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221.
莱州湾大型底栖动物群落结构及其动态变化特征 总被引:1,自引:0,他引:1
本文以莱州湾2009年夏季(8月)、秋季(10月)及2010年春季(5月)、夏季(8月)4个季节大型底栖动物资料为基础,对莱州湾大型底栖动物的种类组成、丰度、生物量、优势种进行了研究,同时与历史资料进行对比,探讨了莱州湾大型底栖动物的群落结构特征及动态变化。4个航次中共鉴定出大型底栖动物272种,其中包括环节动物多毛类122种,软体动物46种,甲壳动物64种,棘皮动物18种,鱼类9种,其他类13种。调查海域平均丰度为(1 102.56±216.32) ind./m2,多毛类在丰度上占绝对优势;平均生物量为(28.16±8.45) g/m2,软体动物占据优势。丰度和生物量空间分布规律具有很强的相似性,低值区位于莱州湾西部黄河口邻近海域,高值区位于渤海中部海域。丰度和生物量季节变化明显,夏季最高,秋季其次,春季最低。多毛类不倒翁虫(Sternaspis sculata)、寡鳃齿吻沙蚕(Nephthys oligobranchia)、紫壳阿文蛤(Alvenius ojianus)等是莱州湾调查海域的优势种。通过与历史资料的对比发现,莱州湾大型底栖动物种类组成及优势种类出现小型化的趋势。 相似文献
222.
Thermokarst lakes play a key role in the hydrological and biogeochemical cycles of permafrost regions. Current knowledge regarding the changes caused by permafrost degradation to the hydrochemistry of lakes in the Qinghai-Tibet Plateau (QTP) is limited. To address this gap, a systematic investigation of thermokarst lake water, suprapermafrost water, ground ice, and precipitation was conducted in the hinterland of the QTP. The thermokarst lake water in the QTP was identified to be of the Na-HCO3-Cl type. The mean concentrations of HCO3− and Na+ were 281.8 mg L−1 (146.0–546.2 mg L−1) and 73.3 mg L−1 (9.2–345.8 mg L−1), respectively. The concentrations of Li+, NH4+, K+, F−, NO2−, and NO3− were relatively low. Freeze-out fractionation concentrated the dissolved solids within the lake water during winter, which was deeply deepened on lake depth and lake ice thickness. Owing to solute enrichment, the ground ice was characterized by high salinity. Conversely, repeated replenishment via precipitation led to lower solute concentrations in the ground ice near the permafrost table compared to that within the permafrost. Although lower solute concentration existed in precipitation, the soil leaching and saline ground ice melting processes enhanced the solute load in suprapermafrost water, which is considered an important water and solute resource in thermokarst lakes. The influencing mechanism of permafrost degradation on thermokarst lake hydrochemistry is presumably linked to: (1) the liberation of soluble materials sequestered in ground ice; (2) the increase of solutes in suprapermafrost water and soil pore water; and (3) the changes in lake morphometry. These results have major implications on the understanding of the effects of ground ice melting on ecosystem functions, biogeochemical processes, and energy balance in a rapidly changing climate. 相似文献
223.
本文利用重力剩余异常计算得出的玲珑大岩体的几何形体为一南厚北薄的楔形体,其与毕郭岩体及北部的滦家河岩体在深部则是互相连接的。岩体重心并不是传统认为的以郭家店为中心,而是从曲家至崔苕附近长达50km以上的区域重心带,重心带厚度均在6km以上。 相似文献
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226.
理论地理学的内涵认知 总被引:7,自引:1,他引:6
本文从理论地理学的科学地位出发,介绍了近代理论地理学发展过程中形成的一些主要观点和其所具备的特点,最后对理论地理学的基本内容进行了归纳。 相似文献
227.
Multiple cropping index (MCI) is the ratio of total sown area and cropland area in a region, which represents the regional time intensity of planting crops. Multiple cropping systems have effectively improved the utilization efficiency and production of cropland by increasing cropping frequency in one year. Meanwhile, it has also significantly altered biogeochemical cycles. Therefore, exploring the spatio-temporal dynamics of multiple cropping intensity is of great significance for ensuring food and ecological security. In this study, MCI of Huang-Huai-Hai agricultural region with intensive cropping practices was extracted based on a cropping intensity mapping algorithm using MODIS Enhanced Vegetation Index (EVI) time series at 500-m spatial resolution and 8-day time intervals. Then the physical characteristics and landscape pattern of MCI trends were analyzed from 2000–2012. Results showed that MCI in Huang-Huai-Hai agricultural region has increased from 152% to 156% in the 12 years. Topography is a primary factor in determining the spatial pattern dynamics of MCI, which is more stable in hilly area than in plain area. An increase from 158% to 164% of MCI occurred in plain area while there was almost no change in hilly area with single cropping. The most active region of MCI change was the intersection zone between the hilly area and plain area. In spatial patterns, landscape of multiple cropping systems tended to be homogenized reflected by a reduction in the degree of fragmentation and an increase in the degree of concentration of cropland with the same cropping system. 相似文献
228.
