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151.
152.
The water quality guideline trigger value for ammonia in estuarine and marine waters has been revised with the addition of 38 new results to the data set of 21 used in earlier guideline derivations. Using species sensitivity distributions, a new trigger value of 460 μg total NH3-N/L was derived for slightly to moderately disturbed systems (95% protection concentration, PC95), with a value of 160 μg total NH3-N/L applying to waters of high conservation value (PC99). For sediment pore waters, a guideline trigger value of 3.9 mg total NH3-N/L, derived from the 80th percentile of background data from Sydney Harbour, is recommended. This value is likely to be exceeded in degraded sediments subject to dredging; however, ocean disposal of such sediments results in rapid decreases in porewater ammonia and a guideline trigger value for dissolved ammonia during disposal of dredged sediments of 1550 μg total NH3-N/L is proposed. 相似文献
153.
154.
Graeme H.McVerry 《地震工程与工程振动(英文版)》2010,9(2):177-187
A landslide displacement (DLL) attenuation model has been developed using spectral intensity and a ratio of critical acceleration coefficient to ground acceleration coefficient. In the development of the model,a New Zealand earthquake record data set with magnitudes ranging from 5.0 to 7.2 within a source distance of 175 km is used. The model can be used to carry out deterministic landslide displacement analysis,and readily extended to carry out probabilistic seismic landslide displacement analysis. DLL attenuation models have also been developed by using earthquake source terms,such as magnitude and source distance,that account for the effects of earthquake faulttype,source type,and site conditions. Sensitivity analyses show that the predicted DLL values from the new models are close to those from the Romeo model that was developed from an Italian earthquake record data set. The proposed models are also applied to an analysis of landslide displacements in the Wenchuan earthquake,and a comparison between the predicted and the observed results shows that the proposed models are reliable,and can be confidently used in mapping landslide potential. 相似文献
155.
156.
T. S. Switzer B. L. Winner N. M. Dunham J. A. Whittington M. Thomas 《Estuaries and Coasts》2006,29(6):1011-1018
We examined nekton community-level responses to Hurricanes Frances and Jeanne, which made landfall 20 d apart in the St. Lucie
estuary in southeastern Florida in 2004. The passage of these storms contributed to large freshwater discharges that exceeded
150 m3 s−1, as well as estuary-wide reductions in salinity and near-hypoxic conditions in the North Fork of the estuary that persisted
for several months. Although such environmental variations are not uncommon, seasonal patterns of community structure were
disturbed throughout much of the estuary, likely in response to uncharacteristically-rapid reductions in salinity. Immediately
following the hurricanes, abundances of several freshwater and oligohaline taxa (i.e., blue crabCallinectes sapidus, shadDorosoma spp., and ladyfishElops saurus) increased markedly in the inner estuary, while abundances of several other fishes (i.e., striped mulletMugil cephalus, white mulletM. curema, lookdownSelene vomer, pigfishOrthopristis chrysoptera, and pinfishLagodon rhomboides) declined. Nekton communities recovered quickly, and by spring, community structure throughout much of the estuary was indistinguishable
from pre-hurricane conditions. Although nekton communities were resilient to hurricane-related disturbances, projected increases
in Atlantic hurricane activity and associated freshwater discharges over the coming decades may test the resilience of estuarine
communities in Florida. 相似文献
157.
Graeme Hugo 《The Australian geographer》2006,37(2):211-231
Australia's labour market is most influenced by international migration among OECD nations, but Australian research on this issue focuses almost exclusively on permanent settlement migration. The present paper, however, demonstrates that non-permanent migration has an important impact on the Australian labour market, although such migrants are not included in standard data collections and research on migrants and the labour market. A number of data sources are utilised to estimate the labour-market impact of Working Holiday Makers, Temporary Business Entrants, Overseas Students, and New Zealand temporary migrants. It is shown that their impact is equivalent to more than 400?000 full-time jobs. However, the effect is magnified because it is concentrated in particular sectors of the economy and in particular communities within Australia. A number of issues relating to temporary migration are discussed, including the nature of its relationship with permanent migration, the effects on job training, and the implications for regional development. 相似文献