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Athabasca County No. 12 AB

Primary productivity and decomposition in fens and marshes in the boreal region of Alberta

Author(s): Thormann, M. N.

Year: 1995

Net primary production (NPP), decomposition, changes in C, N and TP tissue concentrations and responses to N or P fertilization of aboveground vascular vegetation along a bog--fen--marsh peatland gradient in central Alberta, Canada, were measured during the 1993 and 1994 growing seasons. The peatlands were a bog, an open rich fen (ORF), a lacustrine sedge fen (LSF), a riverine sedge fen (RSF), a riverine marsh (RM) and a lacustrine marsh (LM). Total plant NPP of the bog and the fens were similar but significantly lower than that of the marshes. The plant production values obtained conform to a latitudinal gradient for North American wetlands, although the marshes of this study were substantially less productive than Canadian counterparts at similar latitudes. Moss and herb production varied significantly between years and among sites, whereas shrubs production only varied significantly among sites but not years. Litter quality and the surface water nutrient status of the sites partially explained the rates of decomposition of the dominant and standard plant litters and cellulose (filterpaper) over varying lengths of time. Decay of the plant litter was similar in fens and marshes, but cellulose decomposed significantly faster in the eutrophic marshes than in the oligotrophic fens. Nitrogen and phosphorus surface water parameters related best to litter decay in these peatlands. The carbon to nitrogen (C:N) ratio changes during plant litter decay depended on the litter type and quality and the surface water nutrient concentrations within sites. The nutrient status of the site, plant species, life history and stand density partly explained the C:N ratio changes throughout the growing season. Generally, C:N ratios decreased towards late August. Fertilization with N or P generally did not reveal which nutrient limits plant production in Alberta peatlands. In the bog, ericaceous and deciduous shrubs, mosses and herbs were variable in their responses to fertilization. Fen and marsh plant species generally did not respond significantly to N or P addition, possibly due to luxury consumption of the fertilizers or immediate microbial uptake.

Response of Sphagnum fuscum to nitrogen deposition: A case study of ombrogenous peatlands in Alberta, Canada

Year: 2003

Peatlands cover about 30% of northeastern Alberta and are ecosystems that are sensitive to nitrogen deposition. In polluted areas of the UK, high atmospheric N deposition (as a component of acid deposition) has been considered among the causes of Sphagnum decline in bogs (ombrogenous peatlands). In relatively unpolluted areas of western Canada and northern Sweden, short-term experimental studies have shown that Sphagnum responds quickly to nutrient loading, with uptake and retention of nitrogen and increased production. Here we examine the response of Sphagnum fuscum to enhanced nitrogen deposition generated during 34 years of oil sands mining through the determination of net primary production (NPP) and nitrogen concentrations in the upper peat column. We chose six continental bogs receiving differing atmospheric nitrogen loads (modeled using a CALPUFF 2D dispersion model). Sphagnum fuscum net primary production (NPP) at the high deposition site (Steepbank-mean of 600 g/m2; median of 486 g/m2) was over three times as high than at five other sites with lower N deposition. Additionally, production of S. fuscum may be influenced to some extent by distance of the moss surface from the water table. Across all sites, peat nitrogen concentrations are highest at the surface, decreasing in the top 3 cm with no significant change with increasing depth. We conclude that elevated N deposition at the Steepbank site has enhanced Sphagnum production. Increased N concentrations are evident only in the top 1-cm of the peat profile. Thus, 34 years after mine startup, increased N-deposition has increased net primary production of Sphagnum fuscum without causing elevated levels of nitrogen in the organic matter profile. A response to N-stress for Sphagnum fuscum is proposed at 14-34 kg ha-1 yr-1. A review of N-deposition values reveals a critical N-deposition value of between 14.8 and 15.7 kg ha-1 yr-1 for NPP of Sphagnum species.

The role of sulphur in the carbon balance of boreal peatlands

Author(s): Vile, M. A.

Year: 2001

With the exception of photosynthesis, carbon dioxide (CO2 ) emissions from soils exceed all other terrestrial-atmospheric carbon fluxes. Due to the magnitude of this soil-to-atmosphere CO2 flux, and the great mineralization capabilities associated with this large soil carbon pool, any increases in soil carbon fluxes have the potential to provide a large positive feedback to global warming. This dissertation examines the role of atmospheric sulfur deposition on anaerobic carbon fluxes from peatland soils, which contain one-third of the world's soil carbon pool. The first objective of this dissertation was to determine the contribution of sulfate reduction to anaerobic carbon mineralization in peatlands across a regional atmospheric sulfur deposition gradient. The second objective was to determine the fate of currently retained sulfur in peatlands under changing atmospheric sulfur depositional regimes, using stable sulfur isotopes as a tool. We determined the relationship between rates of sulfate reduction, and CO2 and CH4 production in peatlands spanning a wide atmospheric sulfur gradient in central Alberta, Canada and Cervené Blato and Oceán bog, The Czech Republic. Results from this study suggest that although peatlands are important global sources of CH4 , methanogenesis is responsible for a small proportion of anaerobic carbon cycling in these ecosystems. We further tested the hypothesis that in peatlands receiving low sulfate inputs, methane production will predominate during anaerobic carbon mineralization. We hypothesized that with sulfate amendments, anaerobic carbon mineralization at Bleak Lake Bog would be governed by sulfate reduction. In opposition to our hypotheses, sulfate amendments did not increase rates of sulfate reduction, increase CO 2 production, or decrease CH4 production. We conducted a peat transplant experiment to evaluate the impact of atmospheric sulfur deposition on sulfur cycling processes in soil under alternate scenarios of increasing and decreasing atmospheric sulfur deposition. We found that a substantial fraction of the sulfur that enters a peatland via atmospheric deposition is retained in the peat, and this fraction increases with a concomitant increase in rates of atmospheric sulfur deposition. Implications for total sulfur pools, extrapolated to the long term, may be a gain of total sulfur under a scenario of both increasing and decreasing rates of sulfate reduction.