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51.
A case study was conducted on the potential impacts of climate change on fish habitat in a southeastern reservoir. A reservoir water quality model and one year of baseline meteorologic, hydrologic, and inflow water quality input were used to simulate current reservoir water quality. Total adult striped bass habitat, defined by specific quantitative temperature and dissolved oxygen criteria, was simulated. Daily reservoir volumes with optimal, suboptimal, and unsuitable temperature and DO were predicted for the year. Output from recent runs of atmospheric general circulation models (GCMs), in which atmospheric carbon dioxide concentrations have been doubled, was then used to adjust the baseline inputs to the water quality model. New sets of input data were created for two grid cells for each of three GCMs. All six climate scenarios are predicted to cause overall declines in the available summer striped bass habitat, mostly due to lake water temperatures exceeding striped bass tolerance levels. These predictions are believed to result from the consensus among GCM scenarios that air temperatures and humidity will rise, and the sensitivity of the reservoir model to these parameters. The reservoir model was found to be a promising tool for examining potential climate-change impacts. Some of the assumptions required to apply GCM output to the reservoir model, however, illustrate the problems in using large-scale gridcell output to assess small-scale impacts. 相似文献
52.
53.
D.D. Bogard E.K. Gibson D.R. Moore N.L. Turner R.B. Wilkin 《Geochimica et cosmochimica acta》1973,37(3):547-557
Total carbon determinations on the Haverö, Dingo Pup Donga, and North Haig ureilites yield values of 2.07, 3.17, and 5.58 wt.%, respectively. Haverö and Dingo Pup Donga contain relatively large amounts of trapped Ar, Kr and Xe, which like the carbon content varies with grain size for Haverö. These two meteorites also contain dominant cosmic rayproduced He and Ne, and show 3He exposure ages of ~23 m.y. and ~7 m.y., respectively. North Haig contains much smaller amounts of trapped gases and spallogenic gases, which may result from loss due to terrestrial weathering. The isotopic composition of Xe in five grain size analyses of Haverö and a whole rock analysis of Dingo Pup Donga shows the presence of a major solar-like Xe component. The presence of this solar component adds an additional complication to the concept of forming ureilites from carbonaceous chondrites. 相似文献
54.
Hot water effluent from power stations kills juvenile menhaden migrating through Long Island Sound. Since the fish sink to the bottom, losses are unrecorded or at best under-estimated. Other fish are probably also affected. Menhaden in Long Island Sound contribute to the commercial fishery off the eastern seaboard of the United States. At present the losses have little impact on the fishery, but if the projected increase in hot water discharges into the Sound materializes the consequences may be serious. 相似文献
55.
56.
John A. E. Gibson Warwick F. Vincent Patrick Van Hove Claude Belzile Xioawa Wang Derek Muir 《Aquatic Geochemistry》2002,8(2):97-119
The geochemical processes occurring within meromictic Lake A (maxdepth 120 m) on northern Ellesmere Island, Canada, were investigated to determinethe history of the lake and to provide a baseline for future studies. The lake contained seawaterdiluted by freshwater input that had been mixed prior to the lake's isolation from tidalaction. Input of freshwater after isolation of the lake created vertical stratification resultingin the creation of distinct oxic, suboxic and anoxic zones. Dissolved oxygen was present to 13 m,and sulphide beneath 32 m. Manganese and iron cycling dominated the redox chemistrybetween these depths. Total manganese concentrations reached 176 M, higher thanin most other natural stratified lake or marine environments. 相似文献
57.
Apatite fission track thermochronology (AFTT) and paleomagnetic (PM) results have been used to constrain the Late Paleozoic to Cenozoic landscape evolution of the Lachlan Fold Belt (LFB) around the Northparkes copper-gold deposit in east-central New South Wales. The present-day landscape of this region of the LFB is relatively flat with little expression of the underlying rock and has previously been interpreted to indicate long-term stability of the region since the end of LFB orogenesis in the Early Carboniferous. This was presumably borne out by PM analyses from thick weathered horizons within open pits at the mine, which suggested that significant periods of weathering, and hence relative landscape stability, prevailed during the Early to middle Carboniferous and at some time during the Cenozoic. Results from AFTT analyses, however, indicate that the region must have experienced significant episodes of cooling/denudation during the mid-Permian to mid-Triassic and during the early Cenozoic, as well as episodes of heating/burial during the Late Carboniferous to mid-Permian and during the late Mesozoic. When combined, the AFTT and PM results are in fact consistent and indicate that since the late Paleozoic the landscape of the LFB around the Northparkes deposit has evolved through multiple episodes of denudation and deposition as well as periods of relative stability during which the thick weathering horizons formed. Together these results establish a complementary chronological framework that constrains the Late Palaeozoic to Cenozoic landscape evolution of the Northparkes region and highlights the importance of using dual data sets in elucidating the long-term landscape evolution of similar "stable" terranes. 相似文献
58.
