Plant suitability for floating treatment wetland applications in brackish waters Ecological Engineering

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. Grant no. NA22OAR4170114

半咸水水体在沿海地区提供关键的生态系统服务，助力人类与生态环境健康。对半咸水水体中的污染物进行治理至关重要。浮床处理湿地（Floating Treatment Wetlands, FTWs）是一类常用于改善淡水系统水质的修复技术。然而，浮床处理湿地对于盐度波动水体的适用性尚未明确。本研究的目标为定量分析四种植物的生长与存活情况，并明确哪些水生大型植物适用于部署在半咸水水体中的浮床处理湿地。
本研究针对美国东南部盐沼常见的四种物种（Distichlis spicata、Juncus roemerianus、Spartina alterniflora、Spartina patens），设置0.5、5.0、18 g·L⁻¹三种盐度暴露条件，开展了为期7周的栽培试验。本研究同时定量测定了这四种植物体内的大量与微量营养元素浓度，以明确浮床处理湿地中的植物生长如何改变其根系与地上部分的营养元素分配模式。盐沼原生植物与浮床处理湿地栽培植物的组织内固定营养元素比例发生了偏移。植物组织内的钠钙比（Na:Ca）在盐沼原生植株中高于浮床处理湿地栽培植株。
就生物量产出而言，长穗鼠狐黍（D. spicata）与柔茎蔺（J. roemerianus）的生长量均极低，且不受盐度暴露条件影响。柔茎蔺在18 g·L⁻¹盐度条件下无法存活。互花米草（S. alterniflora）与海滨米草（S. patens）在所有盐度条件下均实现了最高的生物量产出与最终组织营养元素浓度。
本试验结果表明，在所测试的四种物种中，互花米草与海滨米草最具备应用于半咸水环境浮床处理湿地的潜力。项目编号：NA22OAR4170114