Floating treatment wetlands for brackish ponds: plant salinity tolerance evaluation
摘要
Floating treatment wetlands (FTWs) enhance the nutrient removal efficiency of ponds. However, most FTW research has focused on freshwater applications, with little plant selection guidance for ponds along the salinity gradients that are common in coastal regions. Salinity can damage or kill the typical freshwater plants used in FTWs, decreasing overall nutrient removal efficacy and important aesthetic value. Four greenhouse studies were performed to assess the performance of 11 native aquatic macrophytes under salinity regimes that span oligohaline and mesohaline conditions. After the 8-week experimental period, Canna flaccida Salisb, and Verbena hastata L. were not salt-tolerant and did not survive in salinity exposures above 0.5 g l−1. Phyla nodiflora (L.) Greene demonstrated low salt tolerance (< 5 g l−1). Crinum americanum L., Kosteletzkya virginica (L.) C. Presl ex. Al. Gray, Bacopa monnieri L., and Uniola paniculata L. were moderately salt-tolerant, surviving with salinity exposures < 10 g l−1. Solidago sempervirens L., Spartina patens (Aiton) Muhl., Sporobolus virginicus (L.) Kunth, and Borrichia frutescens (L.) DC. were the most salt-tolerant and showed minimal signs of stress (mean visual stress scores above 3) in salinity exposure scenarios up to 18 g l−1. Plants were more compact in growth habit with higher salinity exposures. Results from this study provide a baseline for practitioners detailing plants that may be suitable for installation in FTWs deployed in brackish ponds.