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21.
A phase-resolving wave transformation module is combined with an intra-wave sediment transport module to calculate the on-/offshore sediment transport rates. The wave module is based on the Boussinesq equations extended into the surf zone. The vertical variation of the mean undertow and the intra-wave sediment concentrations are calculated. The net sediment transport rates are calculated, and the equation for conservation of sediment is solved to predict the beach profile evolution. The results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone, even for eroding beaches, suggesting that other contributions should not be neglected. The present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded. 相似文献
22.
23.
黄河三角洲潮滩发育时空谱系 总被引:3,自引:0,他引:3
研究黄河三角洲潮滩发育的时空话系指出:在时间上,黄河三角洲潮滩系由不同时期河口滩发育而成,各段潮滩发育时间因素的差异在比较形态学上有清晰反映,在空间上,并存着处于不同发育阶段上的四种类型(阶段)。由此构成了黄河三角洲前沿所特有的湖滩形态时空体系。 相似文献
24.
虾肤诱食剂改善南美白对虾植物蛋白日粮的作用 总被引:6,自引:0,他引:6
用900尾平均体质量为0.106 g/尾±0.012 g/尾的南美白对虾(Peneausvannamei)进行虾肽改善植物蛋白日粮试验,结果表明:(1)大豆粕、杂粕组南美白对虾的成活率显著高于鱼粉组(P<0.05);(2)大豆粕、鱼粉组南美白对虾相对生长率、饲料系数、虾体组成相似,杂粕组最差,且与大豆粕、鱼粉组有显著性差异(P<0.05)。结果表明,在南美白对虾日粮中虾肽作为营养性诱食剂可显著改善植物蛋白的适口性,提高南美白对虾对大豆蛋白的的消化吸收功能,达到与鱼粉组相同的养殖效果,从而明显降低南美白对虾日粮成本。 相似文献
25.
秋茄和榕树叶片中正构烷烃分布和单体化合物δ13C值及其光合作用 总被引:1,自引:0,他引:1
对深圳福田、阳江、海南新竹红树林秋茄Kandelia candel及海口榕树Ficusm icrocarpa叶中类脂物进行萃取,分离出正构烷烃,通过气相色谱(GC)及色谱-质谱(GC MS)分析,测出了正构烷烃的碳数分布和相对含量.气相色谱-稳定同位素比质谱仪(GC-IRMS)测定了正构烷烃单体化合物的稳定同位素组成δ13C.秋茄叶和榕树叶正构烷烃的碳数分布均为C17C33,主要集中在C23-C31(>90%).化合物含量最高为C27的有深圳福田秋茄、海南新竹秋茄、海口榕树,而阳江秋茄为C25.单体化合物的稳定同位素δ13C深圳福田秋茄为-31.42‰-34.48‰,阳江秋茄为-31.69‰-33.62‰,海南新竹秋茄为-30.30‰-33.04‰,海口榕树为-29.92‰33.56‰;平均值分别为-32.95‰、32.67‰、31.67‰、-31.74‰.结果表明,秋茄和陆地植物榕树的光合作用都是通过C3途径,是典型C3植物. 相似文献
26.
Changes in soils and vegetation in a Mediterranean coastal salt marsh impacted by human activities 总被引:10,自引:0,他引:10
J. lvarez-Rogel F.J. Jimnez-Crceles M.J. Roca R. Ortiz 《Estuarine, Coastal and Shelf Science》2007,73(3-4):510-526
This paper reports changes in vegetation distribution and species cover in relation to soil factors and hydrology in a semiarid Mediterranean salt marsh adjacent to the Mar Menor saline lagoon. Species cover, soil salinity, and the groundwater level were monitored between 1991 and 1993 and between 2002 and 2004, and total organic carbon, total nitrogen, total phosphorus, nitrates, ammonium and exchangeable phosphorus were measured in the soils in both study periods. In addition, three soil profiles were described in August 1992 and August 2004. The results indicate an elevation of the water table throughout the 13-year period, which was attributable to water flowing from areas with intensive agriculture. Flooding increased and soil salinity dropped in the most saline sites and increased in the least saline ones. The morphology of the soil profiles reflected the increase in flooding periods, due to the appearance of a greyer matrix in the deeper horizons and a more diffuse pattern of Fe mottles. Following these environmental changes, Sarcocornia fruticosa, Phragmites australis and Juncus maritimus strongly expanded at the wettest sites, which led to the disappearance of the original zonation pattern. The cover of Limonium delicatulum, in turn, decreased with the increase in moisture but increased following the increase in salinity. Changes in soil nutrients were only very evident in the sandy soils of the beach, probably due to the influence of organic debris deposited on the shoreline by the storms and due to the strong increase in the colonisation of this habitat by perennial species. According to the results obtained, control measures are needed in order to preserve habitat diversity in this and other salt marshes of this area. Monitoring of the vegetation distribution could be a useful tool to identify environmental impacts, in order to implement remedial actions. 相似文献
27.
28.
