Spatio-temporal patterns of land use and cropping frequency in a tropical catchment of South India     

《Applied geography (Sevenoaks, England)》2017

India's rapid population and economic growth leads to fast changing land use and management practices that have a major impact on the environment. Therefore, this study assesses spatio-temporal dynamics of land use and cropping frequencies using moderate resolution spaceborne data (Landsat 7 and LISS III). Based on a hierarchical knowledge-based classification approach, multi-temporal satellite data from the years 2000/2001 and 2010/2011 have been used to derive land use and cropping frequency maps. The approach adopted in this study resulted in a satisfactory classification quality as indicated by overall accuracies >90% for the individual classifications. A reduced land use pressure on mountainous areas was found, indicated by an increasing development of forests within the transition zones between cultivated land and steep slopes. Furthermore, an increase of tree plantations points to a shift from drought vulnerable plants to less risk prone perennial plants. We found a higher cropping frequency in 2010/11 related to both inter-annual precipitation differences over the course of the rainy season and long-term socio-economic changes. While low yield areas are left for natural succession or switched to tree plantations, the cultivation of high yield areas was intensified.  相似文献   

Solar and anthropogenic imprints on Lake Masoko (southern Tanzania) during the last 500 years   总被引：1，自引：0，他引：1  

Yannick Garcin  David Williamson  Laurent Bergonzini  Olivier Radakovitch  Annie Vincens  Guillaume Buchet  Joël Guiot  Simon Brewer  Pierre-Etienne Mathé  Amos Majule 《Journal of Paleolimnology》2007,37(4):475-490

The Masoko crater-lake in southern Tanzania provides a continuous record of environmental changes covering the last 500 years. Multi-proxy studies were performed on a 52 cm sediment core retrieved from the deepest part of the lake. Magnetic, organic carbon, geochemical proxies and pollen assemblages indicate a dry climate during the ‘Little Ice Age’ (AD 1550–1850), confirming that the LIA in eastern Africa resulted in marked and synchronous hydrological changes. However, the direction of response varies between different African lakes (low versus high lake-levels), indicating strong regional contrasts that prevent the clear identification of climate trends over eastern Africa at this time. Inferred changes in Masoko lake-levels closely resemble the record of solar activity cycles, indicating a possible control of solar activity on the climate in this area. This observation supports previous results from East African lakes, and extends this relationship southward. Finally, anthropogenic impact is observed in the Masoko sediments during the last 60 years, suggesting that human disturbance significantly affected this remote basin during colonial and post-colonial times.  相似文献   

Elemental composition of sediment cores from a mangrove environment using neutron activation analysis     

Julio Cesar Wasserman  Ana Maria G Figueiredo  Fabio Pellegatti  Emmanoel V Silva-Filho 《Journal of Geochemical Exploration》2001,72(2):1013

The geochemistry of Sepetiba Bay was studied in four sediment cores using a multi-element approach. Two cores were sampled in the more contaminated eastern part of the bay and two cores were sampled in the western region. The aim was to determine whether less common elements like the rare earths or the actinides are associated with contaminant metals like zinc in the Bay. Samples were analysed by instrumental neutron activation analysis that permits the quantification of total concentrations of metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), rare earth elements (Ce, Eu, La, Lu, Sm and Yb), actinides (Th, U), non-metals and semi-metals (As, Br). Organic carbon and total sulphur were also analysed. The results show very strong zinc contamination in the top layers (more than 1000 μg g⁻¹) and background concentrations in the bottom (15 μg g⁻¹). Elements like chromium which would be expected to be released by the heavy industries of Sepetiba Bay, did not show a contamination profile, and concentrations remained close to those of natural environments. No evidence of any association between the zinc and other potential contaminant elements could be identified in this work.  相似文献   

Experimental calibration of a cost-effective X-band weather radar for climate ecological studies in southern Ecuador     

Rütger Rollenbeck  Jrg Bendix 《Atmospheric Research》2006,79(3-4):296-316

In this paper setup, operational problems and a straightforward calibration approach for a cost-effective X-Band radar are presented. The LAWR (Local Area Weather Radar) system is based on conventional ship radar technology which is adapted to register rainfall within a range of about 60 km with a spatial resolution of 500 m per pixel. The instrument offers neither Doppler processing nor vertical scan capabilities but uses 20° wide (vertical) beam. The calibration suffers from an unfavorably distributed and very sparse rain gauge network, heavy clutter contamination of the signal and obstructions by surrounding terrain. A specific scaling approach is developed, that includes satellite data on cloud frequency and distribution, to overcome these limitations. Observed clutter is removed and missing values are replaced by bilinear interpolation of the undisturbed signals. A temporal and spatial bias of the radar signal is corrected using an omni-directional spatial distribution hypothesis. This is possible because of the location of the radar site in the transition zone between high rainfall on the eastern Andean slopes and low rainfall on the leeward side. A further limitation of the system is that the LAWR does not provide information on the measured reflectivity Z but dimensionless counts (8 bit resolution). Calibration is performed assuming a linear relation between radar output and rainfall as recommended by the systems manufacturer. The intercomparison of rain gauge and scatterometer data with calibrated radar rainfall reveals a good performance of the developed calibration approach.  相似文献   

