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南水北调中线工程是我国水资源配置的战略工程,水质保护十分重要。掌握输水渠道的水质时空变化趋势,对与中线工程的水质管理工作具有重要意义。由于南水北调中线工程为长距离跨流域明渠输水,输水干渠具有硬化程度高、生物群落结构单一的基本特点,渠道水质变化可能与普通河流系统存在较大的差异。针对中线工程的水质变化和影响因素,已有一些学者进行了研究和探讨,如水源区的水质安全与生态影响[1-2],部分渠段的浮游植物、真核生物、浮游细菌分布特征[3-6],输水渠道水质指标的沿程变化等,但对渠道水质的时空变化趋势还缺少整体认识。
层次聚类 (hierarchical clustering) 是使用欧式距离通过计算不同类别数据点间的相似度将研究对象进行分类,并进行系统研究的一种方法[7],可有效降低原始监测数据集的维度,简化数据的复杂程度。以监测点位、时间、指标和评价结果等为对象进行聚类分析,便于分析各指标时空分布特征及指标间的相关性。近年来,层次聚类分析作为传统多元统计方法,被广泛应用于地表水环境监测数据分析。传统的水质类别评价采用单因子评价方法,虽然简单易行,但反映的水质信息有限[8]。水质指数法 (water quality index, WQI) 是基于物理、生物和化学水质参数提出的一种实用、高效的地表水质量评价方法。它可以充分利用水质参数信息,通过标准化的计算方法,有效呈现水质整体状况。自20世纪60年代以来,水质指数法在水质评价研究中被广泛应用[9],特别是在河流、湖泊和水库的水质评价中取得了良好效果[10-12]。本研究基于聚类分析与WQI对南水北调中线干渠进行水质分区与评价,为中线工程水质管理提供参考。
基于层次聚类和水质指数法的南水北调中线总干渠典型年份水质变化特征分析
Characteristics of water quality change in the canal of middle route project of South-to-North Water Diversion in typical years based on hierarchical clustering and water quality index method
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摘要: 为探明南水北调中线总干渠水质变化特征和时空分异规律,选择总干渠典型年份30 个断面 10 个水质指标的逐月监测数据,利用层次聚类和WQI水质指数法对水质变化进行分析。层次聚类将总干渠划分为3个渠段,陶岔至柳家佐连续24个断面为第一渠段,该渠段各项水质指标浓度相对较低,其中F.coli ( (44.41±56.11) 个·L−1) 、CODMn ( (1.94±0.11) mg·L−1) 、SO42− ( (29.38±1.68) mg·L−1) 和DO ( (9.74±1.42) mg·L−1) 等指标明显低于其他渠段;霸州、王庆坨、西黑山、惠南庄和团城湖为第二渠段,F.coli ( (184.5±323.16) 个·L−1) 、CODMn ( (2.08±0.29) mg·L−1) 、SO42− ( (27.21±1.81) mg·L−1) 和DO ( (10.82±2.15) mg·L−1) 等水质指标浓度有所升高;天津外环河为第三渠段,该渠段TN、NH3-N和BOD5浓度达到最大值,分别为(1.32±0.15)、(0.07±0.05) 和(1.52±0.51) mg·L−1) 。WQI计算结果表明,中线干渠WQI平均值在81~86之间,水质优良;夏季WQI平均值最低 (81) ,低于春季 (84) 、秋季 (83) 和冬季 (84) ,且WQI平均值沿程逐渐降低。该研究结果可为中线工程水质保护和管理提供理论依据。Abstract: In order to investigate the characteristics and spatiotemporal differentiation of water quality in the middle route of the South-to-North Water Diversion project. The monthly monitoring data of 10 water quality indexes in 30 sections of the main canal in typical years were selected, and the variation of water quality was analyzed by hierarchical clustering and WQI water quality index method. The main canal was divided into 3 types of water quality canal segments by hierarchical clustering. The 24 sections from Taocha to Liujiazuo were the first section,and the concentration of water quality indexes in this section was relatively low, the indexes of F.coli ((44.41±56.11) colonies·L−1), CODMn ((1.94±0.11) mg·L−1), SO42− ((29.38±1.68) mg·L−1) and DO ((9.74±1.42) mg·L−1) were lower than those of other canals. Bazhou, Wangqingtuo, Xiheishan, Huinanzhuang and Tuancheng Lake were the second type of canals. Compared with the first type of canals, the concentrations of water quality indexes such as F.coli ((184.5±323.16) colonies·L−1), CODMn ((2.08±0.29) mg·L−1), SO42− ((27.21±1.81) mg·L−1) and DO ((10.82±2.15) mg·L−1) increased. Tianjin Waihuan River is the third type of canal section, and the concentrations of TN, NH3-N and BOD5 in this section reached the maximum values, which were ((1.32±0.15) mg·L−1), ((0.07±0.05) mg·L−1) and ((1.52±0.51) mg·L−1), respectively. The results of WQI calculation showed that, the average value of WQI was between 81 and 86, and the water quality was good. The mean value of WQI in summer was the lowest (81), lower than that in spring (84), autumn (83) and winter (84), and the mean value of WQI gradually decreased along the way. The research results can provide theoretical basis for water quality protection and management of the Middle Route Project.