Lisa L. Etherington Philip N. Hooge Elizabeth R. Hooge David F. Hill 《Estuaries and Coasts》2007,30(6):927-944
Alaska, U.S.A, is one of the few remaining locations in the world that has fjords that contain temperate idewater glaciers.
Studying such estuarine systems provides vital information on how deglaciation affects oceanographic onditions of fjords and
surrounding coastal waters. The oceanographic system of Glacier Bay, Alaska, is of particular interest ue to the rapid deglaciation
of the Bay and the resulting changes in the estuarine environment, the relatively high oncentrations of marine mammals, seabirds,
fishes, and invertebrates, and the Bay’s status as a national park, where ommercial fisheries are being phased out. We describe
the first comprehensive broad-scale analysis of physical and iological oceanographic conditions within Glacier Bay based on
CTD measurements at 24 stations from 1993 to 2002. easonal patterns of near-surface salinity, temperature, stratification,
turbidity, and euphotic depth suggest that freshwater nput was highest in summer, emphasizing the critical role of glacier
and snowmelt to this system. Strong and persistent tratification of surface waters driven by freshwater input occurred from
spring through fall. After accounting for seasonal nd spatial variation, several of the external physical factors (i.e., air
temperature, precipitation, day length) explained a large mount of variation in the physical properties of the surface waters.
Spatial patterns of phytoplankton biomass varied hroughout the year and were related to stratification levels, euphotic depth,
and day length. We observed hydrographic atterns indicative of strong competing forces influencing water column stability
within Glacier Bay: high levels of freshwater ischarge promoted stratification in the upper fjord, while strong tidal currents
over the Bay’s shallow entrance sill enhanced ertical mixing. Where these two processes met in the central deep basins there
were optimal conditions of intermediate tratification, higher light levels, and potential nutrient renewal. These conditions
were associated with high and sustained hlorophylla levels observed from spring through fall in these zones of the Bay and provide a framework for understanding he abundance
patterns of higher trophic levels within this estuarine system. 相似文献
59.
The growing interest in and emphasis on high spatial resolution estimates of future climate has demonstrated the need to apply
regional climate models (RCMs) to that problem. As a consequence, the need for validation of these models, an assessment of
how well an RCM reproduces a known climate, has also grown. Validation is often performed by comparing RCM output to gridded
climate datasets and/or station data. The primary disadvantage of using gridded climate datasets is that the spatial resolution
is almost always different and generally coarser than climate model output. We have used a Bayesian statistical model derived
from observational data to validate RCM output. We used surface air temperature (SAT) data from 109 observational stations
in California, all with records of approximately 50 years in length, and created a statistical model based on this data. The
statistical model takes into account the elevation of the station, distance from coastline, and the NOAA climate region in
which the station resides. Analysis indicates that the statistical model provides reliable estimates of the mean monthly SAT
at any given station. In our method, the uncertainty in the estimates produced by the statistical model are directly determined
by obtaining probability density functions for predicted SATs. This statistical model is then used to estimate average SATs
corresponding to each of the climate model grid cells. These estimates are compared to the output of the RCM to assess how
well the RCM matches the observed climate as defined by the statistical model. Overall, the match between the RCM output and
the statistical model is good, with some deficiencies likely due in part to the representation of topography in the RCM. 相似文献
60.
Lisa K. Whalley Kate L. Furneaux Tom Gravestock Helen M. Atkinson Catherine S. E. Bale Trevor Ingham William J. Bloss Dwayne E. Heard 《Journal of Atmospheric Chemistry》2007,58(1):19-39
A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere.
An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of
the IO A2Π3/2 ← X2Π3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument
was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N2O/CF3I/N2 mixtures with O3 actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration
period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer)
campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured
significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing
the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum
at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF. 相似文献