北京城市绿化的时空动态分析     

胡云锋  赵冠华  张云芝 《地球信息科学学报》2018,20(3):332-339

城市绿化覆盖是城市生态系统的重要组成部分,合理的绿化率和绿化布局可以改善城市环境,提高城市人居适宜性。研究中将2005、2010、2015年北京市土地利用（LUC）数据中的城市居民用地作为城区范围,应用Landsat 5、GF-1影像数据和MODIS产品,利用支持向量机的监督分类方法,提取了2005、2010、2015年的北京市城市绿化覆盖数据,并获取了同期的植被指数（NDVI）数据;继而以城市绿化覆盖率、绿化覆盖均匀度和植被指数为评价指标,在公里栅格和行政区2个尺度上探讨了北京市城市绿化覆盖的空间分布格局和时间变化动态特征。研究表明：① 3个指标在空间和时间2个维度、区县和栅格2个尺度上都表现一致。这反映北京市过去10年中,在绿化面积增加的同时,绿化的空间布局得到优化改善,绿化的质量得到提高。② 2005-2015年,北京市城市绿化覆盖面积由518.93 km² 增加到1405.54 km²,绿化覆盖率由39.9%增加到49.13%,绿化覆盖均匀度由0.598增加到0.653,植被指数由0.42增加至0.5。③ 北京市城市绿化建设存在明显的时空差异。中心城区绿化建设缓慢,成效不明显;重大绿化建设成果主要集中在城市边缘地区和远郊区县。城市绿化改善过程主要发生在2005-2010年。  相似文献   

不同盐度对文蛤(Meretrix meretrix)呼吸代谢及体内酶活性的影响     

白奕天  丁天扬  李东东  聂鸿涛  闫喜武 《海洋科学》2018,42(6):123-131

为研究不同盐度对文蛤呼吸代谢的影响,本实验设置5个盐度(‰)梯度(11、18、25、32、39),检测不同盐度对文蛤(Meretrixmeretrix)耗氧和排氨的影响,以及文蛤的外套膜、鳃、肝胰腺三种组织中乳酸脱氢酶和Na+/K+-ATP酶活性的变化。结果表明:随着盐度的不断升高,文蛤耗氧率先升后降再升,在盐度18时达到最大值;排氨率先升后降,在盐度32时达到最大值。随着盐度不断升高和胁迫时间延长,文蛤的肝胰腺中乳酸脱氢酶活力总体呈先升高后下降再升高的趋势(P0.05),酶活力在盐度39时为最高;随着盐度不断升高和胁迫时间延长,文蛤的外套膜中Na+/K+-ATP酶活力总体呈先下降再升高后下降的趋势(P0.05),在盐度32时为最高;文蛤的外套膜和鳃中乳酸脱氢酶活力以及鳃和肝胰腺中Na+/K+-ATP酶活力受盐度影响不显著(P0.05),酶活力变化也多呈现"W"形的变化趋势。研究结果为文蛤的人工养殖提供参考。  相似文献   

The spawning and early life-history of a New Zealand endemic amphidromous eleotrid,bluegill bully (Gobiomorphus hubbsi)     

Matt G. Jarvis  Hannah A. Harland  Manna L. Warburton  Gerard P. Closs 《新西兰海洋与淡水研究杂志》2018,52(1):55-68

The larval stage of fishes is critical in determining their dispersal, survival and recruitment, but little is known of the larval behaviours and tolerances of amphidromous fishes, particularly in New Zealand. We report the results of a series of observational and experimental studies on bluegill bully (Gobiomorphus hubbsi), including spawning sites and behaviours, larval characteristics at hatch, phototactic responses of larvae, and larval survival at different salinity levels. Spawning primarily occurred in the lower reaches of the river, and larvae from different nests exhibited marked differences in, and trade-offs between, larval characteristics at hatch, potentially affecting larval success. Larvae were positively phototactic to intense light, an unexpected result based on diel drift patterns and international research. Finally, larvae exhibited markedly higher survival rates when reared at intermediate salinities compared to freshwater or seawater, suggesting estuaries may play an important role as nursery grounds for bluegill bully and other amphidromous fish.  相似文献   

