lower (~10–35 × 105 atoms/g SiO2). In these arid, high-elevation environments, 10Be concentrations in catchment sediments have more to do with bedrock weathering and transport times than steady-state denudation rates. © 2020 John Wiley & Sons, Ltd. 相似文献
69.
The assessment of vitellogenin as a biomarker of exposure to estrogenic compounds in two Australian perciformes 总被引:1,自引:0,他引:1
Vitellogenin (Vtg) is a yolk protein precursor that has been identified as a sensitive biomarker for exposure to estrogenic compounds. We evaluated specific monoclonal and polyclonal antibodies for reactivity with plasma Vtg from two Australian Perciformes, the tropical barramundi (Lates calcarifer) and the temperate black bream (Acanthopagrus butcheri). Blood plasma from 17beta-estradiol exposed (E2) male barramundi (20 mg kg(-1)) and male black bream (2.5-5.0 mg kg(-1)) were sent to Biosense Laboratories (Norway) for cross-reactivity testing using their extensive anti-Vtg antibody selection. Indirect ELISA results determined barramundi plasma displayed the highest binding affinities to ND-3G2 (monoclonal-Mab) and PO-1 (polyclonal-Pab). Black bream was most cross-reactive with ND-1C8 (Mab) and PO-2 (Pab). Next, plasma was assessed for Vtg induction in E2-dosed (5 mg kg(-1)), hatchery-reared barramundi and black bream versus a non-injected control group. Vtg production was assessed by Western blot and indirect ELISA using ND-3G2 and ND-1C8 Mabs, respectively. A prominent band was identified in the range of 100-200 kDa for all female black bream and for all E2-treated barramundi and black bream males, which was confirmed as Vtg by Western blot. Indirect ELISA results for barramundi demonstrated highly significant differences in E2-dosed fish as compared to control fish (Student t, P<0.001). E2 male black bream were significantly different than control males (Student t, P<0.001) and control and E2 females displayed highly significant differences (Student t, P<0.001). These results indicate that exposure to 17beta-estradiol induces significant Vtg production in males of the two Australian Perciformes, with potential use as a biomarker for exposure to estrogenic compounds. 相似文献
70.
McMahon K Bengtson Nash S Eaglesham G Müller JF Duke NC Winderlich S 《Marine pollution bulletin》2005,51(1-4):325-334
Low concentrations of herbicides (up to 70 ng l(-1)), chiefly diuron (up to 50 ng l(-1)) were detected in surface waters associated with inter-tidal seagrass meadows of Zostera muelleri in Hervey Bay, south-east Queensland, Australia. Diuron and atrazine (up to 1.1 ng g(-1) dry weight of sediment) were detected in the sediments of these seagrass meadows. Concentration of the herbicides diuron, simazine and atrazine increased in surface waters associated with seagrass meadows during moderate river flow events indicating herbicides were washed from the catchment to the marine environment. Maximum herbicide concentration (sum of eight herbicides) in the Mary River during a moderate river flow event was 4260 ng l(-1). No photosynthetic stress was detected in seagrass in this study during low river flow. However, with moderate river flow events, nearshore seagrasses are at risk of being exposed to concentrations of herbicides that are known to inhibit photosynthesis. 相似文献