摘要:

Insects and other related arthropods make up about 90% of all plant and animal species in the world. They are vital to the functioning of the ecosystem and biosphere, and neither of these systems can operate effectively without insect interactions. Because of their major ecological and economic roles in nature and society, the beneficial and pest activities of insects need to be clearly understood. Insect populations are being stressed directly by the action of temperature, moisture, and a wide array of chemical Ö öpollutants (pesticides, fertilizers, air pollutants, and numerous other chemicals) that are dispersed through air, water, and soil. Insects are affected by this same group of stresses indirectly, through their food plants, parasites, and predators. Depending on the species and the particular stress affecting it, insect populations respond by increasing or decreasing in numbers. The responses of insect populations to various direct and indirect environmental stresses and chemical pollutants are assessed. Some insect populations increase, while others decline. The responses were determined by the particular environmental stress, the insect species, and the stage at which they were exposed to the stress.Key words: insects, environment, pollutants, stress, water, herbicides.

ISSN:1208-6053    

DOI:10.1139/a94-001

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Evidence is reviewed, linking physical oceanographic processes in the marine environment to changes in fish and shellfish stocks in the Northwest Atlantic. A case history study of the cod (Gadus morhua) stock of the northern Grand Banks and Labrador Shelf indicates a long slow amelioration of the environment between about 1945 and 1965, followed by a deterioration in the period 1965–1992. The most important environmental factors for the cod stocks appear to have been salinity and temperature. The trends can be traced back to climatic factors involving the Icelandic Low and the Azores–Bermuda High. When the atmospheric pressure difference in winter tended to be high, there was a progressive increase in the area of sea ice off Labrador and in the volume of cold water at depth. These factors have been shown to affect temperature and salinity conditions on the Grand Banks in spring and summer and are associated with poor growth and recruitment in the cod stocks. A similar case study of lobster (Homarus americanus) stocks indicates that temperature and river discharge are important environmental correlates, but neither can be shown to fully account for the recent trends in the stocks. Evidence is reviewed to show that physical environmental processes also influence recruitment and distribution of stocks of haddock, capelin, and squid. Some of the problems with correlational analysis are also discussed. It is recognized that factors other than the environment are influencing the stocks. Fishing mortality (detailed consideration of which is not included in this review) has clearly been important. Interactions between environmental factors and fishing mortality are probably of major importance.Key words: ocean environment, fish production, recruitment, northern cod, American lobster.

ISSN:1208-6053    

DOI:10.1139/a94-002

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The Canadian forest industries are based on the extensive harvesting and management of forests, with attendant effects on biodiversity at all levels of organization. In large part, conflicts between forestry and biodiversity occur because lands that are harvested and managed are mostly natural and seminatural ecosystems. Prior to being affected by forestry, such lands provided habitat for native species of wild life and their communities. Some of these elements of biodiversity may not find silvicultural habitats, especially plantations, to be suitable to their needs. In addition, the longer term integrity of some natural ecosystems, for example old-growth forests, is not compatible with any but the softest types of exploitation and management. This report discusses interactions of forestry and biodiversity at three levels of organization: (i) genetic variation within populations and species; (ii) the richness of species within communities; and (iii) the richness of community types on the landscape. A broader conclusion of our report is the following: If forestry systems of harvesting and management are to be practised in an ecologically sustainable fashion, then all elements of biodiversity must be accommodated within a landscape comprised of an integration of working lands and ecological reserves. The spatial scale of this integration could be various, ranging from large watersheds, to the "woodsheds" of particular industrial facilities, to provincial and national areas. Therefore, resolution of the substantial conflicts between biodiversity and forestry requires the design of ecologically sustainable landscapes that can provide a flow of timber and other valuated forest products, while still sustaining natural biodiversity resources.Key words: forest management, biodiversity, ecological reserves, eastern Canada, harvesting practices, old growth.

ISSN:1208-6053    

DOI:10.1139/a94-003

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Past and recent changes in the position of the arctic tree line and spatial structure of nearby forests are reviewed. The advancing tree line in the arctic tundra in the first half of the Holocene was promoted by sexual regeneration because of warmer climate. The northernmost tree-line positions were reached in early Holocene in western North America and northern Eurasia, and during or after mid-Holocene in central and eastern North America. The position of the arctic tree line remained rather stable across the northern hemisphere from 3500 years BP to the present. General cooling during the late Holocene did not induce significant retreat of the tree line at sites not affected by catastrophic disturbances (fire) because trees and forests were able to survive through vegetative regeneration. Minor displacements deduced from dendroecological data were recorded during the last 500 years, whereas more important structural changes occurred in the nearby northernmost forests and tree groves through the shifting dominance of growth forms in preestablished tree and forest populations. The spatiotemporal pattern of tree-line and forest changes along the arctic border suggests that both equilibrium and nonequilibrium conditions prevailed during the Holocene.Key words: tree line, Arctic, climate change, paleoecology, Holocene.

