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1.
This paper describes a set of mathematical models to calculate runoff, soil erosion and chemical substance yields for drainage areas. The models represent different degrees of complexity and details of describing hydrological and hydrochemical processes. The availability of initial information and the requirements of the task determine the choice of a model for each particular case. These models have been written as PC/AT programs, to enable their use by a wide range of specialists. The models have been tested in different physical and geographical conditions, e.g. in some small watersheds on the Karelian Isthmus, west of Lake Ladoga, and in experimental catchment areas located in the Valdai Hills area in the southern part of Lake Ladoga drainage area. In further applications the drainage area models have been combined with models of the recipient water body, to obtain a single model of a watershed-lake system. The results of tests have proved that the models can be used for evaluation, simulation and forecasting of the processes of rainfall and snowmelt runoff, infiltration, evaporation, water erosion and pollutant wash-off from drainage areas. 相似文献
2.
Four fish species,Pollimyrus isidori (Mormyridae),Barbus paludinosus, Labeo forskalii (Cyprinidae), andNemacheilus abyssinicus (Balitoridae), new to the Omo-Turkana basin, were recorded from the Gojeb River, a tributary of the Omo River (south-western Ethiopia). Occurrence of the latter species in the upper reaches of the Blue Nile and of the Omo drainage substantiates the belonging of the upper parts of these water systems to the Abyssinian highlands ichthyofaunal province. 相似文献
3.
Estimating regional carbon stocks and spatially covarying edaphic factors using soil maps at three scales 总被引:2,自引:1,他引:1
Most estimates of regional and global soil carbon stocks are based on extrapolations of mean soil C contents for broad categories
of soil or vegetation types. Uncertainties exist in both the estimates of mean soil C contents and the area over which each
mean should be extrapolated. Geographic information systems now permit spatially referenced estimates of soil C at finer scales
of resolution than were previously practical. We compared estimates of total soil C stocks of the state of Maine using three
methods: (1) multiplying the area of the state by published means of soil C for temperate forests and for Spodosols; (2) calculating
areas of inclusions of soil taxa in the 1:5,000,000 FAO/UNESCO Soils Map of the World and multiplying those areas by selected
mean carbon contents; and (3) calculating soil C for each soil series and map unit in the 1:250,000 State Soil Geographic
Data Base (STATSGO) and summing these estimates for the entire state. The STATSGO estimate of total soil C was between 23%
and 49% higher than the common coarse scale extrapolations, primarily because STATSGO included data on Histosols, which cover
less than 5% of the area of the state, but which constitute over one-third of the soil C. Spodosols cover about 65% of the
state, but contribute less than 39% of the soil C. Estimates of total soil C in Maine based on the FAO map agreed within 8%
of the STATSGO estimate for one possible matching of FAO soil taxa with data on soil C, but another plausible matching overestimated
soil C stocks. We also compared estimates from the 1:250,000 STATSGO database and from the 1:20,000 Soil Survey Geographic
Data Base (SSURGO) for a 7.5 minute quadrangle within the state. SSURGO indicated 13% less total soil C than did STATSGO,
largely because the attribute data on depths of soil horizons in SSURGO are more specific for this locality. Despite localized
differences, the STATSGO database offers promise of scaling up county soil survey data to regional scales because it includes
attribute data and estimates of areal coverage of C-rich inclusions within map units. The spatially referenced data also permit
examination of covariation of soil C stocks with soil properties thought to affect stabilization of soil C. Clay content was
a poor predictor of soil C in Maine, but drainage class covaried significantly with soil C across the state. 相似文献
4.
Much of eastern Australia's coastal lowlands are underlain by Holocene sulfidic sediments. Large areas have been drained for agriculture. Drained, sulfidic sediments oxidize and produce highly acidic discharge (pH<4) with significant impacts on estuarine ecosystems. The rate of production of acid from drained floodplains is between 100 to 300 kg H2SO4 /ha/y and hundreds of tonnes of H2SO4 can be discharged in a single flood from the floodplain. Generation and export of acidity is controlled by the water balance of the floodplain, the characteristics of the drainage system and the distribution of sulfides. Evapotranspiration by native plants and crops plays a dominant role in the oxidation of sediments in dry periods. In wet periods, upland discharges to floodplains dominate the water balance. Drain spacing and drain depth are critical factors in the export of acidity into coastal streams. Amelioration of acidic outflows requires an understanding of the interaction between chemical and hydrological processes in sulfidic landscapes. Redesign of drainage systems to manage surface waters and reduce drain density with the treatment of drains with lime offer promise for treating acidic discharge and reducing impacts. Reflooding of drained, partially oxidized floodplains with freshwater may not be a panacea because of the large volumes of acid stored in the soil, a lack of labile organic matter in the sediments needed to reduce sulfate and irreversible changes to the soil due to oxidation. Tidal brackish water reflooding of unproductive acidified lowlands offers promise for rehabilitating wetlands. Sulfidic wetlands which are still undrained should remain so unless all acidic discharge can be treated. 相似文献
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7.
