Chloride removal capacity and salinity tolerance in wetland plants

Deicing with sodium chloride maintains safe roads in the winter, but results in stormwater runoff with high chloride (Cl-) content that causes various downstream problems. Chloride-rich water risks contaminating groundwater, shortening the lifespan of concrete and metal constructions, and being toxic to aquatic organisms. Current stormwater treatment methods are unable to remove Cl-, but wetland plants with high chloride uptake capacity have potential to decrease Cl- concentrations in water. The aim was to identify suitable plant species for removing Cl- from water for future studies on phytodesalination of water, by comparing 34 wetland plant species native to Sweden in a short-term screening. Additionally, Carex pseudocyperus, C. riparia, and Phalaris arundinacea was further compared as to their salinity tolerance and tissue Cl- concentration properties. Results show that Cl- removal capacity, tissue accumulation, and tolerance varied between the investigated species. Removal capacity correlated with biomass, dry:fresh biomass ratio, water uptake, and transpiration. The three tested species tolerated Cl- levels of up to 50-350 mg Cl- L-1 and accumulated up to 10 mg Cl- g(-1) biomass. Carex riparia was the most Cl(-)tolerant species, able to maintain growth and transpiration at 500 mg Cl- L-1 during 4 weeks of exposure and with a medium removal capacity. Due to a large shoot:plant biomass ratio and high transpiration, C. riparia also had high shoot accumulation of Cl-, which may facilitate harvesting. Phalaris arundinacea had the highest removal capacity of the investigated species, but displayed decreased growth above 50 mg Cl- L-1. From this study we estimate that wetland plants can remove up to 7 kg Cl- m(-2) from water if grown hydroponically, and conclude that C. riparia and P. arundinacea, which have high tolerance, large biomass, and high accumulation, are suitable candidates for further phytodesalination studies.

Automated summary

This study compared the chloride removal capacity of 34 wetland plant species native to Sweden and further examined the salt tolerance and tissue chloride concentration of Carex pseudocyperus, C. riparia, and Phalaris arundinacea. The results showed variations in chloride removal capacity, accumulation, and tolerance among the species. C. riparia and P. arundinacea were identified as suitable candidates for further phytodesalination studies due to their high tolerance, large biomass, and high accumulation.