Field-scale simulation of runoff and water quality in a paddy field: A study of novel RWQSPad model

Abstract

A Runoff & Water Quality Simulation model for Paddy fields (RWQSPad) based on water balance and nutrients mass balance was developed to simulate paddy hydrological process, nutrients (nitrogen and phosphorous) and chlorophyll-a dynamics at field scale. A paddy field was separated into flooded water layer and soil layer, and a plant growth component of EPIC model was applied to simulate crop interception and evapotranspiration. Parameters named minimum suitable water depth (H_d), maximum suitable water depth (H_u) and minimum ridge height (H_t) were introduced to control the processes of irrigation and runoff. Besides that, all the important nutrients transformation processes that take place in flooded rice field were considered by the first-order reaction kinetics equations. The effect of limitations of light, temperature and nutrients to floating-algae dynamics indicated by chlorophyll-a was taken into account. The application of RWQSPad model in a paddy field plot of the Shangzhuan Town, Beijing, China showed that the model can simulate well the hydrological, nitrogen and phosphorous transformation processes and chlorophyll-a dynamics in surface water in the paddy field. Simultaneously, it also demonstrated a good level of runoff simulation which can fit quite well with the observed data and a great potential in simulating rainfall-runoff-pollution. RWQSPad model gives more reasonable results of the runoff amount and nutrient losses, and shows a better performance on the modelling of drainage processes.