Joint Russian-American hydrogeological-geochemical studies of the Karachai-Mishelyak system, South Urals, Russia

 In September 1994, a Russian-American team conducted hydrogeological, geochemical, geophysical, and radiometric measurements in the territory of the Mayak Production Association, Russia. The primary purpose of these operations was to examine the frontal area of a radioelement- and nitrate-laden groundwater plume moving from the disposal site, Lake Karachai, toward the Mishelyak River. Activities encompassed (1) isolation of hydrologic intervals in two wells and production of water from these intervals, to compare isolated versus open-well sampling methods and to determine hydraulic transmissivities of the aquifer(s); (2) surface and soil-water sampling, accompanying radiometric measurements and subsequent chemical analyses; and (3) electrical resistivity profiling in areas of expected contrasting resistivity. Preliminary results indicate that (1) ⁶⁰Co, ¹³⁷Cs, and ⁹⁰Sr are present in small concentrations (∼0.1% of permissible levels) in water of the Mishelyak River; (2) analyses of water samples collected by a downhole sampler and of water produced from packed-off intervals agree within limits of laboratory accuracy, attesting to the efficacy of the sampling methods presently used by the Russian workers; (3) considerable differences in contaminant concentrations exist between nearby wells, supporting the concept that the plume from Lake Karachai toward the Mishelyak River is controlled by steeply dipping fractures and shear zones; and (4) strong contrasts occur between the electrical resistivities of soil and bedrock. Further collaborative work is strongly recommended and should include more detailed isolation of intervals in wells by multi-packer installations, to better determine the geochemical and hydrological characteristics of the Karachai-Mishelyak system; deployment of a broader soil water and soil sampling array; a more detailed examination of the distribution and concentration of radionuclides by high-resolution field gamma spectrometry; and a detailing of the area's electrical resistivity setting, using a mobile electromagnetic measurement system. Received: 22 January 1996 · Accepted: 1 April 1996     

A preliminary methods comparison for measurement of dissolved organic nitrogen in seawater

Routine determination of dissolved organic nitrogen (DON) is performed in numerous laboratories around the world using one of three families of methods: UV oxidation (UV), persulfate oxidation (PO), or high temperature combustion (HTC). Essentially all routine methods measure total dissolved nitrogen (TDN) and calculate DON by subtracting the dissolved inorganic nitrogen (DIN). While there is currently no strong suggestion that any of these methods is inadequate, there are continuing suspicions of slight inaccuracy by UV methods.This is a report of a broad community methods comparison where 29 sets (7 UV, 13 PO, and 9 HTC) of TDN analyses were performed on five samples with varying TDN and DIN concentrations. Analyses were done in a “blind” procedure with results sent to the first author. With editing out one set of extreme outliers (representing 5 out of 145 ampoules analyzed), the community comparability for analyzing the TDN samples was in the 8–28% range (coefficient of variation representing one standard deviation for the five individual samples by 28 analyses). When DIN concentrations were subtracted uniformly (single DIN value for each sample), the comparability was obviously worse (19–46% cv). This comparison represents a larger and more diverse set of analyses, but the overall comparability is only marginally better than that of the Seattle workshop of a decade ago. Grouping methods, little difference was seen other than inconclusive evidence that the UV methods gave TDN values for several of the samples higher than HTC methods. Since there was much scatter for each of the groups of methods and for all analyses when grouped, it is thought that more uniformity in procedures is probably needed. An important unplanned observation is that variability in DIN analyses (used in determining the final analyte in most UV and PO methods) is essentially as large as the variability in the TDN analyses.This exercise should not be viewed as a qualification exercise for the analysts, but should instead be considered a broad preliminary test of the comparison of the families of methods being used in various laboratories around the world. Based on many independent analyses here, none of the routinely used methods appears to be grossly inaccurate, thus, most routine TDN analyses being reported in the literature are apparently accurate. However, it is not reassuring that the ability of the international community to determine DON in deep oceanic waters continues to be poor. It is suggested that as an outgrowth of this paper, analysts using UV and PO methods experiment and look more carefully at the completeness of DIN conversion to the final analyte and also at the accuracy of their analysis of the final analyte. HTC methods appear to be relatively easy and convenient and have potential for routine adoption. Several of the authors of this paper are currently working together on an interlaboratory comparison on HTC methodology.     

