The performance of the DNCW achieved high removal rates for COD, BOD, PO4-P, and NH3-N. No seasonal or water temperature effect on nitrogen removal was observed in the DNCW in subtropical Taiwan. Mass loading was a major factor in the nitrogen removal. However, atmospheric gains (precipitation minus evapotranspiration) appear to cause an increase in water flow, therefore reducing the loading rate, which reduces the nitrogen removal rate.