关键词: 水源地, 非点源污染, 事件平均浓度, 负荷系数, 初期冲刷比率

Abstract:

Under climate change, the increasing frequency of high-intensity rainfall has complicated non-point source pollution (NPS) dynamics, necessitating further research to elucidate emission patterns and support refined pollution control in water source areas. Based on field monitoring data from moderate, heavy, and torrential rain events, this study analyzed the dynamic emission patterns and first-flush effects of NPS pollution from typical underlying surfaces in water source areas. Runoff coefficients ranged from 0.55 to 0.99 for roads and residential areas, but only 0-0.71 for paddies, vegetable fields, and forests, with peak runoff delayed by 4-12 h in the latter. The results showed that under the three rainfall events, the runoff coefficients of traffic roads and residential areas ranged from 0.55 to 0.99, whereas those of paddy fields, vegetable fields, and forestlands ranged from 0 to 0.71, with the peak runoff of the latter lagging 4-12 h behind that of former. The peak fluxes of COD, TN, and TP from traffic roads were 0.10-0.53, 0.01-0.04, and 0.0047-0.0006 g·h⁻¹·m⁻² higher than those from residential areas, respectively. Under torrential rainfall, paddy and vegetable fields exhibited even higher peak fluxes, reaching 1.3-1.6 times (COD), 4.0-5.4 times (TN), and 2.9-4.6 times (TP) the fluxes of traffic roads. Under moderate rainfall, the Event Mean Concentrations (EMCs) of COD, TN, and TP from both traffic roads and rural residential areas were 1.4-1.7 times, 6.5-7.8 times, and 5.9-6.6 times higher than those under torrential rainfall, respectively. Notably, moderate rainfall events following longer antecedent dry periods significantly elevated pollutant EMCs. Under torrential rainfall, the pollution load coefficients of COD, TN, and TP were relatively highest in vegetable fields, being 1.2-1.5 times higher than those in paddy fields, 1.4-6.8 times higher than those on traffic roads, 3.2-8.1 times higher than those in forestlands, and 2.2-10.6 times higher than those in rural residential areas. Regarding the initial flush ratio (R_MFF30) of the three pollutants, under moderate and heavy rain, the order was COD> TN>TP, whereas under torrential rainfall, TP and TN were generally greater than COD. For COD and TN, the R_MFF30 was generally higher for traffic roads and rural residential areas than for vegetable fields, paddy fields, and forestlands. Intercepting the initial 30% of runoff can reduce 30%‒72% of the COD load and 33%‒39% of the TN load. Conversely, for TP, the R_MFF30 was higher in vegetable fields, paddy fields and forestlands. Capturing 30% of the runoff reduced the TP load by 58%‒62%, compared with a reduction of only 20%‒52% from traffic roads and rural residential areas. Therefore, during moderate-to-heavy rainfall events, priority attention should be given to non-point source pollution from impervious underlying surfaces, particularly during rainfall events following extended dry periods. During high-intensity torrential rainfall events, additional focus must be placed on agricultural non-point source pollution, as its flux peaks and initial flush loads may adversely affect the water quality in source water areas.

Key words: water source area, non-point source (NPS) pollution, event mean concentration, load coefficient, first flush ratio