基于1980-2020年山西省109个气象观测站点的逐日降水资料,选取10个极端降水指数,采用气候倾向率、相关分析、因子分析、R/S预测方法等方法,对山西省极端降水进行了时空分布的研究,以期为山西省的气候变化、生态环境保护、防灾减灾、气象服务工作提供参考依据,结果表明:(1)从时间尺度来看,1980-2020年期间,山西省极端降水的强度和极值都有明显增加,连续干旱日数和连续湿日日数呈下降趋势,其余均表现出不同程度的增加,其中年总降水量增加幅度最明显;从空间尺度来看,年总降水量、降水强度、降水频率、极值均为从西北向东南逐渐增多,空间差异较明显;从各站点的空间分布来看,北部和中部地区的极端事件增加最显著,北部地区的干旱日数仍以增加趋势为主,连续湿日日数气候倾向率的空间差异较大,中部地区站点显著增加,南北部以减少趋势为主;(2)基于相关分析方法表明各极端降水指数(除干旱日数外)与年总降水量都有很好的相关关系,强降水量和极强降水量对年总降水量的贡献值呈现出增加趋势;采用因子分析方法提取了3个公共因子,方差贡献率累计达到了87%,可以看出极端降水强度和降水量指数在对极端降水方面影响较大;利用R/S分析法可以得到年总降水量、中雨日数、大雨日数、最大5日降水量这几个指数未来呈现弱减少趋势,而干旱日数仍为减少趋势,连续湿日日数为持续弱增加趋势。总体看来,山西省极端降水近年来呈现出增加趋势,在空间分布有明显差异。 相似文献
229.
Guo Chaonan Sun Chengjun Yang Guipeng Zhang Honghai Chen Yan Yin Xiaofei Jiang Fenghua Huang Yuhuan Niu Jiaohong Ding Haibing 《中国海洋湖沼学报》2020,38(3):606-618
Journal of Oceanology and Limnology - The concentrations of dissolved monosaccharides (MCHO), polysaccharides (PCHO), and total carbohydrates (TCHO) in the seawater samples collected from the north... 相似文献
230.
Contribution of syncollisional felsic magmatism to continental crust growth: A case study of the Paleogene Linzizong volcanic Succession in southern Tibet 总被引:50,自引:0,他引:50
Xuanxue Mo Yaoling Niu Guochen Dong Zhidan Zhao Zengqian Hou Su Zhou Shan Ke 《Chemical Geology》2008,250(1-4):49-67
The Linzizong volcanic succession (~ 65–45 Ma) and the coeval batholiths (~ 60−40 Ma) of andesitic to rhyolitic composition represent a magmatic response to the India–Asia continental collision that began at ~ 70–65 Ma and ended at ~ 45–40 Ma with convergence continuing to present. These syncollisional felsic magmatic rocks are widely distributed along much of the > 1500 km long Gangdese Belt immediately north of the India–Asia suture (Yarlung–Zangbo) in southern Tibet. Our study of the Linzizong volcanic rocks from the Linzhou Basin (near Lhasa) suggests that syncollisional felsic magmatism may in fact account for much of the net contribution to continental crust growth. These volcanic rocks show a first-order temporal change from the andesitic lower Dianzhong Formation (64.4–60.6 Ma), to the dacitic middle Nianbo Formation (~ 54 Ma), and to the rhyolitic upper Pana Formation (48.7–43.9 Ma). The three formations show no systematic but overlapping Nd–Sr isotope variations. The isotopically depleted samples with εNd(t) > 0 indicate that their primary sources are of mantle origin. The best source candidate in the broad context of Tethyan ocean closing and India–Asia collision is the remaining part of the Tethyan ocean crust. This ocean crust melts when reaching its hydrous solidus during and soon after the collision in the amphibolite facies, producing andesitic melts parental to the Linzizong volcanic succession (and the coeval batholiths) with inherited mantle isotopic signatures. Ilmenite as a residual phase (plus the effect of residual amphibole) of amphibolite melting accounts for the depletion of Nb, Ta and Ti in the melt. The effect of ocean crust alteration plus involvement of mature crustal materials (e.g., recycled terrigeneous sediments) enhances the abundances of Ba, Rb, Th, U, K and Pb in the melt, thus giving the rocks an “arc-like” geochemical signature. Residual amphibole that possesses super-chondritic Nb/Ta ratio explains the sub-chondritic Nb/Ta ratio in the melt; residual plagioclase explains the slightly depleted, not enriched, Sr (and Eu) in the melt, typical of continental crust. These observations and reasoning plus the remarkable compositional similarity between the andesitic lower Dianzhong Formation and the model bulk continental crust corroborates our proposal that continental collision zones may be sites of net crustal growth (juvenile crust) through process of syncollisional felsic magmatism. While these interpretations are reasonable in terms of straightforward petrology, geochemistry and tectonics, they require further testing. 相似文献