Soil carbon pools and fluxes following the regreening of a mining and smelting degraded landscape.

Increasing forest cover by regreening mining and smelting degraded landscapes provides an opportunity for global carbon (C) sequestration, however, the reported effects of regreening on soil C processes are mixed. One of the world's largest regreening programs is in the City of Greater Sudbury, Canada and has been ongoing since 1978. Prior to regreening, soils in the City of Greater Sudbury area were highly eroded, acidic, rich in metals, and poor in nutrients. This study used a chronosequence approach to investigate how forest soil C pools and fluxes have changed with stand age in highly "eroded" sites with minimal soil cover (n = 6) and "stable" sites covered by soil (n = 6). Encouragingly, the relationship between stand age and soil C processes (litterfall, litter decomposition, soil respiration, fine root growth) at both stable and eroded sites were comparable to observations reported for jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Ait.) plantations that have not been subject to over a century of industrial impacts. There was a strong "home-field advantage" for local decomposers, where litter decomposition rates were higher using a site-specific pine litter compared with a common pine litter. Higher soil respiration at eroded sites was linked to higher soil temperature, likely because of a more open tree canopy. Forest floor C pools increased with stand age while mineral soil C and aggregate C concentrations decreased with stand age. This loss of soil C is small relative to the substantial increases in aboveground tree and forest floor C pools, leading to a sizeable increase in total ecosystem C pools following regreening.

Peatland microbial communities and decomposition processes in the james bay lowlands, Canada.

Northern peatlands are a large repository of atmospheric carbon due to an imbalance between primary production by plants and microbial decomposition. The James Bay Lowlands (JBL) of northern Ontario are a large peatland-complex but remain relatively unstudied. Climate change models predict the region will experience warmer and drier conditions, potentially altering plant community composition, and shifting the region from a long-term carbon sink to a source. We collected a peat core from two geographically separated (ca. 200 km) ombrotrophic peatlands (Victor and Kinoje Bogs) and one minerotrophic peatland (Victor Fen) located near Victor Bog within the JBL. We characterized (i) archaeal, bacterial, and fungal community structure with terminal restriction fragment length polymorphism of ribosomal DNA, (ii) estimated microbial activity using community level physiological profiling and extracellular enzymes activities, and (iii) the aeration and temperature dependence of carbon mineralization at three depths (0-10, 50-60, and 100-110 cm) from each site. Similar dominant microbial taxa were observed at all three peatlands despite differences in nutrient content and substrate quality. In contrast, we observed differences in basal respiration, enzyme activity, and the magnitude of substrate utilization, which were all generally higher at Victor Fen and similar between the two bogs. However, there was no preferential mineralization of carbon substrates between the bogs and fens. Microbial community composition did not correlate with measures of microbial activity but pH was a strong predictor of activity across all sites and depths. Increased peat temperature and aeration stimulated CO(2) production but this did not correlate with a change in enzyme activities. Potential microbial activity in the JBL appears to be influenced by the quality of the peat substrate and the presence of microbial inhibitors, which suggests the existing peat substrate will have a large influence on future JBL carbon dynamics.

Effect of moisture and temperature variation on DOC release from a peatland: conflicting results from laboratory, field and historical data analysis.

Peatlands are large repositories of atmospheric carbon and concern has been raised over the stability of this carbon store because increasing dissolved organic carbon (DOC) concentrations have been observed in peatland drainage waters. A number of potential causes have been proposed in the literature, and conflicting results among studies conducted at different spatial and temporal scales suggest that the methodological approach may be an important confounding factor. The objective of this study was to determine the influence of moisture and temperature on DOC release from a south-central Ontario peatland during the fall (a major export period) following three commonly used approaches: laboratory microcosms, an intensive field study and analysis of long-term data (1980-2008). The effect of variations in temperature and moisture differed among microcosm, field study and analysis of the long-term record. Water content was important at the microcosm scale as DOC concentration and aromaticity increased with peat water-saturation. Drought caused a decrease in DOC concentration and pH, and an increase in sulphate and base cation concentrations. In contrast, the field study indicated that DOC concentration was strongly associated with temperature, and weakly correlated (negatively) with stream discharge. Average fall DOC concentration (but not export) increased over the 29 year record, and was correlated with fall discharge and precipitation (negative) and summer precipitation and fall stream pH (positive). As no common strong predictor of fall DOC was found at three scales of investigation at a single, well-studied site, it may be unreasonable to expect to identify a universal driver behind the widespread increase in DOC concentration.