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1.
Mass transport triggered by heavy rainfall: the role of endorheic basins and epikarst in a regional karst aquifer 
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下载免费PDF全文 Maria Dolores Fidelibus Gabriella Balacco Andrea Gioia Vito Iacobellis Giuseppe Spilotro 《水文研究》2017,31(2):394-408
This study aims at recognizing the mechanisms of mass transport between the karst surface and the saturated zone in a morphostructural relief of the Mesozoic karst carbonate platform of Murgia (Puglia, Southern Italy). The large dimension of the karst aquifer, the regional scale of the flow system, the boundary condition constituted by the sea, and the lack of freshwater springs constrain to the use of wells as monitoring points and limit the study area to the recharge area comprising 986 endorheic basins. The concentrations of non‐reactive tracers (nitrates) in the waters of autogenic recharge (from endorheic basins) have been modeled through the evaluation of effective infiltration, land use, and nitrogen surplus, with reference to a time window, which includes a low precipitation period followed by significant rainfall events. The comparison between the modeled nitrate concentrations and the nitrate concentrations measured in ground waters, coupled with the analysis of groundwater chemograms and records of hydraulic heads (all referred to the same time window), allows inferring the mechanism of mass transport between the karst surface and the groundwater table. The mass transport conceptual model requires the presence of the epikarst. The infiltration of significant rainfall in the endorheic basins after a low precipitation period displaces waters stored in the epikarst toward the saturated zone. Ground waters in the post‐event period show higher concentrations of nitrates, lower concentrations of total organic carbon, and higher Mg/Ca ratios than both those of the pre‐event period and the autumn‐winter recharge period. The post‐event recharge from epikarst storage determines a transient hazard of groundwater pollution with a time lag from the occurrence of the heavy rainfall. 相似文献
2.
Rate constants for the reaction of OH radicals with some branched alkyl nitrates have been measured applying a competitive technique. Methyl nitrite photolysis in synthetic air was used as OH radical source at 295±2 K and 1000 mbar total pressure. Using a rate constant of 2.53×10-12 cm3 s-1 for the reaction of OH radicals with n-butane as reference, the following rate constants were obtained (units: 10-12 cm3 s-1): isopropyl nitrate, 0.59±0.22; isobutyl nitrate, 1.63±0.20; 3-methyl-2-butyl nitrate, 1.95±0.15; 2-methyl-1-butyl nitrate, 2.50±0.15; 3-methyl-1-butyl nitrate, 2.55±0.35. These values have been combined with the literature data to recalculate the substituent factors F(X) for the different nitrate groups which can be used to predict OH rate constants for organic nitrates for which experimental data are not available.Preliminary measurements of the photolysis frequency of isopropyl nitrate have shown that for this nitrate as a model substance, OH reactions and direct photolysis are of equal importance under tropospheric conditions. 相似文献
3.
S.N. De Sousa 《Estuarine, Coastal and Shelf Science》1983,16(3):299-308
Behaviour of silicate, nitrate and phosphate in the Mandovi Estuary was studied during the premonsoon season. The study shows that silicate is removed from the water column while nitrate showed an internal source. This nitrate source has been identified as the wash water from an iron ore screening plant which discharges the muddy waste directly into the river. Applying mixing relations, the distribution of this nitrate both up- and downstream of the outfall has been studied. Phosphate showed very low concentrations in the low salinity region; however, its concentration increased slightly towards the higher salinity region. 相似文献
4.
Tidal effect on dynamics of pore water nitrate in intertidal sediment of a eutrophic Estuary 总被引：2，自引：0，他引：2
To evaluate the effect of the tidal cycle on the pore water nitrate dynamics in intertidal sediment, concentrations of inorganic
nitrogen in water and sediment were monitored during tidal cycles in the mud flat of Tama Estuary, Japan. During submergence,
nitrate concentration was highest in the overlying water and decreased monotonically with increasing depth in the sediment,
suggesting that the primary source of nitrate in the sediment was nitrate transported from the overlying water. Pore water
nitrate decreased remarkably during the initial 3–4 hours after the onset of exposure. Thereafter, it was constant or slightly
increased until tidal flooding.In situ accumulation of nitrate at the end of exposure, however, did not exceed the nitrate concentrations in the overlying water.
