A period of prolonged warmer, drier-than-normal weather in northwestern Ontario during the 1970s and 1980s resulted in severe forest fires that caused dramatic changes to lake and stream catchments. The changed interactions of weather with catchments and hydrological processes caused unexpected changes in physical, chemical, and biological processes in lakes and streams. Permanent first-order streams became ephemeral. Flows at spring melt were lower, and chemical exports from catchments were reduced. Although catchments burned by forest fire had slightly higher flows and chemical exports than unburned basins in the years following fires, chemical exports generally declined due to lower streamflow. Decreased exports of silica indicated lower rates of weathering. Base cation exports also decreased, as did the ratio of base cations to strong acid anions in streams.Changes in lakes included warmer temperatures, clearer waters, deeper thermoclines and euphotic zones, higher alkalinities, and higher concentrations of base cations and nitrogen, but lower concentrations of dissolved organic C, silica, and P. The increase in alkalinity was caused by increases in the ratio of base cations to strong acid anions, resulting from the interaction of increased water retention, microbial sulfate reduction, and exchanges of cations between water and sediments. Declines in chlorophyll and increases in phytoplankton biomass were observed, but there was no detectable effect on areal phytoplankton production. Summer subthermocline habitats for cold stenotherms were reduced slightly in extent as the results of thermocline deepening and lower hypolimnetic oxygen. There is considerable potential for interaction between climatic change and other human perturbations affecting boreal lakes, including acidification, increased incident UV radiation, eutrophication, and overharvesting.

Experimental evidence of trophic cascades initiated by large vertebrate predators is rare in terrestrial ecosystems. A serendipitous natural experiment provided an opportunity to test the trophic cascade hypothesis for wolves (Canis lupus) in Banff National Park, Canada. The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley (low‐wolf area), whereas wolves made full use of an adjacent area (high‐wolf area). We investigated the effects of differential wolf predation between these two areas on elk (Cervus elaphus) population density, adult female survival, and calf recruitment; aspen (Populus tremuloides) recruitment and browse intensity; willow (Salix spp.) production, browsing intensity, and net growth; beaver (Castor canadensis) density; and riparian songbird diversity, evenness, and abundance. We compared effects of recolonizing wolves on these response variables using the log response ratio between the low‐wolf and high‐wolf treatments. Elk population density diverged over time in the two treatments, such that elk were an order of magnitude more numerous in the low‐wolf area compared to the high‐wolf area at the end of the study. Annual survival of adult female elk was 62% in the high‐wolf area vs. 89% in the low‐wolf area. Annual recruitment of calves was 15% in the high‐wolf area vs. 27% without wolves. Wolf exclusion decreased aspen recruitment, willow production, and increased willow and aspen browsing intensity. Beaver lodge density was negatively correlated to elk density, and elk herbivory had an indirect negative effect on riparian songbird diversity and abundance. These alternating patterns across trophic levels support the wolf‐caused trophic cascade hypothesis. Human activity strongly mediated these cascade effects, through a depressing effect on habitat use by wolves. Thus, conservation strategies based on the trophic importance of large carnivores have increased support in terrestrial ecosystems.

Surface and subsurface (0.5, 1.0, and 1.5 m depths) water was sampled weekly in 1989 and biweekly in 1990 during the ice-free season along a bog-rich fen gradient in central Alberta. Acidity–alkalinity were most closely related to peatland type and were the most useful parameters for characterizing peatlands. Potassium, nitrogen, and phosphorus concentrations were more related to season, year, or peatland–year interactions and cannot be used to categorize the bog–fen gradient. Hydrogen ion, ammonium, alkalinity, and corrected conductivity were relatively constant throughout the ice-free season, while total metal ions (Al, Fe, Mn, and Zn), base cations (Ca2+, Mg2+, Na+, K+), nitrate, and components of phosphorus fluctuated seasonally. Nitrate remained constant with depth in all peatland types, whereas ammonium increased with depth. Relationships of surface water chemistry to pH for all sites showed three patterns: a positive and highly significant correlation with little seasonal variation within peatland types (base cations, alkalinity, and corrected conductivity); less significant correlation with strong seasonal variation within peatland types (N and P); and a general negative and highly significant correlation with some seasonal variation in peatland types (metals and S). Water temperatures increased along the bog-rich fen gradient.

