An investigation of the impact of afforestation on stream-water chemistry in the Loch Dee catchment, SW Scotland

The impact of conifer afforestation on stream-water chemistry was investigated in the acidified catchment of Loch Dee, SW Scotland. Long-term trends in stream-water chemistry were evaluated during a period of forest growth from age 6 to 17 years. A significant increase was observed for pH (0.2 units) and a significant decline for aluminium (0.05 mg litre(-1)), sulphate (1.2 mg litre(-1)) and nitrate (0.02 mg litre(-1)) concentrations. The long-term decrease in stream-water acidity was ascribed to the marked reductions in sulphur depositions during the 1970s and early 1980s. There was no evidence that this response had been attenuated by afforestation, the improvements in stream-water chemistry being of a similar magnitude to those recorded in nearby moorland lochs and exceeding that in an adjacent moorland-catchment stream. The lack of a clear forest acidification effect is consistent with deposition-model estimates which show the increased scavenging of occult and dry deposition by the growing forest to be small at this site (相似文献   

Changes in the atmospheric deposition of acidifying compounds in the UK between 1986 and 2001

Emissions of a precursor of acidity in precipitation, sulphur dioxide (SO2), declined in the UK and the EU (15) by 71% and 72%, respectively, between 1986 and 2001, while nitrous oxide emissions declined by about 40%. Acidity in UK precipitation and the deposition of sulphate in precipitation halved during this period, but reductions were larger in the English Midlands than at the west coast and in high rainfall areas (>2000 mm). There is evidence that the smaller reductions in sulphur deposition in the west and south are due in part to shipping sources of SO2. Reductions in sulphur dry deposition (74%) are larger than in wet deposition (45%), due to changes in the canopy resistance to dry deposition. For reduced nitrogen, there has been a small (10%) reduction in emissions and deposition, while for oxidized nitrogen, a substantial reduction in emissions (40%) occurred but wet deposition of nitrate changed by less than 10%.     

Effect of different radiotracer labelling techniques on radionuclide excretion from marine organisms

Experiments were designed to assess the effect of different techniques of radiotracer labelling on subsequent radioisotope excretion rates in marine crustaceans. A small amphipod (Gammarus locusta) that accumulated ⁶⁵Zn under a close approximation of natural conditions excreted the radiotracer during a 3-month period at a markedly different rate than those of comparable amphipods labelled with ⁶⁵Zn in the laboratory via different combinations of radioactive food and seawater. Shrimp (Lysmata seticauda) administered ⁶⁵Zn by three different methods in the laboratory displayed different excretion kinetics during the first 2 months of loss. The difference between excretion rates most likely was a reflection of the degree to which the various zinc pools within the shrimp had equilibrated with the radiotracer. During the next several months all ⁶⁵Zn loss rates were quite similar, probably indicating that radiotracer excretion was taking place from similar zinc pools within the shrimp. The importance of adequate radiotracer labelling techniques as well as proper design of subsequent excretion experiments, used to gain reliable information on flux rates of the corresponding stable metal, is discussed. It is concluded that laboratory radiotracer experiments which are intended to supply information on actual situations in the sea require careful design and execution.     

Factors affecting methyl and inorganic mercury dynamics in mussels and shrimp

Radiotracer experiments were designed to study the effect of certain factors on the accumulation and loss of methyl and inorganic mercury in mussels (Mytilus galloprovincialis) and benthic shrimp (Lysmata seticaudata). Methyl mercury was accumulated from both food and water to a greater degree than inorganic mercury by both species. There was a tendency for small mussels to concentrate more mercury than larger individuals, but the reason for this difference remains unclear. A trend towards greater mercury accumulation at higher temperatures was noted for mussels, but the temperature effect was relatively small over a 10 C^o range between 8° and 19°C. Methyl mercury residues were eliminated by both species more slowly than those of the inorganic form. Loss from mussels was somewhat more rapid at higher temperatures; however, as in the case of accumulation, the effect of temperature was relatively small. Loss rates for small mussels were not significantly different from those for large individuals. Enhanced methyl mercury elimination was noted for the group of mussels maintained in their natural environment. The more rapid metal turnover in these individuals compared with mussels held in the laboratory was attributed to differences in the availability of natural particulate food matter and, hence, subsequent growth of the animals in the two experimental systems. The observed differences underscore the need for caution in predicting in situ flux of metals such as mercury in certain species based solely on data derived from laboratory experiments.     

A pest is a pest is a pest? The dilemma of neotropical leaf-cutting ants: Keystone taxa of natural ecosystems

Leaf-cutting ants of the generaAcromyrmex andAtta are considered the principal polyphagous pests of the Neotropics Although some members of these genera are of economic importance, have a broad geographic distribution, and are extremely good colonizers, others are endemic and closely interact with native ecosystems. Control is generally practiced against any colony, irrespective of its taxonomic status. Indiscriminate control coupled with habitat destruction threatens endemic species with extinction, and, through habitat simplification, favors other pest species. As nests ofAtta are large, having several square meters of nest surface, the endemic taxa can be easily used as environmental indicators for natural ecosystems Likewise, the pest species can be used to detect environmental disturbance As these ants are keystone species and easily identified by nonspecialists, efforts should be made to integrate these into viable conservation programs     

大气腐蚀试验标准中相对湿度和温度控制的考虑

<正>在本文中,我们将讨论操作腐蚀试验箱的实验室工程师和研究员提出的众多问题:如何测量和控制这些试验箱中的相对湿度和温度。腐蚀试验标准中对相对湿度测量和控制的描述不具体,甚至某些时候是错误的,导致试验者产生了很大的困惑。设备制造商已经使用了各种各样的测量技术,每种测量技术代表对标准的一种合理解释,但是它们相互之间产生的结果不尽相同。除了这些困惑外,对相对湿度控制的需求和人们所期望的现代测试标准同样不明确。最后,实验室条件     