Computational fluid dynamics (CFD) modelling based on a commercial package, FLUENT, has been used in the present study. The primary aim of this study is to develop a novel implant by employing CFD techniques. Firstly, CFD analyses on the best design commercially available, which is the Ahmed Glaucoma Valve (AGV®), are accomplished. In the light of the results, the new design focus is selected as the valve. The new design is analysed using GAMBIT and FLUENT software. CFD analyses of the new design and the AGV® are compared and the strengths of the new design are revealed. The results are also compared with the experimental studies AGV® in the literature. It is deduced that the proposed model shows a nonlinear pressure drop response, which is quite similar to that of AGV®. The optimum combination would be a flow rate of 2.5 μl/min and a pressure drop of 1054.58 Pa for the proposed model. 相似文献
8.
F. Sassetti F. A. Guarnieri L. Garelli M. A. Storti 《Computer methods in biomechanics and biomedical engineering》2013,16(12):1273-1280
Glaucoma drainage device (GDD) has the potential to eliminate hypotony but still suffers from poor flow control and fibrosis. The ideal shunt should change its hydraulic resistance to achieve the desired intraocular pressure (IOP). In this study, the characterisation of a preliminary design of a new GDD is presented. This is activated by means of a diaphragm, which is actuated by conducting polymers. The valve can be manufactured employing microelectromechanical system technology by soft lithography. The characterisation process is performed by numerical simulation using the finite element method, considering the coupling between the fluid and the structure (diaphragm) obtaining the hydraulic resistance for several positions of the diaphragm. To analyse the hydraulic system of the microvalve implanted in a human eye, an equivalent circuit model was used. The parameters of the equivalent circuit model were obtained from numerical simulation. The hydraulic resistance of the designed GDD varies in the range of 13.08–0.36 mmHg min/μl compared with 3.38–0.43 mmHg min/μl for the Ahmed valve. The maximum displacement of the diaphragm in the vertical direction is 18.9 μm, and the strain in the plane is 2%. The proposed preliminary design allows to control the IOP by varying the hydraulic resistance in a greater range than the existing passive valves, and the numerical simulation facilitates the characterisation and the improvement of the design before its construction, reducing time and costs. 相似文献
9.
Climate‐related declines in lake area have been identified across circumpolar regions and have been characterized by substantial spatial heterogeneity. An improved understanding of the mechanisms underlying lake area trends is necessary to predict where change is most likely to occur and to identify implications for high latitude reservoirs of carbon. Here, using a population of ca. 2300 lakes with statistically significant increasing and decreasing lake area trends spanning longitudinal and latitudinal gradients of ca. 1000 km in Alaska, we present evidence for a mechanism of lake area decline that involves the loss of surface water to groundwater systems. We show that lakes with significant declines in lake area were more likely to be located: (1) in burned areas; (2) on coarser, well‐drained soils; and (3) farther from rivers compared to lakes that were increasing. These results indicate that postfire processes such as permafrost degradation, which also results from a warming climate, may promote lake drainage, particularly in coarse‐textured soils and farther from rivers where overland flooding is less likely and downslope flow paths and negative hydraulic gradients between surface water and groundwater systems are more common. Movement of surface water to groundwater systems may lead to a deepening of subsurface flow paths and longer hydraulic residence time which has been linked to increased soil respiration and CO2 release to the atmosphere. By quantifying relationships between statewide coarse resolution maps of landscape characteristics and spatially heterogeneous responses of lakes to environmental change, we provide a means to identify at‐risk lakes and landscapes and plan for a changing climate. 相似文献
10.
Carlos Arturo García-Alzate Flavio Lima Donald Charles Taphorn Jose Ivan Mojica Alexander Urbano-Bonilla Tulio Franco Teixeira 《Journal of fish biology》2020,96(6):1444-1453
Hyphessobrycon chiribiquete n. sp. is described from the Río Caquetá drainage in Colombia and the Río Ucayali drainage in Peru, western Amazon. The new species is diagnosed from its congeners by having the following combination of characters: a conspicuous narrow midlateral stripe, starting on the sides of the body behind the opercle near the lateral line; lateral stripe overlapped anteriorly with a vertically elongated humeral blotch; inner premaxillary teeth pentacuspid; margin of anal fin falcate in mature males. 相似文献