Ecosystems In Canada Research Articles

Pelagic fish outburst or suprabenthic habitat occupation: legacy of the Atlantic cod (Gadus morhua) collapse in eastern Canada

The use of bottom-trawl research survey data to estimate population trends for small pelagic fishes, despite the extremely low selectivity of this gear for these species, has created the impression of a pelagic fish outburst along eastern Canada in the 1990s as a top-down response resulting from the demise of the Atlantic cod ( Gadus morhua ) and other groundfish. Using Atlantic herring ( Clupea harengus ) population assessments, fisheries statistics, and an acoustic database, as well as grey seal (Halichoerus grypus) diet studies, I demonstrate that contrary to a pelagic outburst, pelagic catches in research bottom trawls increased in several eastern Canadian ecosystems as these species increasingly occupied the suprabenthic habitat vacated by their diminishing groundfish predators. Although several herring populations were actually decreasing in abundance, bottom-trawl indices (BTIs) were dramatically increasing as their availability to research bottom-trawl surveys increased. Studies using BTIs have systematically underestimated pelagic fish abundances before the cod decline and therefore have dramatically overestimated their importance since, seriously biasing our view of the past and present state of many Canadian east coast ecosystems.

Modelling the impacts of ammonia emissions reductions on North American air quality

Abstract. A unified regional air-quality modelling system (AURAMS) was used to investigate the effects of reductions in ammonia emissions on regional air quality, with a focus on particulate-matter formation. Three simulations of one-year duration were performed for a North American domain: (1) a base-case simulation using 2002 Canadian and US national emissions inventories augmented by a more detailed Canadian emissions inventory for agricultural ammonia; (2) a 30% North-American-wide reduction in agricultural ammonia emissions; and (3) a 50% reduction in Canadian beef-cattle ammonia emissions. The simulations show that a 30% continent-wide reduction in agricultural ammonia emissions lead to reductions in median hourly PM2.5 mass of <1 μg m−3 on an annual basis. The atmospheric response to these emission reductions displays marked seasonal variations, and on even shorter time scales, the impacts of the emissions reductions are highly episodic: 95th-percentile hourly PM2.5 mass decreases can be up to a factor of six larger than the median values. A key finding of the modelling work is the linkage between gas and aqueous chemistry and transport; reductions in ammonia emissions affect gaseous ammonia concentrations close to the emissions site, but substantial impacts on particulate matter and atmospheric deposition often occur at considerable distances downwind, with particle nitrate being the main vector of ammonia/um transport. Ammonia emissions reductions therefore have trans-boundary consequences downwind. Calculations of critical-load exceedances for sensitive ecosystems in Canada suggest that ammonia emission reductions will have a minimal impact on current ecosystem acidification within Canada, but may have a substantial impact on future ecosystem acidification. The 50% Canadian beef-cattle ammonia emissions reduction scenario was used to examine model sensitivity to uncertainties in the new Canadian agricultural ammonia emissions inventory, and the simulation results suggest that further work is needed to improve the emissions inventory for this particular sector. It should be noted that the model in its current form neglects coarse mode base cation chemistry, so the predicted effects of ammonia emissions reductions shown here should be considered upper limits.

