Turning a New Leaf on Salinization: Phytoremediation of Saline Soils using Canadian Halophytes

Abstract

Soil salinization is an increasing issue around the globe. Two key sources of anthropogenic salinization include road salting and saltwater production from oil exploration. Widespread soil and freshwater salinization are impacting ecosystem health and biodiversity. Phytoremediation is a ‘green’ technology that is less costly than chemical or physical means of salt removal and has the added benefit of controlling soil erosion. Over two field seasons beginning in the spring of 2022, four native halophytes; - two accumulators (Panicum virgatum and Sporobolus cryptandrus) and two recretohalophytes (Sporobolus michauxianus and Bouteloua curtipendula) were evaluated at a field site in the Greater Toronto Area (GTA) impacted by road salt ([Cl-]soil = 365 mg/kg). Remediation calculations for 2023 estimate that it would take the accumulator species, P. virgatum was 2 years, to remediate soil to 20 mg/kg (background level at this site). Using the same calculations, the excretor species, S. michauxianus and B. curtipendula would take 2 and 13 years, respectively to remediate the soil. At a former oil and gas battery site in Western Canada ([Cl-]soil = 1200 mg/kg), three naturalized (Puccinellia distans, Atriplex patula, Chenopodium album) and one native (Distichlis spicata) halophyte were evaluated for their phytoremediation potential. Calculations of salt accumulation for 2023 data indicate that A. patula and C. album and would remediate the soil from 1200 mg/kg to 350 mg/g (the British Columbia guideline) within 3 years while P. distans and D. spicata would take 2.5 and 1.5 years, respectively. The composting of plant biomass was explored as a method of re-purposing harvested accumulator halophytes. Following the first season of phytoextraction, portions of the aboveground biomass of the accumulator halophytes, P. virgatum and B. curtipendula were collected from the GTA site. Following nine months of composting the plant biomasses were significantly reduced. Furthermore, with sufficient washing, chloride was effectively leached out of the biomasses of both halophytes (i.e. >99% reduction in chloride). Together, the two field studies demonstrate the potential of halophytic plant species to remediate of salt-impacted soils. Furthermore, composting the salt-laden plant biomass is a viable management strategy and a sustainable alternative to common methods of disposal including incineration or landfilling.