长江口入海通道水质综合分析与模型预测

以中国最大河口地区为例,2004—2018年对包括徐六泾、启东港、南港、北港在内的4个长江口主要入海通道断面进行定期监测。对水样中的高锰酸盐指数、氨氮(NH₃-N)、总磷(TP)等水质参数进行测定,运用综合水质标识指数法(WQII)对入海通道断面水质进行综合分析。选择溶解氧(DO)作为响应变量,建立各断面逐步回归方程、季节性差分自回归移动平均模型(SARIMA),并对2018年10—12月进行预测以检验模型精度,比较2种模型在各断面的适用性。结果显示:1)长江口各入海通道断面DO浓度在空间上呈现徐六泾最高、北支其次、南支最低的规律,平均值为8.73 mg/L;2)各断面综合水质标识指数从相对最优开始排列依次为启东港(3.110)>徐六泾(3.120)>北港(3.220)>南港(3.420);3)除南港断面外,SARIMA模型相较逐步回归方程对长江口断面DO浓度预测的相对偏差更小。

COMPREHENSIVE ANALYSIS AND MODEL PREDICTION OF WATER QUALITY IN THE SEA-ENTRY CHANNELS OF YANGTZE ESTUARY

Taking the largest estuary in China as an example, regular monitoring was carried out at four major cross-sections, including Xuliujing, Qidonggang, Nangang and Beigang in Yangtze Estuary from 2004 to 2018. Water quality parameters such as permanganate index, ammonia nitrogen(NH₃-N) and total phosphorus(TP) were measured in water samples. A comprehensive analysis of the water quality at the cross-sections was conducted via the comprehensive water quality identification index(WQII) method; dissolved oxygen(DO) was selected as the response variable to establish stepwise regression equations and seasonal autoregressive integrated moving average model(SARIMA) for each cross-section, and predictions were made from October to December 2018 to test the accuracy of the models and compare the applicability of the two models at each cross-section. The results showed that:1) based on the monthly data from 2004 to 2018, the average DO concentration at the representative cross-sections of the main sea-entry channels of the Yangtze Estuary was 8.73 mg/L; spatially, the DO concentration in the Yangtze Estuary showed a pattern that Xuliujing was the highest and the northern branch was higher than the southern branch. 2) based on the comprehensive water quality marker index, the sections, water quality was in the order of Qidonggang(3.110)>Xuliujing(3.120)>Beigang(3.220)>Nangang(3.420);3) when predicting DO, the SARIMA model was more accurate than the stepwise regression equation in predicting DO at the Xuliujing, Qidonggang and Beigang section, while the stepwise regression equation performed better at the Nangang section.