Characterizing the forest fragmentation of Canada’s national parks

Characterizing the amount and configuration of forests can provide insights into habitat quality, biodiversity, and land use. The establishment of protected areas can be a mechanism for maintaining large, contiguous areas of forests, and the loss and fragmentation of forest habitat is a potential threat to Canada's national park system. Using the Earth Observation for Sustainable Development of Forests (EOSD) land cover product (EOSD LC 2000), we characterize the circa 2000 forest patterns in 26 of Canada's national parks and compare these to forest patterns in the ecological units surrounding these parks, referred to as the greater park ecosystem (GPE). Five landscape pattern metrics were analyzed: number of forest patches, mean forest patch size (hectare), standard deviation of forest patch size (hectare), mean forest patch perimeter-to-area ratio (meters per hectare), and edge density of forest patches (meters per hectare). An assumption is often made that forests within park boundaries are less fragmented than the surrounding GPE, as indicated by fewer forest patches, a larger mean forest patch size, less variability in forest patch size, a lower perimeter-to-area ratio, and lower forest edge density. Of the 26 national parks we analyzed, 58% had significantly fewer patches, 46% had a significantly larger mean forest patch size (23% were not significantly different), and 46% had a significantly smaller standard deviation of forest patch size (31% were not significantly different), relative to their GPEs. For forest patch perimeter-to-area ratio and forest edge density, equal proportions of parks had values that were significantly larger or smaller than their respective GPEs and no clear trend emerged. In summary, all the national parks we analyzed, with the exception of the Georgian Bay Islands, were found to be significantly different from their corresponding GPE for at least one of the five metrics assessed, and 50% of the 26 parks were significantly different from their respective GPEs for all of the metrics assessed. The EOSD LC 2000 provides a heretofore unavailable dataset for characterizing broad trends in forest fragmentation in Canada's national parks and in their surrounding GPEs. The interpretation of forest fragmentation metrics must be guided by the underlying land cover context, as many forested ecosystems in Canada are naturally fragmented due to wetlands and topography. Furthermore, interpretation must also consider the management context, as some parks are designed to preserve fragmented habitats. An analysis of forest pattern such as that described herein provides a baseline, from which changes in fragmentation patterns over time could be monitored, enabled by earth observation data.

Disturbance history affects lightning fire initiation in the mixedwood boreal forest: Observations and simulations

The emulation of natural disturbances such as fire is a prominent harvest management strategy for ecosystems in Canada's boreal forest region, but the effect of harvesting on subsequent lightning fire occurrence has not been studied systematically in the mixedwood boreal forest. We quantified the relationship between annual patterns of lightning fire initiation, forest composition, lightning, and fire weather conditions over eight years (1994–2001) in a 60,000 km 2 region of actively harvested mixedwood boreal forest in western Canada. Our analyses illustrated that forest harvesting and burning had opposite effects on subsequent fire initiation, so harvest was not a surrogate for fire. Fire initiation increased in landscapes with more area harvested and decreased with area recently burned. Our data suggested that increased fire initiation was most pronounced in harvested stands up to a decade old, and there was some evidence that the effect might last as long as 30 years. We then used a dynamic fire-succession simulation model to quantify the long-term effects of these fuel-based relationships using two metrics. As expected, the first metric demonstrated that the number of years between disturbances was significantly less in stands that were harvested and then burned, than those that were burned and then burned again. However, the more revealing component of the simulations was an illustration that despite the strong, positive relationship between harvested areas and fire initiation, the area affected over the long-term by a reduced disturbance interval was relatively small. Accordingly, our study shows that spatiotemporal regulation of lightning fire initiation through harvesting activity results in a systematic accelerated frequency of disturbance that is novel to the mixedwood boreal system, but the area affected by these events amount to local peculiarities rather than broad-scaled regularities.

Protecting marine biodiversity in Canada: Adaptation options in the face of climate change

Climate change adds a significant stress to biodiversity in Canada, compounding the effects of continuing habitat loss and over-exploitation of natural resources. These cumulative threats to flora and fauna heighten the need for conservation strategies. Policy in the climate change area has focused on greenhouse gas mitigation, but the complementary response of adaptation must also be addressed as changing climate will have effects on biodiversity even if global emission targets are met. It is internationally recognized that protected area networks support the ability of ecosystems to cope with climate change. Natural ecosystems have greater resilience in the face of climate change impacts when additional stresses from industrial and commercial exploitation are reduced, and when species migrating to more suitable locations are facilitated through protected areas. Conservation as part of an adaptation policy is good insurance against the risk of species extinctions due to climate change. In Canada's biodiversity and conservation policies there is little evidence to date of explicit recognition of, or action on, climate change adaptation, especially in the oceans. In Canada's oceans, there is an urgent need to create comprehensive networks of large protected areas to assist in buffering the effects of climate change. While some marine protected areas have been established in Canada, their sufficiency and their ability to facilitate connections between them needs to be examined in light of climate change. Marine ecosystems are vulnerable to the impacts of climate change and this is compounded by the many stresses they already face from overharvesting, habitat destruction, alien species, and pollution. Minimizing these chronic stresses and employing ecosystem based management approaches are key strategies to reducing the impact of climate change on marine ecosystems in Canada.

