对加拿大东南部湖泊从酸沉降效应中恢复的评价

北美洲SO2排放量的减少激起了人们对加拿大东南部的水生态系统能迅速摆脱酸化的状态的期待.但是只有那些明显减少了排放量的冶炼厂附近的湖泊达到了这种期望值.在临近大西洋的省份魁北克和安大略,受远程污染源影响的湖泊的硫酸根离子(SO2- 4)浓度都有一定降低,但pH和碱度则仅有较少量的提高.对于这种延迟的酸度响应,有如下几种因素可以解释:碱基阳离子含量的下降,干旱加速SO2- 4的迁移,水体内部碱性物质生成机制遭到破坏;同时硝酸盐和有机阴离子含量的提高也可能是其中的原因.对加拿大东南部生物恢复的监测资料非常有限,即使有的话,在萨德伯里(Sudbury)和基拉尼(Killarney)地区以外也很难找到恢复的证据.比如,尽管除了酸化作用外其他因素也对上述现象有一定影响,新思科舍河中的大西洋鲑鱼出现率和安大略湖潜鸟的繁殖成功率实际上正在下降.化学和生物学模型预测,只有比目前法规要求严格的多的SO2排放削减额才能促进广泛的化学恢复和其后的生物恢复,而在加拿大东南部的众多湖泊中重建工业化前的化学与生物学条件或许很难实现.     

Regioselective oxidation of tetracycline by permanganate through alternating susceptible moiety and increasing electron donating ability

Permanganate has attracted much attention in wide range of chemistry and particularly in degradation of environmental pollutants. However, few studies have discussed the feature of regioselective reactivity of permanganate with specific moiety of the target compound. Herein, we studied the reaction between permanganate and tetracycline that is an emerging micropollutant with different species containing several electron-rich groups. The second-order rate constants increased from 6.0 to 9.0 and could be quantitatively modeled by considering the speciation of both reactants, yielding k_TC⁰?=?11.7 (mol/L)^?1?sec^?1, k_TC^??=?35.7 (mol/L)^?1?sec^?1, k_TC^2??=?43.1 (mol/L)^?1?sec^?1 for individual reaction channels. Degradation products were then identified as the hydroxylated and demethylated compounds. The result suggested a rate-limiting step of simple hydroxylation at the phenolic and/or alkene moieties, while the demethylation should be caused by the unavoidably formed manganese oxide via single electron oxidation. This is supported by the DFT calculation, indicating the primary oxidation of phenolic group of TC⁰ with activation barrier of 44.5?kcal/mol and of alkene group of TC^? and TC^2? with activation barriers of 44.0 and 43.4?kcal/mol, respectively. This is in agreement with the experimental results, implying the alternation of regioselectivity associated with the deprotonation process. The result was further supported by performing the Fukui function and electrostatic potential analysis, reflecting the more probable site and better electron donating tendency beneficial to the permanganate oxidation.     

An investigation into the occurrence and distribution of polycyclic aromatic hydrocarbons in two soil size fractions at a former industrial site in NE England,UK using in situ PFE–GC–MS

Polycyclic aromatic hydrocarbon (PAH) concentrations were determined in 16 topsoils (0–10 cm) collected across the site of a former tar works in NE England. The soils were prepared in the laboratory to two different particle size fractions: <250 μm (fraction A) and >250 μm to <2 mm (fraction B). Sixteen priority PAHs were analysed in the soils using in situ pressurised fluid extraction (PFE) followed by gas chromatography—mass spectrometry (GC–MS). The average total PAH concentration in the soils ranged from 9.0 to 1,404 mg/kg (soil fraction A) and from 6.6 to 872 mg/kg (soil fraction B). These concentrations are high compared with other industrially contaminated soils reported in the international literature, indicating that the tar works warrants further investigation/remediation. A predominance of higher-molecular-weight compounds was determined in the samples, suggesting that the PAHs were of pyrogenic (anthropogenic) origin. Statistical comparison (t-test) of the mean total PAH concentrations in soil fractions A and B indicated that there was a significant difference (95% confidence interval) between the fractions in all but two of the soil samples. Additionally, comparisons of the distributions of individual PAHs (i.e. 16 PAHs × 16 soil samples) in soil fractions A and B demonstrated generally higher PAH concentrations in fraction A (i.e. 65.8% of all individual PAH concentrations were higher in soil fraction A). This is important because fraction A corresponds to the particle size thought to be most important in terms of human contact with soils and potential threats to human health.     

OXYGEN SAG EQUATION FOR THREE-HALVES ORDER BOD REACTION1

Several published BOD data sets are examined to show that approximately half of them are described best in the least squares sense by treating the BOD equation as being of the three-halves order instead of first order. A dissolved oxygen (DO) sag equation for a stream is developed in which the BOD is described as a three-halves order reaction. The time when the minimum DO concentration occurs is calculated numerically. The DO sag model applied to example problems shows that an increase in the BOD reaction rate constant results in a smaller minimum DO concentration and a decrease in the time to reach the minimum DO.     

