Organic matter decomposition at a constructed fen in the Athabasca Oil Sands region: Effect of substrate type and environmental conditions

Abstract

Fen construction has recently been tested in the Athabasca Oil Sands Region, Alberta, Canada in an effort to return peatlands to the post-mining landscape. Understanding the drivers of organic matter decomposition in constructed fens will improve our capacity to evaluate the return of ecosystem function while also helping to inform management activities that could optimize peat accumulation. At a four year old constructed fen, we measured the decomposition of Carex aquatilis and Juncus balticus tissue over one year along with soil physical and chemical properties including concentrations of phenolic compounds in pore water, and potential phenol oxidase and hydrolase enzyme activities. Results were compared to three reference fens. Averaged across both species, decomposition of aboveground plant tissue was significantly slower at the constructed fen than the reference fens. Across the reference fens, a positive relationship between phenolic compound concentrations and decomposition constant (k) suggests microbial use of phenolic compounds as substrates. We found no evidence that phenolic compounds suppressed decomposition. At the constructed fen, a negative relationship between total potential hydrolase activity and k was observed, suggesting that nutrient limitation may suppress microbial activity at the site. There was little evidence that mulch or planting treatments altered short-term litter decomposition rate at the constructed fen, indicating that future research should focus on differences in biomass production between species, below ground nutrient cycling and the longer term preservation of litter as peat to determine strategies for optimizing peat accumulation.