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71.
An approach is developed to simulate leaching of a dissolved chemical constituent in the vadose zone of an aquifer. Specifically,
nitrate loading at the water table for different water table depths, for a range of aquifer permeability values, and for different
cases of heterogeneity of the aquifer, are considered. Models from the literature are first used to derive soil–water characteristic
curves (water retention and hydraulic conductivity) from a grain size distribution curve for unsaturated conditions. Given
infiltration from the surface, the initial conditions for the chemical concentration, and the water content profile, leaching
of the chemical in the vadose zone is simulated as a function of both time and depth. The methodology is illustrated for a
permeable aquifer. Simulations are undertaken using a finite element code for saturated and unsaturated flow. Different scenarios
are simulated depending on the heterogeneity of the aquifer and the depth of the water table. Modeling results show that in
the example case studied, nitrate concentration loading at the water table does not depend strongly on the position of the
water table, but rather on the material properties of the aquifer. The contribution of this endeavor resides in the methodology
which allows a prediction of nitrate leaching using only the grain size property of the aquifer. It allows practitioners to
obtain a first assessment of leaching with limited data. 相似文献
72.
The European Community asks its Member States to provide a comprehensive and coherent overview of their groundwater chemical
status. It is stated that simple conceptual models are necessary to allow assessments of the risks of failing to meet quality
objectives. In The Netherlands two monitoring networks (one for agriculture and one for nature) are operational, providing
results which can be used for an overview. Two regression models, based upon simple conceptual models, link measured nitrate
concentrations to data from remote sensing images of land use, national forest inventory, national cattle inventory, fertiliser
use statistics, atmospheric N deposition, soil maps and weather monitoring. The models are used to draw a nitrate leaching
map and to estimate the size of the area exceeding the EU limit value in the early 1990s. The 95% confidence interval for
the fraction nature and agricultural areas where the EU limit value for nitrate (50 mg/l) was exceeded amounted to 0.77–0.85
while the lower 97.5% confidence limit for the fraction agricultural area where the EU limit value was exceeded amounted to
0.94. Although the two conceptual models can be regarded as simple, the use of the models to give an overview was experienced
as complex. 相似文献
73.
Krywult M Smykla J Kinnunen H Martz F Sutinen ML Lakkala K Turunen M 《Environmental pollution (Barking, Essex : 1987)》2008,156(3):1105-1111
Needles of 20-year-old Scots pine (Pinus sylvestris L.) saplings were studied in an ultraviolet (UV) exclusion field experiment (from 2000 to 2002) in northern Finland (67 °N). The chambers held filters that excluded both UV-B and UV-A, excluded UV-B only, transmitted all UV (control), or lacked filters (ambient). UV-B/UV-A exclusion decreased nitrate reductase (NR) activity of 1-year-old needles of Scots pines compared to the controls. The proportion of free amino acids varied in the range 1.08-1.94% of total proteins, and was significantly higher in needles of saplings grown under UV-B/UV-A exclusion compared to the controls or UV-B exclusion. NR activity correlated with air temperature, indicating a “chamber effect”. The study showed that both UV irradiance and increasing temperature are significant modulators of nitrogen (N) metabolism in Scots pine needles. 相似文献
74.
George R. Holdren Jr. Timothy C. Strickland Bernard J. Cosby David Marmorek David Bernard Robert Santore Charles T. Driscoll Linda Pardo Carolyn Hunsaker Robert S. Turner John Aber 《Environmental management》1993,17(3):355-363
The critical loads approach is emerging as an attractive means for evaluating the effects of atmospheric deposition on sensitive
terrestrial and aquatic ecosystems. Various approaches are available for modeling ecosystem responses to deposition and for
estimating critical load values. These approaches include empirical and statistical relationships, steady-state and simple
process models, and integrated-effects models. For any given ecosystem, the most technically sophisticated approach will not
necessarily be the most appropriate for all applications; identification of the most useful approach depends upon the degree
of accuracy needed and upon data and computational requirements, biogeochemical processes being modeled, approaches used for
representing model results on regional bases, and desired degree of spatial and temporal resolution. Different approaches
are characterized by different levels of uncertainty. If the limitations of individual approaches are known, the user can
determine whether an approach provides a reasonable basis for decision making. Several options, including point maps, grid
maps, and ecoregional maps, are available for presenting model results in a regional context. These are discussed using hypothetical
examples for choosing populations and damage limits.
The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared
at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with ManTech Environmental
Technology, Inc., and Interagency Agreement #1824-B014-A7 with the U.S. Department of Energy and at Oak Ridge National Laboratory
managed by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-84OR21400 with the US Department of Energy. Environmental
Sciences Division Publication No. 3904. It has been subjected to the agency’s peer and administrative review and approved
for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 相似文献
75.