Atmospheric composition change: Climate–Chemistry interactions

Chemically active climate compounds are either primary compounds like methane (CH₄), removed by oxidation in the atmosphere, or secondary compounds like ozone (O₃), sulfate and organic aerosols, both formed and removed in the atmosphere. Man-induced climate–chemistry interaction is a two-way process: Emissions of pollutants change the atmospheric composition contributing to climate change through the aforementioned climate components, and climate change, through changes in temperature, dynamics, the hydrological cycle, atmospheric stability, and biosphere-atmosphere interactions, affects the atmospheric composition and oxidation processes in the troposphere. Here we present progress in our understanding of processes of importance for climate–chemistry interactions, and their contributions to changes in atmospheric composition and climate forcing. A key factor is the oxidation potential involving compounds like O₃ and the hydroxyl radical (OH). Reported studies represent both current and future changes. Reported results include new estimates of radiative forcing based on extensive model studies of chemically active climate compounds like O₃, and of particles inducing both direct and indirect effects. Through EU projects like ACCENT, QUANTIFY, and the AeroCom project, extensive studies on regional and sector-wise differences in the impact on atmospheric distribution are performed. Studies have shown that land-based emissions have a different effect on climate than ship and aircraft emissions, and different measures are needed to reduce the climate impact. Several areas where climate change can affect the tropospheric oxidation process and the chemical composition are identified. This can take place through enhanced stratospheric–tropospheric exchange of ozone, more frequent periods with stable conditions favoring pollution build up over industrial areas, enhanced temperature induced biogenic emissions, methane releases from permafrost thawing, and enhanced concentration through reduced biospheric uptake. During the last 5–10 years, new observational data have been made available and used for model validation and the study of atmospheric processes. Although there are significant uncertainties in the modeling of composition changes, access to new observational data has improved modeling capability. Emission scenarios for the coming decades have a large uncertainty range, in particular with respect to regional trends, leading to a significant uncertainty range in estimated regional composition changes and climate impact.     

210Po in the marine environment with emphasis on its behaviour within the biosphere

The distribution and behaviour of the natural-series alpha-emitter polonium-210 in the marine environment has been under study for many years primarily due to its enhanced bioaccumulation, its strong affinity for binding with certain internal tissues, and its importance as a contributor to the natural radiation dose received by marine biota as well as humans consuming seafoods. Results from studies spanning nearly 5 decades show that ²¹⁰Po concentrations in organisms vary widely among the different phylogenic groups as well as between the different tissues of a given species. Such variation results in ²¹⁰Po concentration factors ranging from approximately 10³ to over 10⁶ depending upon the organism or tissue considered. ²¹⁰Po/²¹⁰Pb ratios in marine species are generally greater than unity and tend to increase up the food chain indicating that ²¹⁰Po is preferentially taken up by organisms compared to its progenitor ²¹⁰Pb. The effective transfer of ²¹⁰Po up the food chain is primarily due to the high degree of assimilation of the radionuclide from ingested food and its subsequent strong retention in the organisms. In some cases this mechanism may lead to an apparent biomagnification of ²¹⁰Po at the higher trophic level. Various pelagic species release ²¹⁰Po and ²¹⁰Pb packaged in organic biodetrital particles that sink and remove these radionuclides from the upper water column, a biogeochemical process which, coupled with scavenging rates of this radionuclide pair, is being examined as a possible proxy for estimating downward organic carbon fluxes in the sea. Data related to preferential bioaccumulation in various organisms, their tissues, resultant radiation doses to these species, and the processes by which ²¹⁰Po is transferred and recycled through the food web are discussed. In addition, the main gaps in our present knowledge and proposed areas for future studies on the biogeochemical behaviour of ²¹⁰Po and its use as a tracer of oceanographic processes are highlighted in this review.     

Nitrogen deposition threatens species richness of grasslands across Europe

Evidence from an international survey in the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is reducing plant species richness in acid grasslands. Across the deposition gradient in this region (2-44 kg N ha⁻¹ yr⁻¹) species richness showed a curvilinear response, with greatest reductions in species richness when deposition increased from low levels. This has important implications for conservation policies, suggesting that to protect the most sensitive grasslands resources should be focussed where deposition is currently low. Soil pH is also an important driver of species richness indicating that the acidifying effect of nitrogen deposition may be contributing to species richness reductions. The results of this survey suggest that the impacts of nitrogen deposition can be observed over a large geographical range.     

Enhancing Reductive Dechlorination With Nutrient Addition

Enhanced reductive bioremediation (ERB) of halogenated organics has become widely accepted and implemented to reduce risks to human health and the environment posed by these compounds. The family of chlorinated ethenes (e.g., trichloroethene) is among the most common contaminants treated using ERB techniques. The number of microbial species able to fully dechlorinate ethenes is small, and many times their population numbers are low. As a result, many ERB practitioners have turned to the injection of designer bacteria within treatment zones as a means to accelerate the process. Otherwise, many remediation projects encounter “cis‐stall,'' or the accumulation of the cis‐1,2‐dichloroethene and vinyl chloride intermediates. This article discusses three unique case studies where the addition of a balanced macro‐ and micro‐nutrient source substantially accelerated the chlorinated ethene ERB process, independent of the electron‐donor substrate applied. © 2013 Wiley Periodicals, Inc.