Arcellaceans (thecamoebians) as indicators of land-use change: settlement history of the Swan Lake area, Ontario as a case study   总被引：1，自引：0，他引：1  

R. Timothy Patterson  Andrew Dalby  Arun Kumar  Lori A. Henderson  Robert E.A. Boudreau 《Journal of Paleolimnology》2002,28(3):297-316

Arcellaceans have been used as indicators of a variety of paleolimnological conditions including pH, eutrophication, oxygen level, and heavy metal contamination, but there has only been limited application of the group to climate and land-use change research. The limnological evolution of Swan Lake in southwestern Ontario was documented using arcellaceans as proxies, and compared to the results of a palynological analysis, with which it closely correlated. The palynological record documents the rapid disappearance of forest by around 1850 as the area was cleared for agriculture and settlements. The change was characterized by a shift in the palynological record from the Woodland to High Diversity assemblages. Similarly the arcellacean fauna changed from the Pre-European Settlement Assemblage to the distinctive low diversity, stressed environment European Deforestation Assemblage. The introduction of high-yield chemical fertilizers in the post World War II era, and the resultant eutrophication of the lake, was clearly recognizable in the palynological record as indicated by the dramatic increase in the algae Pediastrum (High Nutrient Assemblage). This change in farming practice was also identifiable with arcellacean proxies, as indicated by the appearance of the algalphilic Eutrophication Assemblage. The arcellacean Ecologically Destabilized Assemblage dominated the lake for short intervals during the transition between the Pre-European Settlement and European Deforestation assemblages and again at the transition between the European Deforestation and Eutrophication Assemblages, indicative of periods of ecological destabilization as the lake adjusted to new trophic inputs. A stressed environment arcellacean Ecologically Destabilized Assemblage found in a portion of the core estimated to have been deposited between AD 1350 and AD 1700 may provide evidence of an earlier phase of deforestation associated with Huron Indian agricultural practices. The close correlation between the palynological and arcellacean proxy data clearly demonstrates the potential of arcellaceans as land-use change proxies, and indicates that changes in land-use had an almost immediate impact on the Swan Lake ecosystem. This observation raises concerns about the impact that rapid urbanization is having on the environmentally sensitive Oak Ridges Moraine watershed, of which Swan Lake is a part.  相似文献   

Monitoring Colima Volcano,Mexico, using satellite data     

Michael Abrams  Lori Glaze  Michael Sheridan 《Bulletin of Volcanology》1991,53(7):571-574

The Colima Volcanic Complex at the western end of the Mexican Volcanic Belt is the most active andesitic volcano in Mexico. Short-wavelength infrared data from the Landsat Thematic Mapper satellite were used to determine the temperature and fractional area of radiant picture elements for two January data acquisitions in 1985 and 1986. The 1986 data showed four 28.5 m by 28.5 m pixels (picture elements) whose hot subpixel components had temperatures ranging from 511–774° C and areas of 1.8–13 m². The 1985 data had no radiating areas above background temperatures. Ground observations and measurements in November 1985 and February 1986 reported the presence of hot fumaroles at the summit with temperatures of 135–895° C. This study demonstrates the utility of satellite data for monitoring volcanic activity.  相似文献   

Slope failures along the western continental margin of India: a consequence of gas-hydrate dissociation, rapid sedimentation rate, and seismic activity?     

Hanumantha Y. Rao  C. Subrahmanyam  A. Rastogi  B. Deka 《Geo-Marine Letters》2002,22(3):162-169

Along the western continental margin of India (WCMI), several bottom simulating reflectors were identified on analogue single-channel seismic records, some of these located in areas where slumping and mass wasting were observed. The causes, consequences and degree of geographic variation of these geomorphic processes are assessed in terms of possible gas-hydrate dissociation during Pleistocene sea-level changes, high sedimentation resulting in underconsolidation, and seismotectonic activity prevailing along the WCMI margin. One consequence of possible gas-hydrate dissociation along the continental slope could be sediment failure and mass transport down the slope. By contrast, in the flat deep-sea areas, gas-hydrate dissociation may have led to gas seepage and the development of pockmarks at the seafloor.  相似文献   

Probabilistic Assessment of Earthquake Hazard in Gujarat and Adjoining Region of India     

Ram Bichar Singh Yadav  Jayant Nath Tripathi  Bal Krishna Rastogi  Sumer Chopra 《Pure and Applied Geophysics》2008,165(9-10):1813-1833