磷处理粉煤灰可作农业土壤磷源 总被引:2,自引:0,他引:2
粉煤灰(简称CCP或ash)具有改良土壤,增加植物产量的功能。此外,由于它特殊的多孔结构,也可用作吸纳并承载植物养分的载体。用NaH2PO4配制成含磷0.10mol/L浓度的溶液,对采自加拿大西安大略省Sarnia地区Lambton电厂的底灰(bottomash)进行振荡浸渍处理。结果表明,振荡浸渍66h后的粉煤灰中磷含量可达784×10-6。以磷处理粉煤灰、未进行磷处理的粉煤灰和石英砂按比例混合,作为基本生长介质进行玉米种植实验,其中实验配方设计为生长介质中含磷量分别为标准含磷浓度(50×10-6)的10%、25%、50%、75%和100%。生长26、34和46d后分别与不含磷的空白配方、施加含氮-磷-钾为0-20-0标准磷肥并控制磷含量为标准浓度(50×10-6)配方进行生物产量对比。生长实验结果表明,以磷处理粉煤灰供磷的生长介质,当含磷量为标准浓度的25%至100%时,其植物生长量就比添加标准浓度磷肥的配方好。种植46d后的生物生长量统计结果显示,含磷分别为标准浓度50%、75%和100%的实验介质中,玉米杆的鲜重较施标准磷肥介质中玉米分别增长39.46%、42.73%和46.13%;玉米杆干重依次增加29.71%、13.39%和28.87%;根鲜重平均增加16.62%;根干重平均增加14.03%。上述实验结果启示,粉煤灰可以很好地吸纳承载磷养分,并持续供给植物吸收生长,如果采用吸纳磷(或其他养分)的粉煤灰改良砂质土壤将有重要意义。 相似文献
29.
Surface contamination with radioactive caesium introduced into the environment after the accident at the Chernobyl nuclear
plant was high enough in the Crimean Mountains to allow using radiocaesium as an indicator of penetration of radioactive contamination
into a karst system. Caesium concentrations have been studied in soils above Marble Cave, Tchatyrdag Plateau, in percolation
waters and in sediments transported by percolation waters within the cave. Contamination of the daylight surface with 137Cs is about 30 kqB m–2 which is approximately 13 times higher than the density of global fallouts. Besides 137Cs, almost all samples showed presence of 134Cs with the 137Cs/134Cs ratio close to that of Chernobyl contaminations.
Concentrations of 137Cs range from 9 to 15 mBq l–1 in the present percolation waters in the cave. In sediments related to percolation waters 134Cs is detected in some samples besides 137Cs, although the effect of 228Ac is not ruled out. Surprisingly, the highest concentrations of radiocaesium were measured in "old" sediments in the cave's
lower series. These sediments are not associated with modern percolation and are represented by a clay/moonmilk alternating
sequence deposited in an old dried cave lake. Moonmilk layers have higher caesium content than clay. It is assumed that Chernobyl
caesium was transported into the cave with aerosols which were then deposited mainly in areas where condensation occurs. The
sampling site is located just in the boundary between two microclimatic zones with a temperature gradient of 0.5 °C. Active
condensation processes occur in this area. Caesium was not detected in another similar sampling site (old lake deposits) located
within homogeneous microclimatic conditions. If the above interpretation is correct, these results show the geochemical significance
of the aerosol-condensation mechanism of mass transport and localisation.
Received: 1 June 1995 · Accepted: 4 December 1995 相似文献
30.
Rinse L. de Swart Francesca Ribas Gonzalo Simarro Jorge Guillén Daniel Calvete 《地球表面变化过程与地形》2021,46(15):3252-3270
Nearshore sandbars are important features in the surf zone of many beaches because they strongly influence the mean circulation and evolving morphology. Due to variations in wave conditions, sandbars can experience cross-shore migration and vary in shape from alongshore uniform (shore-parallel) to alongshore rhythmic (crescentic). Sandbar dynamics have been studied extensively, but existing observational studies usually do not quantify the processes leading to crescentic bar formation and straightening. This study analyses the dynamics of crescentic bar events at the fetch-limited beach of Castelldefels (northwestern Mediterranean Sea, Spain) using 7.5 years of hourly time-exposure video images and detailed wave conditions. The results show that, despite the generally calm wave conditions, the sandbars were very dynamic in the cross-shore and longshore directions. They often migrated rapidly offshore during storms (up to 70 m in one day) and more slowly onshore during post-storm conditions. Crescentic bars were often present at the study site (48% of the time), but only when the sandbar was at least 10 m from the shoreline. They displayed a large variability in wavelengths (100–700 m), alongshore migration speeds (0–50 m/day) and cross-shore amplitudes (5–20 m). Wavelengths increased for larger bar–shoreline distances and the alongshore migration speeds were strongly correlated with the alongshore component of the radiation stresses. Crescentic patterns typically developed during low–medium energetic waves with limited obliquity ( ° at 10 m depth), while bar straightening occurred during medium–high energetic waves with strong oblique angles of incidence ( °). Overall, this study provides further proof for the important role of wave direction in crescentic bar dynamics and highlights the strong dependence of crescentic bar development on the initial bathymetric configuration. 相似文献