A Note on the Relationship Between Temperature and Water Vapor over Oceans, Including Sea Surface Temperature Effects     

C.-L. SHIE  W.-K. TAO  J. SIMPSON 《大气科学进展》2006,23(1):141-148

An ideal and simple formulation is successfully derived that well represents a quasi-linear relationship found between the domain-averaged water vapor, Q (mm), and temperature, T (K), fields for the three tropical oceans (i.e., the Pacific, Atlantic and Indian Oceans) based on eleven GEOS-3 [Goddard Earth Observing System (EOS) Version-3] global re-analysis monthly products. A Q ? T distribution analysis is also performed for the tropical and extra-tropical regions based on in-situ sounding data and numerical simulations [GEOS-3 and the Goddard Cumulus Ensemble (GCE) model]. A similar positively correlated Q ? T distribution is found over the entire oceanic and tropical regions; however, Q increases faster with T for the former region. It is suspected that the tropical oceans may possess a moister boundary layer than the Tropics. The oceanic regime falls within the lower bound of the tropical regime embedded in a global, curvilinear Q ? T relationship. A positive correlation is also found between T and sea surface temperature (SST); however, for one degree of increase in T, SST is found to increase 1.1 degrees for a warmer ocean, which is slightly less than an increase of 1.25 degrees for a colder ocean. This seemingly indicates that more (less) heat is needed for an open ocean to maintain an air mass above it with a same degree of temperature rise during a colder (warmer) season [or in a colder (warmer) region]. Q and SST are also found to be positively correlated. Relative humidity (RH) exhibits similar behaviors for oceanic and tropical regions. RH increases with increasing SST and T over oceans, while it increases with increasing T in the Tropics. RH, however, decreases with increasing temperature in the extratropics. It is suspected that the tropical and oceanic regions may possess a moister local boundary layer than the extratropics so that a faster moisture increase than a saturated moisture increase is favored for the former regions. T,Q, saturated water vapor, RH, and SST are also examined with regard to the warm and cold “seasons” over individual oceans. The Indian Ocean warm season dominates in each of the five quantities, while the Atlantic Ocean cold season has the lowest values in most categories. The higher values for the Indian Ocean may be due to its relatively high percentage of tropical coverage compared to the other two oceans. However, Q is found to increase faster for colder months from individual oceans, which differs from the general finding in the global Q?T relationship that Q increases slower for a colder climate. The modified relationship may be attributed to a possible seasonal (warm and cold) variability in boundary layer depth over oceans, or to the small sample size used in each individual oceanic group.  相似文献   

热带大气能量频散波射线的低频动力学特征   总被引：2，自引：0，他引：2  

徐祥德  苗秋菊 《气象学报》2000,58(5):534-544

首先在非零频波条件下采用有、无辐散两类数学模型 ,讨论热带大气低频波传播动力特征 ,研究结果表明 ,非零频的波频率参数是热带大气低频振荡源能量频散波路径及其波振幅的关键影响因子 ,且热带地区低频振荡的经向传播与其伴随着的强对流云团有显著相关 ,并与热带低纬 β因子等相关。文中还进一步揭示了低纬大气低频振荡经向传播伴随的积云对流现象及向高中纬传播机理 ,描述了 WKB近似方法数学模型及其波射线方程解模态对大气低频动力特性及其水汽分布垂直结构、不稳定层结等因子的响应特征。  相似文献   

简单热带海气耦合模型中不同扰动形式的作用   总被引：3，自引：2，他引：1       下载免费PDF全文

林一骅  曾庆存 《地球物理学报》2000,43(3):304-311

在局地热平衡情况下,将物理量先用韦伯函数展开,然后去掉相应分量的滤波方 法,讨论了简单热带海气耦合模型中不同形式扰动的作用和贡献,结果表明,在热带海气耦合 系统中,大气准定常 Ｒｏｓｓｂｙ波和海洋 Ｒｏｓｓｂｙ波对于耦合系统贡献较大,它们决定着耦合系统 与耦合扰动的性质,而大气准定常Ｋｅｌｖｉｎ波和海洋Ｋｅｌｖｉｎ波对于耦合系统贡献相对较小．  相似文献   