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表 1 水质指标的权重值 (Pi) 和归一化值 (Ci)
Table 1. Weight Value (Pi) and Normalized Value (Ci) of Water Quality Index
水质指标 权重Pi 归一化值Ci 100 90 80 70 60 50 40 30 20 10 0 水温(WT)/ ℃ 1 21/16 22/15 24/14 26/12 28/10 30/5 32/0 36/-2 40/-4 45/-6 45/<-6 pH 1 7 7-8 7-8.5 7-9 6.5-7 6-9.5 5-10 4-11 3-12 2-13 1-14 溶解氧(DO)/ (mg·L−1) 4 ≥7.5 >7 >6.5 >6 >5 >4 >3.5 >3 >2 ≤1 <1 硫酸盐(SO42−)/ (mg·L−1) 2 <25 <50 <75 <100 <150 <250 <400 <600 <1 000 ≤1 500 >1 500 总磷(TP)/(mg·L−1) 1 <0.2 <1.6 <3.2 <6.4 <9.6 <16 <32 <64 <96 ≤160 >160 氨氮(NH3-N)/(mg·L−1) 3 <0.01 <0.05 <0.1 <0.2 <0.3 <0.4 <0.5 <0.75 <1 ≤1.25 >1.25 高锰酸盐指数(CODMn)/(mg·L−1) 3 <1 <2 <3 <4 <6 <8 <10 <12 <149 ≤15 >15 总氮(TN)/ (mg·L−1) 2 <0.8 <3.8 <7.5 <13 <18 <27 <48 <85 <149 ≤265 >265 五日生化需氧量(BOD5)/(mg·L−1) 3 <0.5 <2 <3 <4 <5 <6 <8 <10 <12 ≤15 >15 粪大肠菌群(F.coli)/(个·L−1) 3 <5 <50 <100 <200 <300 <400 <500 <700 <1 000 ≤1 400 >1 400 表 2 2018年中线干渠水质参数季节变化
Table 2. Seasonal changes of middle route canal water quality parameters in 2018
水质指标 春季 夏季 秋季 冬季 pH 8.19±0.16 8.29±0.24 8.39±0.15 8.14±0.18 NH3-N/(mg·L−1) 0.05±0.02 0.05±0.02 0.03±0.02 0.03±0.01 F.coli/(个·L−1) 19.11±18.21 115.44±175.04 127.06±234.34 18.06±19.31 CODMn/(mg·L−1) 1.94±0.11 2.03±0.16 2.02±0.2 1.88±0.16 SO42−/(mg·L−1) 28.81±1.4 28.22±1.39 25.52±1.39 28.09±1.79 DO/(mg·L−1) 9.93±1.34 8.67±0.73 9.44±1.32 11.76±1.4 BOD5/(mg·L−1) 0.9±0.49 0.81±0.4 0.92±0.45 1.21±0.49 WT/(℃) 14.57±5.12 27.29±3.13 21.61±4.73 6.79±3.89 TN/(mg·L−1) 1.27±0.14 1.22±0.15 1.12±0.13 1.26±0.16 TP/(mg·L−1) 0.01±0.004 0.01±0.010 0.01±0.004 0.01±0.004 表 3 中线干渠不同渠段水质参数变化
Table 3. Changes of water quality parameters in different sections of the middle route canal
水质指标 第一类渠段 第二类渠段 第三类渠段 pH 8.25±0.23 8.25±0.05 8.23±0.08 NH3-N/ (mg·L−1) 0.04±0.01 0.04±0.02 0.07±0.05 F.coli/ (个·L−1) 44.41±56.11 184.50±323.16 109.17±197.02 CODMn/ (mg·L−1) 1.94±0.11 2.08±0.29 2.09±0.32 SO42−/ (mg·L−1) 27.21±1.68 29.38±1.81 29.91±2.46 DO/ (mg·L−1) 9.74±1.42 10.82±2.15 10.76±2.57 BOD5/ (mg·L−1) 0.91±0.45 1.11±0.48 1.52±0.51 WT/ ℃ 17.69±8.42 17.06±10.13 16.95±10.01 TN/ (mg·L−1) 1.22±0.16 1.18±0.11 1.32±0.15 TP/ (mg·L−1) 0.01±0.005 0.01±0.003 0.01±0.004 -
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