摘要:

The recent spread of air pollution, particularly sulphur dioxide, throughout Europe and elsewhere over the past 200 years is accurately reflected by the decline of lichens. Lichens have proved highly versatile for monitoring not only increasing but also decreasing levels of air pollution in general and, more recently, qualitative differences brought about by changes in energy policies, clean air legislation, and agricultural practices. The use of lichens as biological monitors of sulphur dioxide pollution over the past 150 years is reviewed, and techniques such as zonal mapping, pollution indexes, monitoring scales, and modelling are covered to demonstrate their effectiveness in air quality surveillance, often over wide geographical areas, where physicochemical equipment is often inadequate or indeed nonexistent.Key words: lichens, air pollution, sulphur dioxide, field studies.

ISSN:1208-6053    

DOI:10.1139/a93-007

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Mortality of aquatic birds occurs regularly as a consequence of spills of petroleum oils. There are three different ways in which such oils can affect birds. (i) External contamination of feathers is the most common form of exposure, and the effect of oils on feathers is the single most devastating effect of oil on birds. Feathers absorb oil, become matted, and lose the critical properties of water repellency, insulation, and flight. Death results from combinations of hypothermia, starvation, and drowning. (ii) Avian embryos are highly sensitive to oil that contaminates the egg shell; amounts as little as 1–10 μL are lethal to embryos during the first half of incubation. (iii) Birds ingest oil when preening oiled plumage or ingesting oiled nutrients. At least three toxic effects of ingested oil are well documented: a nonspecific response as a stressor that is additive or synergistic with those of other stressors, impairments in reproduction ranging from lowered fertility to abandonment of reproductive effort, and severe oxidant damage to red blood cells. The effect of oil pollution on bird populations is very difficult to document and is likely to remain uncertain because of the many ecological factors that may occur in association with an oil-spill event.Key words: oil, petroleum, pollution, bird, toxicity, poison.

ISSN:1208-6053    

DOI:10.1139/a93-008

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The inputs of industrial wastes have changed the levels and forms of chromium in many lakes, and there is growing concern about the accumulation of Cr(VI), a known carcinogen, in drinking water supplies. This report provides a critical review of the effects of speciation, transformations, and solubility on the cycling of chromium in lacustrine environments. Unique features of chromium dynamics associated with the decoupling of redox-driven chromium cycle from those of iron and manganese at the sediment–water and air–water interfaces are highlighted. Reductive precipitation is important in the immobilization of pollutant chromium in sediments. Photooxidative dissolution of Cr(III) especially at the air–water interface is identified as a key area for further research. The available database is inadequate for establishing any linkages between the chromium and biological cycles in lakes.Key words: chromium, lakes, cycling, speciation, redox, geochemistry.

ISSN:1208-6053    

DOI:10.1139/a93-009

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Clear-cutting is a controversial practice that is widely applied in forests managed for wood production in many parts of the world. This paper aims to provide an objective synthesis of the ecological effects of clear-cutting as a basis for more informed discussion of its merits and disadvantages. A definition of clear-cutting is put forward, and its place in modern productive forestry is described. Effects on microclimate, water, soil, nutrient cycling, and the diversity and composition of plant and animal species are reviewed. The effects of clear-cutting vary considerably depending on site conditions (such as climate, geology, and topography) and on the structure and composition of the forest, the extent and distribution of harvesting, the method used to extract the logs, and the length of time before the forest is removed again. However, it is evident that many of the ecological impacts commonly ascribed to clear-cutting, in fact, result from other stages of the wood-production process, such as the quality and intensity of roading, site preparation practices (such as mechanical disturbance or slash burning), and the intensity of control of noncrop vegetation. Situations where clear-cutting is inappropriate are described. It is argued that in the right situations, with appropriate safeguards, it is an environmentally sound practice that offers many advantages in terms of the production of wood fibre.Key words: clear-cutting, environmental impacts, microclimate, hydrology, soil, forest production, nutrient cycling, wildlife.

