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1.
Although fish are usually thought of as victims of water quality degradation, it has been proposed that some planktivorous species may improve water quality through consumption of algae and sequestering of nutrients via growth. Within most numerical water quality models, the highest trophic level modeled explicitly is zooplankton, prohibiting an investigation of the effect a fish species may be having on its environment. Conversely, numerical models of fish consumption do not typically include feedback mechanisms to capture the effects of fish on primary production and nutrient recycling. In the present study, a fish bioenergetics model is incorporated into CE-QUAL-ICM, a spatially explicit eutrophication model. In addition to fish consumption of algae, zooplankton, and detritus, fish biomass accumulation and nutrient recycling to the water column are explicitly accounted for. These developments advance prior modeling efforts of the impact of fish on water quality, many of which are based on integrated estimates over an entire system and which omit the feedback the fish have through nutrient recycling and excretion. To validate the developments, a pilot application was undertaken for Atlantic menhaden (Brevoortia tyrannus) in Chesapeake Bay. The model indicates menhaden may reduce the algal biomass while simultaneously increasing primary productivity.  相似文献   
2.
The distribution of polycyclic aromatic hydrocarbons was determined in surface sediments collected at 36 stations along the Spanish Northern continental shelf in March and September 2003, and February 2005. Concentrations of PAHs (Σ13 parent components) were in the range of 22-47528 μg/kg dw, the highest values corresponding to coastal urban-industrial hotspots and decreasing offshore. Sediment quality guidelines (SQGs) showed that concentrations of total PAHs were below the threshold effect level (TEC) in 27 stations (81%) and above in 7, two of which (Gijon and Bilbao) were above the probable effect concentration (PEC). The detailed study of diagnostic ratios suggested a rather uniform mixture of petrogenic and pyrolytic PAH sources along the continental shelf, with a slight decrease of the latter moving westwards and offshore. In order to assess the incidence of sediment sampling on the variability of the results, selected stations were also monitored in February and September 2004 and September 2005. The average field variance of the values obtained for each station was 31% that decreased to 23% when the values were normalized to TOC.  相似文献   
3.
Water samples were collected in the Northeast Atlantic Ocean (33-37° N and 11-16° W) in May 1983, and vertical profiles of chemical and physical parameters allowed us to identify the different water masses. A significant difference in salinity and its maximum can be found at different places and depths, as a consequence of the spreading of the Mediterranean Water (MW) from the Strait of Gibraltar. The apparent oxygen utilization shows a correlation with nutrients in North Atlantic Central Water. The relative percentages of water masses were assessed in order to examine the depth of maximum influence of MW as a function of latitude and to apply this knowledge to the black scabbard fish long-line strategy. The long-line fishing depth location was adapted to the specific MW distribution of the different banks with improvements in the mean catch efficiency. The thickness of the MW prevalence layer has a pronounced decrease to the south. MW influence clearly sinks and decrease to south-west. The highest percentage of the MW was found in the Gorringe Bank area and the lowest in the Madeira area.  相似文献   
4.
For hundreds of years, the seas have been used as a place to dispose of wastes from human activities. Although no high level radioactive waste has been disposed of into the sea, variable amounts of packaged low level radioactive wastes have been dumped at 47 sites in the northern part of the Atlantic and Pacific Oceans. in 1946 the first sea dumping operation took place at a site in the North-East Pacific Ocean. the last dumping operation was in 1982, at a site off the European continental shelf in the Atlantic Ocean. Between these two dates, an estimated 46 PBq (1.24 MCi) of radioactive waste coming from research, medical, military and industrial activities have been disposed of at sea. the present trend, through the Convention for the Prevention of Marine Pollution by Dumping of Wastes and other Matter and other Regional Conventions, points towards the prohibition of the dumping of any radioactive waste into the marine environment.  相似文献   
5.
Tissues of foetus-mother pairs of common dolphins (Delphinus delphis) stranded along the French coasts (Bay of Biscay and English Channel) were analysed for their Cd, Cu, Hg, Se and Zn contents. In the kidneys, foetal Cd levels were extremely low, and strong relationships between Cu and Zn suggested the involvement of metallothioneins since early foetal life. The results also indicated a limited maternal transfer of Hg during pregnancy since levels in the tissues of foetuses were below 1 microg g(-1) w.wt. However, hepatic Hg levels in foetuses increased with body length, and were also proportionate to maternal hepatic, renal and muscular Hg levels. Lastly, affinities between Hg and Se in tissues would participate in Hg neutralisation in both mothers--through tiemannite granules--and fetuses--through reduced glutathione--counteracting the toxic effects linked to the particularly high quantities of methyl-Hg to which marine mammals are naturally exposed.  相似文献   
6.
