釜溪河自贡城区段季节性低氧成因研究

Research on the Causes of Seasonal Low Dissolved Oxygen of Fuxi River in Zigong Urban Section

釜溪河为沱江一级支流,在自贡城区段设有国考碳研所断面。收集碳研所断面近10年来水质自动站数据,分析溶解氧(DO)变化特征,采样调查釜溪河自贡城区段水质及河道底泥污染状况,采用相关性分析、数值模拟等,研究分析釜溪河自贡城区段溶解氧分布特征及碳研所断面季节性低氧成因。研究结果表明,碳研所断面的溶解氧质量浓度变化特征呈现春末夏初最低,白天高晚上低的特征。釜溪河碳研所断面河水耗氧类污染物质量浓度较沱江流域内其他断面高,耗氧强度较大,溶解氧质量浓度较沱江流域其他断面偏低;其次,研究河段中釜溪河污水厂以下河段受污水厂低氧水排入和金子凼堰底层低氧水下泄影响,其溶解氧水平整体较污水厂以上河段低;最后,河段底泥有机质含量较高,春夏季气温升高将导致微生物分解活性增强大量消耗溶解氧,同时,闸坝和外来水体排入的水文扰动造成污水厂以下河段水温梯度弱,表层溶解氧易受底层低氧水影响,促使断面形成季节性低氧现象。溶解氧预测模型结果也进一步证实了温度变化和垂向温度梯度弱是碳研所断面溶解氧质量浓度季节性偏低的主要因素。

This paper collected the automatic monitoring water quality data for the past 10 years from a National Surface Water Assessment Cross-Section(Tanyansuo)of Fuxi River(a tributary of Tuojiang River),and investigated the water quality and sediment pollution by sampling along this river reach in 2021.An in-situ experiment on oxygen consumption rate of water and sediment was conducted in Tanyansuo cross-section as well.The temporal and spatial distribution characteristics of dissolved oxygen(DO)and the causes of seasonal low DO were researched by times series analysis,correlation analysis and numerical simulation.The results showed that:the lowest DO in the surface water of Tanyansuo was observed during late spring and early summer,and DO in daytime was higher than at night;the concentration of oxygen-consuming pollutants in the surface water of Tanyansuo was higher than that of other sections in the Tuojiang River Basin,which leading to relatively higher oxygen consumption intensity and lower DO;DO was low in downstream than that in upstream of the sewage treatment plant due to the low-oxygen drainage from the plant and bottom water of Jinzidang barrage;high content of organic matter in sediment of the river reach provided basis for microbial decomposition activity and consumption of DO when temperature increased in spring and summer,along with weak water temperature gradient brought by disturbance from drainage,promoted the formation of seasonal low DO phenomenon in the section.It is further confirmed by dissolved oxygen prediction model that temperature change and weak water temperature gradient was the main factor for the seasonal low DO of Tanyansuo.