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1.
百花湖是一个具有季节性分层的富营养小型湖泊,在秋季湖水倒转期经常发生水质恶化事件,碳氮循环出现异常。文章研究特选择在秋初,湖泊分层开始消失时,测定了湖水中不同深度的N2O,CH4,CO2,有机和无机碳同位素以及其他化学参数变化。结果发现:采样时百花湖在约6m和16m深度附近出现了两个温度不连续层(SDL和PDL),并影响到有机颗粒的沉降和分解。相对而言,有较多的有机质在这两个层内发生降解,但降解的途径有所不同,上部主要是有氧降解,下部则主要是无氧降解过程。N2O的产生和消耗与有机质的降解过程完全对应:PDL层以上,ΔN2O与AOU的线性关系反映了N2O主要形成于硝化作用;PDL层以下反硝化作用导致N2O严重不饱和;PDL内位于硝化作用和反硝化作用过渡带的N2O峰,显然是硝化与反硝化联合作用的结果。PDL层内较大的CH4浓度变化梯度,说明嗜甲烷细菌可能通过氧化NH+4贡献了部分N2O。百花湖秋、冬季表层湖水N2O都是过饱和的,都是大气N2O的源,依据分子扩散模型计算湖泊N2O的释放通量在12～14μmol/m·day之间,秋、冬季没有明显的差别。秋季底层湖水的反硝化作用是湖泊N2O的汇,其消耗通量与表层的释放通量基本相当。  相似文献   

2.
土壤温室气体昼夜变化及其环境影响因素研究   总被引：16，自引：3，他引：13       下载免费PDF全文
通过对北京东灵山草地和桦树林土壤气体CO2,N2O和CH4浓度及其排放通量的昼夜连续观测,探讨了生长季节草地和森林土壤温室气体昼夜变化及其环境影响因素。研究表明:1)土壤CO2排放通量昼高夜低,N2O排放通量有明显小时尺度波动,但昼夜变化不突出;土壤CO2和N2O浓度昼夜变化不明显,且与排放通量波动不一致;土壤是大气CH4的一个汇,相对厌氧的环境可能有利于土壤吸收CH4。2)无雨时气温昼夜变化通过影响土壤表层的气体扩散和CO2产生过程,来影响土壤CO2和N2O的地表排放通量,而对土壤10cm以下CO2和N2O的产生影响不大。小时尺度的土壤CO2和N2O浓度波动则可能还有其他影响因素或机制。3)降雨时土壤渗水引起的土壤空气对流取代气体浓度扩散成为土壤与大气空气交换的主要方式,导致土壤CO2和N2O排放通量的同步波动。降雨渗水较多时,较多的溶解氧随着雨水进入土壤内,会促进土壤CO2的生成和抑制N2O的产生。4)土壤CO2与N2O浓度存在显著的正相关关系,反映出土壤CO2和N2O有相对稳定的产率比。土壤有效碳可能是造成土壤CO2与N2O浓度正相关的主要原因,土壤空气的氧分压则可能是造成土壤CO2和N2O浓度波动不一致的重要因素。  相似文献   

3.
太湖及其周围河流中N2O的空间分布与释放通量   总被引：2，自引：1，他引：1       下载免费PDF全文
本次研究选择中国东部一个生态和环境空间分异极大的浅水湖泊（太湖）以及周围河流,分别于2003年7月和9月两次采集湖水和河水样品,分析其中的N2O浓度,并利用扩散模型公式估算水-气界面N2O交换通量。结果显示N2O饱和度的空间变化从70％不饱和到2708％过饱和变化范围很大。N2O饱和度的空间分布,N2O与CH4、无机氮、TDS（总溶解固体物质）之间的相关性都表明：   太湖重度富营养区N2O的产生极大地受到人为N输入的影响。然而,初步的通量分析显示湖泊N2O的释放因子不超过0.63％,小于河流中的默认值,N2O产率也略低于水环境中的平均值,太湖以面积为权重的释放通量平均值并不高,在7月和9月分别为14.0μmol/m2·d和9.7μmol/m2·d。这些结果表明流域人为N输入对整个湖泊N2O的促进作用是有限的,预计未来湖泊N2O释放不会因为人为活动增加而出现大幅度增加的状况。流域内各生态景观N2O释放量的比较,也表明富营养湖泊总体上仍然是一个十分有限的大气N2O释放源。相反,太湖周围河流存在较大的N2O释放速率,在7月和9月估算的N2O释放通量分别为142.1μmol/m2·d和28.8μmol/m2·d。将这一释放速率推广到整个流域后,预计河网的N2O释放量将占到耕作土壤的10％～50％,显示了河流对区域N2O质量平衡具有较重要的影响。  相似文献   

