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231.
The concentrations of various organic pollutants (benzo(a)pyrene (BaP), hexachlorobenzene (HCB) and pentachlorophenol (PCP)) were determined in samples of water, sediment and biota (flounder, killifish, shrimp, crabs and squid) from San Luis Pass, Texas. Sediment was also analyzed for polychlorinated biphenyls (PCBs), phthalic acid esters (PAEs) and various pesticides. Only PCP was detectable in water. In sediment, the relative concentrations were PAEs > BaP > (PCBs HCB) > PCP. In biota, BaP was not detectable in any animal; HCB was highest in crabs and PCP was highest in all others (flounder, killifish, shrimp and squid). The relative concentrations of HCB and PCP were different in the different organisms. The differences between the relative concentrations in the biota and in sediment are discussed. The results of this study are compared to values measured at other sites. This study is part of a larger effort to identify and quantitate pollutants in various Texas estuaries and to serve as a basis for monitoring marine pollution. 相似文献
232.
233.
George F. Ray 《Resources Policy》1984,10(2):75-80
This article analyses the lifetimes of reserves of three dozen important minerals. Despite the high rate of their extraction in the past 30 years, the recorded reserves of these non-renewable materials were higher in 1981 than in 1950 and they seem to meet foreseeable demand for a long time to come, as indicated by the estimated static lifetime for each of the minerals covered. The dynamic nature of ‘reserves’ is emphasized: further exploration and scientific and technological advance will add to the present proven reserves, and at a higher price further resources will be ‘upgraded’ into commercially exploitable reserves. Apparent long-term security can be disturbed by natural disasters, political events or other factors, especially in the case of minerals whose reserves and production are highly concentrated in one country. However, any such interruption in the continuity of supply is likely to be short-lived. 相似文献
234.
We grew marineSynechococcus Clones WH7803 and WH8018 at 150µE m–2 s–1 in dilute batch cultures with NH
4
+
as the limiting nutrient. The maximal uptake capacities for NH
4
+
and NO
3
-
were measured in frequent experiments during log and stationary phases of growth. Clone WH7803, originally isolated from oceanic waters, had a specific uptake rate of NH
4
+
that approximated the maximum (log phase) specific growth rate (ca ~ 0.025 h–1). NO
3
-
uptake was observed only after nitrogen in the media was depleted; the NO
3
–
uptake capacity was ca 12% the capacity for NH
4
+
uptake throughout the nitrogen depleted period. Growth was arrested upon nitrogen depletion, but resumed soon after reinoculation into fresh media, even after 5 d of starvation. Clone WH8018, originally isolated from coastal waters, revealed a five-fold enhancement in the NH
4
+
uptake rate relative to growth rate at the time of nitrogen depletion. As nitrogen starvation proceeded, this enhancement was reduced. This clone, too, was able to take up NO
3
-
once nitrogen in the media was depleted, but only after ca 20 h. Growth continued for a limited period during nitrogen depletion, but nitrogen-starved cells were slow to recover upon reinoculation into fresh media. We speculate that clonal differences may reflect differences in the molecular regulation of nitrogen assimilation. 相似文献
235.
236.
Yang RJ Xia AG Michelangeli DV Plummer DA Neary L Kaminski JW McConnell JC 《Journal of environmental monitoring : JEM》2003,5(1):40-46
The simulated concentrations from a numerical 3-dimensional regional air quality model (MC2AQ) are compared to those of ground-based observations in north-eastern Canada and the United States. The model has oxidant chemistry for both inorganic and organic species and deposition routines driven online by a mesoscale compressible community meteorological model (MC2). A standard emission inventory of anthropogenic, natural and biogenic sources for the year 1990 for 21 atmospheric trace species was used in the simulation. The model was run for July 1999, because of the occurrence of a high ozone episode and the availability of the monitoring data for surface O3, SO2, NO, NO2 and NOx. The comparisons during the episode show that the model performs quite well for predicting concentrations and diurnal variations of the surface ozone. The predictions for other gaseous species show some discrepancies with observations, but they are consistent with the results from other models evaluated in the literature. The uncertainties in the emission inventory for these species might be the main causes of the discrepancies. Further studies are needed to improve the predictability of SO and NOx, especially as the model is developed to include particulate matter formation as a result of these gaseous precursors. 相似文献
237.
