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321.
Total annual nutrient loads are a function of both watershed characteristics and the magnitude of nutrient mobilizing events.
We investigated linkages among land cover, discharge and total phosphorus (TP) concentrations, and loads in 25 Kansas streams.
Stream monitoring locations were selected from the Kansas Department of Health and Environment stream chemistry long-term
monitoring network sites at or near U.S. Geological Survey stream gauges. We linked each sample with concurrent discharge
data to improve our ability to estimate TP concentrations and loads across the full range of possible flow conditions. Median
TP concentration was strongly linked (R
2 = 76%) to the presence of cropland in the riparian zones of the mostly perennial streams. At baseflow, discharge data did
not improve prediction of TP, but at high flows discharge was strongly linked to concentration (a threshold response occurred).
Our data suggest that on average 88% of the total load occurred during the 10% of the time with the greatest discharge. Modeled
reductions in peak discharges, representing increased hydrologic retention, predicted greater decreases in total annual loads
than reductions of ambient concentrations because high discharge and elevated phosphorus concentrations had multiplicative
effects. No measure of land use provided significant predictive power for concentrations when discharge was elevated or for
concentration rise rates under increasing discharge. These results suggest that reductions of baseflow concentrations of TP
in streams without wastewater dischargers may be managed by reductions of cropland uses in the riparian corridor. Additional
measures may be needed to manage TP annual loads, due to the large percentage of the TP load occurring during a few high-flow
events each year. 相似文献
322.
M. Inés Toral Pablo Richter Mónica Cavieres Walter González 《Environmental monitoring and assessment》1999,54(2):191-203
A simple method by first derivative spectrophotometry is proposed for the simultaneous determination of o-nitrophenol and p-nitrophenol. The analytes were separated from samples by liquid-liquid extraction (pH = 7.4) as tetrabutylammonium ion pairs into the 1,2-dichloroethane organic phase and subsequently the extracts were evaluated directly by derivative spectrophotometry. Simultaneous determination of both analytes could be carried out using the zero-crossing and the graphical methods for o-nitrophenol and p-nitrophenol, respectively. The determination ranges were found to be between 0.115 to 3.00 ppm and 0.130 to 3.00 ppm for o-nitrophenol and p-nitrophenol, respectively. The relative standard deviations were in all instances less than 2.0%. The proposed method was applied to the determination of these compounds in fruit juices. 相似文献
323.
刘成君 《应用与环境生物学报》2000,6(4)
用成团肠杆菌(Enterobacter agglomerans) T7(pEA9∷Km)为供体菌,以E.a.339(pEA9-)为受体菌在天然土壤中进行接合实验,测定各种营养物质对重组质粒pEA9∷Km同源接合转移频率的影响.实验发现,如果在土壤中只加入生理盐水或无机盐培养基,就观察不到细菌数量的增加和质粒的转移;只有加入碳源物质后才检测到细菌数量的增加和质粒的接合转移,接合转移频率的大小位于1.2×10-4~4.4×10-4之间,与所加碳源物质的种类关系不大.图2 表1 参13 相似文献
324.
Wioletta Rogula-Koz?owsk Barbara Kozielsk Grzegorz Majewski Patrycja Rogula-Kopie Walter Much Karolina Kociszewska 《环境科学学报(英文版)》2018,30(2):235-244
The goal of the work was to investigate the concentrations of the 16 US EPA priority polycyclic aromatic hydrocarbons(PAH) bound to submicrometer particles(particulate matter, PM_1) suspended in the air of university teaching rooms and in the atmospheric air outside. Two teaching rooms were selected in two Polish cities, Gliwice, southern Poland,and Warsaw, central Poland, differing with regard to the ambient concentrations and major sources of PM and PAH. The variabilities of indoor and outdoor 24-hr concentrations of PM_1-bound PAH, the ratio(I/O) of the indoor to outdoor 24-hr concentrations of PM_1-bound PAH, probable sources of PAH and the level of the hazard from the mixture of the 16 PAH(ΣPAH) to humans at both sites were analyzed. In both Warsaw and Gliwice, the mean concentrations of PM_1-bound ΣPAH were slightly higher in the atmospheric air than in the rooms. The indoor and outdoor concentrations of individual PAH in Gliwice were correlated,in Warsaw – they were not. Most probably, the lack of the correlations in Warsaw was due to the existence of an unidentified indoor source of gaseous PAH enriching PM_1 in phenanthrene, fluorene, and pyrene. Although the ambient concentrations of PM_1-bound PAH were low compared to the ones observed earlier at both sites, they were much higher than in other urbanized European areas. However, because of low mass share of heavy PAH in ΣPAH, the various indicators of the health hazard from the 16 PAH mixture were low compared to other regions. 相似文献
325.
P. Coelho S. Costa C. Costa S. Silva A. Walter J. Ranville M. R. Pastorinho C. Harrington A. Taylor V. Dall’Armi R. Zoffoli C. Candeias E. Ferreira da Silva S. Bonassi B. Laffon J. P. Teixeira 《Environmental geochemistry and health》2014,36(2):255-269
In the Panasqueira mine area of central Portugal, some environmental media show higher metal(loid) concentrations when compared with the local geochemical background and the values proposed in the literature for these environmental media. In order to evaluate the effect of the external contamination on selected indexes of internal dose, As, Cd, Cu, Cr, Fe, Hg, Mg, Mn, Mo, Ni, Pb, S, Se, Si, and Zn were quantified by inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry in blood, urine, hair and nail samples from individuals environmentally (N = 41) and occupationally exposed (N = 41). A matched control group (N = 40) was also studied, and data from the three groups were compared. Results obtained agreed with those reported by environmental studies performed in this area, pointing to populations living nearby and working in the mine being exposed to metal(loid)s originated from mining activities. Arsenic was the element with the highest increase in exposed populations. The concentration of other elements such as Cr, Mg, Mn, Mo, Ni, Pb, S, Se, and Zn was also increased, although at a lesser extent, specifically in the individuals environmentally exposed and in females. These findings confirm the need for competent authorities to act as soon as possible in this area and implement strategies aimed to protect exposed populations and the entire ecosystem. 相似文献
326.
327.
Nonylphenols and nonylphenolethoxylates with one, two, and three oxyethylene groups were identified in effluents from activated sludge sewage treatment plants. The complex mixtures of isomers are considered to be refractory metabolites of nonionic detergents. 相似文献
328.
329.
330.
Walter Nagl 《Die Naturwissenschaften》1987,74(1):30-34
Recent models for the organization of the chromosomes of eukaryotes in mitosis and interphase are discussed with respect to their condensation hierarchy. Possible functional interpretations are indicated. At present, an alternating coiling and loop formation, induced by histones and nonhistone proteins, respectively, appears to be the most probable structure. The relationship of DNA properties to chromatin structure and function is also briefly discussed. 相似文献