摘要:

The common loon remains remarkably anonymous and biologically little-known during its winter season. A major portion of the breeding population winters off coasts of the United States: Atlantic, Gulf, and Pacific. Adult common loons are flightless for a few weeks in midwinter during a simultaneous molt of their wing feathers. This apparently makes loons especially sensitive to environmental disturbance, because they are among the most commonly recorded dead and dying birds on coastal beaches from winter through spring. Loons' large size, slowness to die, and tendency to beach themselves as a last resort also render their mortality more visible. Contributing causes of mortality include storms, food limitation, entanglement in fishing nets, oil, and possibly, other toxic substances. Occasional, unpredictable die-offs of many hundreds (1993) or even thousands (1983) of emaciated loons have occurred in southeastern U.S. waters. Loons offer a prime opportunity for study of this unexplained marine mortality. In the 1980s, neurotoxic bioaccumulated mercury was hypothesized as a cause of mass mortality, but data on the mercury and selenium loading of loons and other long-lived marine carnivores, and on the marine mortality patterns of loons and other seabirds, indicate that mercury is not the cause. Algal neurotoxins in marine food chains have caused some seabird die-offs and are one useful hypothesis for future research. Interdisciplinary study of unusual seabird mortality events can provide a major paradigm for the study of marine environmental health.Key words: common loon, mortality, mercury, biotoxin, bioindicator, marine environment.

ISSN:1208-6053    

DOI:10.1139/a95-011

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Questions about the compatibility of forest harvesting practices and conservation of biological diversity are largely driven by concerns that habitat quality for many species may be degraded in intensively managed forest landscapes. We review the literature on relationships between common forest harvesting practices and the distribution and abundance of amphibians, a group that has attracted considerable attention in recent years because of their potential ecological importance in forest ecosystems and because of reports of widespread population declines. Clear-cut harvesting generally has negative short-term impacts on local amphibian populations, especially salamanders. An analysis of the results of 18 studies that examined the effects of clear-cutting on amphibians yielded a 3.5-fold median difference in abundance of amphibians on controls over clear-cuts. However, research on the influence of forest age suggests that the long-term effects of forest harvesting on amphibians are variable, and for many species these effects can be mitigated if regeneration practices leave adequate microhabitat structure intact. In contrast, long-term effects can be significant in forest plantations, which are often associated with intensive site preparations and stand management practices that modify levels of coarse woody debris and other microhabitats. Other forest practices reviewed for their effect on amphibians include prescribed fire, logging roads, and streamside harvesting. We discuss problems commonly encountered in the experimental design and measurement of forest amphibian populations, including a notable lack of pretreatment data, and outline several aspects of amphibian–forestry relationships in need of further research. Management recommendations relevant to conserving upland and riparian zone amphibian habitat during forest harvesting are offered.Key words: amphibians, clear-cutting, coarse woody debris, forest management, logging roads, plantations, prescribed fire, riparian, succession.

ISSN:1208-6053    

DOI:10.1139/a95-012

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The elasticity (nutrient storage, litter decomposition, bioturbation of soil) and diversity of central European forest ecosystems has been reduced by centuries of overutilization. Since the middle of the nineteenth century, their development has been influenced by silvicultural measures, as well as by the deposition of acids and nutrients, especially nitrogen from anthropogenic sources, i.e., by a mixture of stabilizing and destabilizing external influences. During recent decades, most forest soils have been acidified by acid deposition resulting in low levels of nutrient cations and negative alkalinity in the soil solution. Widespread acute acidification of soil in the rooting zone is indicated by extremely high manganese (Mn) contents in leaves (fingerprint). Soil acidification has caused drastic losses of fine roots in subsoil, indicated by denuded structural root systems where adventitious fine root complexes exist only sporadically. Research at the organ (leaf, fine root, mycorrhiza) and cellular levels has provided much information on the effects of air pollutants and soil acidification on leaves and roots. There are considerable uncertainties, however, as to how changes in the status of leaves or roots are processed within the tree and ecosystem from one level of hierarchy to the next on an increasing spatial and time scale, and how these lead to decline symptoms like crown thinning, stand opening (as a consequence of dieback or perturbations), and changes in species composition (soil biota, ground vegetation, tree regeneration). At the tree level, nutrient imbalances (due to cation losses from soil, changes in the acid/base status of the soil, proton buffering in leaves, and N deposition), as well as disturbances in the transport system of assimilates and water, are suspected of causing the decline symptoms. Information on the filtering mechanisms at various hierarchical levels, especially in the case of a break in the hierarchy, is missing. The null hypothesis (no effects of air pollutants on forest ecosystems) can be considered to be falsified. Forest ecosystems are in transition. The current state of knowledge is not sufficient to define precisely the final state that will be reached, given continuously changing environmental conditions and human impacts. The hypothesis, however, of large-scale forest dieback in the near future is not backed by data and can be discarded.Key words: forest ecosystem, process hierarchy, air pollution, deposition, acidity, nitrogen.

