APPLICATION OF FLOATING WETLANDS TO IMPROVE URBAN STREAM QUALITY

Increasing impervious surface associated with urbanization leads to degradation of a stream draining the area. Urban stream syndrome is the series of ecological changes, including high nutrient concentration, that negatively impact urban streams. The abundance of nutrients can lead to algae growth and eutrophication, deteriorating the ecological health of waterbodies and aquatic ecosystem. To address nutrient pollution, floating wetlands have emerged as an in-situ phytoremediation of stream ecosystems. Floating wetlands are constructed with buoyant substrate that allow plants to grow hydroponically. Along with the uptake of nutrients by plants, microbial biofilms formed on the roots of these plants absorb nutrients, improving water quality. Limited studies have been done on floating wetlands performance in urban streams. Using a 90m² floating wetland system located on a side canal on the north branch of the Chicago River, we aim to answer the following questions: 1) Do the floating wetland lower concentrations of nitrate as nitrogen ([NO₃-N]) and of phosphate ([PO₄^3-]) in the river? and 2) Are there differences in the effectiveness of floating wetlands in lowering nutrient concentration during growing season (April-September) where plant activity is at its peak, as compared to dormant season (October to March), where plant activity is minimal or cease? Between April 29th, 2018, and December 16th, 2023, water samples were collected upstream and downstream of the wetland and analyzed for [NO₃-N] and [PO₄^3-] using ion chromatography. From analysis, the mean [NO₃-N] upstream (5.8 mg/L) and downstream (4.6 mg/L) and [PO₄^3-] upstream (3.9 mg/L) and downstream (3.3 mg/L) show that the floating wetland lowered the overall [NO₃-N] and [PO₄^3-] by 20% and 15%, respectively over the entire sampling period. Decrease in nutrient concentration occurred during both the growing and dormant season. The mean [NO₃-N] concentration upstream and downstream for the growing season was (5 mg/L) and (3.9 mg/L); and (7 mg/L) and (5.5 mg/L) for the dormant season. While the mean [PO₄^3-] concentration upstream and downstream for the growing season was (3 mg/L) and (2.5 mg/L); and (5.1 mg/L) and (4.3 mg/L) for the dormant season. The floating wetland demonstrates potential for improving water quality in urban streams impacted by urbanization despite its small coverage area.