Mixing Methods in Fertility Research

Fertility research in population geography is rooted in a spatial demography tradition which places emphasis on the use of quantitative methodologies to analyse, model and project fertility. As data sources have become more sophisticated and abundant some have questioned whether research within the discipline is now too data-oriented resulting in a reluctance to embrace new methods and concepts. Alternative conceptualisations of fertility and reproduction are outlined which represent a shift away from general explanation to more differentiated understandings of reproductive behaviour and favour the use of qualitative methodologies in combination or in a multi-level framework. The paper illustrates, with reference to a research project in the Kalahari of Botswana, the potential for methodological pluralism in the study of fertility.     

Using Ancillary Information to Improve Hypocenter Estimation: Bayesian Single Event Location (BSEL)

We have developed and tested an algorithm, Bayesian Single Event Location (BSEL), for estimating the location of a seismic event. The main driver for our research is the inadequate representation of ancillary information in the hypocenter estimation procedure. The added benefit is that we have also addressed instability issues often encountered with historical NLR solvers (e.g., non-convergence or seismically infeasible results). BSEL differs from established nonlinear regression techniques by using a Bayesian prior probability density function (prior PDF) to incorporate ancillary physical basis constraints about event location. P-wave arrival times from seismic events are used in the development. Depth, a focus of this paper, may be modeled with a prior PDF (potentially skewed) that captures physical basis bounds from surface wave observations. This PDF is constructed from a Rayleigh wave depth excitation eigenfunction that is based on the observed minimum period from a spectrogram analysis and estimated near-source elastic parameters. For example, if the surface wave is an Rg phase, it potentially provides a strong constraint for depth, which has important implications for remote monitoring of nuclear explosions. The proposed Bayesian algorithm is illustrated with events that demonstrate its congruity with established hypocenter estimation methods and its application potential. The BSEL method is applied to three events: 1) A shallow Mw 4 earthquake that occurred near Bardwell, KY on June 6, 2003, 2) the Mw 5.6 earthquake of July 26, 2005 that occurred near Dillon, MT, and 3) a deep Mw 5.7 earthquake that occurred off the coast of Japan on April 22, 1980. A strong Rg was observed from the Bardwell, KY earthquake that places very strong constraints on depth and origin time. No Rg was observed for the Dillon, MT earthquake, but we used the minimum observed period of a Rayleigh wave (7 seconds) to reduce the depth and origin time uncertainty. Because the Japan event was deep, there is no observed surface wave energy. We utilize the prior generated from the Dillon, MT event to show that even in the case when a prior is inappropriately applied, high quality data will overcome its influence and result in a reasonable hypocenter estimate.     

An attenuation-based sediment classification technique using Chirp sub-bottom profiler data and laboratory acoustic analysis

A remote sediment classification technique based on attenuation measurements from Chirp sub-bottom profiler data is described. This differs from previously published work in that attenuation measurements are obtained for each stratigraphic unit within a complex, thinly interbedded sedimentary sequence. Compressional wave attenuation measurements are obtained for a wide variety of lithologies, including muds, silts, sands, clayey sands, silty clays and gravel lags, with grain sizes ranging from 8 Phi to -4 Phi. In addition, attenuation measurements from sub-bottom profiler data were calibrated against laboratory acoustic measurements of vibracores and seabed samples from corresponding geographic locations, under simulated in-situ conditions using a Pulse Tube method. We adapt an instantaneous frequency matching method using a causal attenuation filter to model the decay of the Chirp transmitted waveform. From this modelling, a relationship between t* (a causal attenuation operator) and change in instantaneous frequency is established. The Hilbert transform is used to extract instantaneous frequency information from Chirp seismic, which is used to derive attenuation information for selected individual stratigraphic layers imaged by the sub-bottom profiler. This paper draws attention to the limitations in comparing attenuation measurements derived from Chirp sub-bottom profiler data against previously published literature on experimental attenuation measurements, which are limited by the wide variance of these data, and the difficulty in finding a meaningful best fit to these data. This demonstrates the importance of calibrating remote sediment classification observations using complimentary acoustic analysis of seabed samples to generate a site-specific geoacoustic database. A positive correlation between laboratory and sub-bottom profiler attenuation measurements was obtained, with a correlation coefficient of 0.885. Poorly sorted gravels with a mixed lithic and biogenic pebble component are characterised by very high attenuation with values of Q from 4 to 19. These sediments are considerably coarser-grained than those typically described in previously published experimental studies.     

