Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations. 相似文献
REGIONAL GEOGRAPHY: Current Developments and Future Prospects edited by R. J. Johnston, J Hauer and G. A. Hoekveld. 14 × 22 cm, xiii and 216 pages. Routledge: London 1990 (ISBN 0 415 05247 5) $A89.95 (hard).
THE MAKING OF THE AMERICAN LANDSCAPE edited by M. P. Conzen. 19 × 25 cm, xvi and 433 pages. Unwin Hyman: Boston 1990 (ISBN 0 04 917010 4) $A59.95 (soft).
EASTERN EUROPE: An Historical Geography 1815–1945 by D. Turnock. 14 × 22 cm, ix and 357 pages. Routledge: London 1989 (ISBN 0 415 01269 4) $A115.00 (hard), distributed by the Law Book Co.
THE HUMAN GEOGRAPHY OF EASTERN EUROPE by D. Turnock. 14 × 22 cm, xii and 345 pages. Routledge: London 1989 (ISBN 0 415 00469 1) $A105.00 (hard), distributed by the Law Book Co.
A HISTORY OF THE PACIFIC ISLANDS by I. C. Campbell. 14 × 21 cm, 239 pages. University of Queensland Press: St Lucia 1990 (ISBN 0 7022 2291 7) $A34.95 (soft).
THE CORPORATE FIRM IN A CHANGING WORLD ECONOMY: Case Studies in the Geography of Enterprise edited by M. de Smidt and E. Wev‐er. 14 × 23 cm, xiv and 247 pages. Routledge: London 1990 (ISBN 0 415 03497 3) $A105.00 (hard).
THE CAPITALIST CITY: Global Restructuring and Community Politics by M. P. Smith and J. R. Feagin. 15 × 23 cm, 393 pages. Basil Black‐well: Oxford 1988 (ISBN 0 631 15182 6) £35 (hard).
CONFLICT AND CHANGE IN THE COUNTRYSIDE: Rural Society, Economy and Planning in the Developed World by G. M. Robinson. 15 × 23 cm, xxvi and 482 pages. Belhaven Press: London 1990 (ISBN 1 85293 043 8) £40.00 (hard); (ISBN 1 85293 044 6) £14.95 (soft).
ENVIRONMENTAL SCIENCE (Collins Reference Dictionary) by G. Jones, A. Robertson, J. Forbes and G. Hollier. 13 × 20 cm, vi and 473 pages. Collins: London 1990 (ISBN 0 00 434348 4) £5.95 (soft).
THE HUMAN IMPACT ON THE NATURAL ENVIRONMENT (Third Edition) by A. Goudie. 17 × 24 cm, xi and 388 pages. Blackwell: Oxford 1990 (ISBN 0 631 16164 3) $A39.95 (soft).
PATTERNS OF LIFE: Biogeography of a Changing World by H. W. Mielke. 19 × 24 cm, xiv and 370 pages. Unwin Hyman: London 1989 (ISBN 0 04 574032 1). 相似文献
The loss of a metamorphic fluid via the partitioning of H2O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H2O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H2O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely. 相似文献
Fe‐rich metapelitic granulites of the Musgrave Block, central Australia, contain several symplectic and coronal reaction textures that post‐date a peak S2 metamorphic assemblage involving garnet, sillimanite, spinel, ilmenite, K‐feldspar and quartz. The earliest reaction textures involve spinel‐ and quartz‐bearing symplectites that enclose garnet and to a lesser extent sillimanite. The symplectic spinel and quartz are in places separated by later garnet and/or sillimanite coronas. The metamorphic effects of a later, D3, event are restricted to zones of moderate to high strain where a metamorphic assemblage of garnet, sillimanite, K‐feldspar, magnetite, ilmenite, quartz and biotite is preserved. Quantitative mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (KFMASHTO) using Thermocalc 3.0 and the accompanying internally consistent dataset provide important constraints on the influence of TiO2 and Fe2O3 on biotite‐bearing and spinel‐bearing equilibria, respectively. Biotite‐bearing equilibria are shifted to higher temperatures and spinel‐bearing equilibria to higher pressures and lower temperatures in comparison to the equivalent equilibria in K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH). The sequence of reaction textures involving spinel is consistent with a D2 P–T path that involved a small amount of decompression followed predominantly by cooling within a single mineral assemblage stability field. Thus, the reaction textures reflect changes in modal proportions within an equilibrium assemblage rather than the crossing of a univariant reaction. The D3 metamorphic assemblage is consistent with lower temperatures than those inferred for D2. 相似文献
The legacy inherited from anthropogenic processes needs to be addressed in order to provide reliable and up-to-date ground information relevant to development and regeneration in the urban environment. The legacy includes voids as well as anthropogenic deposits (artificial ground). Their characteristics derive from former quarrying and mining activities industrial processes creating derelict ground, variably consolidated made ground, and contaminated groundwater and soils. All need to be systematically assessed to inform the planning process and provide the basis for engineering solutions. Site-specific investigation needs to be conducted on the back of good quality geoscientific data. This comes from ‘field’ survey, remotely sensed data interpretation, historical maps, soil geochemical sampling, and geotechnical investigation. Three-dimensional and, in the future, four dimensional, characterization of superficial deposits is required to reach an understanding of the potential spatial lithological variability of artificial ground and the geometry of important surfaces, i.e. the boundary conditions. The classification scheme for artificial ground outlined in this paper and adopted by the British Geological Survey, will help in achieving this understanding. 相似文献
The use of coal fly ash and domestic sewage sludge in agriculture is being considered as one of the methods for recycling of these wastes in an environmental beneficial manner. Mixtures with soil were prepared at different proportions of fly ash and sludge, either alone or in combination at a maximum application rate of 52 t ha-1. The changes in the selected properties and heavy metal contents of three soil types in India were studied after incubating the respective mixtures for 90 days at near field capacity moisture level. Sewage sludge, due to its acidic and saline nature, high organic matter and heavy metals content, had more impact on soil properties than the fly ash. Sludge application produced several changes including an increase in available nitrogen, organic carbon, salinity and water-holding capacity of the soils. The concentrations of major cations and heavy metals also increased because of the sludge application and the pH was decreased. However, the levels of individual metal concentrations in all the mixture types were below the allowable limits prescribed by several environmental agencies. Using fly ash either alone or in equal quantity with sewage sludge had little influence on soil properties and heavy metal content. The relative availability (RA) of heavy metals in three soils amended with 52 t ha-1 of sewage sludge was observed to be highest in oxisol, followed by alfisol and vertisol. 相似文献