长江河口主槽地貌形态观测与分析

人类活动可以改变流域至河口的泥沙输运与沉积。尽管一些近期的研究已经调查了长江河口的形态演变,然而,流域和河口工程如何影响河口河床的形态演变仍然是不清楚的。该文利用2010年至2015年多波束测深系统和浅地层剖面仪等先进现场测量仪器的长江口主槽走航测量资料,并结合主槽表层沉积物资料,分析了近年来人为强干扰下的长江河口主槽底床微地貌形态,以理解近期人类活动对河口的影响。结果显示:近年来长江河口主槽底床上除了存在平床、沙波、冲沟和冲刷痕等常见微地貌形态外,还存在着疏浚痕和凹坑等人为微地貌形态。在流域和河口大型工程的共同影响下,近年来南北港中上段、横沙通道和南槽上段均受到不同程度的冲刷,其主槽底床上呈现出不同程度冲沟和冲刷痕等侵蚀性微地貌。而由于疏浚工程的影响,南港下段、圆圆沙航槽和北槽航道底床上出现了大范围的疏浚痕和凹坑。近年来包括南槽上段、北槽主槽中段和下段的局部区域和北港拦门沙河段局部区域在内的长江河口最大浑浊带的河床沉积物有粗化趋势。南北港中上段和横沙通道的大部分区域均发育了大量沙波微地貌;总体上,长江河口沙波的波高在0.12~3.12 m,波长在2.83~127.89 m,波高/波长在0.003~0.136,长江河口中上段的沙波尺度(波高的均值为0.91 m,波长的均值为20.08 m)大于密西西比河下游(波高的均值为0.87 m,波长的均值为17.62 m),且两区域沙波的几何形态差异性较小。     

基于无人船的大洋中尺度涡观测系统展望

中尺度涡在大洋中普遍存在,研究发现其能量比大尺度海洋环流的能量大一个量级,在海洋物质能量输运和全球气候变化中起着重要的作用。受观测条件限制,目前对中尺度涡的观测主要通过卫星高度计实现,只能从海面高度来推算中尺度涡大小、分布、强度及其伴随的水体和能量输送,而卫星高度计对中尺度涡垂直结构特征认识不足,也导致了对中尺度涡所引起的上层海洋能量、热量输送估计误差偏大。目前对中尺度涡三维结构观测认识不足,展望未来将会出现基于无人船平台的大洋中尺度涡三维结构自动观测系统,该平台将集成自动水下剖面观测功能等先进技术,以便观测中尺度涡的垂直结构特征及其时空变化特征,进而可对中尺度涡带来的物质和能量输送进行系统认识。     

From sequential to parallel growth of cities: Theory and evidence from Canada

This paper examines city growth patterns and the corresponding city size distribution evolution over long periods of time using a simple New Economic Geography(NEG) model and urban population data from Canada. The main findings are twofold. First, there is a transition from sequential to parallel growth of cities over long periods of time: city growth shows a sequential mode in the stage of rapid urbanization, i.e., the cities with the best development conditions will take the lead in growth, after which the cities with higher ranks will become the fastest-growing cities; in the late stage of urbanization, city growth converges according to Gibrat′s law, and exhibits a parallel growth pattern. Second, city size distribution is found to have persistent structural characteristics: the city system is self-organized into multiple discrete size groups; city growth shows club convergence characteristics, and the cities with similar development conditions eventually converge to a similar size. The results will not only enhance our understanding of urbanization process, but will also provide a timely and clear policy reference for promoting the healthy urbanization of developing countries.     

Soil phosphorus composition and phosphatase activities along altitudes of alpine tundra in Changbai Mountains,China

Alpine tundra ecosystems have specific vegetation and environmental conditions that may affect soil phosphorus(P) composition and phosphatase activities. However, these effects are poorly understood. This study used Na OH-EDTA extraction and solution31 P nuclear magnetic resonance(NMR) spectroscopy to determine soil P composition and phosphatase activities, including acid phosphomonoesterase(Ac P), phosphodiesterase(PD) and inorganic pyrophosphatase(IPP), in the alpine tundra of the Changbai Mountains at seven different altitudinal gradients(i.e., 2000 m, 2100 m, 2200 m, 2300 m, 2400 m, 2500 m, and 2600 m). The results show that total P(TP), organic P(OP), OP/TP, Na OH-EDTA extracted P and AcP, PD, and IPP activities over the altitude range of 2500–2600 m are significantly lower than those below 2400 m. The dominant extracted form of P is OP(73%–83%) with a large proportion of monoesters(65%–72%), whereas inorganic P is present in lower proportions(17%–27%). The activity of Ac P is significantly positively correlated with the contents of soil OP, total carbon(TC), total nitrogen(TN), and TP(P 0.05), indicating that the Ac P is a more sensitive index for responding P nutrient storage than PD and IPP. Soil properties, P composition, and phosphatase activities decrease with increased altitude and soil p H. Our results indicate that the distribution of soil P composition and phosphatase activities along altitude and Ac P may play an important role in P hydrolysis as well as have the potential to be an indicator of soil quality.     

