Preparation of volume table of SAL (Shorea robusta) - an approach using satellite data     

V. K. Srivastava  A. M. Rai  R. K. Dixit  M. P. Oza  A. Narayana 《International Journal of Applied Earth Observation and Geoinformation》1999,1(3-4)

Sal (Shorea robusta) is an important forest tree species in north and north-eastern India. Large-scale plantations of this species have been raised there under taungya and coppice system of management. The conventional volume table prepared for high sal forest is referred to infer the volume of production of this species. Earlier workers have used aerial remote sensing data to develop volume tables of this species. In the present study a volume table for sal is developed based on remotely sensed satellite data using a regression technique. A two-step method was developed to estimate mean tree volume from satellite data. In step 1, mean crown diameter — an intermediate variable - was estimated from satellite data. In step 2, the estimated mean crown diameter was used to estimate the mean tree volume. Addition of age of the crop as an independent variable improved the predictive ability of the regression equation.  相似文献   

Dissolution kinetics of biogenic silica collected from the water column and sediments of three Southern California borderland basins     

Tao Cheng  Douglas E. Hammond  William M. Berelson  Janet G. Hering  Suvasis Dixit 《Marine Chemistry》2009,113(1-2):41-49

Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 °C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d^? 1 for plankton tow samples and 0.07 d^? 1 for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0–0.5 cm) were at least 3–5 times less, and sediments at depths > 2 cm had rate constants at least 6–13 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.  相似文献   

Deep seismic sounding studies in the north Cambay and Sanchor basins, India   总被引：1，自引：0，他引：1  

K. L. Kaila  H. C. Tewari  V. G. Krishna  M. M. Dixit  D. Sarkar  M. S. Reddy 《Geophysical Journal International》1990,103(3):621-637

  相似文献   

Evaluation of fertility indicators associated with arsenic-contaminated paddy fields soil   总被引：1，自引：0，他引：1  

P. S. Chauhan  S. K. Mishra  S. Misra  V. K. Dixit  S. Pandey  P. Khare  M. H. Khan  S. Dwivedi  A. Lehri 《International Journal of Environmental Science and Technology》2018,15(11):2447-2458

Emerging environmental issues related to heavy metal contamination in rice draw great concern about the soil quality of paddy farming lands irrigated with groundwater. Investigating the functioning of soil microorganisms exposed to heavy metal contamination is imperative for agricultural soil manipulations. The current study accentuates the influence of heavy metals on microbial activity and community composition in arable soil of West Bengal State of India. The result revealed that the fertility indicators (activity of all soil enzymes) and growth-limiting factors (soil N and P) were negatively correlated with the heavy metal stress except the soil total organic content which demonstrated significant positive correlation with the heavy metals. In case of functional diversity of soil, all the considered diversity indices exhibited no specific pattern along with the availability of heavy metals. Further, despite the heavy metal contamination, we observed a very complex and indifferent pattern of bacterial community composition along the heavy metal contamination sites. Overall, we found that γ-Proteobacteria had been the most abundant bacterial community followed by Actinobacteria, Firmicutes, β-Proteobacteria and α-Proteobacteria. Commemorating all the results, we can infer that arsenic and other heavy metal contamination is deteriorating the soil quality and hence warrants immediate attention of concerned soil scientist and agronomists.  相似文献   

Processes controlling solubility of biogenic silica and pore water build-up of silicic acid in marine sediments   总被引：1，自引：0，他引：1  

Suvasis Dixit  Philippe Van Cappellen  A. Johan van Bennekom 《Marine Chemistry》2001,73(3-4)

