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991.
992.
Zhibao Dong Junfeng Lu Duoqing Man Ping Lv Guanqiang Qian Zhengcai Zhang Wanyin Luo 《地球表面变化过程与地形》2011,36(10):1292-1299
The erosion of sediment by wind and the resulting mass flux density profile is thought to be described by a mathematical function that bears information on the mechanisms responsible for the movement of individual particles by the wind, and such functions have been studied extensively. In this study several functions are evaluated that have been proposed to describe the variation in mass flux density with height of wind‐blown sediment, with the flux containing a mixture of particles in suspension and saltation, based on detailed field data at four land types in the Minqin area of north‐western China, where severe wind erosion occurs. High‐resolution mass flux density measurements at 50 heights, collected at 20 mm intervals to a height of 1 m above the surface, were obtained using vertically segmented samplers. Three kinds of functions fit the measured flux density profiles reasonably well, but a three‐parameter modified exponential function is preferred because it contains fewer coefficients to be defined and provides a reasonably good fit to the measured mass flux density profiles. This and previous conclusions suggest that the decay with height of mass flux density of sediments dominated by saltation particles as in the present study tends to follow a modified exponential function law, but a modified power function law replaces the modified exponential function law when the height extends to a level high enough to be dominated by suspension particles. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
993.
Mussel farming as a nutrient reduction measure in the Baltic Sea: consideration of nutrient biogeochemical cycles 总被引：1，自引：0，他引：1
Nutrient loads from the land to the sea must be reduced to combat coastal eutrophication. It has been suggested that further mitigation efforts are needed in the brackish Baltic Sea to decrease nutrients, especially in eutrophic coastal areas. Mussel farming is a potential measure to remove nutrients directly from the sea. Mussels consume phytoplankton containing nitrogen (N) and phosphorus (P); when the mussels are harvested these nutrients are removed from the aquatic system. However, sedimentation of organic material in faeces and pseudo-faeces below a mussel farm consumes oxygen and can lead to hypoxic or even anoxic sediments causing an increased sediment release of ammonium and phosphate. Moreover, N losses from denitrification can be reduced due to low oxygen and reduced numbers of bioturbating organisms. To reveal if mussel farming is a cost-effective mitigation measure in the Baltic Sea the potential for enhanced sediment nutrient release must be assessed. 相似文献
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996.
Phosphorus release from coastal Baltic Sea sediments as estimated from sediment profiles 总被引：1，自引：0，他引：1
We used the decline in total phosphorus (P) concentration with depth in sediment profiles from the North-western Baltic Proper coastal zone to calculate the site-specific amount of sediment P eventually to be released to the water column: The potentially mobile P. P fractionation revealed that iron bound P dominated the potentially mobile P at sites with oxic surface sediment layers. Organic P forms were also a major constituent of the potentially mobile P pool. We determined that 1–7 g P/m2 were potentially mobile at our sites, and the turnover time of this P pool was considered short, i.e., less than a decade. To determine long-term average P fluxes to and from the surface sediment layer, we first multiplied the constant and relatively low P concentration in deeper sediment layers with the sediment accumulation rate to gain the P burial rate. Then the average total P concentration in settling matter was multiplied with the sediment accumulation rate to estimate the depositional P flux at each site. The difference between the depositional and burial rates represents the long-term average release rate of sediment P and varied between 1.0 and 2.7 g P/m2 yr among our sites. These rates are at the same order of magnitude as values reported from other areas of the Baltic Sea, and constitute a major source of P to the water column. 相似文献
997.
Patrick Martin Richard S. LampittMary Jane Perry Richard SandersCraig Lee Eric D'Asaro 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(4):338-349
Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m−2 d−1. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360-620 mg POC m−2 d−1, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m−2 d−1, with a settled volume of particles of 1000-1500 mL m−2 d−1. This implies that 25-43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements. 相似文献
998.
为了更准确地计算由平台晃动所带来的通量观测误差, 从平台晃动与风速仪测点位置变化角度以分层平均消除垂向均值差异的办法建立了新的涡相关通量误差矫正模型。结果是： 在中高海况下由平台晃动引起的通量观测误差是显著的。有鉴于此, 将晃动平台视为固定平台来处理的常用通量计算公式在中高海况下可能会给出严重失真的结果, 建议采用新公... 相似文献
999.
NCEP再分析资料和浮标观测资料计算海气热通量的比较 总被引：1，自引：0，他引：1
对来自于美国国家环境预报中心公布的NCEP1、NCEP2 再分析资料和来自于定点布放在黄海北部的浮标观测资料进行了比较和分析。结果是： NCEP 再分析资料中的海表气象参数（风速、湿度、气温、海表温度）是可信的。在统计意义上, NCEP2 给出的海表气象参数比NCEP1 与浮标观测值更接近,而净辐射通量则是NCEP1 ... 相似文献
1000.