Environmental controls on the carbon isotope composition of ecosystem-respired CO2 in contrasting forest ecosystems in Canada and the USA

We compared the carbon isotope composition of ecosystem-respired CO2 (delta13C(R)) from 11 forest ecosystems in Canada and the USA and examined differences among forest delta13C(R) responses to seasonal variations in environmental conditions from May to October 2004. Our experimental approach was based on the assumption that variation in delta13C(R) is a good proxy for short-term changes in photosynthetic discrimination and associated shifts in the integrated ecosystem-level intercellular to ambient CO2 ratio (c(i)/c(a)). We compared delta13C(R) responses for three functional groups: deciduous, boreal and coastal forests. The delta13C(R) values were well predicted for each group and the highest R2 values determined for the coastal, deciduous and boreal groups were 0.81, 0.80 and 0.56, respectively. Consistent with previous studies, the highest correlations between delta13C(R) and changes in environmental conditions were achieved when the environmental variables were averaged for 2, 3 or 4 days before delta13C(R) sample collection. The relationships between delta13C(R) and environmental conditions were consistent with leaf-level responses, and were most apparent within functional groups, providing support for our approach. However, there were differences among groups in the strength or significance, or both, of the relationships between delta13C(R) and some environmental factors. For example, vapor pressure deficit (VPD) and soil temperature were significant determinants of variation in delta13C(R) in the boreal group, whereas photosynthetic photon flux (PPF) was not; however, in the coastal group, variation in delta13C(R) was strongly correlated with changes in PPF, and there was no significant relationship with VPD. At a single site, comparisons between our delta13C(R) measurements in 2004 and published values suggested the potential application of delta13C(R) measurements to assess year-to-year variation in ecosystem physiological responses to changing environmental conditions, but showed that, in such an analysis, all environmental factors influencing carbon isotope discrimination during photosynthetic gas exchange must be considered.

Scale analysis of airborne flux measurements over heterogeneous terrain in a boreal ecosystem

A wavelet analysis was applied to airborne flux measurements over a boreal ecosystem in Canada to investigate thermally induced mesoscale circulations and turbulent organized structures, which are according to large eddy simulation studies considered as one major reason for the energy balance closure problem. Fluxes of sensible heat, latent heat, carbon dioxide, and ozone were separated into a mesoscale and a small‐scale turbulence part to quantify those flux contributions that cannot be captured with single‐tower measurements. Mesoscale fluxes were comparable in magnitude to the energy balance residuals from ground‐based tower measurements close to the flight track. A scale‐dependent correlation analysis between the fluxes of different scalar quantities could not justify the common practice of correcting eddy covariance measurements of the sensible and the latent heat flux for the lack of energy balance closure according to the Bowen ratio or of correcting carbon dioxide fluxes according to the energy balance residual.