The Gujarat and adjoining region falls under all four seismic zones V, IV, III and II of the seismic zoning map of India, and is one of the most seismically prone intracontinental regions of the world. It has experienced two large earthquakes of magnitude M _w 7.8 and 7.7 in 1819 and 2001, respectively and several moderate earthquakes during the past two centuries. In the present study, the probability of occurrence of earthquakes of M ≥ 5.0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely, Weibull, Gamma and Lognormal. A complete earthquake catalogue has been used covering the time interval of 1819 to 2006. The whole region has been divided into three major seismic regions (Saurashtra, Mainland Gujarat and Kachchh) on the basis of seismotectonics and geomorphology of the region. The earthquake hazard parameters have been estimated using the method of maximum likelihood. The logarithmic of likelihood function (ln L) is estimated and used to test the suitability of models in three different regions. It was found that the Weibull model fits well with the actual data in Saurashtra and Kachchh regions, whereas Lognormal model fits well in Mainland Gujarat. The mean intervals of occurrence of earthquakes are estimated as 40.455, 20.249 and 13.338 years in the Saurashtra, Mainland Gujarat and Kachchh region, respectively. The estimated cumulative probability (probability that the next earthquake will occur at a time later than some specific time from the last earthquake) for the earthquakes of M ≥ 5.0 reaches 0.9 after about 64 years from the last earthquake (1993) in Saurashtra, about 49 years from the last earthquake (1969) in Mainland Gujarat and about 29 years from the last earthquake (2006) in the Kachchh region. The conditional probability (probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake) is also estimated and it reaches about 0.8 to 0.9 during the time interval of about 57 to 66 years from the last earthquake (1993) in Saurashtra region, 31 to 51 years from the last earthquake (1969) in Mainland Gujarat and about 21 to 28 years from the last earthquake (2006) in Kachchh region.  相似文献   

Self-organized Fractal Seismicity and b Value of Aftershocks of the 2001 Bhuj Earthquake in Kutch (India)   总被引：1，自引：0，他引：1  

Prantik?MandalEmail author  B.K.?Rastogi 《Pure and Applied Geophysics》2005,162(1):53-72

— The devastating intraplate earthquake of M_w 7.7 of 26 January, 2001 took place along the south-dipping reverse fault in the lower crust ( 23 km) of Kutch, Gujarat, India, obliterating some 14,000 people. The aftershock activity has ensued for three years. We analyzed 997 aftershocks of M 3.0 to study the b value and fractal correlation dimensions in time and space. The b value is found to be 0.8 ± 0.03 from the Gutenberg-Richter relation and 0.76 ± 0.02 from the maximum-likelihood, suggesting a typical value for the intraplate region. The spatial correlation is 1.71 ± 0.02, indicating that events are approaching a two-dimensional region. Further, the temporal correlation dimension is estimated to be 0.78 ± 0.02, confirming the structure is mono-fractal in time domain. The depth section of b value shows a peak at 15–35 km depth range coinciding with the maximum occurrence of aftershocks ( 47%), which is inferred as a fluid-filled highly fractured rock matrix with fractures of high density. It will be important to note that tomographic results also suggest a low Vp, low Vs and a large Poissons ratio for the same depth range, further confirming this inference. Additionally, we have studied the variation of D₂^s and b value with time. During the first two months of aftershock activity the results show a marked negative correlation between spatial correlation dimension D₂ (large) and b value (low), indicating the predominance of large events associated with weak clustering. The negative correlation means the stress release along faults of a larger surface area. After two months the fractal dimension (D₂^s) and b value suggests a positive correlation implying more numerous smaller shocks with stress release along faults of a smaller surface area. This would indicate a reduced probability of large magnitude earthquakes due to fragmentation of the fault zone.Acknowledgement. The authors thank Dr. V.P. Dimri, Director, NGRI for his encouragement and kind permission to publish this work. The Department of Science and Technology, New Delhi supported this study.  相似文献   

Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 2001 Kachchh earthquake   总被引：1，自引：0，他引：1  

A. Ugalde  J.N. Tripathi  M. Hoshiba  B.K. Rastogi   《Tectonophysics》2007,429(1-2):111-123

176 vertical-component, short period observations from aftershocks of the M_w 7.7, 26 January, 2001 Kachchh earthquake are used to estimate seismic wave attenuation in western India using uniform and two layer models. The magnitudes (M_w) of the earthquakes are less than 4.5, with depths less than 46 km and hypocentral distances up to 110 km. The studied frequencies are between 1 and 30 Hz. Two seismic wave attenuation factors, intrinsic absorption (Q_i^− 1) and scattering attenuation (Q_s^− 1) are estimated using the Multiple Lapse Time Window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. We first assume spatial uniformity of Q_i^− 1, Q_s^− 1 and S wave velocity (β). A second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient (g), intrinsic absorption strength (h), density of the media (ρ) and shear wave velocity structure. The predicted coda envelopes are computed using Monte Carlo simulation. Results show that, under the assumption of spatial uniformity, scattering attenuation is greater than intrinsic absorption only for the lowest frequency band (1 to 2 Hz), whereas intrinsic absorption is predominant in the attenuation process at higher frequencies (2 to 30 Hz). The values of Q obtained range from Q_t = 118, Q_i = 246 and Q_s = 227 at 1.5 Hz to Q_t ≈ 4000, Q_i ≈ 4600 and Q_s ≈ 33,300 at 28 Hz center frequencies, being Q_t^− 1 a measure of total attenuation. Results also show that Q_i^− 1, Q_s^− 1 and Q_t^− 1 decrease proportional to f^−ν. Two rates of decay are clearly observed for the low (1 to 6 Hz) and high (6 to 30 Hz) frequency ranges. Values of ν are estimated as 2.07 ± 0.05 and 0.44 ± 0.09 for total attenuation, 1.52 ± 0.21 and 0.48 ± 0.09 for intrinsic absorption and 3.63 ± 0.07 and 0.06 ± 0.08 for scattering attenuation for the low and high frequency ranges, respectively. Despite the lower resolution in deriving the attenuation parameters for a two layered crust, we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle. Also, for a crustal layer of thickness 42 km, intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle, respectively.  相似文献   

