Abstract:

Total nitrogen (TN) in the surface water is an important factor affecting water ecological environment. The increase of TN concentration will lead to eutrophication, red tide, and other phenomena, which are harmful for aquatic organisms and even human health. In order to analyze the temporal and spatial variation characteristics of TN concentration in the surface water in China in recent years and provide basis and support for the decision making and deployment of TN pollution control of surface water, the temporal variation trend and spatial distribution characteristics of TN concentration in surface water in China during 2016-2020 were systematically analyzed based on the monitoring results of national environmental quality monitoring network of surface water, using Surface Water Environmental Quality Standard and Evaluation Method of Surface Water Environmental Quality (Trial) as the evaluation basis, combined with Pearson correlation coefficient method. From 2016 to 2020, TN concentrations in the surface water, rivers, and lakes were in the range of 2.54-3.00 mg∙L^-1, 2.72-3.23 mg∙L^-1 and 1.19-1.31 mg∙L^-1 respectively. TN concentration in rivers was much higher than that in lakes and reservoirs. In terms of time variation, the interannual variation of TN concentration in the surface water in China showed a trend of rising first and then falling. The monthly variation of TN concentration showed seasonal characteristics of higher in spring and winter and relatively lower in summer and autumn. In terms of the watershed distribution, the order of TN concentrations of each watershed ranked from high to low was: Haihe River>Yellow River>Liaohe River>Huaihe River>Pearl River>Zhejiang and Fujian area River>Yangtze River>Songhua River>Northwest River>Southwest River. The order of TN concentrations of each lake area from high to low was: Yunnan and Guizhou>Eastern Plain>Mongolia and Xinjiang>Northeast> Qinghai Tibet Plateau. TN concentrations in Haihe River, Liaohe River, Yellow River and Huaihe River basin were generally higher, all over 3.00 mg∙L^-1, while TN concentrations in Northwest River and Southwest River basin were much lower, which were 1.39 mg∙L^-1 and 1.23 mg∙L^-1 respectively. In addition, the into-lake rivers had a strong correlation with the TN concentration of the corresponding lakes and reservoirs. TN concentrations of into-lake rivers and into-ocean rivers reached or exceeded 4.00 mg∙L^-1 and 2.00 mg∙L^-1 respectively higher than those of the corresponding lakes and ocean regions, showing a great influence on lakes and ocean regions. It's important to take nitrogen control measures for into-lake rivers and into-ocean rivers to control or alleviate nitrogen loads and prevent the eutrophication of lakes and ocean regions.

Key words: total nitrogen, basins, eutrophication, into-lake rivers, into-ocean rivers, lakes and reservoirs

摘要：

地表水中总氮是影响水生态环境状况的重要因素,总氮浓度升高会导致水体富营养化、赤潮等现象,危害水生生物甚至人体健康。为分析近年来全国地表水中总氮浓度时空变化特征,为水污染防治中总氮污染治理的决策和部署提供依据和支撑,基于国家地表水环境质量监测网总氮监测结果,以《地表水环境质量标准》和《地表水环境质量评价办法 (试行)》为评价依据,结合皮尔逊相关系数法,系统分析了中国2016—2020年（“十三五”时期）地表水中总氮浓度的时间变化趋势和空间分布特征。2016—2020年,全国地表水、河流与湖库总氮质量浓度范围分别在2.54—3.00、2.72—3.23和1.19—1.31 mg∙L^-1,河流总氮浓度远高于湖库。从时间变化来看,全国地表水总氮浓度年际变化呈现先升后降的趋势,总氮浓度月际变化具有季节性特征,春季与冬季较高,夏季与秋季相对较低。从流域分布来看,各流域总氮浓度由高到低为海河>黄河>辽河>淮河>珠江>浙闽片>长江>松花江>西北>西南;湖区总氮浓度由高到低为云贵>东部平原>蒙新>东北>青藏高原;海河、辽河、黄河和淮河流域总氮质量浓度较高,均在3.00 mg∙L^-1以上;珠江、浙闽片、长江和松花江流域总氮年均值在2.00 mg∙L^-1附近波动;西北诸河和西南诸河总氮质量浓度较低,分别为1.39 mg∙L^-1和1.23 mg∙L^-1。此外,入湖河流与对应湖库总氮浓度相关性较强;入湖河流与入海河流总氮年均值分别达到或超过4.00 mg∙L^-1与2.00 mg∙L^-1,均远高于汇入的湖体与海区,对湖体和海区的水质产生重要影响,因此入湖河流和入海河流的控氮措施对于防控或缓解湖体和海区的氮素负荷及富营养化具有重要意义。

关键词: 总氮, 富营养化, 流域, 入湖河流, 入海河流, 湖库