Agriculture driven nitrogen wet deposition in a karst catchment in southwest China
Agriculture driven nitrogen wet deposition in a karst catchment in southwest China
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DOI：
10.1016/j.agee.2020.106883
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
Jie Zeng;F. Yue;Si‐Liang Li;Zhong-Jun Wang;Caiqing Qin;Qixin Wu;Sheng Xu
中科院分区：
文献类型：
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作者：
Jie Zeng;F. Yue;Si‐Liang Li;Zhong-Jun Wang;Caiqing Qin;Qixin Wu;Sheng Xu
氮沉降作为天然植被氮的主要来源之一，在生态系统功能中起着关键作用，特别是在土壤覆盖薄的喀斯特农业区，氮沉降通过雨水驱动喀斯特氮的宿命。为了解西南喀斯特农业区（后寨流域）氮沉降的季节和空间变化特征，确定湿沉降中硝酸盐的主要来源，选择2个不同土地利用方式的样地进行了为期1年的干湿沉降评价。后寨村是一个受农业影响较大的地区，而木竹水库则是一个较为原始的环境，人为影响较小。分析了含氮物种和双硝酸盐同位素。结果表明，农业来源的NH4+是年总湿氮沉降的主要贡献者（> 55%）。NH4+对湿态氮沉降的贡献是NO3−和溶解有机氮（DON）的1.63倍。研究区年氮沉降量约为中国平均湿态氮沉降量的两倍，而干态氮沉降量低于中国其他监测点。δ15N-NO3−呈夏季负、冬季正的季节变化趋势，主要受nox排放源变化控制。δ18O-NO3−的季节变化主要受nox氧化途径控制，其变化趋势与δ15N-NO3−相似。使用稳定同位素混合模型计算了四个端元（煤燃烧、汽车尾气、生物质燃烧和土壤排放）的贡献。除机动车尾气外，四种污染源的贡献呈现出明显的季节变化，在HZV分别占20.0%、25.6%、22.9%和31.5%（年平均概率估计，AMPE），在MZR分别占19.0%、27.8%、23.2%和30.0% （AMPE）。同位素证据表明，农业土壤排放是夏季生长季雨水的主要来源，对农业生态系统产生重大影响。
Nitrogen (N) deposition plays a key role in ecosystem function as one of the major N sources for natural vegetation, particularly in karst agricultural areas with thin soil cover, which drive the karst N fate via rainwater. To understand the seasonal and spatial variation in nitrogen deposition and to identify the major sources of nitrate in wet deposition in a karst agricultural area (Houzhai Catchment) in southwestern China, two sites with different land use were selected to assess wet and dry deposition for one year. Houzhai village (HZV) is an area highly influenced by agriculture, whereas Muzhu reservoir (MZR) is a more pristine environment with less anthropogenic influence. Nitrogenous species and dual nitrate isotopes were analyzed. The results showed that agriculture-derived NH4+was the major contributor of annual total wet N deposition (>55 %). The contribution of NH4+to wet N deposition was 1.63 times higher than that of NO3−and dissolved organic nitrogen (DON). The annual nitrogen deposition in this study was approximately twice as much as the average wet N deposition over China, while lower dry N deposition relative to other Chinese monitoring sites was observed. The δ15N-NO3−showed a seasonal trend of negative summer values and positive winter values, which were primarily controlled by the variations in NOxemission sources. Seasonal variation in δ18O-NO3−was mainly controlled by NOxoxidation pathways and showed a similar trend to δ15N-NO3−. The contributions from four endmembers (coal combustion, vehicle exhaust, biomass burning, and soil emission) were calculated using a stable isotope mixing model. Contributions show a clear seasonal variation (except vehicle exhaust), with the four sources accounting for 20.0 %, 25.6 %, 22.9 % and 31.5 % respectively (annual mean probability estimate, AMPE) at HZV, and 19.0 %, 27.8 %, 23.2 % and 30.0 % (AMPE) at MZR. Isotopic evidence determined agricultural soil emission is a major contributor to rainwater during the summer growing season, which can significantly impact the agricultural ecosystems.