Evaluation of a digital echo sounder system for detection of submersed aquatic vegetation

A technique is presented for rapid detection of submersed aquatic vegetation (SAV) using a high-frequency, high-resolution digital echo sounder linked with global positioning system equipment. The acoustic reflectivity of SAV allows for detection and explicit meaqsurement of canopy geometry using a digital signal processing algorithm described here. Comparing output data from this system with physical measurements shows good detection and measurement performance over a wide range of conditions for freshwater tape grass (Vallisneria americana) and seagrasses (Thalassia testudinum, Halodule wrightii, andSyringodium filiforme) in a sandy-bottom, south Florida estuary. The range of environmental conditions for which the system can be used is defined. Based on these measured performance data and a review of existing literature, this system appears to fill a gap in the inventory of established methods for measuring the distribution and abundance of submersed macrophytes.     

Core-mantle interactions

Several aspects of core-mantle interactions were considered during a Royal Astronomical Society Discussion Meeting on 12th May 1989, including modelling the geomagnetic field at the core surface, the morphology of the field between 1600 and 1820 AD, dynamo theory, Taylor's constraint, fluid motions at the top of the core that reproduce the observed secular variation, pressure coupling between the core and mantle and its geophysical consequences, topographic core-mantle coupling, angular momentum transfer at the core-mantle interface, the detection and implications of core oscillations, particularly those with associated fluctuations in the Earth's rotation rate, and the seismological determination of the core-mantle boundary topography from lateral inhomogeneities in the mantle.     

Geomagnetism in the satellite era

Kathryn A Whaler considers the opportunities and challenges arising from the greatly enhanced geomagnetism data sets now available, in her 2006 Presidential Address.     

What is the Meaning of ‘Social Mix’? Shifting perspectives in planning and implementing public housing estate redevelopment

This paper unravels a variety of perspectives about the concept of social mix, drawing on a case study of the implementation of a redevelopment project in Melbourne. The first part provides a theoretical overview of two internationally predominant academic debates around policy interpretations of this concept, namely social mix as a means for promotion of social inclusion; and as a state-led form of gentrification. These two arguments are usually presented as one, with social inclusion and reductions of concentrations of disadvantage one side of the ‘social mix policy’ coin, and state-led gentrification the other. This paper contributes to the national and international literature on public housing estate regeneration and social mix policies through exploring the question of whether these two ideas about social mix were shared by different stakeholders as the ‘messy’ process of redevelopment unfurled. Interviews were conducted with public tenants, homeowners and homebuyers, private renters and local service providers at the Carlton Housing Estate to explore the diverse perspectives of various stakeholder groups as estate design and implementation shifted. The study identified that as a result of the global financial crisis and the developers exerting pressure on government there was a gradual move away from perceiving social mix as a policy tool for encouraging social inclusion at Carlton, between public housing tenants and private residents, towards a different form of social mix and inclusion. Contrary to intentions, the revised form of social mix at Carlton was perceived as a means to harness market capital and attract higher income residents to the inner city.     

A comparison of intertidal species richness and composition between Central California and Oahu,Hawaii

The intertidal zone of tropical islands is particularly poorly known. In contrast, temperate locations such as California's Monterey Bay are fairly well studied. However, even in these locations, studies have tended to focus on a few species or locations. Here we present the results of the first broadscale surveys of invertebrate, fish and algal species richness from a tropical island, Oahu, Hawaii, and a temperate mainland coast, Central California. Data were gathered through surveys of 10 sites in the early 1970s and again in the mid‐1990s in San Mateo and Santa Cruz counties, California, and of nine sites in 2001–2005 on Oahu. Surveys were conducted in a similar manner allowing for a comparison between Oahu and Central California and, for California, a comparison between time periods 24 years apart. We report a previously undocumented richness of intertidal species in both locations: 516 for Oahu and 801 for Central California. Surprisingly, when differences in search efforts are controlled, overall (alpha) diversity appears to be similar between locations, although site level (beta) diversity is much higher in California. Species richness in California generally increased along a wave exposure gradient and distance from an urban area. Much higher numbers of both invasive and endemic species were found on Oahu. In California, more invertebrate species were found in the 1990s, likely due to an improvement in taxonomic resources since the 1970s, and species composition was different in the two surveys due to the high incidence of rare species. Although some southern species increased in number between the two time periods and some northern species decreased, we detected little evidence of change favoring southern or northern species. These results are in line with recent findings that water temperatures in the Monterey Bay have been in a cooling trend since the 1980s, in contrast to many locations elsewhere in the world.     

The regional nature of global challenges: a need and strategy for integrated regional modeling

Glaciers of the conterminous United States have been receding for the past century. Since 1900 the recession has varied from a 24 % loss in area (Mt. Rainier, Washington) to a 66 % loss in the Lewis Range of Montana. The rates of retreat are generally similar with a rapid loss in the early decades of the 20th century, slowing in the 1950s–1970s, and a resumption of rapid retreat starting in the 1990s. Decadal estimates of changes in glacier area for a subset of 31 glaciers from 1900 to 2000 are used to test a snow water equivalent model that is subsequently employed to examine the effects of temperature and precipitation variability on annual glacier area changes for these glaciers. Model results indicate that both winter precipitation and winter temperature have been important climatic factors affecting the variability of glacier variability during the 20th Century. Most of the glaciers analyzed appear to be more sensitive to temperature variability than to precipitation variability. However, precipitation variability is important, especially for high elevation glaciers. Additionally, glaciers with areas greater than 1 km² are highly sensitive to variability in temperature.