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Sahadev Sharma Md. Kamruzzaman A. T. M. Rafiqul Hoque Akio Hagihara 《Journal of Oceanography》2012,68(6):831-840
Data on leaf phenological traits and longevity of mangroves are important for improved understanding of the adaptation strategies, growth, and productivity of these trees. We studied leaf phenological traits and longevity of Rhizophora stylosa, Bruguiera gymnorrhiza, and Kandelia obovata monthly from April 2008 to March 2009. Both tree sampling (direct observation) and litterfall (indirect observation) were used. All leaves and branches of each sample tree were numbered and marked with tags at the beginning of the experiment. Peaks of leaf recruitment and death occurred in July and June, respectively, for B. gymnorrhiza and K. obovata but both occurred in July for R. stylosa. Leaf recruitment for all the species was lowest in January; leaf death was minimum in December for R. stylosa and B. gymnorrhiza, and in January for K. obovata. Leaf recruitment for the three species was significantly correlated with monthly mean air temperature and monthly hours of sunshine. K. obovata and R. stylosa leaf death was correlated with monthly mean air temperature, monthly hours of sunshine, monthly mean air vapor pressure deficit, and monthly rainfall; B. gymnorrhiza leaf death was not correlated with any environmental factors. Specific leaf area for R. stylosa (45.4?±?1.0?cm2?g?1) and K. obovata (48.6?±?0.8?cm2?g?1) was not significantly different, but means for these two species were significantly different from that for B. gymnorrhiza (71.0?±?2.8?cm2?g?1). Mean leaf longevity was 13.9?months for R. stylosa, 17.2?months for B. gymnorrhiza, and 12.1?months for K. obovata. Different measured variables between B. gymnorrhiza and the other two species may have been because of the growth strategy and shade tolerance of B. gymnorrhiza. Mean leaf longevity increased with increasing mean annual air temperature. 相似文献
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Hahn Chul Jung James Hamski Michael Durand Doug Alsdorf Faisal Hossain Hyongki Lee A. K. M. Azad Hossain Khaled Hasan Abu Saleh Khan A.K.M. Zeaul Hoque 《地球表面变化过程与地形》2010,35(3):294-304
The Surface Water and Ocean Topography (SWOT) satellite mission will provide global, space‐based estimates of water elevation, its temporal change, and its spatial slope in fluvial environments, as well as across lakes, reservoirs, wetlands, and floodplains. This paper illustrates the utility of existing remote sensing measurements of water temporal changes and spatial slope to characterize two complex fluvial environments. First, repeat‐pass interferometric SAR measurements from the Japanese Earth Resources Satellite are used to compare and contrast floodplain processes in the Amazon and Congo River basins. Measurements of temporal water level changes over the two areas reveal clearly different hydraulic processes at work. The Amazon is highly interconnected by floodplain channels, resulting in complex flow patterns. In contrast, the Congo does not show similar floodplain channels and the flow patterns are not well defined and have diffuse boundaries. During inundation, the Amazon floodplain often shows sharp hydraulic changes across floodplain channels. The Congo, however, does not show similar sharp changes during either infilling or evacuation. Second, Shuttle Radar Topography Mission measurements of water elevation are used to derive water slope over the braided Brahmaputra river system. In combination with in situ bathymetry measurements, water elevation and slope allow one to calculate discharge estimates within 2.3% accuracy. These two studies illustrate the utility of satellite‐based measurements of water elevation for characterizing complex fluvial environments, and highlight the potential of SWOT measurements for fluvial hydrology. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Current dual-frequency GPS measurements can only eliminate the first-order ionospheric term and may cause a higher-order range
bias of several centimeters. This research investigates the second-order ionospheric effect for GNSS users in Europe. In comparison
to previous studies, the electron density profiles of the ionosphere/plasmasphere are modeled as the sum of three Chapman
layers describing electron densities of the ionospheric F2, F1 and E layers and a superposed exponential decay function describing the plasmasphere. The International Geomagnetic Reference