ISSN:1208-6053    

DOI:10.1139/a93-010

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Critical loads are used in the assessment of air pollution and regulation of the causative emissions to prevent or mitigate ecological damage. We critically review four mass balance methods for calculating critical loads for nitrogen deposition: the steady-state water chemistry method, the nitrogen mass balance method, the basic cation mass balance method, and the steady-state mass balance method. The critical loads may be calculated with respect to effects of acidification associated with nitrate leaching or effects of elevated nitrogen such as eutrophication, excess nitrate loss, and nutrient imbalances. The most useful method for calculating the critical load for nitrogen with respect to effects of elevated atmospheric deposition of nitrogen is the nitrogen mass balance method. The steady-state water chemistry method can be readily applied for regional-scale calculations because it requires only water chemistry data from synoptic surveys of surface waters and does not explicitly consider biogeochemical processes. Both of the other approaches are severely limited by lack of quantitative information on rates of mineral weathering. If weathering data were available, the steady-state mass balance method could be more effectively used to assess critical loads with respect to acidification. Similarly, the basic cation mass balance method could be used to calculate critical loads for both acidity and elevated nitrogen effects. Because of the complexity of the nitrogen cycle, it is not possible to obtain a single critical load for the whole ecosystem. Rather, one should analyze and synthesize several values of critical loads that reflect different components of the ecosystem and different ecological effects of elevated nitrogen deposition (e.g., acidification and eutrophication effects).Key words: atmospheric deposition of nitrogen, acidification, critical loads, nitrogen cycling.

ISSN:1208-6053    

DOI:10.1139/a93-011

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Watershed liming has been proposed to mitigate lake acidification and depletion of soil base cations. This paper reviews and synthesizes literature describing the effects of liming on natural terrestrial ecosystems, with a specific emphasis on watershed liming studies. Specifically, we look at the purpose of liming, types of lime, physiological role of calcium, lime effects on soil and belowground processes, and plant response to liming with special attention to growth and tissue chemistry, roots, and plant–plant interactions. Liming increases soil pH and either increases or decreases soil nutrient availability. Liming affects litter decomposition, mineral soil processes, root growth, plant nutrient uptake, and plant productivity. Interspecific plant interactions can be affected after liming. Specific soil and biotic responses depend upon the type and amount of lime applied, the period of observation, soil characteristics, and species composition.Key words: watershed liming, CaCO3, calcite, dolomite, calcium, ecosystem response to liming, wetland liming, forest liming, nutrient availability, soil acidity.

ISSN:1208-6053    

DOI:10.1139/a93-012

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The tissues of wild mammals and birds from uncontaminated environments generally contain from ~0.1 to 5 μg nickel∙g dry weight−1, whereas in Ni-polluted environments, tissues accumulate from -0.5 to 10 (mammals) and -0.5 to 80 (birds) μg nickel∙g dry weight−1. The highest concentrations in these ranges are usually associated with tissues directly exposed to the external environment (fur, feathers, skin). Bone frequently contains higher Ni concentrations than other internal tissues. Ni concentrations in the most commonly analysed internal organs (liver, kidneys) range from nondetectable to about 3 μg∙g dry weight−1, the kidneys often containing higher concentrations than the liver. There is some evidence that birds may tend to accumulate higher Ni burdens in polluted habitats than do mammals. For mammals, reduced growth and survival occur in response to chronic exposure to 500–2500 μg Ni∙g diet−1(10–50 mg∙kg body weight−1∙d−1). Effects on reproduction and essential trace metal (especially iron) metabolism have been reported at levels as low as 5 μg∙g−1in food or drinking water (0.2–0.4 mg∙kg body weight−1∙d−1), but these findings have not always been corroborated. Toxicological data on birds are more limited than those pertaining to mammals. Newly hatched chickens suffered reduced growth rates when fed ≥300 μg∙g diet−1, and chicks began to die when fed diets containing ≥500 μg∙g−1. In newly hatched mallard ducklings, chronic exposure to ≥800 μg∙g diet−1resulted in ataxia, tremors, and significant mortality, whereas adult mallards fed 800 μg∙g−1showed no evidence of systemic or reproductive toxicity. Tissue concentrations of Ni were not reliable indicators of potential toxicity in either mammals or birds, because significant effects, including mortality, frequently occurred in the absence of elevated tissue Ni concentrations. However, when there is evidence of elevated tissue Ni concentrations (>10 μg∙g−1in the kidneys, and (or) >3 μg∙g−1dry weight in the liver), Ni exposure sufficient to cause significant toxic effects should be suspected. Nickel has been reported in aquatic macrophytes and lower plants (but not in invertebrates or zooplankton) in the vicinity of Ni smelters in Canada in concentrations that approach or exceed dietary levels known to cause adverse effects in young animals. Sensitive species of wildlife ingesting this vegetation for considerable periods of time could experience Ni-related toxicity. In addition, wildlife food chains involving aquatic organisms (plants, invertebrates, fish) risk alterations in community structure in Ni-contaminated environments as Ni-sensitive taxa are eliminated or their abundance is reduced.Key words:

ISSN:1208-6053    

DOI:10.1139/a93-013

出版商:NRC Research Press    

年代:1993

数据来源: NRC