Application of the forest ecosystem model EFIMOD 2 to jack pine along the Boreal Forest Transect Case Study

Sustainability of forest ecosystems and climate change are two critical issues for boreal forest ecosystems in Canada that require an understanding of the links and balance between productivity, soil processes and their interaction with natural and anth ropogenic disturbances. Forest ecosystem models can be used to understand and predict boreal forest ecosystem dynamics. EFIMOD 2 is an individual tree model of the forest-soil ecosystem capable of modelling nitrogen feedback to productivity in response to changes in soil moisture and temperature. It has been successfully applied in Europe, but has not been calibrated for any forest ecosystem in Canada. The objective of this study was to parameterize and validate EFIMOD 2 for jack pine in Canada. Simulated and measured results agreed for changes in tree biomass carbon and soil carbon and nitrogen with increasing stand age and across a climatic gradient from the southern to northern limits of the boreal forest. Preliminary results from scenario testing indicate that EFIMOD 2 can be successfully applied to predict the impacts of forest management practices and climate change in the absence of natural disturbances on jack pine in the boreal forest of Canada. Model development is underway to represent the effects of natural disturbances. Key words: EFIMOD 2, forest soil, carbon, nitrogen, model, jack pine

Insect Visitation to Wildflowers in the Endangered Garry Oak, <em>Quercus garryana</em>, Ecosystem of British Columbia

The Garry Oak Ecosystem (GOE) is a fragmented and endangered ecosystem in Canada, and is currently the focus of conservation and restoration efforts in British Columbia. However, little is known about the basic biology of GOE forbs, or their relationships with pollinating insects. We monitored wildflowers and their insect visitors in 25 quadrats within a 25 × 25 metre plot, located in a fragment of the GOE near Duncan, British Columbia, for six weeks (the majority of the flowering period). Overall, 21 native and non-native forb species flowered in our quadrats during the survey, and we observed an additional six forb species flowering outside of our quadrats. Eight forbs were visited within quadrats by a total of 13 insect taxa, identified to morphospecies. Visits by eight additional morphospecies were observed outside of the quadrats. In general, visitation was low; however, most insect morphospecies were observed visiting more than one plant species, and most plant species were visited by more than one insect morphospecies, suggesting that pollination may be generalised in this community. A Chi-squared analysis indicated that insect visitation was not proportional to the relative abundance of forbs, with higher than expected visitation to Common camas (Camassia quamash), and no observed visits to 11 species, most with very small (putatively unattractive) flowers. The most frequent insect visitor was the introduced Honeybee, Apis mellifera, followed by native mason bees (Osmia spp.) and mining bees (Andrena spp.). Our observations provide baseline data for future, detailed studies that should investigate the importance of plant-pollinator mutualisms for sustainability of populations and communities in this rare ecosystem.

The Urban Cliff Hypothesis and its relevance to ekistics

The Cliff Ecology Research Group (CERG), Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada, has been in existence since 1985 when its members began working on the ecology of the Niagara Escarpment (fig. 1). In 1988 they discovered a stand of ancient trees growing on the cliffs and in 1989 they discovered that in fact the escarpment cliffs support the oldest and least disturbed forest ecosystem in Canada. Individual living trees older than 1,300 years are still present and the forest appears to be in steady state. CERG's work on the ancient trees led to the idea that cliffs serve as refuges for many species including ancient humans. That observation led to the development of the Urban Cliff Hypothesis that is described in this paper and was presented at the international symposion on The Natural City, Toronto, 23-25 June, 2004, sponsored by the University of Toronto's Division of the Environment, Institute for Environmental Studies, and the World Society for Ekistics, and also led to the recent book entitled The Urban Cliff Revolution.

The Urban Cliff Hypothesis and its relevance to ekistics

The Cliff Ecology Research Group (CERG), Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada, has been in existence since 1985 when its members began working on the ecology of the Niagara Escarpment (fig. 1). In 1988 they discovered a stand of ancient trees growing on the cliffs and in 1989 they discovered that in fact the escarpment cliffs support the oldest and least disturbed forest ecosystem in Canada. Individual living trees older than 1,300 years are still present and the forest appears to be in steady state. CERG's work on the ancient trees led to the idea that cliffs serve as refuges for many species including ancient humans. That observation led to the development of the Urban Cliff Hypothesis that is described in this paper and was presented at the international symposion on " The Natural City, " Toronto, 23-25 June, 2004, sponsored by the University of Toronto's Division of the Environment, Institute for Environmental Studies, and the World Society for Ekistics, and also led to the recent book entitled The Urban Cliff Revolution.

