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71.
Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
72.
R. Tatavarti A. C. Narayana P. Manoj Kumar Shyam Chand 《Journal of Earth System Science》1999,108(1):57-68
Field experiments conducted in the nearshore ocean to understand the dynamics of mudbank off Kerala, south-west coast of India,
are highlighted. Real time monitoring of the nearshore ocean off Purakkad, Kerala was accomplished using pressure transducers
for nearshore surface wave measurements, and current sensors for nearshore velocity measurements. Comprehensive information
on the spatial structure of mudbank was obtained from aerial surveys. Extensive data collected on surface waves and currents
in the nearshore ocean, indicate that the infra-gravity (IG) waves (leaky modes and trapped edge wave modes), and far infra-gravity
(FIG) waves coupled with strong shoreline reflections and undertow play an important role in the dynamics associated with
the mudbanks off Kerala during the monsoon season. During the non-monsoon season evidence for progressive edge waves in the
infragravity frequency band, an energetic gravity wave band and a strong undertow with weak reflections was observed. 相似文献
73.
Martin?J.?WhitehouseEmail author G.?R.?Ravindra Kumar Andrius?Rim?a 《Contributions to Mineralogy and Petrology》2014,168(2):1042
Zircon crystals from a locally charnockitized Paleoproterozoic high-K metagranite from the Kerala Khondalite Belt (KKB) of southern India have been investigated by high-spatial resolution secondary ion mass spectrometry analysis of U–Th–Pb and rare earth elements (REE), together with scanning ion imaging and scanning ion tomography (depth-profiled ion imaging). The spot analyses constrain the magmatic crystallization age of the metagranite to ca. 1,850 Ma, with ultrahigh-temperature (UHT) metamorphism occurring at ca. 570 Ma and superimposed charnockite formation at ca. 520–510 Ma, while the ion imaging reveals a patchy distribution of radiogenic Pb throughout the zircon cores. Middle- to heavy-REE depletion in ca. 570 Ma zircon rims suggests that these grew in equilibrium with garnet and therefore date the UHT metamorphism in the KKB. The maximum apparent 207Pb/206Pb age obtained from the unsupported radiogenic Pb concentrations is also consistent with formation of the Pb patches during this event. The superimposed charnockitization event appears to have caused additional Pb-loss in the cores and recrystallization of the rims. The results of depth-profiling of the scanning ion tomography image stack show that the Pb-rich domains range in size from <5 nm to several 10 nm (diameter if assumed to be spherical). The occurrence of such patchy Pb has previously been documented only from UHT metamorphic zircon, where it likely results from annealing of radiation-damaged zircon. The formation of a discrete, heterogeneously distributed and subsequently immobile Pb phase effectively arrests the normal Pb-loss process seen at lower grades of metamorphism. 相似文献
74.
We made comparative studies of three tropical ox-bow lakes in India with different trophic states. The species number of zooplanktons
was negatively correlated with the degree of water eutrophication, and lakes of similar trophic status had higher similarity
of species. The most significant differences of species composition were observed with rotifers and zoobenthos. The density
and biomass of phytoplankton, rotifers, oligochaetes and chironomids tended to increase with increasing nutrients. We observed
a significant difference of dominant species in different waters, especially the eutrophic lake, which was dominated by a
few species of oligochaetes. The abundance of Tanypus bilobatus showed a highly significant correlation with the degree of eutrophication. Rotifers and zoobenthos showed considerably lower
biodiversity in the eutrophic lake. 相似文献
75.
Birendra Nath Ghosh Narinder Kumar Sharma Nurnabi Meherul Alam Raman Jeet Singh Gopal Prasad Juyal 《山地科学学报》2014,11(5):1208-1217
On farm bio-resource recycling has been given greater emphasis with the introduction of conservation agriculture specifically withclimate change scenarios in the mid-hills of the north-west Himalaya region(NWHR). Under this changing scenario, elevation, slope aspect and integrated nutrient management(INM) may affect significantly soil quality and crop productivity. A study was conducted during 2009-2010 to 2010-2011 at the Ashti watershed of NWHR in a rainfed condition to examine the influence of elevation, slope aspect and integrated nutrient management(INM) on soil resource and crop productivity. Two years of farm demonstration trials indicated that crop productivity and soil quality is significantly affected by elevation, slope aspect and INM. Results showed that wheat equivalent yield(WEY) of improved technology increased crop productivity by -20%-37% compared to the conventional system. Intercropping of maize with cowpea and soybean enhanced yield by another 8%-17%. North aspect and higher elevation increased crop productivity by 15%-25% compared to south aspect and low elevation(except paddy). Intercropping of maize with cowpea and soybean enhanced yield by another 8%-15%. Irrespective of slope, elevation and cropping system, the WEY increased by -30% in this region due to INMtechnology. The influence of elevation, slope aspect and INM significantly affected soil resources(SQI) and soil carbon change(SCC). SCC is significantly correlated with SQI for conventional(R2 = 0.65*), INM technology(R2 = 0.81*) and for both technologies(R2 = 0.73*). It is recommended that at higher elevation.(except for paddy soils) with a north facing slope, INM is recommended for higher crop productivity; conservation of soil resources is recommended for the mid hills of NWHR; and single values of SCC are appropriate as a SQI for this region. 相似文献
76.
Natural Resources Research - Investigations on the Paleogene lignites were carried out through geochemical, mineralogical and petrographic analyses to assess their paleodepositional environment,... 相似文献
77.
Shiv S. Kumar 《Astrophysics and Space Science》1972,17(1):219-222
It is suggested that the minimum mass of a star at the time of its formation is approximately 0.01M
. Making use of this fact and the stellar mass functionF(M) M
–, it is found that the hidden mass (or the missing mass) in the solar neighborhood may be explained by the presence of a large number of invisible stars of very low mass (0.01M
M<0.07M
). 相似文献
78.
有孔虫生活在海洋和半咸水环境。底栖有孔虫的存在很大程度上受物理因素(深度、温度、光量、水体扰动)、化学因素(盐度、溶解氧和可用元素)和生物因素(食物供给量和底层沉积物特征)的制约。研究人员对印度东、西岸现代底栖有孔虫生态学和分布状态进行了研究。Naidu等在对Visakhapatnam港复合体有孔虫进行分析后提出 ,可以将有孔虫作为海洋污染的指示物。SreenivasaRao等采用Q模式系数分析对尼赞伯德讷姆湾有孔虫的分布进行了研究 ,确认此区域存在4种组合 ,受不同环境条件的影响。Khare等对门格… 相似文献
79.
The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information. 相似文献
80.
Interpolation of wave heights 总被引:1,自引:0,他引:1
Remote sensing of waves often necessitates presentation of data in the form of wave height values grouped over large time intervals. This restricts their use to long-term applications only. This paper describes how such data can be made suitable for short-term usage in the field. Weekly mean significant wave heights were derived from their monthly mean observations with the help of different alternative techniques. These include model-free neural network schemes as well as model-based statistical and numerical methods. Superiority of neural networks was noted when the estimations were compared with corresponding observations. The network was trained using three different training algorithms, viz., error back propagation, conjugate gradient and cascade correlation. The technique of cascade correlation took minimum training time and showed better coefficient of correlation between observations and network output. 相似文献