Effects of Low Impact Development Practices on the Mitigation of Nutrient Pollution in Deep Bay, China

摘要

In this study, storm water management model (SWMM) was coupled with environment fluid dynamic code (EFDC) to investigate the effects of low impact development (LID) controls at urban catchment scale on mitigating the nutrient pollution in Deep Bay, southeastern China. Six scenarios with different area percentage of LTD practices were proposed and simulations were carried out using an annual historical rainfall in 2014 and the 0.25-year return period (T=0.25) design rainfall event. The output rainfall runoff nutrient loads (RRNLs) from the Deep Bay Basin and water quality variations were observed using ocean-land coupled model. RRNLs mainly occurred during May and September, with 2866.6t dissolved inorganic nitrogen (DIN) and 169.7t phosphate (PO_4~3-P), accounting for 77% of the annual load. The RRNL reduction rates had a positive correlation with the area LID practices with annual historical rainfall and design rainfall event. The annual reduction rates for DIN and PO_4~3-P were approximately 58.1% and 62.3%, respectively, when the LID practice area accounted for 90% of impervious land. The monthly mean concentration of seawater nutrient decreased with the increase of the LID practices' area percentage to impervious land area. Configuring 90% impervious land to LID practices, the maximum monthly mean concentration of nutrient could be reduced by about 15.2%~18.3%. And the peak concentration of seawater nutrient could be decreased by about 15% after episodic event and be delayed about a half day. The impact of rainfall runoff load from basin could be alleviated by LED practices, thereby mitigating the nutrient pollution in coastal zone. The method and simulation results in this study will provide a scientific basis for integrated coastal zone water environment management and LED practice planning.