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401.
Abstract The surface distribution of salinity, temperature, nitrate‐nitrogen (N03‐N), and chlorophyll a in the southern New Zealand, Foveaux Strait region in February 1977, 1978, 1979, and 1980 was highly variable. The source of new nitrogen appears to be incursions of high‐salinity water west and east of Stewart Island. Although it seems likely that the source of this high‐nutrient, high‐salinity water is vertical, a horizontal advective source cannot be ruled out The chlorophyll a content of surface waters was not related directly to the NO3‐N concentrations. This lower food chain variability may be linked to variability in economically important species. Oysters grew twice as fast in the summer of 1978/79 as they did in 1979/80. But the mean chlorophyll a values were very similar for February of both years (2.5 and 2.2 μg 1?1, respectively). The elevated NO3‐N levels in 1979 may have resulted in much higher phytoplankton levels later that summer and resulted in the higher oyster growth rate that year. The mechanisms driving this variability have yet to be determined. 相似文献
402.
Le Gall A. C.; Hydes D. J.; Kelly-Gerreyn B. A.; Slinn D. J. 《ICES Journal of Marine Science》2000,57(4):1050-1059
403.
The intensity of agriculture has increased significantly during the past 30 years, resulting in increased detection of agricultural
contaminants (nutrients, pesticides, salts, trace elements, and pathogens) in groundwater. Till, glaciolacustrine, and loess
deposits of Quaternary age compose the most common surficial deposits underlying agricultural areas in North America. Quaternary
aquitards generally contain higher concentrations of solid organic carbon (SOC, as much as 1.4%), dissolved organic carbon
(DOC, as much as 205 mg/L), and reduced sulfur (as much as 0.9%) than do aquifers. Their potential to sorb pesticides increases
with the percent of older SOC, because diagenesis increases Koc. Denitrification consistently reduces nitrate to non-detectable levels in unweathered Quaternary aquitards. Organic carbon
of Quaternary age is a more labile electron donor than carbon from shale clasts. Pyrite is a more labile electron donor than
carbon in many instances. Unweathered Quaternary aquitards provide a high degree of protection for underlying aquifers, due
to their large reserves of SOC and reduced sulfur for sorption and denitrification, combined with their typically low hydraulic
conductivity. In contrast, agricultural contaminants are common in weathered Quaternary aquitards. Lower reserves of reduced
sulfur and sorptive/labile organic carbon, and a higher bulk K due to fractures, limit their ability to attenuate nitrate
and pesticides. Subsurface drainage, which is common in Quaternary aquitards because of high water tables, bypasses the attenuation
capacity of Quaternary aquitards and facilitates the transport of agricultural contaminants to surface water.
Electronic Publication 相似文献
404.
In nature selenate reduction and nitrate denitrification both follow a similar biogeo-chemical mechanism.It has been proved that abiotic stresses such as alternative drying and wetting can exert an important influence on nitrate denitrification as well as on selenate reduction.Our experimental results lend great support to the above conclusion. 相似文献
405.
Chloe Nikitas Kevin C. Clemitshaw David E. Oram Stuart a. Penkett 《Journal of Atmospheric Chemistry》1997,28(1-3):339-359
Peroxyacetyl nitrate (PAN,CH3C(O)O2NO2) has been measured inthe polluted boundary layer and free troposphere by thermal conversion tonitrogen dioxide (NO2) followed by detection of thedecomposition product with a Scintrex LMA-3 NO2-luminolinstrument. Following laboratory tests of the efficiency of PAN conversionand investigations of possible interferences, the technique was evaluated atthe West Beckham TOR (Tropospheric Ozone Research) Station near the northNorfolk coast in Eastern England between September 1989 and August 1990. PANmeasured by the new technique was reasonably well correlated with PANrecorded using electron capture gas chromatography (EC/GC). PAN was alsowell correlated with ozone (O3) in the summer months. Springand autumn episodes of simultaneously high concentrations of PAN andO3 were examined in conjunction with air parcelback-trajectories and synoptic- and local-scale meteorology in a study ofthe sources of photooxidants on the east coast of England. Spring-timemeasurements of PAN made in the free troposphere in a light aircraft ataltitudes up to 3.1 km showed the presence of 0.54 and 0.26 ppbv PAN inpolar maritime and mid-latitude oceanic air masses, respectively. Thetechnique is particularly suited to airborne applications because potentialinterferences are minimised and the frequency of measurements is higher thangenerally achieved with EC/GC methods. 相似文献
406.
