The Effects Of Invasive Macrophytes Phragmites Australis And Typha Angustifolia On Nitrate Removal In High Nitrate Wetland Sediments

Constructed wetlands are quickly becoming inundated with invasive species like Phragmites australis and Typha angustifolia which are capable of changing whole ecosystem function and community composition. We wanted to assess how plants affect dissolved oxygen (DO) and dissolved organic carbon concentrations (DOC), and in turn if they increase nitrate (NO3-N) removal rates relative to barren sediments. Using a NO3-N/Br tracer test, we tested NO3-N removal rates, DO, and DOC concentrations. After the tracer test, we measured above- and below-ground plant biomass and sediment characteristics. NO3-N removal did not differ across the treatments. Phragmites australis microcosms had significantly higher sediment bulk density and organic matter concentrations compared to T. angustifolia (P=0.0049, df=5,23) and barren sediment (P=0.0033, df=5,23) microcosms, however T. angustifolia and barren sediment treatments were not significantly different (P=0.1021, df=5,23). In NO3-N saturated environments, carbon outputs from roots may be insufficient to sustain microbial demands for denitrification. With DOC and DO concentrations near zero at all times in the rhizosphere, it seems likely that detritus and organic matter build up drive nitrate removal.