Oil sands mining in the Athabasca oil sands region disturbs large tracts of peatlands as the vegetation-soil layer must be removed. Processing oil sands produces large volumes of wet material containing oil sand process-affected water (OSPW) that has elevated concentrations of sodium (Na) and naphthenic acids (NAs). Attempts to reclaim mined landscapes to peat-forming systems command knowledge of the transport, fate and impact of OSPW in organic soils. Four mesocosms placed in a greenhouse were randomly assigned with two treatments: 1) a moss carpet (Bryum pseudotriquetrum) and 2) graminoids (Carex aquatilis and Calamagrostis stricta). Transport of Na and NAs through peat was significantly delayed by sorption and diffusion in peat matrix. After two growing seasons of receiving OSPW, the graminoid plants continued to grow without showing stress from OSPW, while mosses showed a considerable decline in health. Microorganisms were more active under sedges than mosses and their activity varied over time either because of seasonal variation or as a consequence of variation in Na concentration. The findings of this study are limited due to the small number of replicates and the lack of a control, but represent a first step towards the creation of peatlands in the post-mined areas.