Influencing factors of seed long-distance dispersal on a fragmented forest landscape on Changbai Mountains,China

Seed long-distance dispersal(LDD) events are typically rare, but are important in the population processes that determine large-scale forest changes and the persistence of species in fragmented landscapes. However, previous studies focused on species dispersed via animal-mediated LDD, and ignored those dispersed by wind. The aim of this study was to assess the effects of canopy openness, edge, seed source, and patch tree density on the LDD of seeds by wind in forest. We collected birch seeds, a typical wind-dispersed species, throughout a larch plantation. We then assessed the relationship between birch LDD and each factor that may influence LDD of seeds by wind including distance to edge, canopy openness size, distance to mature forest, and the tree density of the larch plantation. We used univariate linear regression analysis to assess the influence of those factors on birch LDD, and partial correlations to calculate the contribution of each factor to LDD. The results showed that both canopy openness and edge had significant influences on birch LDD. Specifically, a negative relationship was observed between distance to edge and birch LDD, whereas there was a positive correlation between canopy openness size and LDD. In contrast, the distance to the mature forest was not correlated with birch LDD. Our results suggest that patch tree density could potently affect the probability of LDD by wind vectors, which provides novel and revealing insights regarding the effect of fragmentation on wind dynamics. The data also provide compelling evidence for the previously undocumented effect of habitat fragmentation on wind-dispersed organisms. As such, these observations will facilitate reasonable conservation planning, which requires a detailed understanding of the mechanisms by which patch properties hamper the delivery of seeds of wind-dispersed plants to fragmented areas.     

Impact factors identification of spatial heterogeneity of herbaceous plant diversity on five southern islands of Miaodao Archipelago in North China

Herbaceous plants are widely distributed on islands and where they exhibit spatial heterogeneity. Accurately identifying the impact factors that drive spatial heterogeneity can reveal typical island biodiversity patterns. Five southern islands in the Miaodao Archipelago, North China were studied herein. The spatial distribution of herbaceous plant diversity on these islands was analyzed, and the impact factors and their degree of impact on spatial heterogeneity were identified using CCA ordination and ANOVA. The results reveal 114 herbaceous plant species, belonging to 94 genera from 34 families in the 50 plots sampled. The total species numbers on different islands were significantly positively correlated with island area, and the average α diversity was correlated with human activities, while the β diversity among islands was more affected by island area than mutual distances. Spatial heterogeneity within islands indicated that the diversities were generally high in areas with higher altitude, slope, total nitrogen, total carbon, and canopy density, and lower moisture content, pH, total phosphorus, total potassium, and aspect. Among the environmental factors, pH, canopy density, total K, total P, moisture content, altitude, and slope had significant gross effects, but only canopy density exhibited a significant net effect. Terrain affected diversity by restricting plantation, plantation in turn influenced soil properties and the two together affected diversity. Therefore, plantation was ultimately the fundamental driving factor for spatial heterogeneity in herbaceous plant diversity on the five islands.     

Phylogenetic diversity of culturable bacteria in surface seawater from the Drake Passage,Antarctica

The Drake Passage is located between the Antarctic Peninsula and Tierra del Fuego in the south of South America. Surface seawater samples were collected at seven sites in the Drake Passage during the austral summer of 2012. The 16S rRNA sequences were analyzed from 187 isolated bacterial strains. Three phyla, 29 genera and 56 species were identified. The three phyla were Actinobacteria, Firmicutes and Proteobacteria; the Proteobacteria included α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria. γ-Proteobacteria, Actinobacteria and Firmicutes were the dominant class or phyla in terms of quantity and species. Gram-positive bacteria (Actinobacteria and Firmicutes) accounted for 57.8% of all types identified. There were nine dominant genera, including Curtobacterium, Staphylococcus, and Halomonas, and 14 dominant species including Curtobacterium flaccumfaciens, Curtobacterium pusillum, and Staphylococcus sciuri. Of the strains identified, 87.2% were catalase positive or weakly positive.     

