Net Nitrogen Mineralization in Boreal Wetlands: A Test of Early Success for Canadian Oil Sands Reclamation.

Globally, peat-forming wetlands store 9-16% of the world’s soil organic nitrogen. In the boreal zone, peatlands are classified into three general site types (bogs, poor fens, and rich fens) based on differences in vegetation, pore-water chemistry, and source of water. Bogs and poor fens have a ground layer and peat profile dominated by the genus Sphagnum, whereas rich fen ground layers and peat profiles are true moss-dominated, and exhibit increased vascular plant cover. Using the buried bag technique, we determined that net nitrogen mineralization rates increase markedly along this Sphagnum-dominated to true-moss dominated gradient, with rich fen net mineralization rates up to 50 times higher than those in Sphagnum-dominated systems. Despite these higher net mineralization rates in rich fens, inorganic N concentrations in pore-water remain low. We conclude that along the bog-rich fen gradient, the type of ground layer vegetation, and hence peat type, controls rates of net N mineralization. In Alberta Canada, peatlands occupy approximately 45% of the boreal zone. Underlying this peatland/upland landscape are large bitumen deposits (i.e., ‘oil sands'). Open-pit mining for bitumen removes all surface vegetation and soil, and sterile saline sand is deposited into ‘in-pits’ after bitumen extraction. We measured net N mineralization rates along a moisture gradient within a reclamation watershed established on an in-pit.  The objective was to use net N mineralization as one indicator of below-ground ecosystem health, and determine if net N mineralization rates at this site are comparable to six nearby benchmark fens. Two years after watershed establishment, net N mineralization rates were similar to the fen benchmarks; however, at drier sites, net N mineralization was dominated by high net nitrification rates not common in fens.  We conclude that net N mineralization in early successional stages of reclamation, where ground layers have not yet developed, is strongly influenced by soil wetness, and could be a key indicator of below-ground system health.