Watershed Impacts of Logging and Wildfire: Case Studies in Canada

ABSTRACT In Canada, disturbance of boreal forests has increased due to expanding anthropogenic activities, particularly forestry. A first attempt was made to evaluate impacts of forest harvesting and wildfire on changes in water quality and biota of lakes. We present case studies in two major geological and climatic subregions of the boreal ecozone in Canada: the Boreal Plain and the Boreal Shield. Responses of lake ecosystems to wildfire and logging differed. In upland Boreal Plain lakes, total phosphorus (P), inorganic nitrogen (N) and algal biomass were higher in lakes with burned watersheds, whereas, only total P increased in lakes with watershed logging. Logging on the Boreal Shield and wildfire in wetland-and permafrost-dominated watersheds on the northern Boreal Plain were associated with increases in dissolved organic carbon (DOC) and water colour, possibly causing light-limitation of algae in both regions, and a decrease in calanoid biomass in eastern Boreal Shield lakes. The number of water quality indicators affected by watershed disturbances was greater in the oligotrophic ecosystems of the Boreal Shield. The nutrient response of disturbed lakes was strongly related to lake drainage ratios: lakes with high drainage ratios had the strongest response to disturbance. Effects were also dependent on climate, wetland coverage, and regional lake characteristics. Morphometric, chemical, and biological indicators are recommended to monitor natural and anthropogenic watershed disturbances of aquatic ecosystems in Canada's Boreal forest.

Modeling soil thermal and carbon dynamics of a fire chronosequence in interior Alaska

In this study, the dynamics of soil thermal, hydrologic, and ecosystem processes were coupled to project how the carbon budgets of boreal forests will respond to changes in atmospheric CO2, climate, and fire disturbance. The ability of the model to simulate gross primary production and ecosystem respiration was verified for a mature black spruce ecosystem in Canada, the age‐dependent pattern of the simulated vegetation carbon was verified with inventory data on aboveground growth of Alaskan black spruce forests, and the model was applied to a postfire chronosequence in interior Alaska. The comparison between the simulated soil temperature and field‐based estimates during the growing season (May to September) of 1997 revealed that the model was able to accurately simulate monthly temperatures at 10 cm (R> 0.93) for control and burned stands of the fire chronosequence. Similarly, the simulated and field‐based estimates of soil respiration for control and burned stands were correlated (R= 0.84 and 0.74 for control and burned stands, respectively). The simulated and observed decadal to century‐scale dynamics of soil temperature and carbon dynamics, which are represented by mean monthly values of these variables during the growing season, were correlated among stands (R= 0.93 and 0.71 for soil temperature at 20‐ and 10‐cm depths,R= 0.95 and 0.91 for soil respiration and soil carbon, respectively). Sensitivity analyses indicate that along with differences in fire and climate history a number of other factors influence the response of carbon dynamics to fire disturbance. These factors include nitrogen fixation, the growth of moss, changes in the depth of the organic layer, soil drainage, and fire severity.

Thallium Contamination of Water in Canada

Abstract Thallium is highly toxic but has been an obscure element compared to its three popular neighbours, lead, mercury and cadmium. It is partly due to the scarcity of its analytical data, caused by its high analytical detection limit relative to the other three elements and by its generally low level in the environment. We have developed a highly sensitive instrument, a Laser-Excited Atomic Fluorescence Spectrometer, to study thallium contamination in some important Canadian ecosystems from the Arctic (containing very low thallium concentration) to coal-related industries across Canada and even to the study of thallium toxicity in an invertebrate, Hyalella azteca. Overall, our data indicate that the coal power plants and mines contain higher thallium concentrations than the other ecosystems studied, and the eastern region has the highest Tl concentrations compared to other regions. The range of thallium concentration in ng/L for the Arctic snow and ice was between not detected and 8.4, for the Great Lakes waters 0.9 to 48, for pore waters 0.1 to 213, for western coal power plants and mines 0.1 to 1326, for central coal power plants 1.2 to 175, for eastern coal power plants and mines 0.2 to 23605, and for miscellaneous sites across Canada not detected to 4390 ng/L. Some of these high concentrations and those high ones reported in industrial wastewaters exceeded the chronic toxicity endpoints for Hyalella azteca mortality, growth and reproduction, thus can cause serious distress to the environment. All data were integrated into a map of thallium distribution, the first one in Canada. Natural background level of thallium for the Arctic was estimated to be 0.02 to 0.03 pg/g.