Dissolution experiments in batch and flow-through reactors were combined with data on sediment composition and pore water silicic acid profiles to identify processes controlling the solubility of biogenic silica and the build-up of silicic acid in marine sediments. The variability of experimentally determined biogenic silica solubilities is due, in part, to variations in specific surface area and Al content of biosiliceous materials. Preferential dissolution of delicate skeletal structures and frustules with high surface areas leads to a progressive decrease of the specific surface area. This may cause a reduction of the solubility of deposited biosiliceous debris by 10–15%, relative to fresh planktonic assemblages. Dissolution of lithogenic (detrital) minerals in sediments releases dissolved aluminum to the pore waters. This aluminum becomes structurally incorporated into deposited biogenic silica, further decreasing its solubility. Compared to Al-free biogenic silica, the solubility of diatom frustules is lowered by as much as 25% when one out of every 70 Si atoms is substituted by an Al(III) ion.The build-up of silicic acid in pore waters of sediments with variable proportions of detrital matter and biogenic silica was simulated in batch experiments using kaolinite and basalt as model detrital constituents. The steady-state silicic acid concentrations measured in the experiments decreased with increasing detrital-to-opal ratios of the mixtures. This trend is similar to the observed inverse relationship between asymptotic pore water silicic acid concentrations and detrital-to-opal ratios in Southern Ocean sediments. Flow-through reactor experiments further showed that in detrital-rich sediments, precipitation of authigenic alumino-silicates may prevent the pore waters from reaching equilibrium with the dissolving biogenic silica. This agrees with data from Southern Ocean sediments where, at sites containing more than 30 wt.% detrital material, the pore waters remain undersaturated with respect to the experimentally determined in situ solubility of biogenic silica.The results of the study show that interactions between deposited biogenic silica and detrital material cause large variations in the asymptotic silicic acid concentration of marine sediments. The production of Al(III) by the dissolution of detrital minerals affects the build-up of silicic acid by reducing the apparent silica solubility and dissolution kinetics of biosiliceous materials, and by inducing precipitation of authigenic alumino-silicate minerals.  相似文献   

Three dimensional velocity structure of the Koyna-Warna region using local earthquake tomography     

Sanjay Kumar  Madan M. Dixit 《Journal of the Geological Society of India》2017,90(6):692-697

A dense seismic network (～100 stations) was operated in the Koyna-Warna region from January 2010 to May 2010, that allow us to collect 400 high-quality local earthquake data of magnitude less than 4. In this region, the fault structure and tectonic setting that accommodate the induced seismicity is not well understood. To investigate the seismotectonics of the region, we have inverted 7826 P- and 7047 S-P arrival times for 3-D Vp and Vp/Vs tomographic models along with hypocenters parameters in the region. Although, Dixit et al. (2014) have performed 3-D local earthquake tomography with double-difference tomography code using catalog differential time data. In this paper, Simulps14 code on the same data set is applied. For better approach P arrival time and S-P travel times are inverted directly for Vp, Vp/Vs variations and earthquake locations. High Vp ～5.9 to 6.5 and low to high Vp/Vs ～1.69-1.74 imaged in the hypocenter region. These features interpreted as a fluid bearing rock mass under high pore pressure. It is also observed that below the trap basement form a local topography depression between the Koyna and Warna Reservoirs. To the South of the Warna reservoir, intense seismic activity defines a major cluster of ～ 5 km width at 3 to7 km deep, located under the trap, where the basement is deepening. Such regions are inferred to be associated with the seismically active faults zones. The obtain velocity anomalies are reliable down to a depth of 10 km. This is also confirmed by the analysis of three resolution parameters viz. Hit count, Derivative Weight sum (DWS) and Resolution Diagonal Elements (RDE).  相似文献   

Distribution functions in the statistical theory of MHD turbulence of an incompressible fluid in the presence of the Coriolis force     

T. Dixit  B. N. Upadhyay 《Astrophysics and Space Science》1989,153(2):297-309

In this paper we have made an attempt to define hierarchy of distribution functions for the simultaneous velocity and magnetic fields. Various properties of the constructed functions such as reduction property, separation property, coincidence properties have been discussed, and equations for the evaluation of one- and two-point bivariate distribution functions have been derived.  相似文献   

Utility of scaled chrysophytes for inferring lakewater pH in northern New England lakes     

Sushil S. Dixit  John P. Smol  Dennis S. Anderson  Ronald B. Davis 《Journal of Paleolimnology》1990,3(3):269-286

