Modelling the potential for peat-block transplants to restore industrially contaminated Sphagnum peatlands

For centuries, humans have inadvertently been contaminating peatlands due to industrial emission of pollutants that degrade key peatland ecosystem functions, such as carbon sequestration. Returning the ecosystem functionality to these degraded peatlands remains a challenge due to adverse ecohydrological conditions and elevated peat pollutant concentrations, such as nickel (Ni) and copper (Cu), at the remnant peat surface. However, field-scale trials can be labour, time, and monetarily expensive with no guarantee of success. As a precursor to field-scale trials, we use a 10-year coupled hydrological and solute transport models in Hydrus-1D to assess the feasibility of using peat-block transplants to restore a peatland contaminated by Ni and Cu. The exceedance of critical capitula hydrological (soil water tension >100 mbar) and chemical ([Ni] and [Cu] > 10−6 mmol mL−1) thresholds that correspond with increased Sphagnum physiological stress were assessed using a series of modelled scenarios with varying peat-block thicknesses (5 to 30 cm in 5 cm increments), Sphagnum species (S. fuscum, S. rubellum, S. magellanicum, and an average Sphagnum), and initial contaminant loads (i.e., distance from a smelter). When the remnant peat contaminant load was largest (i.e., closer to a smelter) and the transplant thickness was 5 cm, the combined hydrological threshold and chemical thresholds in the capitula were exceeded in as little as least 2 years, while thicker transplants did not exceed the concentration threshold after 10 years. In general, the average Sphagnum exceeded the hydrological threshold most, followed by S. magellanicum, S. rubellum, and S. fuscum, respectively. A Monte Carlo and sensitivity analyses showed that the results of our modelling scenarios were generally robust. Based on these results, we suggest that targeting thicker (>20 cm) peat-blocks of S. fuscum and S. rubellum (i.e., densely growing Sphagnum spp.), would likely provide a suitable peat-block for transplant. This research provides a critical path forward for restoring contaminated and degraded peatlands.