4.
云贵高原湖泊CO2的地球化学变化及其大气CO2源汇效应   总被引：3，自引：0，他引：3  
湖泊是大气CO2的源还是汇,长期以来一直都存有争议。云贵高原地区的湖泊由于受流域碳酸盐岩风化作用的影响,使这一问题就显得更特殊,也更复杂。本次研究通过化学平衡计算和气相色谱测定两种方法得到了比较一致的湖水CO2浓度结果。研究发现,在夏季强烈的光合作用消耗了湖水CO2,致使湖水中CO2浓度降低。在贵州草海、百花湖以及云南的泸沽湖、杞麓湖,表层湖水CO2分压(为便于与大气CO2比较,文中湖水CO2用分压单位表示)小于200μatm,远低于大气CO2分压,湖泊正不断地从大气中吸收CO2,从而构成大气CO2的汇。  相似文献   

5.
植物——大气N2O的一个潜在排放源   总被引：22，自引：0，他引：22       下载免费PDF全文
N22和CH4的重要温室气体。目前,全球N222O不仅是一个普遍存在的自然现象,而且其排放量可达到与土壤排放相比较的水平,因而植物可能是未知的大气N2O的一个重要排放源;植物排放N2O受植物的种类、生长发育阶段、养分供给、光照强度及CO2浓度等因素的影响。  相似文献   

6.
中国的温室气体排放、减排措施与对策*   总被引：38，自引：0，他引：38       下载免费PDF全文
黄耀 《第四纪研究》2006,26(5):722-732
根据《中华人民共和国气候变化初始国家信息通报》,1994年中国温室气体排放总量约为3650×106t的CO2当量,其中CO2,CH4和N2O分别占73.1 ％ ,19.7 ％ 和7.2 ％ 。CO2排放主要来自能源活动,CH4排放主要来自农业活动和能源活动,N2O排放主要来自农业活动。在过去的20余年里,中国为减缓全球温室气体排放的增长速度做出了重要的贡献。对文献资料和大量研究结果的分析表明,中国可通过采取相关措施和制订相应政策进一步减少温室气体的排放。减少CO2排放的主要措施和对策包括:调整能源结构(降低煤炭消费比例、适度提高天然气比例和发展核能);提高能源生产、转化、分配和使用过程中的效率;开发利用水能、风能、太阳能和生物能等可再生能源;通过植树造林,推广秸秆还田、平衡施肥和少(免)耕等增加陆地生态系统的碳吸收。减少CH4排放的主要措施和对策包括:回收利用煤层气;改造生活垃圾填埋场地和筛选环境适应性强的CH4氧化菌并接种于填埋场;改善反刍动物的营养成分;稻田合理灌溉、提高水稻的收获指数、选育和种植CH4排放低的水稻品种等。减少农田N2O排放的主要措施和对策包括:提高氮肥利用率;推广施用长效肥和控释肥;施用生物抑制剂和实施微生物工程等。  相似文献   