On the diet of Nile tilapia in two eutrophic tropical lakes containing toxin producing cyanobacteria     

Ronald Semyalo  Thomas RohrlackDuncan Kayiira  Yusuf S. Kizito  Stephen ByarujaliGeorge Nyakairu  Petter Larsson 《Limnologica》2011,41(1):30-36

Due to the production of toxins, cyanobacteria may adversely affect economically important fish such as Nile tilapia Oreochromis niloticus in tropical lakes. We studied the diet composition and factors affecting the diet of Nile tilapia in two tropical lakes where cyanotoxins were present. Particle-bound microcystins were present in all analysed water samples, ranging in concentration from 0.00012 to 1.11 and from 0.006 to 0.254 μg L⁻¹ in Murchison Bay in Lake Victoria and Lake Mburo, respectively. Detritus and phytoplankton were the main dietary components of the Nile tilapia, with phytoplankton contributing to over 30% by volume of stomach contents. The cyanobacteria Microcystis spp., which are also the most likely source of microcystins in the lakes, accounted for more than 80% of ingested phytoplankton. Microcystis spp. were also the most abundant cyanobacteria in both lakes (>60%). We found no significant relationship between the contribution of phytoplankton in Nile tilapia diet and the concentration of microcystins in the water but we found a close association between water transparency and the contribution of insects to Nile tilapia diets in Murchison Bay. Our results further show that none of the other measured environmental variables was a good predictor of diet items in Nile tilapia. Adult Nile tilapia in our study lakes, rely heavily on filter feeding, particularly under conditions of low water transparency, trapping detritus and phytoplankton cells especially colonies. They can ingest more mobile prey like insects and insect larvae when the water transparency and visibility increases.  相似文献   

从史前考古论中国热带地理环境的相对稳定性   总被引：1，自引：0，他引：1  

张伟强  黄镇国  江璐明 《热带地理》2003,23(1):1-6

参照60多处考古遗址的资料,认为史前时期古人类的活动及热带动物群的断续繁衍反映了中国热带自然地理环境的相对稳定性,因而生产力的发展比较迟缓,与北方地区相比,磨制石器的出现滞后约3 000a,青铜时代滞后约1 000a,农牧业滞后2 500～3 000a.无陶时代持续到新石器早期;彩陶和白陶的传入比北方迟2 000a.迁徒的采集渔猎生活方式延续到新石器中期,以农业为基础的定居生活比北方迟1 000～2 000a.新石器末期约5 000aBP才进入氏族社会,比北方迟约2 000a.  相似文献   

Discovery and exploration of the Gosowong epithermal gold deposit, Halmahera, Indonesia   总被引：1，自引：0，他引：1  

J. C. Carlile  G. R. Davey  I. Kadir  R. P. Langmead  W. J. Rafferty 《Journal of Geochemical Exploration》1998,60(3):207-227

The Gosowong epithermal gold deposit, on the island of Halmahera in eastern Indonesia, is located in an area of primary tropical rain forest with no previous history of gold mining or record of gold mineralisation. The deposit occurs in a newly recognised mineral district which contains a number of epithermal vein systems and at least two centres of low-grade porphyry style Cu–Au mineralisation. Several zones of argillic and advanced argillic alteration have been noted which may be related to additional centres of mineralisation. Gosowong is classified as a low-sulphidation epithermal quartz vein. Bonanza-grade gold–silver mineralisation is developed in shoots over a 400-m strike section of the vein system. Three types of veining are recognized; quartz–adularia veins and breccias; quartz–chlorite–illite veins and breccias; and crystalline or chalcedonic quartz vein stockworks. The area was targetted using a simple geological concept and the deposit was discovered and tested using basic exploration techniques commonly applied in the rugged tropical terrains of Indonesia. Sequential exploration methods comprised reconnaissance drainage sampling of stream sediment, BLEG and float media, ridge and spur soil sampling, prospect scale grid soil sampling, hand trenching and diamond drilling. Lapse time from identification of the initial reconnaissance anomaly to an inferred resource estimate of almost 1 million ounces of gold was less than 3.5 years. This case history illustrates that very detailed exploration is necessary to locate high-grade vein-type gold deposits in a tropical environment, but demonstrates that such resources still remain to be discovered in the relatively under-explored Neogene magmatic arcs of Indonesia.  相似文献