Isotopic evidence for holocene climatic changes in Bosten Lake, Southern Xinjiang, China     

Zhong Wei  Xiong Heigang 《中国地理科学(英文版)》1997,8(2):176-182

Based on the δ¹³C and δ¹⁸O fluctuation of lacustrine carbonate, CaCO₃ content and sporo-pollen data, a palaeoclimatic history of Bosten Lake during the Holocene has been outlined, several stages of climatic changes are divided, and the following result es are obtained: (1) Palaeoclimatic changes revealed by carbonate isotope around Bosten Lake are basically identical with that revealed by other geological records in Xinjiang. Environmental changes presented apparent Westlies Style model: during cold period, relative humidity increased, δ¹⁸O, δ¹³C and CaCO₃ appeared low; but in warm periods, the dry regime aggravated. (2) The temperature reflected by δ¹⁸O exist evident features being increase in the late period during the Holocene. Together with the δ¹³C, pollen and CaCO₃ analyses, several cold and warm phases which are of broad regional significance can be identified. The warm peaks occurred at about 11.0 ka B.P., 9.4 ka B.P., 7.5 ka B.P., 5.0 ka B.P., 3.0 ka B.P. and 2.0 ka B.P.; the cold peaks at 11.5 ka B.P., 10.5 ka B.P., 8.8 ka B.P., 5.5 ka B.P., 3.3 ka B.P., 2.2 ka B.P. and 1.5 ka B.P.. (3) Several climatic events with the nature of “abrupt climatic changes” are revealed in the periods of 11.0 ka B.P. −10.5 ka B.P., 9.4 ka B.P. −8.8 ka B.P., 5.5 ka B.P. −5.0 ka B.P. and 2.0 ka B.P. −1.5 ka B.P.. (4) The results show that carbonate isotopic record of lacustrine sediment in arid area is very sensitive to climatic changes, and may be play a very important role in understanding the features and mechanism of palaeoclimatic changes.  相似文献   

A note on turbulent perturbations of salinity in a partially mixed estuary     

J.R. West  K. Shiono 《Estuarine, Coastal and Shelf Science》1985,20(1):55-78

Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes $\text{sw}$ and $\text{su}$ were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and c_γ were found to decrease and increase respectively as Ri increases.  相似文献   

Factors affecting the distribution and abundance of Macrobrachium petersi (Hilgendorf) in the Keiskamma River and estuary,South Africa     

G.H.L. Read 《Estuarine, Coastal and Shelf Science》1985,21(3):313-324

A dry (1979–1980) and a wet (1980–1981) season had a marked effect on the freshwater inflow into the Keiskamma estuary. Under low inflow conditions, which results in elevated salinities in the upper reaches, an upstream migration of adult Macrobrachium petersi (Hilgendorf) to freshwater takes place. During periods of increased river inflow adult M. petersi move downstream to the more saline reaches of the estuary. These two migratory responses have been interpreted as (a) a breeding migration under high inflow conditions which ensures that larvae are in close proximity to salinities that favour growth and development, and (b) an adult upstream migration back to freshwater to escape elevated estuarine salinities as a result of the low freshwater inflow.  相似文献   

Hydrodynamic control of phytoplankton in low salinity waters of the James River estuary,Virginia, U.S.A.     

Margaret J. Filardo  William M. Dunstan 《Estuarine, Coastal and Shelf Science》1985,21(5):653-667

Autotrophic biomass and productivity as well as nutrient distributions and phytoplankton cell populations in the James River estuary, Virginia, were quantified both spatially and temporally over a 17-month period. Emphasis was placed on the very low salinity region of the estuary in order to gain information on the fate of freshwater phytoplankters. Differing amounts of freshwater plant biomass are advected into the estuary as living material, DOC or POC and the demonstrated variability of this input must play an important role in marine biogeochemical cycling.Late summer and fall maxima in both chlorophyll a and the photosynthetic production of particulate organic carbon in very low salinity regions were inversely correlated with river discharge.During periods of low river discharge greater than 50% of the chlorophyll a biomass measured at 0‰ disappeared within a narrow range of salinity (0–2‰). Cell enumeration data suggest that species introduced from the freshwater end-member tend to comprise the bulk of the biomass removed. Confounding factors, which may contribute to the regulation of both the abundance and species of phytoplankters mid-river, include the flocculation of colloidal material with phytoplankton cells, the presence of the turbidity maximum and the growth of endemic phytoplankton populations.An inverse relationship exists between the phytoplankton abundance in very low salinity waters and the abundance of biomass measured in the lower portion of the river (estuary). Thus, autotrophic production in the fresh and very low salinity areas may indirectly regulate the onset on the spring bloom in the estuary by controlling the amount of nutrients available.  相似文献   

