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排序方式: 共有150条查询结果,搜索用时 15 毫秒
91.
Richarde Marques da Silva Celso Augusto Guimares Santos José Yure Gomes dos Santos 《国际泥沙研究》2018,33(2):117-125
This paper quantifies the runoff and sediment yield for four different land covers in a semiarid region of Brazil. The WESP model, a distributed, event-oriented runoff-erosion model, was applied and its physical parameters, Ns and KR, were adjusted based on observed runoff and sediment yield data using simulated rainfall with an average intensity of 53 mm h-1. The sediment yield obtained was 53.02 kg ha-1 (caatinga vegetation), 231.96 kg ha-1 (bare soil), 309.75 kg ha-1 (beans), and 847.38 kg ha-1(corn). The results showed that caatinga cover yields the lowest erosion and runoff when compared to the other treatments. The results also show that the sediment yield and runoff values simulated with Ns, KI, and KR parameters were well calibrated, within acceptable deviations. The caatinga vegetation was more effective in protecting the soil, when compared to the other types of coverage. The beans and corn covers had the highest values of runoff and sediment yield, even higher than those observed for bare soil. 相似文献
92.
Carlos A.F. Schettini Nils E. Asp Andrea S. Ogston Vando J.C. Gomes Robin L. McLachlan Marcus E.B. Fernandes Charles A. Nittrouer Eliane C. Truccolo Danilo C.L. Gardunho 《地球表面变化过程与地形》2020,45(3):574-589
The Amazon Macrotidal Mangrove Coast (AMMC) is a large (~7500 km2) contiguous mangrove fringe eastwards from the Amazon River mouth. It encompasses dozens of interconnected bays intercalated with mangrove peninsulas. Mud accumulates on the mangrove flats, whereas the bed of the bays and channels is generally sandy. In this study we investigated the circulation, sediment transport and deposition in a central site at one of these mangrove peninsulas. The study was undertaken during the dry period, when there is no influence of the Amazon River plume and minimum local freshwater inflow. Current and suspended-sediment concentration were monitored in a feeder channel on the mangrove flat along a ~1000 m section oriented along the peninsula axis. Sediment deposition was also measured on the flat. Our results show there was a strong exchange between the neighboring bays. Channel currents were flood dominant, reaching up to >1 m s−1, with residual water and sediment transport westwards. Suspended sediment concentration (SSC) in the channel was directly related to velocity magnitude, ranging between 50 and 350 mg L−1. The flat was flooded in a way that indicated the tidal wave evolves westwards, nearly parallel to the AMMC shoreline. Currents on the flats were much slower than those in the channel and showed slight ebb dominance. However, SSC was higher during the flood than ebb, clearly indicating settling during the current deceleration and limited erosion during the following ebb–flow acceleration. The net sediment transport across the section was 60 tons westwards for the period of the experiment (~4 days). The mean deposition rate was 0.006 kg m−2 s−1 (or 1.4 kg m−2 per tide), which was higher than rates from other reported assessments in mangroves. The set of results indicate very large internal sediment reworking in the AMMC. © 2019 John Wiley & Sons, Ltd. 相似文献
93.
Cesária Gomes Ana Nobre Silva Rui Taborda Filipe Santos Luís Rebelo Aníbal Medina 《地球表面变化过程与地形》2019,44(14):2810-2822
Beach erosion poses significant threat to small island economies which are generally highly dependent on coastal tourism. This work investigates the evolution of the low-lying sandy coast of Boa Vista through an integrated characterization of coastline and shoreline indicators (over the past four decades) based on aerial imagery. It was found that tandem use of the two indicators was important to obtain a reliable perspective of the Boa Vista low-lying coastal evolution across a wide range of coastal environments. Results indicate that between 1968 and 2010 the coast was relatively stable, although some spatial variability was recognized. The largest changes were observed at the tips of embayed beaches and a clear coastal progradation was found at the southern (downwind) coastal sectors. Coastal evolution has been dominated by sediment budget and the results put in evidence the sedimentary connections between the beaches across the island, either through bypass and overpass processes. Findings show that understanding coastal evolution at low-lying islands should be supported on island-scale observations, being the only scale capable to capture the sedimentary connections between beach systems, that often control coastal evolution. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. 相似文献
94.
95.
Selenium in sediments, pore waters and benthic infauna of Lake Macquarie, New South Wales, Australia 总被引:1,自引:0,他引:1
G. M. Peters W. A. Maher F. Krikowa A. C. Roach H. K. Jeswani J. P. Barford V. G. Gomes D. D. Reible 《Marine environmental research》1999,47(5):2518
Measurements of selenium in sediments and benthic infauna of Lake Macquarie, an estuary on the east coast of Australia, indicate that sediments are a significant source of selenium in the lake's food web. Analysis of surficial sediment samples indicated higher selenium concentrations near what are believed to be the main industrial sources of selenium to the lake: a smelter and a power station. Sediment cores taken from sediments in Mannering Bay, near a power station at Vales Point, contained an average of 12 times more selenium in surficial sections than sediment cores from Nord's Wharf, a part of the lake remote from direct inputs of selenium. The highest selenium concentration found in Mannering Bay sediments (17.2 μg/g) was 69 times the apparent background concentration at Nord's Wharf (0.25 μg/g). Pore water concentrations in Mannering Bay were also high, up to 5 μg/l compared to those at Nord's Wharf which were below detection limits (0.2 μg/l). Selenium concentrations in muscle tissues of three benthic-feeding fish species (Mugil cephalus, Platycephalus fuscus, Acanthopagrus australis) were significantly correlated (p<0.05) with surficial sediment selenium concentration. Selenium concentrations in polychaetes and molluscs of Mannering Bay were up to 58 times higher than those from Nord's Wharf. Two benthic organisms, the eunicid polychaete Marphysa sanguinea and the bivalve mollusc Spisula trigonella, were maintained at different densities in selenium-spiked sediments. Both animals accumulated selenium from the spiked sediment, confirming that bioaccumulation from contaminated sediments occurs. Collectively, these data suggest that benthic food webs are important sources of selenium to the fish of Lake Macquarie. 相似文献
96.