Temporal and Spatial Variations in Water Quality on New York South Shore Estuary Tributaries: Carmans,Patchogue, and Swan Rivers     

Lori Zaikowski  Kevin T. McDonnell  Robert F. Rockwell  Fred Rispoli 《Estuaries and Coasts》2008,31(1):85-100

The chemical and biological impacts of anthropogenic physical modifications (i.e., channelization, dredging, bulkhead, and jetty construction) to tributaries were assessed on New York’s Long Island South Shore Estuary. Water-quality data collected on Carmans, Patchogue, and Swan Rivers from 1997 to 2005 indicate no significant differences in nutrient levels, temperature, or pH among the rivers, but significant differences in light transmittance, dissolved oxygen (DO), salinity, and sediments were observed. Patchogue River (PR) and Swan River (SR) were significantly more saline than Carmans River (CR), PR and SR had less light transmittance than CR, and both exhibited severe warm season hypoxia. CR was rarely hypoxic and only at the lower layer of the deepest station in warm seasons. Deep stations on PR had hypoxic readings year round, but the shallower SR was well-oxygenated at all stations after the fall turnover. There were wide diel and seasonal variations in chlorophyll a on each river, and measurements were significantly higher at poorly flushed stations. In warm seasons, this often resulted in hyperventilation with supersaturated DO in the upper water column on sunny days, and suboxic conditions at nights and/or in deeper layers. PR sediments were anoxic, SR sediments ranged from normal to anoxic, and CR sediments were normal at all stations. Polyaromatic hydrocarbon concentrations in PR sediments were over three orders of magnitude higher than SR and CR sediments. Benthic invertebrate assessment of species richness, biotic index, and Ephemeroptera, Plecoptera and Trichoptera richness indicated that PR was severely impacted, SR ranged from slightly to severely impacted, and CR ranged from non-impacted to slightly impacted. Diversity and abundance of plankton were comparable on SR and CR, and were significantly higher than on PR. The data indicate that nutrients do not play a major role in hypoxia in these estuarine tributaries but that physical forces dominate. The narrow inlets, channelization, and abrupt changes in depth near the inlets of PR and SR foster hypoxic conditions by inducing salinity stratification that limits vertical mixing and by restricting horizontal water mass exchange with the bay. The study suggests that other tributaries with such physical modifications should be examined to assess the temporal and spatial extent of hypoxia.  相似文献   

Evaluating Hyperspectral Imager for the Coastal Ocean (HICO) data for seagrass mapping in Indian River Lagoon,FL     

Hyun Jung Cho  Igor Ogashawara  Deepak Mishra  Joseph White  Andrew Kamerosky  Lori Morris 《地理信息系统科学与遥感》2014,51(2):120-138

Differentiation between benthic habitats, particularly seagrass and macroalgae, using satellite data is complicated because of water column effects plus the presence of chlorophyll-a in both seagrass and algae that result in similar spectral patterns. Hyperspectral imager for the coastal ocean data over the Indian River Lagoon, Florida, USA, was used to develop two benthic classification models, Slope_RED and Slope_NIR. Their performance was compared with iterative self-organizing data analysis technique and spectral angle mapping classification methods. The slope models provided greater overall accuracies (63–64%) and were able to distinguish between seagrass and macroalgae substrates more accurately compared to the results obtained using the other classifications methods.  相似文献   

Migration of seismicity and pore pressure diffusion for five decades long Koyna–Warna sequence and precursory nucleation process for earthquake forecasting     

B. K. Rastogi 《Journal of the Geological Society of India》2017,90(6):698-703

The continued reservoir-triggered seismicity for five decades in Koyna area has been attributed to southward migration of seismicity (during 1967–1992 near and south of Koyna dam and from 1993 onwards mostly near the new Warna reservoir). Spread of seismicity in the vicinity of reservoirs is attributed to pore-pressure diffusion. Moderate size Koyna–Warna earthquakes are found to nucleate at shallow depth (≤ 3 km) due to pore pressure caused by water level fluctuation of reservoir(s). The nucleation zone deepens along the critically stressed permeable fault zone to cause the occurrence of mainshock at the base of seismogenic layer (i.e. 5–10 km). The clustering of foreshocks up to 500 hr prior to several moderate size Koyna earthquakes of magnitude Mw 4–5 has been detected and used for quantifying the nucleation process. A static stress transfer by means of cascade model from one foreshock to next for the generation of foreshocks has been proposed for nucleation model. The nucleation process can be considered as an immediate earthquake precursor for the Koyna-Warna region.  相似文献