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随着极端降雨和人类活动的影响,流域水环境治理面临新的挑战[1]。近年来白龙江流域推进水资源管理和生态修复,不断强化水污染治理,白龙江水质有所改善。作为嘉陵江一级支流,长江二级支流的白龙江位于长江水系上游,地处生态脆弱带和敏感区,泥石流、滑坡等地质灾害频发,水土流失严重,水环境系统极易破坏[2-4]。在社会经济快速发展和水环境治理背景下,统筹考虑点源污染和非点源污染对河流水质的共同影响,确保流域水环境得到长期有效治理是白龙江流域生态文明建设的迫切需求。
近年来国内外许多学者在流域水质模拟和水环境治理方面做了大量研究[5-13],如利用WASP模型、QUAL2K模型、输出系数模型等分析流域主要污染源、估算污染负荷、模拟分析面源污染对河流水质的影响等。易绍荣等[14]通过SWAT模型估算污染物入河负荷,分析污染物负荷空间分布特征,识别了重污染区域和关键污染源,提出了水环境保护措施。黄宏等[15]基于Monte Carlo模拟河流水质,利用水质监测数据定量分析各个断面水质健康状况,评价各个水质指标对水体污染的影响程度,得出影响因子主要为TN、NH4+-N和DO。戴君等[16]以松花江哈尔滨段为研究对象,构建EFDC水动力-水质模型,以COD、NH4+-N为主要污染物,结合情景分析方法对松花江哈尔滨段支流污染负荷多情景变化下对干流水质及下游出口断面水质进行量化评估,确定了不同水文情景下污染物最大浓度。
在流域水环境模拟中,应准确分析流域内点源污染和面源污染的时空分布特征和负荷大小,保证模拟结果可靠性[17-20]。但目前大多数研究只考虑非点源污染入河负荷,忽视了农村生活垃圾、城镇生活污水等点源污染入河负荷,导致模型参数率定困难、模拟精度低,且河流水质模拟过程中未能考虑水体中硝化、反硝化、污染物吸附沉积等因素,难以准确模拟河流水质沿程变化情况和污染物时空迁移特征。为此,本次研究通过耦合模型分别计算面源污染和点源污染负荷,在污染源分类调查的基础上,模拟计算各污染物入河负荷,并分析各污染负荷时空分布特征,模拟各污染物在随水体迁移转化过程,探讨白龙江流域甘肃段水污染风险,为流域水环境治理规划提供借鉴。
基于InfoWorks ICM模型的白龙江流域甘肃段水质模拟及分析
Water quality simulation and analysis in Gansu section of Bailong River Basin based on InfoWorks ICM model
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摘要: 针对白龙江沿岸农业种植、畜禽养殖等产业发展影响河流水质的问题,以甘肃省南部白龙江流域为研究对象,采用改进输出系数模型计算丰、平、枯水年等典型水文情景下流域内工业、农村生活垃圾、农村生活污水、畜禽养殖、城镇生活污水、城镇径流和农田径流等污染源污染负荷,基于InfoWorks ICM构建了白龙江水动力水质模型,模拟分析COD、TN、NH4+-N和TP等污染负荷分布特征,评估了最不利水文条件下白龙江水质污染风险,验证了该模型在流域水质污染模拟评估的适用性。研究结果表明,不同水文情景下污染物入河负荷主要来源存在显著差异,如丰水年和平水年农田径流是COD污染的主要来源,污染负荷分别达到1 382.56、1 058.98 t,而枯水年污染源主要是城镇径流。污染物负荷存在明显空间差异,研究区内子流域污染负荷空间分布不均匀,高污染负荷主要出现在中下游子流域。白龙江水质在汛期和非汛期差异较大,非汛期水质更差。通过模拟最不利水文情景 (枯水年非汛期) 发现,研究区内白龙江NH4+-N浓度最大位置出现在中下游,最高可达1.43 mg·L−1,且中下游TP浓度较高,最高值为0.35 mg·L−1,难以满足Ⅲ类水体水质要求,存在水污染风险。利用改进输出系数模型评估污染物负荷具有较好的可靠性,基于InfoWorks ICM构建的河流水动力水质模型在污染物时空分布评估适用性较强,为我国河流水质模拟和流域水环境治理提供示范参考和决策依据。Abstract: Aiming at the problems of river water quality affected by the development of agricultural planting, livestock and poultry breeding and other industries along Bailong River, the Bailong River basin in southern Gansu Province was taken as the research object. The improved output coefficient model was used to calculate the pollution load of industrial, rural domestic waste, rural domestic sewage, livestock and poultry breeding, urban domestic sewage, urban runoff and farmland runoff in the basin under typical hydrological scenarios such as abundant, flat and dry years. Based on InfoWorks ICM, the dynamic water quality model of the Bailong River was constructed. The distribution characteristics of COD, TN, NH4+-N, TP and other pollution loads were simulated and analyzed, and the risk of water pollution in the Bailong River under the most unfavorable hydrological conditions was assessed, and the applicability of the