Phosphorus uptake in emergent macrophytes: An evaluation of Vermont-native wetland plant suitability for floating treatment wetland applications in urban stormwater settings

摘要

The USEPA’s revised total maximum daily load (TMDL) for Lake Champlain has Vermont scientists and legislators seeking effective means for curbing phosphorus loads in the Lake Champlain Basin. Developed lands are a critical nonpoint source for phosphorus loading, and green stormwater infrastructure (GSI) ecologically and effectively slow and/or capture nutrients and other pollutants characteristic of urban stormwater runoff. Floating treatment wetlands (FTWs), buoyant mats fitted with wetland plants, are an inexpensive and effective option for improving the water quality of runoff. In urban settings, FTWs are frequently applied to wet stormwater ponds as retrofits. While there are studies demonstrating the efficacy of this practice worldwide, there is currently no research on FTW performance for Vermont’s climate. The goal of this experiment is to evaluate some commonly used and untested plant species for phosphorus removal. A greenhouse microcosm study was performed using twelve Vermont-native emergent wetland plant species. The plants were grown hydroponically in simulated floating treatment wetlands for a period of twelve weeks. Species tested included common genera for this application, among other less commonly used macrophytes: Carex, Schoenoplectus, Pontederia, Sparganium, Scirpus, Sagittaria, Iris, Asclepias, Symphyotrichum, Lobelia, and Zizania. Plants were grown in high (control) and low (simulated stormwater) nutrient solutions of tap water and diluted 7-9-5 NPK fertilizer. After harvest, plants analyzed for total phosphorus concentration of whole-plant biomass using ICP-AES. In low nutrient conditions, Sparganium, Scirpus, Carex comosa, Asclepias, Schoenoplectus, and Pontederia, respectively, accumulated the most phosphorus in their tissues. The results of nutrient uptake analysis, when considered with qualitative root and shoot growth habit in this setting, will inform plant selection for a FTW to be launched in South Burlington, Vermont in May 2016.