Nitrogen removal from a riverine wetland: A field survey and simulation study of Phragmites japonica

Because Phragmites japonica is one of the dominant plant species in riverine wetlands in South Korea, we constructed an individual-based plant growth model to determine management strategies for maximizing nitrogen removal by P. japonica for water quality improvement purposes. We calibrated our model using field data on the growth, reproduction, and mortality of P. japonica individuals collected over one growing season in 1997 (May-October). The model effectively predicted seasonal changes in the number of the individuals (r² = 0.89), aboveground biomass (r² = 0.85), and nitrogen concentration (r² = 0.91). Total nitrogen, however, was poorly explained by our model (r² = 0.53). To evaluate the effects of biomass removal (e.g. harvest or grazing) on Phragmites management strategies, removal was simulated by manipulating the intensity and period of biomass loss. Distinct patterns in population density and biomass were produced in intensity-period phase planes, suggesting that population dynamics are influenced by a strong relationship between disturbance intensity and period. In addition, the highest rates of nitrogen removal by P. japonica occurred for high-density populations that maintained relatively low biomass levels.