The contribution of advective fluxes to net ecosystem exchange in a high-elevation, subalpine forest

The eddy covariance technique, which is used in the determination of net ecosystem CO2 exchange (NEE), is subject to significant errors when advection that carries CO2 in the mean flow is ignored. We measured horizontal and vertical advective CO2 fluxes at the Niwot Ridge AmeriFlux site (Colorado, USA) using a measurement approach consisting of multiple towers. We observed relatively high rates of both horizontal (F(hadv)) and vertical (F(vadv)) advective fluxes at low surface friction velocities (u(*)) which were associated with downslope katabatic flows. We observed that F(hadv) was confined to a relatively thin layer (0-6 m thick) of subcanopy air that flowed beneath the eddy covariance sensors principally at night, carrying with it respired CO2 from the soil and lower parts of the canopy. The observed F(vadv) came from above the canopy and was presumably due to the convergence of drainage flows at the tower site. The magnitudes of both F(hadv) and F(vadv) were similar, of opposite sign, and increased with decreasing u(*), meaning that they most affected estimates of the total CO2 flux on calm nights with low wind speeds. The mathematical sign, temporal variation and dependence on u(*) of both F(hadv) and F(vadv) were determined by the unique terrain of the Niwot Ridge site. Therefore, the patterns we observed may not be broadly applicable to other sites. We evaluated the influence of advection on the cumulative annual and monthly estimates of the total CO2 flux (F(c)), which is often used as an estimate of NEE, over six years using the dependence of F(hadv) and F(vadv) on u(*). When the sum of F(hadv) and F(vadv) was used to correct monthly F(c), we observed values that were different from the monthly F(c) calculated using the traditional u(*)-filter correction by--16 to 20 g C x m(-2) x mo(-1); the mean percentage difference in monthly Fc for these two methods over the six-year period was 10%. When the sum of F(hadv) and F(vadv) was used to correct annual Fc, we observed a 65% difference compared to the traditional u(*)-filter approach. Thus, the errors to the local CO2 budget, when F(hadv) and F(vadv) are ignored, can become large when compounded in cumulative fashion over long time intervals. We conclude that the "micrometeorological" (using observations of F(hadv) and F(vadv)) and "biological" (using the u(*) filter and temperature vs. F(c) relationship) corrections differ on the basis of fundamental mechanistic grounds. The micrometeorological correction is based on aerodynamic mechanisms and shows no correlation to drivers of biological activity. Conversely, the biological correction is based on climatic responses of organisms and has no physical connection to aerodynamic processes. In those cases where they impose corrections of similar magnitude on the cumulative F(c) sum, the result is due to a serendipitous similarity in scale but has no clear mechanistic explanation.     

Measuring terrestrial subsidies to aquatic food webs using stable isotopes of hydrogen

Understanding river food webs requires distinguishing energy derived from primary production in the river itself (autochthonous) from that produced externally (allochthonous), yet there are no universally applicable and reliable techniques for doing so. We compared the natural abundance stable isotope ratios of hydrogen (deltaD) of allochthonous and autochthonous energy sources in four different aquatic ecosystems. We found that autochthonous organic matter is uniformly far more depleted in deuterium (lower deltaD values) than allochthonous: an average difference of approximately 100% per hundred. We also found that organisms at higher trophic levels, including both aquatic invertebrates and fish, have deltaD values intermediate between aquatic algae and terrestrial plants. The consistent differences between leaves and algae in deltaD among these four watersheds, along with the intermediate values in higher trophic levels, indicate that natural abundance hydrogen isotope signatures are a powerful tool for partitioning energy flow in aquatic ecosystems.     

Organization of Plethodon salamander communities: guild-based community assembly

A long-standing goal in evolutionary ecology is to determine whether the organization of communities is reflective of underlying deterministic processes. In this study, I examined patterns of species co-occurrence among eastern Plethodon salamanders and determined whether they were consistent with predictions from a guild model of competition-based community assembly. Using a database of 45 species and 4540 geographic sites, I found that patterns of co-occurrence were significantly nonrandom at both a regional and continental scale, and species of different size guilds were distributed more evenly in sites than was expected by chance. Sites with the highest species richness had consistent patterns of community composition, and with few exceptions, the same five species were present at all sites. Taken together, these results imply that larger Plethodon communities are assembled from simpler communities in a manner consistent with what is predicted through competitive mechanisms and suggest that stable species combinations are possible to achieve at various levels of species richness. These results also provide strong evidence consistent with the hypothesis that competitive-based community assembly is a general phenomenon in Plethodon and that interspecific competition is prevalent among the eastern species of this group.     

Septic tank and agricultural non‐point source pollution within a rural watershed

This investigation addresses the problem of Non‐Point Source (NPS) pollution in the rural Lake Weatherford watershed in Parker County, Texas. This reservoir is the primary municipal water supply for the City of Weatherford, Texas. The principal method of wastewater disposal is the on‐site system or septic tanks for the small residential areas surrounding the reservoir.

Sources of NPS pollution of interest in this watershed include agricultural operations as well as the residential areas. These sites were identified with the aid of aerial photography and field investigation. Suspected NPS problems were substantiated through a sampling program involving chemical and biological testing of the reservoir. Results indicate that there is significant NPS pollution contamination of Lake Weatherford from agricultural sources and seepage from on‐site wastewater disposal systems. Excessive fecal coliform and fecal streptococcus counts (>500 bacteria/100 ml) were generally associated with rainfall events and several samples showed values > 100000 bacteria/100 ml. The fecal coliform/fecal streptococcus ratios indicated contamination from human sources, animal sources, and a combination of both. Nutrient concentrations fluctuated from quite low to high with ammonia as the most consistent problem. High ammonia values were also associated with rainfall events.     

Work—nonwork conflict and the perceived quality of life

From additive models of overall quality of life, two hypotheses were derived about the relationships among work—family conflict, work—leisure conflict, job satisfaction, family satisfaction, leisure satisfaction and global life satisfaction. In supporting these two hypotheses, path analyses of survey data from a national probability sample of United States workers (n = 823) showed: (1) the direct paths between work—nonwork conflict and global life satisfaction were nonsignificant; and (2) the indirect paths between work—nonwork conflict and global life satisfaction, which are mediated by job satisfaction and nonwork satisfaction, were all significant. Further analyses indicated that, in general, the magnitude of these path coefficients was not significantly moderated by sociodemographic variables. Discussion considered the role of additive models as conceptual frameworks for studies concerned with the effects of work experiences on the overall quality of life.