Monitoring long-term ecological changes through the Ecological Monitoring and Assessment Network: science-based and policy relevant.

Ecological monitoring and its associated research programs have often provided answers to various environmental management issues. In the face of changing environmental conditions, ecological monitoring provides decision-makers with reliable information as they grapple with maintaining a sustainable economy and healthy environment. The Ecological Monitoring and Assessment Network (EMAN) is a national ecological monitoring network consisting of (1) about 100 case study sites across the country characterized by long-term multi-disciplinary environmental work conducted by a multitude of agencies (142 partners and counting); (2) a variety of less comprehensive yet more extensive monitoring sites; (3) a network where core monitoring variables of ecosystem change are measured; and (4) geo-referenced environmental observations. Environment Canada is the co-ordinating partner for the network through the EMAN Co-ordinating Office. EMAN's mission is to focus a scientifically-sound, policy-relevant ecosystem monitoring and research network based on (a) stabilizing a network of case-study sites operated by a variety of partners, and (b) developing a number of cooperative dispersed monitoring initiatives in order to deliver unique and needed goods and services. These goods and services include: (1) an efficient and cost-effective early warning system which detects, describes and reports on changes in Canadian ecosystems at a national or ecozone scale; and (2) cross-disciplinary and cross-jurisdictional assessments of ecosystem status, trends and processes. The early warning system and assessments of ecosystem status, trends and processes provide Environment Canada and partner organizations with timely information that facilitates increasingly adaptive policies and priority setting. Canadians are also informed of changes and trends occurring in Canadian ecosystems and, as a result, are better able to make decisions related to conservation and sustainability.

Understanding the role of forest simulation models in sustainable forest management

Sustainable forest management (SFM) represents a new paradigm for forestry. Traditional forestry objectives aimed at sustainable yield management are being replaced with those of a sustainable ecosystem management. This paradigm shift in forest management requires an effective transfer of results from researchers to forest managers. To predict the potential impacts of future changes in global environment (such as climate, land use, fire disturbance, and forest harvesting) on the sustainability of forest ecosystems, forest resource managers will require forest simulation models. There have been two basic approaches to modeling forest vegetation growth and dynamics: empirical and mechanistic forest simulation models. This paper reviews and compares three major types of forest simulation models: (1) growth and yield models (empirical approach); (2) succession models (empirical–mechanistic hybrid approach); and (3) process models (mechanistic approach), and describes three case studies as examples. The advantages and disadvantages of the different modeling approaches are discussed. The case studies deal with predicting future forest stocks under different management options, simulating the potential effects of climate change, and effects of fire disturbance on structure and function of forest ecosystems in Canada. There is still a gap between foresters and ecologists in developing and using forest simulation models. Diversified modeling approaches integrated into a decision–support system, which will become an important tool for evaluating the sustainability of forest ecosystem in a changing environment, is emphasized.

