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81.
The homogeneous residual circulation in Hauraki Gulf arising from the tides, steady winds, and oceanic inflows is considered by use of a depth‐averaged 2‐dimensional numerical model. Vertical current structure of the wind‐driven circulation is derived by using the computed wind‐induced sea surface slopes, the wind stress, and a prescribed vertical eddy viscosity. Tidal residual circulation is weak, less than 0.01 ms‐1 over most of the Gulf. The response of the Gulf to wind‐forcing indicates a preference for north‐west/south‐east directed winds, the flow through the Gulf being more than 3 times as strong as for winds from other directions. Surface currents are mainly in the wind direction, but subsurface currents reveal closed circulation cells in near‐coastal areas. Simple oceanic inflows give rise to water movements which penetrate to the inner part of the Gulf. 相似文献
82.
83.
The continuing degradation of coral reefs has serious consequences for the provision of ecosystem goods and services to local and regional communities. While climate change is considered the most serious risk to coral reefs, agricultural pollution threatens approximately 25% of the total global reef area with further increases in sediment and nutrient fluxes projected over the next 50 years. Here, we aim to inform coral reef management using insights learned from management examples that were successful in reducing agricultural pollution to coastal ecosystems. We identify multiple examples reporting reduced fluxes of sediment and nutrients at end-of-river, and associated declines in nutrient concentrations and algal biomass in receiving coastal waters. Based on the insights obtained, we recommend that future protection of coral reef ecosystems demands policy focused on desired ecosystem outcomes, targeted regulatory approaches, up-scaling of watershed management, and long-term maintenance of scientifically robust monitoring programs linked with adaptive management. 相似文献
84.
A model-based study of ice and freshwater transport variability along both sides of Greenland 总被引:1,自引:0,他引:1
Camille Lique Anne Marie Treguier Markus Scheinert Thierry Penduff 《Climate Dynamics》2009,33(5):685-705
We investigate some aspects of the variability of the Arctic freshwater content during the 1965–2002 period using the DRAKKAR
eddy admitting global ocean/sea-ice model (12 km resolution in the Arctic). A comparison with recent mooring sections shows
that the model realistically represents the major advective exchanges with the Arctic basin, through Bering, Fram and Davis
Straits, and the Barents Sea. This allows the separate contributions of the inflows and outflows across each section to be
quantified. In the model, the Arctic freshwater content variability is explained by the sea-ice flux at Fram and the combined
variations of ocean freshwater inflow (at Bering) and outflow (at Fram and Davis). At all routes, except trough Fram Strait,
the freshwater transport variability is mainly accounted for by the liquid component, with small contributions from the sea-ice
flux. The ocean freshwater transport variability through both Davis and Fram is controlled by the variability of the export
branch (Baffin Island Current and East Greenland Current, respectively), the variability of the inflow branches playing a
minor role. We examine the respective role of velocity and salinity fluctuations in the variability of the ocean freshwater
transport. Fram and Davis Straits offer a striking contrast in this regard. Freshwater transport variations across Davis Strait
are completely determined by the variations of the total volume flux (0.91 correlation). On the other hand, the freshwater
transport through Fram Strait depends both on variations of volume transport and salinity. As a result, there is no significant
correlation between the variability of freshwater flux at Fram and Davis, although the volume transports on each side of Greenland
are strongly anti-correlated (−0.84). Contrary to Davis Strait, the salinity of water carried by the East Greenland Current
through Fram Strait varies strongly due to the ice-ocean flux north of Greenland. 相似文献
85.
Lilian Alessa Andrew Kliskey Paula Williams Michael Barton 《Global Environmental Change》2008,18(1):153-164
This paper provides empirical evidence to support existing anecdotal studies regarding the mechanisms by which human communities become vulnerable to rapid changes in freshwater resources on the Seward Peninsula, Alaska. We interviewed adults, stratified by age, sex, and extended family, in Inupiat communities on the Seward Peninsula. Using categorical indices as part of a semi-structured interview we elicited a respondent's perception of the availability and quality of freshwater resources in their community as well as their perception of change in the availability and quality of freshwater during the period of their lifetime in that community. Significant relationships were observed between age groups for the perception of change in the availability of the local water source and the perception of change in its quality—older generations perceiving more change than younger age groups. These perceptions of change were examined with respect to recent historic changes in precipitation and temperature on the Seward Peninsula. These findings suggest that individual perceptions are instrumental in determining whether or not change merits response. The findings also provide evidence that oral traditional knowledge systems have shifted from continuous to discontinuous transmission, distancing the users from traditional resources. We discuss the role of collective knowledge, through the transmission of knowledge from elders to subsequent generations, in aiding the development of a community's ability to note and respond to changes in critical natural resources. 相似文献
86.
