A 2,500-year history of anoxia and eutrophication in Chesapeake Bay

Ongoing monitoring programs and historical data are not sufficient to establish anthropogenic effects on the ecology of Chesapeake Bay. However, stratigraphic records preserved in the sediments can be used to reconstruct both prehistoric and historic sedimentation and water conditions of the bay, including anoxia and eutrophication. Pollen, diatoms, total organic carbon (TOC), nitrogen, total sulfur, and an estimate of the degree of pyritization of iron (DOP) are being used as paleoecological indicators in dated sediment cores for the purpose of reconstructing a long-term environmental history of the bay. Analysis of the data indicates that sedimentation rates, anoxic conditions, and eutrophication have increased in the Chesapeake Bay since the time of European settlement. For example, since initial land clearance around 1760, sedimentation rates have increased from as low as 0.02 cm yr^?1 to an average 0.22 cm yr^?1, and TOC from 0.14 mg cm^?2 yr^?1 to a high 4.96 mg cm^?2 yr^?1. Diatom community structure shows a steady decrease in overall diversity since 1760 and the centric:pennate ratio has increased significantly since 1940.     

Geomorphological effects of catastrophic flooding on a small subtropical Estuary

The Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120-150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 × 10⁶ m³ of sediment from the estuary. The normal high tide volume of the estuary (0.35 × 10⁶ m³) increased to 1.85 × 10⁶ m³ after the flood. The post-flood intertidal volume (tidal prism) of the estuary was 0.43 × 10⁶ m³ compared to 0.19 × 10⁶ m³ before the event. The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries.     

STATISTICAL CONCEPTS AND THEIR APPLICATION IN PHOTOGRAMMETRY AND SURVEYING

This paper was prepared as supporting documentation for a tutorial given by the authors under Photogrammetric Society auspices. The authors do not make any claims of novelty or innovation but they feel that the information contained in the paper will provide useful study material, especially for practitioners of photogrammetry and surveying. The following topics are covered: functional and stochastic models; the least squares process; statistical testing; optimal design methods; and numerical examples in the design of a horizontal control network and of a close range photogrammetric survey.     

Spectroscopic and Chromatographic studies of organic carbon in Recent marine sediments from the Peruvian Upwelling Zone

Early diagenesis of organic matter in sediments from two sites in the Peruvian Upwelling Zone (12°05′S, 77°39′W; 15°17′S, 75°24′W) has been studied by observing changes in the total organic carbon and lipid and humin fractions with depth. Transformations of the total carbon and humin fraction have been characterized by conventional and time-dependent solid state NMR techniques, while lipid diagenesis was monitored by measuring the concentration of sterols in the same sedimentary horizons. Both the quantity of total sterols and the relative abundances of individual sterols vary with sampling location, suggesting a difference in the input of biomass to the sediments at the two sites. Total sterol concentrations decrease with depth at both sites, but the loss of sterols occurs much more slowly at the more anoxic northern site, where sedimentation rates and organic carbon contents are approximately twice those at the southern site. ¹³C-NMR spectra of the total organic carbon and the humin fraction suggest that humin-like compounds are an original component of the sedimentary biomass, and dipolar-dephased spectra of the humin residue indicate that diagenetic alterations of the humin fraction are occurring even in these very young sediments. Conventional and time-dependent spectroscopic data support the hypothesis that humin formation results from selective preservation of microbially-resistant biopolymers which are an original component of the sedimentary biomass combined with loss of certain labile compounds.     

The Grüneisen parameter at high pressure: a molecular dynamical study

The method of molecular dynamics is used to calculate values for the thermal Grüneisen parameter, γ, for a face-centred cubic crystal with several simple central force atomic potential functions at three compressions for comparison with free volume and acoustic γ formulations. Neither is found to agree with the computer experiments. A defect in the free-volume formula for γ is shown to arise from the assumption that motions of neighbouring atoms in a crystal at high temperature are uncorrelated whereas the computer models demonstrate a 25–35% correlation of in-line motions and 5% correlation of transverse motions. The formula can be modified to allow for the empirically observed correlations, but it is concluded that there are still difficulties in analytical approaches to equation-of-state studies of the Earth's deep interior and that the computer modelling method of molecular dynamics has important advantages.     