Rangeland Management Impacts on Soil Biological Indicators in Southern Alberta

Quantitative techniques are needed to determine the effects of cultivation and livestock grazing on biological indicators of soils of the Northern Great Plains. Our objective was to determine how various management practices, which were representative of those used since European settlement in the 1880's, affected 3 biological indicators of soil quality. The study was conducted at 3 sites that are representative of the major grassland ecosystems in Canada: a Mixed Prairie site with Stipa comota Trin. R 2) alfalfa (Medicago sativa L. 'Beaver'); 3) continuous spring wheat (Triticum aestivum L. 'Katepwa'): 4) spring wheat and fallow rotation; and 5) abandoned cultivated land. Our hypothesis that mineralizable-N, and phosphatase and dehydrogenase activities would be influenced by cultivation was confirmed by significant changes in these indicators that were detected after only 180 days after treatment establishment. The pool of readily decomposable organic matter was reduced with cultivation and not replenished over the period of the study. The 3 biological indicators were sensitive to not only time following external management changes, but also to seasonal fluctuations. We conclude that soil biological indicators can be used to quantify temporal and botanical changes in diverse ecotypes within the Northern Great Plains. DOI:10.2458/azu_jrm_v53i2_dormaar

Rangeland management impacts on soil biological indicators in southern Alberta

Quantitative techniques are needed to determine the effects of cultivation and livestock grazing on biological indicators of soils of the Northern Great Plains. Our objective was to determine how various management practices, which were representative of those used since European settlement in the 1880's, affected 3 biological indicators of soil quality. The study was conducted at 3 sites that are representative of the major grassland ecosystems in Canada: a Mixed Prairie site with Stipa comota Trin. Rupr. dominant in the Brown (Aridic Haploboroll) Soil Zone, a Mixed Prairie site with S. comata Trin. Rupr. and S. viridula Trin. dominant in the Dark Brown (Typic Haploboroll) Soil Zone, and a Fescue Prairie site with Festuca campestris Rydb. dominant in the Black (Udic Haploboroll) Soil Zone. At each site, 6 treatments representing common production practices were imposed and compared with the native community in a randomized complete block design with 4 replicates and a plot size of 3 x 10 m. The treatments included: 1) monoculture seeding of 2 grass species; 2) alfalfa (Medicago sativa L. 'Beaver'); 3) continuous spring wheat (Triticum aestivum L. 'Katepwa'): 4) spring wheat and fallow rotation; and 5) abandoned cultivated land. Our hypothesis that mineralizable-N, and phosphatase and dehydrogenase activities would be influenced by cultivation was confirmed by significant changes in these indicators that were detected after only 180 days after treatment establishment. The pool of readily decomposable organic matter was reduced with cultivation and not replenished over the period of the study. The 3 biological indicators were sensitive to not only time following external management changes, but also to seasonal fluctuations. We conclude that soil biological indicators can be used to quantify temporal and botanical changes in diverse ecotypes within the Northern Great Plains.

Atmospheric mercury contamination of remote aquatic ecosystems in Canada

The long-range atmospheric transport and deposition of metals, particularly mercury (Hg), into lakes has become a subject of increasing interest. In Canada, the sources of anthropogenic, atmospheric Hg are primarily considered to be power stations in the United States and Europe. Increases in deposition of Hg have been recorded in lake sediment cores from many parts of Canada. Where Hg input to lakes from local sources in Canada has been reduced, concentrations in lake sediments and lake biota have declined. However, in many remote lakes, fish consumption advisories are still in effect for Hg. Debate continues over the sources of this mercury, whether long-range anthropogenic, atmospheric or natural. Where studied, the same applies to remote lakes in other parts of the world.

Atmospheric mercury contamination of remote aquatic ecosystems in Canada

The long-range atmospheric transport and deposition of metals, particularly mercury (Hg), into lakes has become a subject of increasing interest. In Canada, the sources of anthropogenic, atmospheric Hg are primarily considered to be power stations in the United States and Europe. Increases in deposition of Hg have been recorded in lake sediment cores from many parts of Canada. Where Hg input to lakes from local sources in Canada has been reduced, concentrations in lake sediments and lake biota have declined. However, in many remote lakes, fish consumption advisories are still in effect for Hg. Debate continues over the sources of this mercury, whether long-range anthropogenic, atmospheric or natural. Where studied, the same applies to remote lakes in other parts of the world.