ABSTRACT: Simulated daily precipitation, temperature, and runoff time series were compared in three mountainous basins in the United States: (1) the Animas River basin in Colorado, (2) the East Fork of the Carson River basin in Nevada and California, and (3) the Cle Elum River basin in Washington State. Two methods of climate scenario generation were compared: delta change and statistical downscaling. The delta change method uses differences between simulated current and future climate conditions from the Hadley Centre for Climate Prediction and Research (HadCM2) General Circulation Model (GCM) added to observed time series of climate variables. A statistical downscaling (SDS) model was developed for each basin using station data and output from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEPINCAR) reanalysis regridded to the scale of HadCM2. The SDS model was then used to simulate local climate variables using HadCM2 output for current and future conditions. Surface climate variables from each scenario were used in a precipitation‐runoff model. Results from this study show that, in the basins tested, a precipitation‐runoff model can simulate realistic runoff series for current conditions using statistically down‐scaled NCEP output. But, use of downscaled HadCM2 output for current or future climate assessments are questionable because the GCM does not produce accurate estimates of the surface variables needed for runoff in these regions. Given the uncertainties in the GCMs ability to simulate current conditions based on either the delta change or downscaling approaches, future climate assessments based on either of these approaches must be treated with caution.  相似文献   
7.
The cerco-fixo is an artisanal fishing trap widely used by traditional communities in the estuarine region of the southern coast of the state of São Paulo, Brazil. The primary goal of the study was to investigate, through ethnobotanical and ecological approaches, the use of plant species by traditional fishermen to build the cerco-fixo at Cardoso Island State Park and Cananéia Island. Ethnobotanical data were collected through interviews, direct observation, plant collection and identification, and document analysis. An ecological evaluation was also done comparing five 20 × 20 m plots in a managed area to five 20 × 20m plots in an unmanaged area, both within arboreal sandy soil vegetation called restinga arbórea, found within the Brazilian Atlantic Forest domain. This study involved 34 fishermen living at Cardoso and Cananéia Islands. The fishermen know more than 90 Atlantic Forest plant species that can be used to build the cerco-fixo. Tree species from the family Myrtaceae were the most quoted in the interviews. With respect to the ecological evaluation, the cluster analyses showed greater heterogeneity in terms of floristic composition (i.e. greater floristic dissimilarity) within the plots of the managed area. The analyses of diversity showed a slightly higher species richness and slightly lower values for Shannon, Simpson, Hurlbert’s PIE and Evenness indices in the managed area (59 species; H′ = 3.28; 1/D = 10.77; E = 0.80; Hurlbert’s PIE = 0.91) compared to the unmanaged area (54 species; H′ = 3.39; 1/D = 20.21; E = 0.85; Hurlbert’s PIE = 0.95). The Hutcheson’s t test showed no significant difference between both areas’ Shannon diversity indices (t: −1.04; p: 0.30). These results are attributed to the greater dominance of the palm species Euterpe edulis Mart. in the managed area (28.2% of the trees sampled at this area; n = 118), which equals twice the percentage of individuals of the same species found for the unmanaged area (14.6% of the sampled trees; n = 48). We discuss the impact of the fishermen’s harvesting practices in the managed area with an emphasis on three main points: (1) the harvesting practices are likely not contributing to a decrease in diversity in the managed area; (2) the greater heterogeneity in terms of floristic composition found for the managed area may reflect a mosaic pattern created by the opening of small tree-gaps distributed across this area over the course of more than 50 years; (3) the disturbance promoted by the fishermen’s harvesting practices can be compared to natural disturbances of low impact that create mosaic patterns in tropical forests. This study emphasizes the prominence of the human dimension in ecological processes and the importance of considering the perspectives of local people when discussing the conservation of the natural environments in which these people live.  相似文献   
8.
The dipole moment of Earth’s magnetic field has decreased by nearly over the past 150 years and by about 30% over the past 2,000 years according to archeomagnetic measurements. Here, we explore the causes and the implications of this rapid change. Maps of the geomagnetic field on the core–mantle boundary derived from ground-based and satellite measurements reveal that most of the present episode of dipole moment decrease originates in the southern hemisphere. Weakening and equatorward advection of normal polarity magnetic field by the core flow, combined with proliferation and growth of regions where the magnetic polarity is reversed, are reducing the dipole moment on the core–mantle boundary. Growth of these reversed flux regions has occurred over the past century or longer and is associated with the expansion of the South Atlantic Anomaly, a low-intensity region in the geomagnetic field that presents a radiation hazard at satellite altitudes. We address the speculation that the present episode of dipole moment decrease is a precursor to the next geomagnetic polarity reversal. The paleomagnetic record contains a broad spectrum of dipole moment fluctuations with polarity reversals typically occurring during dipole moment lows. However, the dipole moment is stronger today than its long time average, indicating that polarity reversal is not likely unless the current episode of moment decrease continues for a thousand years or more.  相似文献   
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10.
为适应日益严格的环保要求,根据GW型燃油加热炉烟气排放特征和排放规律,设计采用循环流化床工艺进行除尘脱硫。中试结果表明:在最佳工况条件下,系统除尘效率可达97%~98%,脱硫效率达80%~90%,达到国家燃油锅炉一类区域排放标准要求。  相似文献   
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