The inhibition of nitrate reduction and the stimulation of nitrification would explain the change of nitrate concentration,
both consistent with the input of oxygen into the sediment following a 10 mm drop of the water table. In Tama Estuary sediments,
the effect of the tidal cycle on the removal of combined nitrogen is rather negative, because high nitrate concentrations
in the overlying water canceled the positive effect of nitrate accumulation by nitrification during exposure, while tidal
oxygen intrusion have an inhibitory effection sedimentary denitrification. 相似文献
5.
为探讨河西走廊地下水“三氮”的污染现状和个人健康风险。本文以酒泉东盆地为例,通过数据统计、空间分布趋势、污染源和影响因素分析的手段,从“三氮”分布、迁移和影响因素及其健康风险评价进行研究。结果表明：在其独特的地形地貌、氧化还原环境、包气带和含水层岩性、潜水的埋深、酸碱环境和地下径流条件等自然因素以及生态环境的破坏和城市化的发展等人为因素影响下,研究区地下水“三氮”总体含量较低,污染相对较轻,仅有一处NO3--N含量超过标准限值;区域分布上,“三氮”含量具有明显的北高南低的规律,NO3--N和NO2--N含量东、西两侧高,中间低,NH4+-N含量由西北向东南逐渐减少。“三氮”个人年健康风险的整体分布趋势基本一致,由西部人口密集区域向东部人口非密集区域逐渐递减。 相似文献
6.
Difunctional organic nitrates are important products of the atmospheric reaction of NO3 radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH3CH(ONO2)CH2(ONO2); 1,2-butandiol dinitrate, CH3CH2CH(ONO2)CH2(ONO2); 2,3-butandiol dinitrate, CH3CH(ONO2)CH(ONO2)CH3;cis 1,4-dinitrooxy-2-butene, CH2(ONO2)CH=CHCH2(ONO2); 3,4-dinitrooxy-1-butene, CH2(ONO2CH(ONO2)CH=CH2; -nitrooxy acetone, CH3COCH2(ONO2); 1-nitrooxy-2-butanone, CH3CH2COCH2(ONO2); 3-nitrooxy-2-butanone, CH3CH(ONO2)COCH3.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO2 is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO
y
in the atmosphere, especially during the night, is briefly discussed. 相似文献
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8.
Frank?M.?FlockeEmail author Andrew?J.?Weinheimer Aaron?L.?Swanson James?M.?Roberts Rainer?Schmitt Stephen?Shertz 《Journal of Atmospheric Chemistry》2005,52(1):19-43
A fast, automated, gas chromatographic system for the airborne measurement of PAN and a series of its homologues is described
and its performance is evaluated. Response factors for PAN, PPN, APAN, PiBN, and MPAN have been determined and are discussed
with regard to ECD response and to potential losses in the analytical system. Calibration methods used for these tasks are
described and compared. The results from this work should help investigators who are employing the widely used GC/ECD method
for the measurement of peroxyacyl nitrates to evaluate peaks of PAN homologues that cannot be calibrated for by using the
reported response factors. 相似文献
9.
The seasonal and year-to-year variation of bulk precipitation as a source of total N, nitrate and ammonia is reported for a 7-year period at the Rhode River, a subestuary of Chesapeake Bay, U.S.A. These values are placed in perspective by comparison with analogous nitrogen loading due to watershed discharges.Although year-to-year variations were important, in an average year about the same amount of readily available nitrogen entered the system via precipitation as entered in land runoff and, during the summer and fall, precipitation was the largest source. 相似文献
10.
Remote sensing is useful for water quality assessments but current remote sensing applications favour parameters that are easy to detect such as chlorophyll-a. An assessment of the utility of Landsat 8 for detecting nutrients was conducted in Mazvikadei reservoir in Zimbabwe. The main objective was to determine whether nutrients often overlooked by remote sensing and yet are the main determinants of water quality can be remotely sensed. Sampling targeted ammonia, nitrates and reactive phosphorus from May to October 2015. In situ nutrient concentrations were regressed against reflectance derived from Landsat 8 imagery. Strong negative relationships were found between ammonia and the near-infrared band in July (R2 = 0.80, p < 0.05) as well as between nitrates and the blue band (R2 = 0.67, p < 0.05) in June. Overall, the results suggest that the cool dry season is the optimum time to use Landsat 8 for monitoring nutrients in tropical lakes. 相似文献