Interpolating paleovegetation data with an artificial neural network approach     

Bjrn Grieger 《Global and Planetary Change》2002,34(3-4)

To drive an atmospheric general circulation model (AGCM), land surface boundary conditions like albedo and morphological roughness, which depend on the vegetation type present, have to be prescribed. For the late Quaternary there are some data available, but they are still sparse. Here an artificial neural network approach to assimilate these paleovegetation data is investigated. In contrast to a biome model the relation between climatological parameters and vegetation type is not based on biological knowledge but estimated from the available vegetation data and the AGCM climatology at the corresponding locations. For a test application, a data set for the modern vegetation reduced to the amount of data available for the Holocene climate optimum (about 6000 years B.P.) is used. From this, the neural network is able to reconstruct the complete global vegetation with a kappa value of 0.56. The most pronounced errors occur in Australia and South America in areas corresponding to large data gaps.  相似文献   

Palynofacies and sea-level changes in the Upper Cretaceous of the Vocontian Basin, southeast France     

Annette E. Gtz  Susanne Feist-Burkhardt  Katrin Ruckwied 《Cretaceous Research》2008,29(5-6):1047

Upper Cretaceous platform carbonates of the Vocontian Basin (southeastern France) have been investigated in a cross-section from the proximal deposits exposed in the lower Rhône Valley to the distal part of the basin in the Southern Subalpine Ranges north of Nice. The stratigraphic interval studied in detail spans the uppermost Turonian and Coniacian.Palynofacies patterns were used to detect eustatic signals at a third-order scale and are the tool for correlation of proximal and distal platform deposits. The organic constituents observed in the studied samples have been grouped into a continental fraction, including higher plant debris (phytoclasts) and sporomorphs, and a marine fraction with dinoflagellate cysts, acritarchs, prasinophytes, and foraminiferal test linings. The main factors influencing the stratigraphic and spatial distribution of land-derived, allochthonous, and marine, relatively autochthonous, organic particles are the proximity of land, the organic productivity, the degree of biodegradation and the hydrodynamic conditions of the depositional system. Palynofacies parameters used for the sequence stratigraphic interpretation are: (1) the ratio of continental to marine constituents (CONT/MAR ratio); (2) the ratio of opaque to translucent phytoclasts (OP/TR ratio); (3) the phytoclast particle size and shape; and (4) the relative proportion and species diversity of marine plankton. Ternary diagrams illustrating significant proximality changes were used to decipher transgressive-regressive trends within the succession.High amounts of translucent phytoclasts and decreasing values of the CONT/MAR ratio occur during the phase of relative sea-level rise in the upper Turonian. The stratigraphic interval of maximum flooding around the Turonian/Coniacian boundary is marked by the highest abundance and species diversity of dinoflagellate cysts, and by high percentages of opaque, equidimensional particles within the phytoclast group. The OP/TR ratio is still high within the lower Coniacian representing the early highstand deposits, whereas the relative abundance of marine constituents is again decreasing. Sedimentary organic matter of the upper Coniacian is dominated by large, blade-shaped, mainly opaque phytoclasts, which are a characteristic palynofacies signature of late highstand deposits.The present study demonstrates the high potential of palynofacies analysis in high-resolution stratigraphy and correlation of sedimentary series of shallow epeiric seas.  相似文献   

Simultaneous transport of water and solutes under transient unsaturated flow conditions — A case study     

B. K. Purandara  N. Varadarajan  B. Venkatesh 《Journal of Earth System Science》2008,117(4):477-487

The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows. In the present study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid (upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in downstream parts of the study area. In this study we characterized the soil salinity and groundwater quality in both areas. An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and measured results indicating the applicability of the model.  相似文献