Plant suitability for floating treatment wetland applications in brackish waters

Abstract

Brackish water bodies provide critical ecosystem services supporting human and environmental health in coastal regions. Mitigation of contaminants in brackish waters is critical. Floating treatment wetlands (FTWs) are a remediation technology typically applied to improve water quality in freshwater systems. However, the applicability of FTWs to waters with fluctuating salinity has not been determined. The goal of this study was to quantify the growth and survival of four plant species and determine which aquatic macrophytes are suited for use in FTWs deployed in brackish waters. This study trialed four species common to salt marshes of the Southeastern USA (Distichlis spicata, Juncus roemerianus, Spartina alterniflora, and Spartina patens) grown under three salinity exposures (0.5, 5.0, and 18 g⋅L−1) over 7 weeks. We also quantified macro- and micro-nutrient concentrations in these species to enable determination of how plant growth in FTWs may alter nutrient partitioning in roots and shoots. The ratios of nutrients fixed in tissues of plants grown in the salt marsh vs. those grown in FTWs shifted. The ratio of Na:Ca within tissues were higher for plants grown in the saltmarsh than those grown in the FTWs. Regarding biomass production, D. spicata and J. roemerianus grew very little, regardless of salinity exposure. J. roemerianus did not survive at 18 g⋅L−1 salinity. S. alterniflora and S. patens had the highest biomass production and final nutrient concentrations in tissues across all salinities. These trials indicated that of the four species tested, S. alterniflora and S. patens hold the most promise for FTW application in brackish settings.