ISSN:1208-6053    

DOI:10.1139/a94-004

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This review was conducted to evaluate the potential hazards associated with releases of cadmium (Cd) into the Canadian environment. The hazard assessment consists of three elements: a focused review of the available data on the toxicology of Cd in various environmental media, a review of the available information on the concentrations of Cd in the Canadian environment, and a comparison of these data. Based on the review of the toxicological literature, the following lowest observed effect concentrations (LOECs) of Cd were identified for the most sensitive species: 0.17 μg∙L−1in freshwater at a hardness of 48.5 mg∙L−1, 3.5 mg∙kg dry weight (DW)−1in freshwater sediments, 1.2 μg∙L−1in marine waters, 4.2 mg∙kg DW−1in marine sediments, and, 2.0 mg∙kg DW−1in soil. The freshwater LOEC was adjusted for hardness by a regression equation, so that LOECs could be estimated for waters of varying hardnesses; these LOECs ranged from 0.004 μg∙L−1at a hardness of 1 mg∙L−1to 0.99 μg∙L−1at a hardness of 300 mg∙L−1. Critical tissue concentrations (CTCs) in kidneys of 100 mg∙kg fresh weight (FW)−1for birds and 30 mg∙kg FW−1for mammals were also identified. Comparison of the empirically derived LOECs and CTCs with concentrations of Cd in Canadian ecosystems suggested that sensitive biota in the following environments may be adversely affected in some locations: surface freshwaters, freshwater and marine sediments, and soils. Some marine mammals, ungulates, and domestic horses are also at risk because of high renal Cd concentrations. The LOECs were exceeded most seriously in the vicinity of base metal smelters, indicating that these smelters represent significant hazards to local aquatic and terrestrial biota. In parts of Ontario, catchment acidification and deposition of aeolian Cd, presumably from other industrial sources, also appear to contribute to elevated Cd concentrations in freshwater systems. The extent and severity of contamination suggest that Cd is a significant threat to the integrity of Canadian ecosystems.Key words: cadmium, Canada, toxicology, contamina

ISSN:1208-6053    

DOI:10.1139/a94-005

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Heavy metals in sewage sludges accumulate in soils after successive sludge applications and can be toxic to plants, soil organisms, as well as humans and animals along the food chain. Because of this potential threat, many countries have set limits to the additions of metals in sludges to agricultural land, based on (i) the concentrations of metals in sludge itself, (ii) the loading, or total amount, of metal that can be added and often how quickly this can be applied, and (iii) the maximum concentrations of metals in soil which are allowed to build up after sludge applications. This review, based on regulations in the United States and some west European countries, shows that at present three basic approaches to setting limits can be distinguished: (i) a comprehensive analysis of the pathways of pollutant transfer to selected target organisms and an assessment of the likely harmful effects that metals may have on the target; (ii) setting limits consistent with the lowest observed adverse effect concentrations, which are actual cases of effects due to metals, but not necessarily derived from studies that involved land application of sewage sludge; and (iii) attempting to match the metal inputs to soil to the small losses of metals due to crop removal, soil erosion, and leaching ("metal balance approach"). These approaches are shown to result in widely different numerical limits being set for the same constituent, which is creating unease among the regulatory authorities worldwide. These differences appear to arise from at least two main sources. The first is whether, by a policy decision, zero impact is desired. This leads to very low limits, and is the philosophy behind the metal balance approach. The second is that those approaches that allow some increase in metal concentrations in soils often adopt different target organisms and these models suffer from the limited supply of relevant toxicity data, particularly information obtained from metals applied in sewage sludge. Differences in the philosophy behind environmental protection and in the choices of which organisms to protect explain the different metal limits for sewage sludge which have been adopted in the countries examined.Key words: zinc, cadmium, copper, chromium, nickel, lead, mercury, soil microbes, ecotoxicology, soil protection.

ISSN:1208-6053    

DOI:10.1139/a94-006

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:1208-6053    

DOI:10.1139/a94-007

出版商:NRC Research Press    

年代:1994

数据来源: NRC