Sensitivity of the multiannual thermal dynamics of a deep pre‐alpine lake to climatic change
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The study of the multiannual thermal dynamics of Lake Iseo, a deep lake in the Italian pre‐alpine area, is presented. Interflow was found to be the dominant river entrance mode, suggesting future susceptibility of the lake thermal structure to the overall effects of climate change expected in the upstream alpine watershed. A lake model employed the results of a long‐term hydrologic model to simulate the effects of a climate change scenario on the lake's thermal evolution for the period 2012–2050. The model predicts an overall average increase in the lake water temperature of 0.012 °C/year and a reinforced Schmidt thermal stability of the water column in the winter up to 800 J/m2. Both these effects may further hinder the deep circulation process, which is vital for the oxygenation of deep water. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
87.
《Chemie der Erde / Geochemistry》2017,77(1):147-157
The study was carried out on the Sulejów dam reservoir (Central Poland). Water and sediment samples were collected between February and October 2006. Sulfur compounds in the sediment were chemically extracted and subjected to isotopic analysis.Large variability of SO42− concentration in the water column (from 10.3 to 36.2 mg/dm3) and the isotopic composition of sulfur (δ34S from 2.1 to 5.4‰) was observed. The main identified sources of SO42− were watercourses, surface runoff, and phosphorus fertilizers.Both oxidized sulfur species (SO42−) and its reduced forms were found in sediments. Particular sulfur forms were characterized by large variations in both, concentrations and the isotopic composition of sulfur. SO42− in the sediment and in the water column had different genesis. Bacterial oxidation of organic sulfur and its binding in SO42− were observed in the sediment. Under reducing conditions, oxidized and organic sulfur is converted to H2S which reacted with Fe or other metallic ions leading to metal sulfide precipitation. Monosulfides were shown to have a very low concentration, ranging up to 0.07 mg/g of sediment. The transformation of elemental sulfur from sulfides through their chemical oxidation occurred in the sediment. 相似文献
88.
Low flow hydrology: a review 总被引:67,自引:0,他引:67
V. U. Smakhtin 《Journal of Hydrology》2001,240(3-4):147-186
89.
《国际泥沙研究》2020,35(4):417-429
The aim of the current study was to determine the nature of the seasonal variability of the Suspended Particulate Matter (SPM) fluxes from the drainage basin to the estuary in a macrotidal region (Northeastern Brazil), and the estuarine response to a seawater intrusion regarding sediment deposition, which will support the understanding of the global transport of materials at the continent-ocean interface. Thermohaline structure data was acquired using a Conductivity, Temperature, and Depth (CTD) probe with a sampling frequency of 4 Hz. Suspended particulate material was measured by gravimetric measurements applied to exact filtered volume samples. The outflows were measured through the use of an Acoustic Doppler Current Profiler (ADCP) with frequency of 1.5 MHz. The horizontal thermal and saline gradients varied from warmer and less saline waters (2014) to cooler and saline waters (2015). The gradient behavior when linked to volume transport and SPM flows, suggests a minimization of the fluvial flows in 2015, easing the advance of coastal water (CW) towards the inner estuary, leading to an inversion of the baroclinic pressure gradient. The bottom saline front, generated by the entrance of coastal water masses, caused an increase in SPM concentrations due to increased fluid density, resuspension of previously deposited sediment, and erosion of banks. High concentrations of SPM indicate higher volume transport suggesting a hydraulic barrier due to the change/inversion of the baroclinic pressure gradient, resulting in water and material retention. Material deposition was observed during neap tide, while during spring tide the material is resuspended, increasing the concentration, generating cycles of deposition and erosion during the neap-spring tides. The sediment in suspension that reach the estuary, even with low fluvial volume, stay in this environment forming new islands because of deposition. High deposition rates or sediment cycling, if generated by the hydraulic barrier, may indicate that the flows of SPM from the continental drainage to the estuary and adjacent continental shelf are interrupted and the residence time is increased. 相似文献
90.
Spring‐fed rivers of the Barkly karst in tropical northern Australia form an array of tufa and related freshwater carbonate deposits. One of these deposits, calcite rafts, is precipitated at the water–air interface principally as a consequence of CO2 degassing and evaporation. Calcite rafts have been reported in cave environments but have not been described in detail from fluvial systems. Observations using scanning electron microscopy coupled with water chemistry data reveal that they form by a combination of physical, chemical and biological processes. They grow downwards into the water column and form a dentate lower surface, while a flat upper surface occurs at the water–air interface. The rafts are readily inhabited by microorganisms, particularly diatoms, which frequently become entombed by calcite as the rafts develop. The decay of the biological material leaves voids, creating a pock‐marked texture. The rafts are subject to secondary calcite growth along the crystal edges. Once they become submerged in the water column after disturbance of the water surface, they may become completely covered by this overgrowth, creating a homogeneous veneer. The rafts form in quiescent settings, principally behind tufa dams in large, lake‐like water bodies along each river. Therefore, they can be used in conjunction with adjacent exposures of other tufa facies to decipher palaeohydrological conditions. Although the rafts are extremely thin and fragile, they are readily preserved within fossil waterhole facies, and their occurrence has been identified in rocks from the Quaternary to the Tertiary. 相似文献