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BACKGROUND Ecological treatments are effective for treating agricultural wastewater. In this study, wetland microcosms vegetated with Myriophyllum aquaticum were designed for nitrogen (N) removal from two strengths of swine wastewater, and 15N-labelled ammonium ( NH4+-N) was added to evaluate the dominant NH4+-N removal pathway. RESULTS The results showed that 98.8% of NH4+-N and 88.3% of TN ( TN: 248.6 mg L−1) were removed from low-strength swine wastewater ( SW1) after an incubation of 21 days, with corresponding values for high-strength swine wastewater ( SW2) being 99.2% of NH4+-N and 87.8% of TN ( TN: 494.9 mg L−1). Plant uptake and soil adsorption respectively accounted for 24.0% and 15.6% of the added 15N. Meanwhile, above-ground tissues of M. aquaticum had significantly higher biomass and TN content than below-ground ( P < 0.05). 15N mass balance analysis indicated that gas losses contributed 52.0% to the added 15N, but the N2O flux constituted only 7.5% of total gas losses. The dynamics of NO3−-N and N2O flux revealed that strong nitrification and denitrification occurred in M. aquaticum microcosms, which was a dominant N removal pathway. CONCLUSION These findings demonstrated that M. aquaticum could feasibly be used to construct wetlands for high N-loaded animal wastewater treatment. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]