Simulation and evaluation of the water purification function of Zhalong Wetland based on a combined water quantity-quality model

Abstract

The water purification function of natural wetland systems is widely recognized, but rarely studied or scientifically evaluated. Extensive studies have been carried out by various international wetland research communities to quantify the water quality improvement ability of the natural wetlands, in order to maintain such ability and wetland ecological health. This study aims to evaluate the purification function of Zhalong Wetland in China for removing total nitrogen (TN) and phosphorus (TP), based on ex-situ experiments and the development of a combined water quantity-quality model. Experiments and model predictions were carried out with different input TP and TN concentrations. Statistical analyses demonstrated that the relative errors between model simulations and experimental observations for TN and TP were 8.6% and 12.4%, respectively. With water retention time being maintained at 90 d, the removal rate of these pollutants could not reach the required Grade V standards, if the inflow TN concentration was over 42 mg L−1, or the input TP concentration was over 14 mg L−1. The simulation results also demonstrated that, even with Grade V quality standard compliance, when the water inflow from surrounding industries and agriculture lands into Zhalong Wetland reaches 0.3×108 m3 a−1, the maximum TN and TP loads that the reserve can cope with are 1.26×103 t a−1 and 0.42×103 t a−1, respectively. Overall, this study has produced a significant amount of information that can be used for the protection of water quality and ecological health of Zhalong Wetland.