Soil respiration and litter decomposition along a salinity gradient in a saline boreal fen in the Athabasca Oil Sands Region

Abstract

Understanding the controls on soil respiration (SR) and litter decomposition (LD) rates within saline boreal fens can help in the development of wetland reclamation approaches in the Athabasca Oil Sands Region (AOSR), where post-mined landscapes are commonly salt-affected. This study assesses the rates of SR and LD within a saline boreal fen near Fort McMurray (Alberta, Canada) and their relationship with electrical conductivity (EC), water table depth (WTD), soil moisture (SM) and temperature (ST), and nutrient availability. SR was assessed using community-scale CO2 measurements, and LD was estimated using the litter bag technique along a salinity gradient (EC 2–55 mS cm−1). Significant differences in SR between slightly saline, moderately saline, strongly saline, and very strongly saline sites were observed, and ridge sites had significantly higher SR than depressions. SR was strongly positively correlated to ST and strongly negatively correlated to WTD (i.e., shallower water table – lower SR and LD) and SM within both ridges and depressions. Ridges had significantly higher mean LD rates than depressions, and significant differences in LD rates along a salinity gradient were found. Our data suggest that although SR and LD are lower under very strongly saline conditions (EC > 16 mS cm−1), they are mainly driven by WTD and SM. This study reveals the importance of maintaining high and stable water table to decrease decomposition and promote accumulation of organic matter. These attributes could be targeted for constructed peatlands, which are currently being tested in the AOSR.