【作者】 陈能汪；

【导师】 洪华生；

【作者基本信息】 厦门大学 ， 环境科学， 2006， 博士

【摘要】 人类活动对地球系统的影响迅速扩大,活化氮的大量输入使得生态系统氮“超载”,并引发一系列生态环境问题。世界各国正致力于寻求减少氮的排放以缓解环境压力的对策。因此,从机制上对九龙江流域氮的源汇及其过程进行系统的试验研究,对于加强水资源保护、改善流域生态环境、促进社会经济可持续发展有着非常重要的理论与实践意义。本研究融合多学科知识,在GIS技术支持下,综合运用现场定位试验、模型模拟、同位素示踪及故障树风险评价等多种研究手段与方法,揭示了流域氮的大气沉降、地表径流、淋失、反硝化和氨挥发等输入输出过程及其机制,建立了不同尺度流域氮的收支模式,并针对性提出氮流失的控制对策建议。主要研究结论如下:第一,大气氮沉降强度、时空分布和来源。九龙江流域大气氮沉降通量为14.9 kg N/(hm2·y),其中干沉降占34%,湿沉降占66%;受氮的排放状况和气象条件影响,约80%的大气氮沉降发生在春夏两季。干沉降中铵氮、硝氮与有机氮分别占31%、24%和45%。干沉降量在下游及河口地区较大(>7.0 kg N/(hm2·y)),并向上游方向递减(<4.0 kg N/(hm2·y))。湿沉降(雨水)氮浓度平均2.79±1.79 mg N/L,铵氮、硝氮与有机氮分别占39%、25%和36%。雨水氮浓度随降雨量、降雨强度的增大而降低,但在空间尺度上的差异较小。大气氮沉降中以铵态氮为主,这与化肥施用、畜禽养殖引起的氨挥发强烈有关,而雨水硝态氮主要来源于化石燃料燃烧和农业活动。第二,氮的地表径流输出过程及机制。流域氮的地表径流输出主要受降雨、径流、土地利用和施肥状况的多重控制。九龙江向厦门海域输送无机氮10.75 kg N/(hm2·y),春夏秋季流量大(占全年89%),氮输出占全年的90%。五川小流域地表径流氮输出总负荷为67.10 kg N/(hm2·y),基流与降雨径流分别占25%和75%;春夏两季(3–8月)处于作物生长季节,人为氮的输入量大,降雨集中,氮的地表径流输出占全年的85%。基流氮的输出与水量、水质密切相关,但水量起着更为关键的作用。随着上游向下游方向农业用地比例的增加,基流氮浓度递增。各类典型小流域氮的降雨径流输出与农业用地比例呈正相关。地表水硝态氮主要来源于无机化肥,以及有机肥的季节性施用。更多还原

【Abstract】 Excessive reactive nitrogen (N) additions from human activities have resulted in serious and long-term environmental consequences for large regions of the Earth. National and international policies attempt to reduce these impacts on ecosystem health. Understanding of N sources and exports pattern is important for selecting the proper remedial strategies for controlling nutrient losses from watershed.In this study, the N sources and exports were determined for Jiulong River Watershed, an agricultural hill-land watershed with an area of 1.47×104 km2 in coastal region of southeast China. Water quality monitoring, field measurement, mechanism model and GIS technique were linked to estimate N flux of atmospheric deposition, streamflow discharge, leaching, denitrification, and ammonia volatilization. Nitrate isotope tracing, N budgets, and probabilistic risk assessment (PRA) were also used to identify N sources and primary path of N losses. The work provides a sound understanding of the sources of N to landscapes and the associated N fluxes in exports, and highlights how anthropogenic activities impact N cycling in coastal watershed.First, spatio-temporal distributions of atmospheric N deposition were examined for Jiulong River Watershed. The annual deposition atmospheric N flux amounted to 14.9 kg N/hm2, of which dry deposition and wet deposition accounts for 34% and 66%, respectively. About 80% of atmospheric deposition occurred in spring and summer. Ammonium, nitrate and dissolved organic N formed 31%, 24% and 45% of dry deposition flux, 39%, 25% and 36% of wet deposition flux for the whole watershed, respectively. In deposition the spatial pattern of N species was ostensibly linked to local pollution sources. The spatio-temporal variation of atmospheric N deposition indicated that higher ammonia volatilization from fertilizer application in the growing season, and livestock productions together provided the larger N source. Isotope value of nitrateδ15N implied that nitrate in rain droplets mainly originated from agricultural activities, and fuel combustion. Second, annual and seasonal patterns of N loss in streamflow were evaluated based on monitoring data of water quality and flow in 2002–2005. N loss in stormflow was positively related to the ratio of arable land, and varied greatly among the representative subwatersheds, reflecting the differences in precipitation, land cover, and N inputs. Stormflow contributes about 75% of the annual N export (67.1 kg N/(hm2·y)) in Wuchuan subwatershed, a small agricultural watershed in up-stream of Jiulong River. Streamflow export was greatest in spring (43%) and summer (42%) when larger fertilizer used for growing crops, and recorded rainfall contributes about 75% of total rainfall in 2004. The riverine export of dissolved total nitrogen (DTN), dissolved inorganic nitrogen (DIN) formed 83% and 68% of the total flux, respectively. Nitrate in streamflow contributed approximately two-thirds of DIN export, and its potential sources are inorganic N fertilizer and seasonal application of manure. Jiulong River provided DIN transport of 14.6×103 t N/y to estuary, of which more than 60% occurred during March to August (wet season) inducing by higher flow.Third, N leaching in Wuchuan subwatershed was evaluated using shallow water更多还原