ISSN:1208-6053    

DOI:10.1139/a95-013

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Forest managers faced with incorporating the maintenance of biodiversity into their analyses, plans, and decisions need reliable, quantitative measures of biodiversity. This paper reviews and critiques quantitative approaches that have been developed to measure the three basic attributes of diversity: species richness, heterogeneity, and evenness. These approaches are discussed in terms of application to fine- and large-scale land areas. The advantages and disadvantages of each measure are described relative to forest management. Habitat modeling, which combines aspects of both fine- and landscape-scale analysis, may hold the greatest potential for monitoring forest-level diversity in ways that are meaningful, measurable, and manageable.Key words: biodiversity, quantitative indices, forest management.

ISSN:1208-6053    

DOI:10.1139/a95-014

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Production forestry in peatlands, associated with drainage, is a controversial but widely applied forestry practice, especially in northern Europe. This paper aims to provide a synthesis of the ecological effects of forest drainage. Effects of the hydrological change, brought about by drainage on the chemical and physical properties of the surface peat, microbial activity, tree stand and ground vegetation, biodiversity, and faunal change, are reviewed. Finally, the role of forestry use of northern peatlands in the global climatic warming is synthesized.Key words: biodiversity, environmental impacts, forest drainage, global change, peatland hydrology.

ISSN:1208-6053    

DOI:10.1139/a95-015

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Owing to various human activities, arsenic (As) concentrations have increased in lakes and other aquatic ecosystems around the world. This increase of As concentrations has become a concern because of the known toxic, carcinogenic, mutagenic, and teratogenic effects of As on ecosystem organisms and humans. Understanding the biogeochemistry of As in the aquatic environment is therefore a topic of fundamental interest. This study presents a review of the major biogeochemical processes controlling the concentration of solid and dissolved As in freshwater lakes. These processes are dynamic and vary both temporally and spatially because of a complex relationship between microbial activity and various geochemical processes. Particularly the oxidation of As sulphides and the reduction of Fe and Mn oxyhydroxides at the sediment–water interface play an important role in the mobilization of As. These and other interactions among the various biogeochemical processes are synthesized in a conceptual model of As mobility in lakes.Key words: arsenic cycling, biogeochemistry, freshwater lakes.

ISSN:1208-6053    

DOI:10.1139/a95-016

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Waste water from Mexico City metropolitan area has been used to irrigate the Mezquital Valley since 1912. This zone is nowadays the largest area under this situation. Mexico City's drainage is a water mixture emanating from different sources: household, industries, commerce, rain, and runoff. Waste waters used in the valley have greatly increased crop yields. Owing to the increase in the country's industrial development, since the seventies several studies have been carried out in this area, especially related to metal content in water, soils, and crops. The aim of this paper is to present a bibliographical review of the effects of Mexico City's waste water land application on soil fertility and heavy metal accumulation. Pb, Cd, Cu, and Zn levels in soils and crops at present do not represent risks, but there is a clear tendency for these metals to accumulate in the upper layers of soils. Salt content in waste water is intensifying soil salinization in impeded drainage areas. The local conditions of soil, such as high levels of organic matter and high pH values, seem to be preventing the solubility of heavy metals, and hence their transportation or absorption by crops.Key words: heavy metals, waste water irrigation, Mexico City, nutrients, environment, pollutants.

ISSN:1208-6053    

DOI:10.1139/a95-017

出版商:NRC Research Press    

年代:1995

数据来源: NRC