京蒙沙源区水库大气氮沉降变化特征及源解析

以京蒙沙源区大河口水库为研究对象，于2017年1月~12月对水库周围布设的12个大气沉降监测站点收集样品144个，测定大气干、湿沉降物中TN浓度，计算大气总氮干、湿沉降通量，分析大气TN干、湿沉降污染特征及季节性变化特征.另选取水库周边不同典型地块，布设14个采样点采集样品76个，测定土壤δ¹⁵N-TN含量水平，解析水库大气氮沉降主要来源，并借助HYSPLIT4气团后向轨迹模型分析各季节不同类型气团输移营养盐对大河口水库的影响.结果表明：水库全年大气TN干沉降通量变化范围为122.44~425.64kg/（km²·month），平均值为200.83kg/（km²·month）；湿沉降通量变化范围1.23~188.89kg/（km²·month），平均值为66.33kg/（km²·month）.大气总氮年沉降通量为3205.9kg/（km²·a），约为全国氮沉降平均水平（790kg/（km²·a））的4.06倍.从沉降类型上来看，大气沉降主要以干沉降为主，占沉降总量的75.17%，湿沉降占总沉降通量的24.83%.大气氮干沉降通量表现为春、秋季节明显高于夏、冬季节，湿沉降通量春、夏季明显高于秋、冬季节的季节性变化规律.通过对典型地块δ¹⁵N-TN同位素数据分析，表明夏季有71.4%的大气沉降样品来源于不可分辨的混合源输入，春、秋、冬季大河口水库超过45%的样品来源于沙地，另一大污染源为研究区周围的耕地.运用HYSPLIT4后向轨迹模型证明，从蒙古国入境的气团对研究区污染物大气输移影响较大，冬季采暖期间的大气污染和春季频繁发生的沙尘暴是造成北方沙区水体春季水环境变差的因素之一.

Variation characteristics and source analysis of atmospheric nitrogen deposition flux on a reservoir in sand source areas of Beijing-Inner Mongolia

Taking Dahekou reservoir in the sand source areas of Beijing and Inner Mongolia as research area. From January to December 2017, 144 samples were collected from 12 atmospheric deposition monitoring sites along the reservoir shore to determine the concentration of total nitrogen (TN) in dry and wet deposition. Then the dry and wet deposition fluxes of TN were calculated and the pollution characteristics and seasonal variation characteristics were analyzed. A total of 76 soil samples and 14 sampling points were collected from different typical plots around the reservoir. In addition, the soil δ¹⁵N-TN content level was measured and the main sources of atmospheric nitrogen deposition were analyzed. Furthermore, based on HYSPLIT4 air mass backward trajectory model, the influence of different types of air mass on Dahekou Reservoir was analyzed. The results show that the annual variation of atmospheric TN dry deposition flux in the reservoir ranged from 122.44 to 425.64kg/(km²·month), with an average value of 200.83kg/(km²·month); the wet deposition flux varied from 1.23 to 188.89kg/(km²·month), with an average value of 66.33kg/(km²·month); the annual average nitrogen deposition was 3205.9kg/(km²·a), which was about 4.06 times of the national average level of nitrogen deposition (790kg/(km²·a)). In terms of sedimentary types, dry deposition accounts for 75.17% of total deposition and wet deposition accounted for 24.83% of total deposition. Atmospheric nitrogen dry deposition fluxes were significantly higher in spring and autumn than summer and winter, and wet deposition fluxes in spring and summer were significantly higher than that of autumn and winter. Typical plots of δ¹⁵N-TN data analysis showed that 71.4% of the atmospheric deposition samples in summer came from unresolved mixed source inputs, and more than 45% of the samples from Dahekou Reservoir in spring, autumn and winter come from sandy land, the major source of pollution was the cultivated land around the study area. Using the HYSPLIT4backward trajectory model, it was proved that Mongolia's air mass entering into the study area had a greater impact on the atmospheric transport of pollutants. The air pollution during heating period of winter and frequent dust storms in spring were one of the factors leading to the deterioration of the spring water environment in the northern sand area.