GROWTH OF TWO AQUATIC MACROPHYTE SPECIES IN ARTIFICIAL FLOATING ISLANDS IN AN OHIO WETLAND: POTENTIAL FOR NUTRIENT SEQUESTRATION

Nutrient pollution is one of America's most widespread, costly, and challenging environmental problems, affecting all 50 states. Artificial Floating Islands (AFIs) have been documented as an efficient, environment-friendly, and cost-effective method to tack nutrient pollution. However, most AFI studies were conducted in lab scale and AFI applications in Ohio is limited. To assess the nutrient-removal efficiency of AFIs in natural conditions, we conducted a combination of field and mesocosm experiments with two native aquatic plant species, Carex comosa and Eleocharis palustris, in a constructed wetland in north-central Ohio in 2020. During the study period, C. comosa outperformed E. palustris with respect to biomass accumulation and root system development. C. comosa in the field experiments had a total dry biomass production of 58.5 ± 22.2 g/plant compared to 6.1 ± 3.2 g/plant in E. palustris. C. comosa had a relatively balanced growth of above and below-ground tissues, with a ratio of 1.12 for shoots-to-roots dry biomass accumulation, while E. palustris tended to allocate more biomass to the roots, with a shoots-to-roots dry biomass accumulation ratio of 0.02. The maximum estimated N and P storage for C. comosa were 19587 mg/m² and 1287 mg/m², respectively, whereas they were 2239 mg/m² and 161 mg/m² for E. palustris, respectively. Besides direct uptake of nutrients by plants, the more developed root system of C. comosa suggested that AFIs containing C. comosa potentially had a higher total nutrient removal capacity. The growth conditions of both species were significantly affected by the seasonal dynamics with respect to their biomass production and root elongation, in that both species largely reduced their biomass accumulation and plant elongation in late summer. Therefore, to achieve the optimal removal performance of C. comosa, we recommend that the plants should be installed into the AFIs in mid-to-late spring. This study suggested that C. comosa is a promising candidate for AFI applications for nutrient pollution remediation.