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We quantified the wholesale transformation of the boreal landscape by open-pit oil sands mining in Alberta, Canada to evaluate its effect on carbon storage and sequestration. Contrary to claims made in the media, peatland destroyed by open-pit mining will not be restored. Current plans dictate its replacement with upland forest and tailings storage lakes, amounting to the destruction of over 29,500 ha of peatland habitat. Landscape changes caused by currently approved mines will release between 11.4 and 47.3 million metric tons of stored carbon and will reduce carbon sequestration potential by 5,734-7,241 metric tons C/y. These losses have not previously been quantified, and should be included with the already high estimates of carbon emissions from oil sands mining and bitumen upgrading. A fair evaluation of the costs and benefits of oil sands mining requires a rigorous assessment of impacts on natural capital and ecosystem services.wetland reclamation | tar sands A n area larger than the state of Rhode Island will eventually be mined by oil sands companies in northern Alberta. These boreal lands must be reclaimed, but despite claims to the contrary (1), operators are not required to return the land to its original state (2). This study was precipitated by the disparity between statements made by the oil sands industry regarding the extent and anticipated success of mine reclamation and their official closure plans, which serve as agreements between mine operators and the Alberta government regarding actual reclamation expectations.Oil sands deposits accessible by open-pit surface mining cover about 475,000 ha of boreal Alberta, 99% of which is already leased (3). Currently, 10 mines have government approval to operate, covering about 167,044 ha (Fig. 1). This is a conservative estimate that excludes the pipelines, roads, seismic lines, and other infrastructure that support the mines. It also excludes impacts from aerial deposition (4) and aquifer dewatering (5) that extend off-site and the area of land associated with the three additional mines currently undergoing environmental review.Constraints imposed by the postmining landscape and the sensitivity of peatland vegetation prevent the restoration of peatlands that dominated the premining landscape. Mine proponents are required to describe the premining landscape and produce closure plans that detail the postmining landscape. Current reclamation regulations do not require the restoration of previous land covers or the restitution of lost carbon formerly stored in soils and vegetation. In place of destroyed peatlands, operators plan to construct upland forest with well-defined drainage channels and subsaline shallow open water wetlands draining into large tailings ponds capped with freshwater. The net effect of this landscape transformation on biodiversity and ecosystem functions has not been assessed. Here we quantify the land cover changes that will result from approved oil sands mine projects and their impact on carbon storage.

Annual linear growth, net primary production, and decomposition of Sphagnum fuscum, Sphagnum magellanicum, and Sphagnum angustifolium were measured under experimental acidification and natural conditions in a poor fen at the Experimental Lakes Area (ELA), Ontario, Canada. Acidification increased growth and production of most species (2 out of 3 in the oligotrophic zone, and 2 out of 3 in the minerotrophic zone) in the first 2 yr. After 2—3 yr of artificial acidification, growth and production were not stimulated to the same extent in experimental areas as in earlier years. After 4 yr, growth and production in the experimental area declined so that they were the same as controls for 4 of the 6 treatments. Therefore, the effect of the acid treatment changed over the years. With 4 yr of simulated “acid rain,” decomposition was unaffected. Our results suggest that the fertilizing effect of SO42— and NO3— in North American acid precipitation as suggested previously in the literature is a very short—term one, at least for this type of peatland. Under natural conditions, in the oligotrophic central zone of mire 239, production for hollow species was somewhat greater than for hummock species for the 4 yr studied. Since the decomposition rate ratio between hummock—top, mid—hummock, and hollow species is roughly in the ratio 7:9:13, the rate of peat accumulation should be higher in hummocks. Hence hummocks appear to be maintained in this poor fen due to low decomposition rates rather than relatively high production. For 3 of the 4 yr studied (1985—1987) in the minerotrophic edge zone, hummock production (303, 175, and 156 g°m—2°yr—1, respectively) was greater than hollow (198, 100, and 97 g°M—2°yr—1) and mid—hummock production (103, 59, and 52 g°m—2°yr—1). The relative decomposition rates of the species had the same ratio as in the oligotrophic zone. Thus hummocks appear to be expanding in this minerotrophic edge zone at a faster rate than in the oligotrophic zone.

Summary• Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain.• Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data.• We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased *These authors contributed equally to this work.

Peat cores from five Sphagnum-dominated peatlands in boreal continental Canada were analyzed for plant macro fossils. Results indicate that peatland development was influenced both by local autogenic and regional climatic factors. The general direction in peatland development from rich fen to poor fen to bog can primarily be ascribed to internal processes, especially peat accumulation. Quantitative paleoenvironmental reconstructions based on fossil moss assemblages indicate that all five peatlands were initially dominated by brown mosses with inferred pHs of approximately 6.0, and a water table at 5–15 cm below the surface of the peatland. Subsequently, Sphagnum-dominated peatlands developed with pHs of 4.0–4.5 and a water table at 15–30 cm of depth. Chemical factors triggered a rapid transition from rich fen (pH > 6) to poor fen and bog (Ph < 5). The two most southerly peatlands are youngest, with basal dates of 4670 BP and 4230 BP. Sphagnum peat accumulation at these sites started at 2620 BP and 1790 BP, respectively. Two sites located at intermediate latitudes have basal dates of > 5140 BP and 5020 BP, while the development of Sphagnum-dominated ecosystems dates back to ≈ 3100 BP and 3710 BP, respectively. The most northerly site has the oldest basal date (> 7870 BP), and the oldest date for the initiation of Sphagnum peat accumulation (≈ 7000 BP). The younger age of the peat deposits in the four southern sites is due to warm and dry climatic conditions during the middle Holocene that prevented peatland development until after 6000 BP when the climate gradually became cooler and moister. Farther north the climate was cool and moist enough to allow peatland development during the early to middle Holocene. In three southern peatlands, the development into a Sphagnum-dominated ecosystem took > 2000 years, while at the more northerly sites Sphagnum became dominant after < 1500 years. Key words: Sphagnum, peatlands, boreal, Holocene, climate.