A HIGH-RESOLUTION ASSESSMENT OF THE IMPACT OF FLOATING TREATMENT WETLANDS ON NUTRIENT REMOVAL

Floating treatment wetlands (FTW) are a Beneficial Management Practice used to retrofit existing storm water ponds for increased nutrient removal. The long-term efficacy of FTW has been reported from low resolution data (e.g., weekly), but because some removal might be associated with uptake varying with photosynthesis, it is important to capture diel concentration changes to better quantify removal kinetics. This greenhouse experiment consisted of 8 mesocosms: 4 with planted mats, 2 with unplanted mats, and 2 controls, in lake water with added nitrate and phosphate. High resolution absorbance, temperature, and dissolved oxygen (DO) data were collected over 5 weeklong trials. Additionally, we evaluated the impact of water column mixing by turning pumps on halfway through each trial, resulting in significantly increased DO. First order nitrate removal rates were higher with FTW than unplanted mats or controls, but DO, turbidity, and Total Organic Carbon (TOC) were lower.