Scaled chrysophytes in the surface sediments of 58 soft-water northern New England lakes were analyzed to assess their usefulness for inferring pH. The distributions of many taxa are correlated with lakewater pH and associated variables. Canonical correspondence analysis (CCA) and clustering grouped chrysophyte taxa according to their distributions along the pH gradient. For example, Chrysodidymus synuroideus, Mallomonas hindonii, and M. hamata commonly occur in acidic waters (pH<5.5), whereas M. caudata and M. pseudocoronata are common in circumneutral to alkaline waters. Of the five predictive models developed to infer pH, CCA based calibration had the lowest standard error (0.35 pH units). A CCA based predictive model was also developed to infer total alkalinity. The study provides strong evidence that, in the absence of past measured pH data, stratigraphic studies of sedimentary chrysophyte scales will provide accurate reconstructions of pH in northern New England lakes.This is the sixth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.  相似文献   

A comprehensive assessment framework for attributing trends in streamflow and groundwater storage to climatic and anthropogenic changes: A case study in the typical semi-arid catchments of southern India     

Rajesh Nune  Biju A. George  Andrew W. Western  Kaushal K. Garg  Sreenath Dixit  Ragab Ragab 《水文研究》2021,35(8):e14305

The clearest signs of hydrologic change can be observed from the trends in streamflow and groundwater levels in a catchment. During 1980–2007, significant declines in streamflow (−3.03 mm/year) and groundwater levels (−0.22 m/year) were observed in Himayat Sagar (HS) catchment, India. We examined the degree to which hydrologic changes observed in the HS catchment can be attributed to various internal and external drivers of change (climatic and anthropogenic changes). This study used an investigative approach to attribute hydrologic changes. First, it involves to develop a model and test its ability to predict hydrologic trends in a catchment that has undergone significant changes. Second, it examines the relative importance of different causes of change on the hydrologic response. The analysis was carried out using Modified Soil and Water Assessment Tool (SWAT), a semi-distributed rainfall-runoff model coupled with a lumped groundwater model for each sub- catchment. The model results indicated that the decline in potential evapotranspiration (PET) appears to be partially offset by a significant response to changes in rainfall. Measures that enhance recharge, such as watershed hydrological structures, have had limited success in terms of reducing impacts on the catchment-scale water balance. Groundwater storage has declined at a rate of 5 mm/y due to impact of land use changes and this was replaced by a net addition of 2 mm/y by hydrological structures. The impact of land use change on streamflow is an order of magnitude larger than the impact of hydrological structures and about is 2.5 times higher in terms of groundwater impact. Model results indicate that both exogenous and endogenous changes can have large impacts on catchment hydrology and should be considered together. The proposed comprehensive framework and approach demonstrated here is valuable in attributing trends in streamflow and groundwater levels to catchment climatic and anthropogenic changes.  相似文献   

Effect of topography on farm-scale spatial variation in extreme temperatures in the Southern Mallee of Victoria, Australia     

Prakash N. Dixit  Deli Chen 《Theoretical and Applied Climatology》2011,103(3-4):533-542

Extreme temperatures around flowering of wheat have the potential to reduce grain yield and at farm scale their impact can be spatially variable depending on topography. Twenty-five data loggers were installed at 0.8-m height across a 164-ha farm in the southern Mallee of Victoria, Australia to spatially record the daily course of temperatures around the average date of flowering of wheat in the region. The experiment was conducted during 2-years period. In 1 year, the farm had no crop cover and in another year the farm had a wheat crop. Multiple linear regression analysis techniques were used to fit models relating daily extreme temperatures to the farm topographic features of elevation, aspect and slope, and the average maximum and minimum temperatures of each day at the farm in order to identify areas of high risk of extreme temperatures around the time of the flowering of wheat. The fitted regression models explained 90% and 97% of the variability in maximum and minimum temperatures, respectively, when the farm had no crop cover and 80% and 94% of the variability in maximum and minimum temperatures, respectively, when the farm had a wheat crop cover. When the farm had no crop, only minimum temperature was partially explained by the topography however, both maximum and minimum temperatures were partially explained by the topography when the farm had a wheat crop. From this study it was concluded that, (1) high temperature variations were found across the farm (2) temperature variations were only partially explained from the developed model presumably due to the flatter topography of the farm and (3) the relationships obtained from this study could be used in a crop model which can explain variation in grain yield based on the topography of a field.  相似文献