Lakes and streams are acidified by direct precipitation and water channeled through nearby soils, but water in low base-saturation soils can produce highly acidic percolate after prolonged contact and subsequent degassing in surface waters. Theories advanced by Reuss (1983), Reuss and Johnson (1985), and Seip and Rustad (1984) suggest that soils with less than 15% base saturation are susceptible to soil-water pH depression of up to 0.4 unit, which is sufficient to cause negative alkalinity in soil solutions. High concentrations of mobile anions (notably sulfate) are responsible for the negative alkalinity and these solutions on CO2 degassing in surface waters can retain acidities equivalent to a pH value of 5.0 or less. This mechanism purports to explain why some lakes acidify when they are surrounded by acid soils and cation leaching is not required.Ambient precipitation set to pH 5.4 and pH 4.2 was applied to columns of low base-saturated, sand, soils, starting in 1985. The columns (15 cm diameter and 150 cm long) were collected from soils with base saturations falling into one of three groups (0–10, 10–20, and 20–40%) from national forests in the Superior Uplands area (includes Boundary Waters Canoe Area, Rainbow Lakes, Sylvania, Moquah Barrens, and other Wilderness and Natural areas). The soils were Haplorthods and Udipsamments mainly from outwash plains.The soil columns were instrumented and reburied around a subterranean structure used to collect leachate water and to maintain natural temperature, air, and light conditions. Three humus treatments were applied to soil column (none, northern hardwood, and jack pine) to measure the effect of natural acidification compared to acidification by acid precipitation. The cores were treated with precipitation buffered to pH 5.4 to simulate natural rain and pH 4.2 to simulate acid rain.Columns were treated in 1985 and 1986 with approximately 200 cm of buffered precipitation each year over the frost-free season. Data is now being analyzed for the 1986 treatment year. In leachate collected from the upper horizons of the soil colums, there was a significant difference in pH, alkalinity, nitrate, and sulfate concentrations between the pH 5.4 and pH 4.2 precipitation treatments. This difference, however, disappears at the bottom of the columns. This could be partly due to exchange reactions in the B horizon. The pH and alkalinities are higher in bottom leachate. Chloride and nitrate also increased significantly due mainly to concentrating effects. Even with a pickup of sulfate in the B horizon, sulfate adsorption decreased bottom leachate concentrations well below surface values.Alkalinity, pH, and sulfate concentration in the leachate decreased over the treatment season. Nitrate concentration increased by 4- to 5-fold over the season. Leachate from the bottom of the soil columns is becoming more acidic with time with negative alkalinities appearing more frequently in columns with soils of lower base saturation. There were some significant alkalinity differences due to humus treatments; however, these were not consistent between pH treatments, and need further study. This research will eventually answer whether soil processes can be important to the acidification of lakes in poor, sandy, outwash plains of the Superior Uplands, and whether a reduction in acid sulfate deposition will reverse the percolate alkalinity from negative to positive.Contribution from Fourth World Wilderness Congress-Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987. 相似文献
238.
Optimization of exergy and implications of body sizes of phytoplankton and zooplankton in an aquatic ecosystem model 总被引:2,自引:0,他引:2
Size appears to be an important parameter in ecological processes. All physiological processes vary with body size ranging from small microorganisms to higher mammals. In this model, five state variables — phosphorus, detritus, phytoplankton, zooplankton and fish are considered. We study the implications of body sizes of phytoplankton and zooplankton for total system dynamics by optimizing exergy as a goal function for system performance indicator. The rates of different sub-processes of phytoplankton and zooplankton are calculated, by means of allometric relationships of their body sizes. We run the model with different combinations of body sizes of phytoplankton and zooplankton and observe the overall biomass of phytoplankton, zooplankton and fish. The highest exergy values in different combinations of phytoplankton and zooplankton size indicate the maximum biomass of fish with relative proportions of phytoplankton and zooplankton. We also test the effect of phosphorus input conditions corresponding to oligotrophic, mesotrophic, eutrophic system on its dynamics. The average exergy to be maximized over phytoplankton and zooplankton size was computed when the system reached a steady state. Since this state is often a limit cycle, and the exergy copies this behaviour, we averaged the exergy computed for 365 days (duration of 1 year) in the stable period of the run. In mesotrophic condition, maximum fish biomass with relative proportional ratio of phytoplankton, zooplankton is recorded for phytoplankton size class 3.12 (log V μm3 volume) and zooplankton size 4 (log V μm3 volume). In oligotrophic condition the highest average exergy is obtained in between phytoplankton size 1.48 (log V μm3 volume) and zooplankton size 4 (log V μm3 volume), whereas in eutrophic condition the result shows the highest exergy in the combination of phytoplankton size 5.25 (log V μm3 volume) and zooplankton size 4 (log V μm3 volume). 相似文献
239.
240.
Joshua J. Traylor Ray T. Alisauskas F. Patrick Kehoe 《Behavioral ecology and sociobiology》2008,62(7):1085-1097
Young waterfowl can frequently join foster females shortly after hatch, resulting in post-hatch brood amalgamation. Much uncertainty
remains about physiological or ecological factors that motivate adoption including potential costs and benefits to fostered
offspring as well as to females that either lose or accept young. Several hypotheses have been put forth to explain adoption.
In this paper, we examine the salvage strategy (SSH) and accidental-mixing (AMH) hypotheses. According to the SSH, females
abandon or lose their young due to substantial energetic constraints from incubation and brood rearing. The AMH posits that
adoption results from local ecological conditions on breeding areas (i.e., adverse weather conditions, high brood densities)
which act to separate offspring and mothers. We used multistate modeling to estimate relationships between probabilities of
adoption by white-winged scoter (Melanitta fusca) ducklings from natal to foster females and a set of hypothesized ecological covariates. Results showed that most adoption
occurred within 6 days of hatch; additionally, likelihood of adoption was positively related to inclement weather and negatively
related to hatch date, size, and condition of natal females, and duckling condition. We conclude that adoption in this population
is consistent with both the salvage strategy and accidental-mixing hypotheses. Ultimately, we suggest that adoption in our
study population was foremost an outcome of intense gull predation but also of local environmental conditions. 相似文献