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排序方式: 共有127条查询结果,搜索用时 31 毫秒
1.
通过对2014—2016年湖体水质中氮素质量浓度分析,结合出入湖总氮浓度、水量、湖体水生生态等影响因素,发现太湖水体中总氮浓度呈现逐年下降的趋势,各监测点位总氮为0.530 mg/L~5.51 mg/L,时空分布不均,差异明显。时间上,总氮浓度表现为春季最高,夏季和秋季最低,且月均值变化曲线呈现出规律的正弦函数波形。空间上,总氮浓度大致表现出由西部湖区向东部湖区递减的趋势,呈现西部湖区﹥北部湖区﹥南部湖区﹥湖心区﹥东部湖区。要改善湖体水质,不仅要切断污染源,而且要加强水生生态功能修复。 相似文献
2.
A data analysis of three major Korean cities was conducted to assess roadside inhalable particulate matter 10 μm or smaller
in aerodynamic diameter (PM10), including temporal and meteorological variations, over a recent period of 4 to 6 years. The yearly roadside PM10 concentrations presented a well-defined increasing trend or no trend depending on the roadside monitoring station. Most mean
values exceeded or approximated the Korean standard of 70 μg/m3 per year for PM10. A representative roadside diurnal trend was characterized by a distinct morning maximum. In most cases, the Sunday roadside
concentrations were similar to or somewhat lower than the weekday concentrations, and the PM10 concentrations presented a well-defined seasonal variation, with the maximum concentration in March. The monthly maximum
concentrations observed in March were most likely attributable to Asian dust storms. In two metropolitan cities (Seoul and
Busan), the frequency of days with roadside PM10 concentrations exceeding the standard of 150μg/m3 per 24 h was much lower for the roadside monitoring stations than for the residential monitoring station, whereas in the
third city (Daegu), this result was reversed. Interestingly, the average maximum concentrations observed for the roadside
sites in Seoul and Busan during March were higher than those for the residential sites, suggesting that the roadside concentrations
responded more to the dust storms than the residential areas. The relationship between the pollutant concentrations and five
important meteorological parameters (solar radiation, wind speed, air temperature, relative humidity, and precipitation) showed
that the number and type of meteorological variables included in the equations varied according to the monitoring station
or season. Finally, the current results confirmed that attention should be given to the PM10 exposure of residents living near roadways. 相似文献
3.
Life cycle energy impacts of automotive liftgate inner 总被引:1,自引:0,他引:1
This paper compares the life cycle energy use of a cast-aluminum, rear liftgate inner and a conventional, stamped steel liftgate inner used in a minivan. Using the best available aggregate life cycle inventory data and a simple spreadsheet-level analysis, energy comparisons were made at both the single-vehicle and vehicle-fleet levels. Since the product manufacture and use are distributed over long periods of time that, in a fleet, are not simple linear combinations of single product life cycles. Thus, it is all the products in use over a period of time, rather than a single product, that are more appropriate for the life cycle analysis. Using a set of consistent data, analyses also examine sensitivity to the level of analysis and the assumptions to determine the most favorable materials with respect to life cycle energy benefits.As expected, life cycle energy impacts of aluminum are lower than steel at a single-vehicle level – energy savings are determined to be 1.8 GJ/vehicle. Most energy savings occur at the vehicle operation phase due to improved fuel economy from lightweighting. The energy benefits are realized only very close to the average vehicle life of 14 years. With the incremental growth of the vehicle fleet, it takes longer – about 21 years – for aluminum to achieve life cycle equivalence with steel. The number of years aluminum needs to achieve equivalence with steel was found to be quite sensitive to aluminum manufacturing energy and fuel economy. As the steel industry races to compete with other materials for automotive lightweighting, a systems approach, instead of part-to-part comparison, is more appropriate in the determination of viability of aluminum substitution from an energy perspective. 相似文献
4.
5.
在2010~2012年进行的上海某水源地水质监测资料的基础上,应用纳氏试剂分光光度法等分析方法研究该水源地2011年1~10月总氮、氨氮、硝酸盐氮、亚硝酸盐氮等不同形态的氮素在水体中的空间分布规律及时间变化规律。并就其氮的来源、迁移转化机理和对氮的迁移转化有较大影响的因素进行研究和分析,得出该水库水体中各种形态氮以硝酸盐氮为主,平均占总氮的71.6%,氨氮及亚硝酸盐氮各占总氮的4.39%及0.95%;水体中的温度、光照条件、溶解氧、点位位置分布、水深等是影响各氮形态含量与分布的重要环境因子。 相似文献
6.
