Using sediment travel distance to estimate medium‐term erosion rates: a 16‐year record

Fine grained (80 µm) magnetite was introduced onto a semi‐arid grassland hillslope in 1992, as part of a set of rainfall‐simulation experiments. Using measurements of magnetic susceptibility, the median distance travelled by these magnetite grains during subsequent natural runoff events in the 16‐year period up to 2008 was estimated. Coupling this estimate to direct measurements of sediment flux obtained during the rainfall‐simulation experiments has enabled estimation of the erosion rate over this period. The estimated average erosion rate of between 2·61 × 10^?2 and 4·36 × 10^?2 kg m^?1 year^?1, is equivalent to a rate of ground lowering between 0·020 and 0·033 mm year^?1. This estimate is consistent with (in the sense of being less than) an estimate of total sediment detachment over the same period. The rate of erosion measured using this travel‐distance approach is an order of magnitude less that obtained from a study based on ¹³⁷Cs in a nearby catchment, and compatible with the longevity of continents. Copyright © 2010 John Wiley & Sons, Ltd.     

Measurement of towed array position, shape, and attitude

A practical method is described for the three-dimensional determination of the position, shape, and attitude of a hydrophone array towed from a surface vessel. It provides successive snapshots of the array configuration with a maximum rate of about three per minute. The method is intended as an alternative to the use of fixed test ranges and provides results suitable for validating computer models of array motion. It uses the travel-time differences of impulsive waves measured across the array. The waves are generated by two explosive charges dropped from consorts. Results of a typical experiment are presented as an illustrative example. The array position relative to the tow ship is obtained to within an accuracy of a few metres     

ON “BIOREGIONALISM”AND “WATERSHED CONSCIOUSNESS”*

A diffused but philosophically sophisticated social movement, emphasizing the importance of the sense of place and a locally responsible stewardship of Nature, has been emerging in recent years in various parts of North America. Whether “bioregionalism”is a new way of thinking about our place on Earth and our relationship to it, as some would believe, or simply the ecologic perspective familiar to geographers and environmentalists, romanticized and dressed in a new vocabulary, it deserves our attention for its adherents are kindred souls.     

Reversal of eutrophication following sewage treatment upgrades in the New River Estuary, North Carolina

The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km², located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During 1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately 57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate, chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO of 0.9 to 1.4 mg l⁻¹, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for fish and shellfish.     

Probabilistic Analysis of Tsunami Hazards*

Determining the likelihood of a disaster is a key component of any comprehensive hazard assessment. This is particularly true for tsunamis, even though most tsunami hazard assessments have in the past relied on scenario or deterministic type models. We discuss probabilistic tsunami hazard analysis (PTHA) from the standpoint of integrating computational methods with empirical analysis of past tsunami runup. PTHA is derived from probabilistic seismic hazard analysis (PSHA), with the main difference being that PTHA must account for far-field sources. The computational methods rely on numerical tsunami propagation models rather than empirical attenuation relationships as in PSHA in determining ground motions. Because a number of source parameters affect local tsunami runup height, PTHA can become complex and computationally intensive. Empirical analysis can function in one of two ways, depending on the length and completeness of the tsunami catalog. For site-specific studies where there is sufficient tsunami runup data available, hazard curves can primarily be derived from empirical analysis, with computational methods used to highlight deficiencies in the tsunami catalog. For region-wide analyses and sites where there are little to no tsunami data, a computationally based method such as Monte Carlo simulation is the primary method to establish tsunami hazards. Two case studies that describe how computational and empirical methods can be integrated are presented for Acapulco, Mexico (site-specific) and the U.S. Pacific Northwest coastline (region-wide analysis). * The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

The nature of potassium feldspar,exsolution microtextures and development of dislocations as a function of composition in perthitic alkali feldspars

Transmission electron microscope data on the morphology of exsolution lamellae, the nature of the potassium feldspar and the development of dislocations at lamellar interfaces in coherent cryptoperthites and fine microperthites are reviewed. Dislocations have been reported previously in only two crystals, and periodic dislocations noted in only one, an Or-rich microperthite. Periodic dislocations (spacing 100–150 nm) are here described from a ternary mesoperthite (Or₂₆ Ab₅₂ An₂₂). Small crystallites (<30 nm) of other phases have sometimes nucleated on the dislocations. The 020 lattice fringes of the feldspar phases have been imaged; the difference in 020 spacings can be almost entirely accommodated by the regular dislocations, so that the boundaries may be termed nearlyperfectly semicoherent.Dislocations have been found so far only in cryptoperthites with lens-shaped or straight lamellae, either in Or-rich feldspars or in Ab-rich ternary ones. In intermediate compositions with wavy or zig-zag albite lamellae, or lozengeshaped albite areas (braid microperthites) dislocations have not been observed. Strain reduction in intermediate compositions occurs by migration of lamellar interfaces from (¯601) to near (¯6¯61) as microcline forms in the diagonal association. In Ab-rich ternary feldspars the relatively high Ancontent blocks interface migration, and strain reduction occurs by nucleation of dislocations; the Or-rich feldspar phase is tweed orthoclase. In Or-rich bulk compositions the low volume of albite exerts insufficient stress to promote microcline formation, and tweed orthoclase develops. Interfaces do not migrate, and dislocations again develop. Fields in which different potassium feldspar polymorphs occur and in which the different exsolution textures are developed are summarized on a ternary diagram.