model in the simulation and assessment of water pollution in the basin was verified. The results showed that the main sources of pollutant load into the river were different under different hydrological scenarios. For example, farmland runoff was the main source of COD pollution in wet and normal years, and the pollution load reached 1 382.56 t and 1 058.98 t respectively, while the pollution source in dry years was mainly urban runoff. There were obvious spatial differences in pollutant loads, and the spatial distribution of pollution loads in sub-basins in the study area was not uniform, and high pollution loads mainly appeared in the middle and lower sub-basins. The water quality of Bailong River was different in flood season and non-flood season, and the water quality in non-flood season was worse. Through the simulation of the most unfavorable hydrological scenario (non-flood season in dry year), it was found that the maximum concentration of NH4+-N in the Bailong River in the study area appeared in the middle reaches, reaching up to 1.43 mg/L, while the TP concentration was higher in the middle and lower reaches, reaching the highest value of 0.35 mg/L, which was difficult to meet the water quality requirements of Class III water bodies, and there was a risk of water pollution. The improved output coefficient model had good reliability in the assessment of pollutant load, and the hydrodynamic water quality model based on InfoWorks ICM had strong applicability in the assessment of spatial and temporal distribution of pollutants, which provided demonstration reference and decision-making basis for river water quality simulation and watershed water environment management in China.
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表 1 改进输出系数模型主要参数率定结果
Table 1. The main parameter calibration results of the improved output coefficient model
率定参数 具体项目 率定结果 农村生活污水产生系数/
(g·人−1·d−1)COD 16.86 TN 5.32 NH4+-N 4.31 TP 0.47 农村生活垃圾负荷/
(g·kg−1)COD 57 TN 14.3 NH4+-N 8.6 TP 3.1 畜禽养殖产生系数/
(g·头−1·d−1)COD 16.8 TN 6.2 NH4+-N 3.4 TP 0.82 农田径流源强系数/
(kg·亩−1·a−1)COD 10.2 TN 3.5 NH4+-N 2.8 TP 0.53 表 2 InfoWorks ICM河流水动力水质模型主要参数率定结果
Table 2. The main parameters calibration results of InfoWorks ICM river hydrodynamic water quality model
率定参数 具体项目 率定结果 水文参数 河床糙率 0.038 排放系数 0.86 模式上限 0.94 扩散系数/(m2·s−1) COD 12.6 NH4+-N 14.6 TN 16.2 TP 8.3 DO 9.7 衰减系数/d−1 COD 0.13 NH4+-N 0.08 TN 0.15 TP 0.15 复氧系数/(m·hr−1) DO 0.04 表 3 不同水文情景下入河污染负荷
Table 3. Instream pollution load under different hydrological scenarios
t·a−1 水质项目 枯水年 平水年 丰水年 COD 1 724.93 2 372.56 2 891.44 NH4+-N 109.53 182.46 202.99 TN 273.73 435.75 496.55 TP 15.42 22.82 25.76 -
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