Remediation schemes for contaminated sites are often evaluated to assess their potential for source zone reduction of mass, or treatment of the contaminant between the source and a control plane (CP) to achieve regulatory limits. In this study, we utilize a stochastic stream tube model to explain the behavior of breakthrough curves (BTCs) across a CP. At the local scale, mass dissolution at the source is combined with an advection model with first-order decay for the dissolved plume. Field-scale averaging is then employed to account for spatial variation in mass within the source zone, and variation in the velocity field. Under the assumption of instantaneous mass transfer from the source to the moving liquid, semi-analytical expressions for the BTC and temporal moments are developed, followed by derivation of expressions for effective velocity, dispersion, and degradation coefficients using the method of moments. It is found that degradation strongly influences the behavior of moments and the effective parameters. While increased heterogeneity in the velocity field results in increased dispersion, degradation causes the center of mass of the plume to shift to earlier times, and reduces the dispersion of the BTC by lowering the concentrations in the tail. Modified definitions of effective parameters are presented for degrading solutes to account for the normalization constant (zeroth moment) that keeps changing with time or distance to the CP. It is shown that anomalous dispersion can result for high degradation rates combined with wide variation in velocity fluctuations. Implications of model results on estimating cleanup times and fulfillment of regulatory limits are discussed. Relating mass removal at the source to flux reductions past a control plane is confounded by many factors. Increased heterogeneity in velocity fields causes mass fluxes past a control plane to persist, however, aggressive remediation between the source and CP can reduce these fluxes. 相似文献
7.
Studies of habitat selection and movements often use radio-tracking data for defining animal home ranges. Home ranges (HR) can be approximated by a utilization density distribution (UD) that instead of assuming uniform use of areas within HR boundary provides a probabilistic measure of animal space use. In reality, radio-tracking data contain periods of frequent autocorrelated observations interspersed with temporally more independent observations. Using such temporally irregular data directly may result in biased UD estimates, because areas that have been sampled intensively receive too much weight. The problem of autocorrelation has been tackled by resampling data with an appropriate time interval. However, resampling may cause a large reduction in the data set size along with a loss of information. Evidently, biased UD estimates or reduction in data may prejudice the results on animal habitat selection and movement. We introduce a new method for estimating UDs with temporally irregular data. The proposed method, called the time kernel, accounts for temporal aggregation of observations and gives less weight to temporally autocorrelated observations. A further extension of the method accounts also for spatially aggregated observations with relatively low weights given to observations that are both temporally and spatially aggregated. We test the behaviour of the time kernel method and its spatiotemporal version using simulated data. In addition, the method is applied to a data set of brown bear locations. 相似文献
8.
We studied sampling behaviour and mate choice in the fiddler crab Uca mjoebergi. Once a female selects a mate, she copulates in his burrow and remains there until releasing her aquatic larvae. U. mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Females can only release their larvae during
these tides, and release before or after will result in complete failure of reproductive effort. Matings occur over a 5-day
period near the end of neap tides. Our results suggest that within the mating period, females adjust their larval developmental
rates by selecting specific burrows in which to incubate their clutches. We found that at the start of the mating period,
females chose larger males as mates. Since male size was positively correlated to burrow width, females were selecting wide
burrows and effectively incubating at lower temperatures. This would slow down the developmental rates of larvae. In contrast,
females that mated late in the mating period selectively chose small males. By incubating in narrower, warmer burrows, these
females may increase the developmental rates of larvae. We propose that females are selecting burrows to influence incubation
rate and ensure timely release of their larvae. Female U. mjoebergi appear to adjust their preference for the direct benefits of mate choice to increase their reproductive success. 相似文献
9.
Frequency and timing of extrapair fertilisation in the polyandrous red phalarope (Phalaropus fulicarius) 总被引:1,自引:0,他引:1
James Dale Robert Montgomerie Denise Michaud Peter Boag 《Behavioral ecology and sociobiology》1999,46(1):50-56
In sequentially polyandrous bird species, where females mate with different males in succession during a single breeding
season, sperm stored by females can occasionally lead to extrapair fertilisations (EPFs) in clutches cared for by the second
and subsequent males. Thus, we predicted that in red phalaropes (Phalaropus fulicarius) – a sex-role-reversed, sequentially polyandrous, arctic breeding shorebird – EPFs would occur more frequently in clutches
laid later in the breeding season. We used multilocus DNA profiling to examine the frequency and timing of EPFs in a population
of red phalaropes breeding in the Canadian high arctic. Using a technique to determine parentage without maternal DNA, we
inferred that 6 of 70 chicks in 18 broods resulted from EPFs – one extrapair chick in each of 6 broods. These results were
supported by a further analysis using microsatellite DNA. As predicted, broods containing EPFs hatched from clutches laid
significantly later in the season than did broods containing no EPFs. The difference in median hatch dates between broods
with and without EPFs was 9.0 days, or 38% of the entire egg-laying period in that season. For the whole breeding season,
we estimated that 6.5% of chicks were sired by extrapair males, which is similar to extrapair paternity estimates for other
sex-role-reversed birds, but relatively low compared to the majority of socially monogamous species studied so far.
Received: 24 August 1998 / Received in revised form: 18 January 1999 / Accepted: 24 January 1999 相似文献
10.
Dan Yao Guiqian Tang Jie Sun Yinghong Wang Yuan Yang Yiming Wang Baoxian Liu Hong He Yuesi Wang 《环境科学学报(英文版)》2022,34(2):210-217
High loads of ground-level ozone have occurred with the implementation of the Air Pollution Prevention and Control Action Plan. However, the long temporal variation in precursor nonmethane hydrocarbons(NMHCs) has rarely been studied. In this study, we examined the evolution of NMHCs in Beijing based on ambient measurements from 2000 to 2019. The results indicated that the annual variation of ambient NMHCs during 2000 and 2019 could be divided into two stages. The mixing ratios of NMHCs rapidly r... 相似文献