海带和裙带菜硝酸还原酶活性比较 总被引:1,自引:0,他引:1
试验海带和裙带菜孢子体在不同部位、不同生长期硝酸还原酶的活性。指出两种藻硝酸还原酶的活性随年龄增长而增强,叶片横向和纵向酶活性分布。阐明生长在不同水层的海带在同一部位酶活性的差异。 相似文献
407.
本文首次报告了丙烯腈(AN)与甲壳质膜的接枝聚合。在水溶液25±1℃,硝酸铈铵(CAN)引发下得到接枝聚合物。结果表明最适宜条件是在AN1.50molL~(-1)CAN6×10~(-3)molL~(-1),通N_2情况下进行。接枝膜有良好的透明性和张力强度。 相似文献
408.
Nancy ArandaCirerol Jorge A. Herrera-Silveira Francisco A. Comín 《Estuarine, Coastal and Shelf Science》2006,68(3-4):445
This work is the beginning of a coastal water quality monitoring program to establish the baseline for the implementation of an integrated coastal management of the Yucatán Peninsula tropical ecosystem. Coastal water quality is affected by the increasing economic development. This area has no rivers because of its karst geomorphology, and the coastal freshwater comes from springs or seeps. Coastal water quality was studied in four towns from January to December 2000. Statistically significant differences among water quality variables and processes are discussed. Along with groundwater discharge, domestic and shrimp farming sewage are the main sources of nutrients, predominantly of nitrogen and silica. Salinity dilution is used to estimate the groundwater fraction that influences each area in northwestern Yucatán. 相似文献
409.
Oliver Gabriel Dagmar Balla Thomas Kalettka Christian Schilling Matthias Zessner 《洁净——土壤、空气、水》2006,34(4):333-345
Research on the sediment‐surface water transition zone in three study site regions, different in hydrological conditions, was conducted to estimate to which extent nitrate in surface water can contribute to riverbed sediment oxidation and thus prevent release of sediment phosphorus to surface water. Consequently, the Du tch Flow Model (DUFLOW) based water quality model “Spreewald” and results from the emission model “ Mo delling N utrient E missions in Ri ver S ystems” (MONERIS) were used to estimate to which extent wastewater treatment plants (WWTPs) could contribute to the NO3– concentration in surface waters if they were operated without denitrification. It is demonstrated that an effective phosphorus retention in sediments by means of surface water NO3– is possible only under specific conditions, i. e. (i) a sufficient supply of surface water to the sediment by advective fluxes, (ii) a sufficient amount of sediment iron to provide phosphorus binding sites in the case of sediment oxidation, (iii) a redox system not leading to a rapid NO3– and FeOOH depletion and to phosphorus release from organic pools by high microbial activities. Model results show that in‐stream denitrification processes counteract a significant increase of NO3– surface water concentrations from WWTPs operated without denitrification during summer, when eutrophication risk through phosphorus is highest. The increase of NO3– surface water concentrations in winter due to decreased denitrification in the surface water is of minor relevance for phosphorus release from sediments. 相似文献
410.
Salah S. Abdalmogith Roy M. Harrison Zahari Zlatev 《Journal of Atmospheric Chemistry》2006,54(1):43-66
Nitrate and sulphate concentrations were measured over the period January 2002–December 2003 on daily basis at two stations in the UK: a rural site (Harwell) and an urban site (Belfast). The measurements were compared with model results obtained by using the Unified Danish Eulerian Model (UNI-DEM), which was run using both a coarse resolution grid (50 km × 50 km surface cells) and a fine resolution grid (10 km × 10 km surface cells). The results from the comparison show reasonably good agreement between concentrations measured at the two stations and calculated by the model. This is achieved despite the absence of aqueous phase sulphur oxidation chemistry in the model. The model results were also used to predict the spatial distributions of nitrate and sulphate concentrations in the UK which agree well with observations. The contribution of mainland European emission sources and that of UK sources to pollution levels in the UK was estimated. The relative proportions differ substantially across the UK with the imported contribution to UK sulphate and nitrate typically in the range 20–45% and 35–65% respectively. 相似文献