Nitrogen Dynamics and Biomass Production in a Vertical Flow Constructed Wetland Cultivated with Forage Rice and their Mathematical Modeling

Abstract

Forage rice has high potential to produce biomass, and the vertical flow (VF) constructed wetland in which forage rice is cultivated is one of the effective ways to achieve the purification of eutrophicated water and biomass production simultaneously. To design and manage the VF constructed wetlands cultivated with forage rice adequately, nutrient dynamics and the growth of the rice should be understood quantitatively. In this study, we performed a series of experiments replicating VF constructed wetlands involving the cultivation of a variety of forage rice (Kusahonami) using river water (supply rate : 0.1, 0.2, and 0.6 m3/(m2·day)) for 169 days. The results showed that the rice biomass increased with the river water supply rate. A mathematical model was developed based on these experimental observations in order to quantitatively explain the nitrogen dynamics in VF constructed wetlands cultivated with forage rice. The changes in both the rate of nitrogen assimilation by rice and the denitrification rate with the change in the rate of water supply were simulated with the proposed model.