DEFORMATION MEASUREMENT BY PHOTOGRAMMETRY

The application of phorogrammetry to the measurement of deformation is discussed and four different approaches are identified and compared. References to and summaries of recent work are made.     

Sintering of olivine and olivine-basalt aggregates

The sintering behavior of olivine and olivine-basalt aggregates has been examined at temperatures near 1,300° C. Experimental factors contributing to rapid sintering kinetics and high-density, fine-grained specimens include: (i) the uniform dispersion of basalt throughout the specimen, (ii) a very fine, uniform particle size for the olivine powder, (iii) oxygen fugacities near the high P _O2 end of the olivine stability field, and (iv) rapid heating to the sintering temperature. Olivine-basalt specimens prepared from olivine particles coated with a synthetic basalt achieve chemical and microstructural equilibrium more rapidly, as well as produce higher density and finer grain-sized aggregates, than do specimens prepared by mechanical mixing of olivine and natural basalt powders. The grain boundary mobility for olivine, measured for olivine-basalt aggregates which have undergone secondary recrystallization, is on the order of 2×10^?15 (m/s)/(N/m²) in the temperature range 1,300–1,400° C. Solution-precipitation (pressure-solution) processes make an important contribution to the development of the microstructure in olivine-basalt aggregates.     

THE EXTRACTION OF POSITIONAL DATA FROM HISTORICAL PHOTOGRAPHS AND THEIR APPLICATION TO GEOMORPHOLOGY

A technique which enables spatial data to be obtained from historical photography is outlined. The method is applied to a 40 year sequence of oblique aerial photography of the Black Ven landslide in Dorset, England. Some of the possible data processing options are discussed and illustrated by some preliminary results produced from the Dorset landslide.     

Sediment accumulation in lake chicot,Arkansas

Lake Chicot is an oxbow lake located along the western side of the Mississippi River in southeastern Arkansas. A major flood in 1927, levee construction, land use changes from bottomland hardwood to agriculture, a large increase in drainage area, and stream channelization have altered the appearance of contributing watersheds and the lake. The lake often has high suspended sediment concentrations making it undesirable for recreation and aquatic production. As part of a coordinated study to determine changes in the lake, sediment accumulation patterns and rates were determined in Lake Chicot using the¹³⁷Cs technique. Major sediment accumulation is occurring near the major inlet and along the thalweg of the oxbow. Average sediment accumulation of 1.8 cm/yr since 1963 was measured for twelve samples. Calculations show sediment accumulation is decreasing. This study has shown that the¹³⁷Cs technique can provide useful planning information for the environmental geologist or reservoir manager. Results of the current study will be used to develop better sediment and water management strategies for Lake Chicot. Contribution of the U.S. Department of Agriculture, Agricultural Research Service, in cooperation with the Vicksburg District of the U.S. Army Corps of Engineers.     

Distribution of oceanic and continental leads in the Arabian-Nubian Shield

New common lead data for feldspar, whole-rock, and galena samples from the Arabian-Nubian Shield, together with data from previous work, can be divided into two main groups. Group I leads have oceanic (mantle) characteristics, whereas group II leads have incorporated a continental-crustal component of at least early Proterozoic age. The group I leads are found in rocks from the Red Sea Hills of Egypt and the western and southern parts of the Arabian Shield. Group II leads are found in rocks from the northeastern and eastern parts of the Arabian Shield, as well as from the southeastern Shield near Najran. They are also found in rocks to the south in Yemen, to the east in Oman, and to the west at Aswan, Egypt. This distribution of data suggests that the Arabian-Nubian Shield has an oceanic core flanked by rocks that have developed, at least in part, from older continental material. Two mechanisms are suggested by which this older lead component could have been incorporated into the late Proterozoic rocks, and each may have operated in different parts of the Shield. The older lead component either was derived directly from an underlying early Proterozoic basement or was incorporated from subducted pelagic sediments or sediments derived from an adjacent continent.New U-Pb zircon data indicate the presence of an early Proterozoic basement southeast of Jabal Dahul in the eastern Arabian Shield. These data, together with 2,000-Ma-old zircons from the Al Amar fault zone, verify the implication of the common lead data that at least a part of the eastern Arabian Shield has an older continental basement.Because continental margins are particularly favorable locations for development of ore deposits, these findings may have important economic implications, particularly for tin, tungsten, and molybdenum exploration.