Field model is used to calculate the geomagnetic field vectors at numerous points along the incoming ray paths. Based on extended
simulation studies, we derive a correction formula to compute the average value of the longitudinal component of the earth’s
magnetic field along the line-of-sight as a function of geographic latitude and longitude, and geometrical parameters such
as elevation and azimuth angles. Using our correction formula in conjunction with the total electron content (TEC) along the
line-of-sight, the second-order ionospheric term can be corrected to the millimeter level for a vertical TEC level of 1018 electrons/m2. 相似文献
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Deforestation is a major cause of environmental degradation. Tropical countries with huge population pressure and widespread poverty are main frontier of deforestation. Bangladesh, being one the most densely populated country with diminishing tropical forestland, supports lowest per capita forestland. The forests are depleting mainly due to illegal logging and conversion to non-forestry uses. In this paper encroachment of forestland by individuals has been dealt with. The socioeconomic causes and pattern of encroachment have been analyzed. Limited land availability and unemployment have been identified as the major proximate causes of encroachment and, if no measures are adopted within next three decades the existing natural forests might be encroached. 相似文献
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Y. Zheng A. van Geen R. Dhar Z. Cheng I. Gavrieli H.J. Simpson R. Versteeg A. Grazioli-Venier M. Shahnewaz M.A. Hoque 《Geochimica et cosmochimica acta》2005,69(22):5203-5218
Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers (< 28 m) high in As from deeper aquifers (40-90 m) containing < 10 μg/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments > 50 ka ago and a groundwater age of thousands of years. In the other village (Bay), the sediment is < 20 ka old down to 90 m and the deeper aquifer groundwater is younger, on the order of hundreds of years. The shallow aquifers in both villages that are high in As contain bomb-3H and bomb-14C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper aquifers also differ significantly. Deeper aquifer water is of the Na+-HCO3- type, with relatively little dissolved NH4+ (76 ± 192 μmol/L), Fe (27 ± 43 μmol/L) and Mn (3 ± 2 μmol/L). In contrast, shallow aquifer water is of the Ca2+-Mg2+-HCO3- type, with elevated concentrations of dissolved NH4+ (306 ± 355 μmol/L), Fe (191 ± 73 μmol/L), and Mn (27 ± 43 μmol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 ± 0.3 mg/kg, n = 12; 0.1 ± 0.1 mg/kg, n = 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 ± 1.2 mg/kg, n = 9; 1.4 ± 2.0 mg/kg, n = 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper aquifers that are low in As, even though there is a large difference in the time of deposition of these aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of ∼1 cm/yr. 相似文献
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Pollution of groundwater in the Bengal Basin (Bangladesh and West Bengal, India) by arsenic (As) puts at risk the health of more than 100 million consumers. Using 1,580 borehole lithological logs and published hydrochemistry on 2,387 wells, it was predicted that low-As (<10 μg/L) groundwater exists, in palaeo-interfluvial aquifers of brown sand capped by a protective palaeosol, beneath at least 45,000 km2 of the Bengal Basin. The aquifers were predicted to be at a depth of as little as 25 m below ground level (mbgl), and typically no more than 50 mbgl. The predictions were confirmed along an east–west traverse 115 km in length (i.e. across half of Bangladesh) by drilling 28 new boreholes to 91-m depth to reveal subsurface sedimentology, and by mapping As distribution in groundwater. The aquifers identified occur at typically <40 mbgl and so are accessible with local drilling methods. A protective palaeosol that caps the palaeo-interfluvial aquifers prevents downward movement into them of As-polluted groundwater present in shallower palaeo-channel aquifers and ensures that the palaeo-interfluvial aquifers will yield low-As groundwater for the foreseeable future. Their use, in place of the shallower As-polluted palaeo-channel aquifers, would rapidly mitigate the health risks from consumption of As-polluted groundwater. 相似文献