江西牛形坝-柳木坑金银铅锌多金属矿床铋矿物类型及指示意义

江西银坑矿田的牛形坝-柳木坑矿床是赣南于都-赣县矿集区典型的金银铅锌多金属矿床。根据野外调研、系统矿相学研究和电子探针成分分析,表明铋在牛形坝-柳木坑矿床中是一种重要的伴生矿化金属元素,呈独立矿物或呈微细矿物包体分布在早期硫化物内部或边缘。铋矿物种类丰富,主要包括块硫铋银矿、硫铋银矿、板硫铋铜铅矿、针硫铋铅矿、硫铜铋矿、库辉铋铜铅矿、辉碲铋矿等。与同一矿集区石英脉型盘古山钨铋矿床相比,两矿床铋矿物种类均出现Pb-Ag-Bi-S、Te-Bi-S元素组合,赋存形式和含量有所不同,Cu-Pb-Bi-S元素组合仅在牛形坝-柳木坑矿床出现。矿床属于Au-Bi-(低Te)-S体系,铋盐矿物形成于中低温、中高密度、低盐度的成矿环境。从岩浆中分馏出来的成矿流体发生减压沸腾迫使大量蒸汽相逸散,硫逸度增加,铋主要以硫络合物形式运移,随着黄铁矿等硫化物沉淀,硫被大量消耗形成金矿物和碲化物(碲银矿)。成矿流体演化过程中由于温度和硫逸度进一步降低导致在成矿后期沉淀出大量铋硫盐矿物。成矿过程中的Bi促进金的迁移富集。铋矿物在两矿床中的赋存特征、化学成分、形成环境以及沉淀机制等表现出差异,说明铋具有成矿选择性,起到对成矿物质示踪的作用。     

New Zircon U‐Pb Age of Granodiorite in Chifeng at the Northern Margin of North China Craton and Constraints on Plate Tectonic Evolution

正Objective The North China Craton(NCC)is one of the oldest cratons in the world.The accretionary belt at its northern margin has been the focus of scholars both at home and abroad(Zhu Junbing and Ren Jishun,2017).In recent years,a series of Late Paleozoic–Mesozoic intrusions trending E–W have been discovered within the northern margin of the NCC,forming a magmatic belt.The study     

Constraints of molybdenite Re–Os and scheelite Sm–Nd ages on mineralization time of the Kukaazi Pb–Zn–Cu–W deposit,Western Kunlun,NW China

The Kukaazi Pb–Zn–Cu–W polymetallic deposit, located in the Western Kunlun orogenic belt, is a newly discovered skarn-type deposit. Ore bodies mainly occur in the forms of lenses and veins along beddings of the Mesoproterozoic metamorphic rocks. Three ore blocks, KI, KII, and KIII, have been outlined in different parts of the Kukaazi deposit in terms of mineral assemblages. The KI ore block is mainly composed of chalcopyrite, scheelite, pyrrhotite, sphalerite, galena and minor pyrite, arsenopyrite, and molybdenite, whereas the other two ore blocks are made up of galena, sphalerite, magnetite and minor arsenopyrite and pyrite. In this study, we obtained a molybdenite isochron Re–Os age of 450.5 ± 6.4 Ma (2σ, MSWD = 0.057) and a scheelite Sm–Nd isochron age of 426 ± 59 Ma (2σ, MSWD = 0.49) for the KI ore block. They are broadly comparable to the ages of granitoid in the region. Scheelite grains from the KI ore block contain high abundances of rare earth elements (REE, 42.0–95.7 ppm) and are enriched in light REE compared to heavy REE, with negative Eu anomalies (δEu = 0.13–0.55). They display similar REE patterns and Sm/Nd ratios to those of the coeval granitoids in the region. Moreover, they also have similar Sr and Nd isotopes [⁸⁷Sr/⁸⁶Sr = 0.7107–0.7118; ε_Nd(t) = ?4.1 to ?4.0] to those of such granitoids, implying that the tungsten-bearing fluids in the Kukaazi deposit probably originate from the granitic magmas. Our results first defined that the Early Paleozoic granitoids could lead to economic Mo–W–(Cu) mineralization at some favorable districts in the Western Kunlun orogenic belt and could be prospecting exploration targets.