间歇曝气系统中硝酸盐氮负荷对脱氮效率的影响 总被引:1,自引:0,他引:1
本试验主要考察间歇反应器缺氧阶段硝酸盐氮负荷NNO-x-N(KgNO-x-N/KgMLSSd)对脱氮效率的影响。试验结果表明:在一定水温和BOD5/NOx-N下,NNOx-N负荷对脱氮效率有显著影响。在反应器中采用高浓度污泥是降低NNOx-N的有效途径,有利于反应器脱氮速率VDN(mg/l·min)的提高。此外,通过正交试验得出了在BOD5/NO-x一定时,NNO-x-N、T℃与脱氮效率ηNO-x-N之间的数量关系式 相似文献
76.
将样品中的颗粒物分离出来后,向样品中加入适量硝酸银,除去生成的氯化银沉淀,再将预先分离的颗粒物合并到水样中,混匀后测定。经过这样处理,既去除了水样中的Cl-,又保留了水样中原来的组份,保证了COD测定结果的准确性。 相似文献
77.
Analysis and evaluation of nitrate levels in groundwater at Al-Hashimiya area, Jordan 总被引:3,自引:0,他引:3
Obeidat MM Massadeh AM Al-Ajlouni AM Athamneh FS 《Environmental monitoring and assessment》2007,135(1-3):475-486
Water with high nitrate concentration (NO3
−) is unfit for human consumption, especially when its concentration exceeded the threshold limit (50 mg/l) recommended by
the health authorities such as the World Health Organization (WHO). In Jordan, there is a great concern for determination
and monitoring organic and inorganic pollutants that may reach groundwater. Nitrate is highly mobile and present in domestic,
agricultural and industrial waste in Jordan, and thus this study focused initially on nitrate as both a contaminant of concern
and as an indicator of potential groundwater contamination. The present study determined the extent of nitrate contamination
in groundwater in the study area and examined the likely sources of NO3
−. A total of 248 groundwater samples were collected from 16 wells in different sites of Al-Hashimiya area, Zerqa Governorate,
Jordan, and investigated for NO3
− concentrations. Moreover, measurements of temperature, electrical conductivity and pH were carried out in the field. Analysis
was carried out according to the methods described by the American Public Health Association (APHA). Results showed that there
was a dramatic increasing in NO3
− concentrations from the year 2001 to 2006 for some selected wells in the present study. NO3
− concentration in 2006 was ranged from 10 to 330 mg/l with an average of 77 mg/l. Overall, groundwater had elevated nitrate
concentration with 92% of the samples containing more than 20 mg/l NO3
−, indicating the influence of human activities. This study has shown that there is a strong correlation between the nitrate
concentration and the wastewater effluents as a source of pollution. 相似文献
78.
Tipping E Thacker SA Wilson D Hall JR 《Environmental pollution (Barking, Essex : 1987)》2008,152(1):41-49
During the last 50 years nitrate concentrations in Buttermere and Wastwater (Cumbria, UK) have risen significantly, by 70 and 100%, respectively. By estimating contemporary nitrate fluxes in the lakes' catchments and in sub-catchments and comparing them with the fractional areas of different soil types, it is deduced that the surface water nitrate is derived almost entirely from organic-rich ranker soils that have a limited ability to retain atmospherically-deposited nitrogen. Little or no nitrate leaches from the other major soil type, a brown podzol, despite it having a lower C:N ratio (12.0 g g(-1)) than the ranker (17.0 g g(-1)), nor is there much contribution from the small areas of improved (chemically fertilised) grassland within the catchments. Although some nitrate leaching is occurring, total N losses are appreciably smaller than atmospheric inputs, so the catchment soils are currently accumulating between 3 and 4 g N m(-2) a(-1). 相似文献
79.
Trends of nitrogen in air and precipitation: model results and observations at EMEP sites in Europe, 1980--2003 总被引:1,自引:0,他引:1
We analyze trends of some nitrogen compounds using long-term measurements and results from the EMEP (co-operative programme for monitoring and evaluation of the long-range transmissions of air pollutants in Europe) chemical transport model at EMEP sites. We find statistically significant declines at the majority of sites for NH(x) (sum of ammonia and ammonium) in air and for nitrate and ammonium in precipitation, but only at a few sites for xNO3 (sum of nitrate and nitric acid) in air. Model calculations and measurements give similar results. We demonstrate that the lack of trends for xNO3 in air at least partly can be attributed to a shift in the equilibrium between nitric acid and ammonium nitrate towards particulate phase, caused by reductions in the sulfur dioxide emissions. 相似文献
80.
同分异构体喹啉和异喹啉的缺氧降解性能比较 总被引:3,自引:0,他引:3
研究了同分异构体的含氮杂环化合物喹啉和异喹啉在缺氧条件下的降解情况,发现两者表现出不同的缺氧降解特性。喹啉可以在缺氧条件下得到有效降解,其缺氧降解的最佳碳氮比为8。在最佳碳氮比条件下,喹啉的缺氧降解过程符合一级动力学规律,在其降解过程中首先以硝酸盐为电子受体,当硝酸盐氮浓度为零时,亚硝酸盐氮浓度达到最高,此后喹啉的降解主要以亚硝酸盐为电子受体,并和亚硝酸盐氮同时达到最低浓度。异喹啉对硝酸盐的利用甚微,其降解主要表现为厌氧降解特征,降解过程符合零级动力学规律。 相似文献