Environmental issues in urban groundwater systems: a multidisciplinary study of the Paranhos and Salgueiros spring waters,Porto (NW Portugal) 总被引:1,自引:1,他引:0
Maria José Afonso Helder I. Chaminé José M. Marques Paula M. Carreira Laura Guimarães Lúcia Guilhermino Alberto Gomes Paulo E. Fonseca Ana Pires Fernando Rocha 《Environmental Earth Sciences》2010,61(2):379-392
This study presents the results of a multidisciplinary approach, using hydrogeochemical, isotopic and ecotoxicological analyses,
performed to assess the nature and suitability for use of Paranhos and Salgueiros spring waters (Porto city, NW Portugal).
Based on the surface activities located along the course of the springs, 23 water samples were collected. All the samples
were analysed for major element concentrations. The isotopic techniques employed included δ2H, δ18O and 3H. Standard acute bioassays with Daphnia magna were also performed. The hydrogeochemical analyses showed a nitrate and sulphate-enriched composition for these groundwaters,
resulting mainly from urban drainage and sewer leakage. In the ecotoxicological analyses, no significant mortality was observed
in any of the tests performed. The results obtained in this study suggest that Porto urban groundwater could be suitable for
irrigation uses. 相似文献
97.
Sousa OV Macrae A Menezes FG Gomes NC Vieira RH Mendonça-Hagler LC 《Marine pollution bulletin》2006,52(12):1725-1734
The effects of shrimp farm effluents on bacterial communities in mangroves have been infrequently reported. Classic and molecular biology methods were used to survey bacterial communities from four mangroves systems. Water temperature, salinity, pH, total heterotrophic bacteria and maximum probable numbers of Vibrio spp. were investigated. Genetic profiles of bacterial communities were also characterized by polymerase chain reaction (PCR) amplification of eubacterial and Vibrio 16S rDNA using denaturing gradient gel electrophoresis (DGGE). Highest heterotrophic counts were registered in the mangrove not directly polluted by shrimp farming. The Enterobacteriaceae and Chryseomonas luteola dominated the heterotrophic isolates. Vibrio spp. pathogenic to humans and shrimps were identified. Eubacterial genetic profiles suggest a shared community structure independent of mangrove system. Vibrio genetic profiles were mangrove specific. Neither microbial counts nor genetic profiling revealed a significant decrease in species richness associated with shrimp farm effluent. The complex nature of mangrove ecosystems and their microbial communities is discussed. 相似文献
98.
Coelho JP Pimenta J Gomes R Barroso CM Pereira ME Pardal MA Duarte A 《Marine pollution bulletin》2006,52(6):674-680
The focus of this work is to explore the use of the netted whelk, Nassarius reticulatus (L.), as an indicator of mercury (Hg) contamination, by assessing the concentration of Hg in the sediments and in the whelk along the entire Portuguese coast. Total Hg concentrations ranged from below the detection limit (0.01 ng absolute mercury) up to 0.87 mg kg(-1) dry weight (dwt) in sediments and between 0.06 and 1.02 mg kg(-1) (dwt) for organisms, with no significant differences between males and females. Although organic mercury was not detected in the sediments, it represented, on average, 52% of the total Hg in the whelk tissues, and as high as 88% in some cases, suggesting mercury accumulation from dietary intake. Significant negative correlations were found between the total Hg concentrations in the sediments and the log(10) of Hg concentrations in whelk tissues males (r=-0.64; P<0.01) and females (r=-0.52; P<0.01) indicating that the species is a poor indicator of Hg contamination. Nevertheless, since the highest concentrations of organic mercury in the whelk tissues were found in the least contaminated areas, this species must be highly relevant in the trophic web, namely on the possible biomagnification of mercury. The high dietary mercury accumulation from feeding on carrion and the low bioavailability of mercury to whelks in estuarine sediments may be the basis of the mercury accumulation pattern in N. reticulatus. 相似文献
99.
D. Pavlidis G. J. Gorman J. L. M. A. Gomes C. C. Pain H. ApSimon 《Boundary-Layer Meteorology》2010,136(2):285-299
The computational fluid dynamics code Fluidity, with anisotropic mesh adaptivity, is used as a multi-scale obstacle-accommodating
meteorological model. A novel method for generating realistic inlet boundary conditions based on the view of turbulence as
a superposition of synthetic eddies is adopted. It is able to reproduce prescribed first-order and second-order one-point
statistics and turbulence length scales. The aim is to simulate an urban boundary layer. The model is validated against two
standard benchmark tests: a plane channel flow numerical simulation and a flow past a cube physical simulation. The performed
large-eddy simulations are in good agreement with both reference models giving confidence that the model can be used to successfully
simulate urban atmospheric flows. 相似文献
100.