Analysis and simulated diagenesis of kerogen in a Recent bottom mud from Mono Lake,California: a comparison with selected ancient kerogens

The insoluble organic matter, or kerogen, in a Recent bottom mud (<1000yr old) from Mono Lake, California, has been analyzed by vacuum pyrolysis-GC-MS and compared with the kerogen from several Precambrian rocks, including the Belingwe and Transvaal stromatolites. The Mono Lake kerogen consists mainly of cyclic and acyclic aliphatic components with lesser amounts of aromatics present. It is less aromatic and more susceptible to thermal degradation than the Precambrian kerogens, and its products show a much greater diversity especially among the unsaturated aliphatics and the heteroatomic components. The presence of these compounds, most notably 2,5-dimethylfuran, in the Mono Lake kerogen indicates a relatively rapid formation and incorporation into a young kerogen and suggests that their presence in the Precambrian kerogens, such as the Belingwe stromatolite, may be consistent with an ancient biological origin.In simulated diagenesis experiments the Recent mud was heated at 150°C for 3 months or 225°C for 8 months. The former was insufficient to affect the kerogen pyrolysis products. The latter, however, caused a large decrease in the heteroatomic components and a slight increase in the abundance of n-alkanes relative to that of the cyclic and branched alkanes. This suggests that the presence of some of these components in Precambrian rocks should be consistent with a high degree of preservation of these rocks, as appears to be the case for the Belingwe and Transvaal stromatolites.     

Fault scarp identification in side-scan sonar and bathymetry images from the Mid-Atlantic Ridge using wavelet-based digital filters

Digital filters designed using wavelet theory are applied to high resolution deep-towed side-scan sonar data from the median valley walls, crestal mountains, and flanks of the Mid-Atlantic Ridge at 29°10 N. With proper tuning, the digital filters are able to identify the location, orientation, length, and width of highly reflective linear features in sonar images. These features are presumed to represent the acoustic backscatter from axis-facing normal faults. The fault locations obtained from the digital filters are well correlated with visual geologic interpretation of the images. The side-scan sonar images are also compared with swath bathymetry from the same area. The digitally filtered bathymetry images contain nine of the eleven faults identified by eye in the detailed geologic interpretation of the side-scan data. Faults with widths (measured perpendicular to their strike) of less than about 150 m are missed in the bathymetry analysis due to the coarser resolution of these data. This digital image processing technique demonstrates the potential of wavelet-based analysis to reduce subjectivity and labor involved in mapping and analyzing topographic features in side-scan sonar and bathymetric image data.     

Calibrations to estimate absolute numbers of New Zealand fur seal (Arctocephalus forsteri) pups from direct counts

Annual direct counts of seal pups can indicate long‐term trends in population size, but mark‐recapture estimates are needed to deduce absolute numbers. A calibration between results from these two methods would facilitate the use of direct counts to estimate absolute numbers, an outcome that is relatively quick, cheap and minimises disturbance of animals. Mark‐recapture estimates for the numbers of New Zealand fur seal (Arctocephalus forsteri) pups in 2003 at 10 colonies at Otago, southeastern New Zealand, were compared with independent single counts at the same colonies. A single ratio to estimate absolute numbers (y) from direct counts x was not statistically significant. Instead, two ratios were deduced, based on differences in habitat among colonies: y = 1.51x for colonies with hiding places for pups and y = 0.96x for colonies without hiding places. Application of these calibrations and their 95% prediction intervals produce estimates and ranges for the absolute numbers of pups from single annual counts.     

Climate change and population history in the Pacific Lowlands of Southern Mesoamerica

Core MAN015 from Pacific coastal Guatemala contains sediments accumulated in a mangrove setting over the past 6500 yr. Chemical, pollen, and phytolith data, which indicate conditions of estuarine deposition and terrigenous inputs from adjacent dry land, document Holocene climate variability that parallels the Maya lowlands and other New World tropical locations. Human population history in this region may be driven partly by climate variation: sedentary human populations spread rapidly through the estuarine zone of the lower coast during a dry and variable 4th millennium B.P. Population growth and cultural florescence during a long, relatively moist period (2800–1200 B.P.) ended around 1200 B.P., a drying event that coincided with the Classic Maya collapse.