7.
硝化和反硝化对湖泊有机质沉积成岩前降解作用的研究   总被引：8，自引：1，他引：8  
贵州红枫湖10月叶绿素a(chla)和NO3^-含量均比7月明显降低。利用氮同位素等数据对此进行了研究，结果表明，含量的降低是由不同的生物地球化学作用引起的。chla含量的降低主要是水体中有机质降解(硝化)所致，而NO3^- 含量的降低则是缺氧季节湖泊沉积物表层反硝化作用的结果。缺氧季节表层水体仍然能发生较强烈的硝化作用。硝化作用和反硝化作用分别发生在热分层湖泊的上层和沉积物表层。反硝化作用不仅消耗大量的NO3^-，而且还造成了一定量的有机质降解(有机碳作为电子受体)。据估算，在红枫湖后五测点和大坝测点，总有机碳在沉积成岩前分别降解了78％和68％。其中由硝化作用引起的总有机质降解量分别为35．8%和25．9％，而反硝化作用则分别为13．4％和9．2％。  相似文献   

8.
西秦岭新生代高钾质玄武岩流体组成及其地幔动力学意义   总被引：5，自引：4，他引：1  
西秦岭新生代高钾质玄武岩是认识大陆碰撞俯冲体制下地幔流体组成及深部动力学的岩石探针。本文采用分步加热质谱法测定了西秦岭高钾质玄武岩中斑晶及基质的流体化学组成和碳同位素组成,结果表明流体组分在200~400℃、400~800℃和800~1200℃阶段性释出,以H2O为主,其次为CO2和SO2,并含有相对较高的He含量。从橄榄石斑晶到斜长石斑晶和基质H2O和CO2逐步升高。橄榄石斑晶流体挥发份主要释气峰温度(900~1200℃)明显高于中国东部地幔捕虏体及其它地区超镁铁质岩体中的橄榄石,流体组份以SO2和CO2等氧化性组份为主,其CO2的δ13C值(-26.21‰~-20.85‰,平均-23.32‰)和CH4的δ13C值(-42.35‰~-38.17‰,平均-40.03‰)低于基质的δ13CCO2值(-16.43‰~-11.67‰,平均-13.22‰)和δ13CCH4值(-44.22‰~-34.03‰,平均-39.70‰)。基质中CO2和CH4碳同位素组成具有机质热裂解特征。原始岩浆的流体挥发份主要为SO2、N2和CO2,可能起源于较深的混杂地幔源区、演化于高fO2的环境。流体挥发份化学和同位素组成表明高钾质玄武岩浆挥发份中存在地幔和地壳来源组分,幔源岩浆上升演化过程中可能加入了大量的H2O和CO2等,可能存在碳酸岩岩浆的混合或岩浆穿透区域碳酸盐地层的混染;其中的再循环壳源组分可能为古特提斯洋闭合俯冲或其后华北克拉通与扬子克拉通碰撞相关的再循环壳源沉积物脱出的流体组分。  相似文献   

9.
若尔盖高原沼泽湿地CH4排放研究   总被引：26，自引：0，他引：26  
若尔盖高原沼泽湿地海拔 3400 m，面积 4038km2，是我国面积最大的高原沼泽湿地分布区。2001年 5～9月的非冰冻期，其主要沼泽类型木里苔草沼泽的CH4排放通量范围是 0.51～ 8.20 m g/（m 2· h），平均值为 2.87 m g/（m 2· h）；乌拉苔草沼泽CH4排放通量范围是 0.36～10.04 m g/（m 2· h），平均值为 4.51 m g/（m 2· h）。在空间分布上，不同沼泽类型之间CH4排放通量具有一定的差异。在季节变化上，没有明显的排放高峰。根据代表性观测点的CH4平均排放量、日数和沼泽总面积推算，非冰冻期若尔盖高原沼泽湿地CH4的排放量为 0.052Tg/a。  相似文献   

10.
高永宝  李文渊  张照伟 《岩石学报》2011,27(6):1829-1839
对祁漫塔格白干湖-戛勒赛钨锡矿带石英脉型矿石石英中流体包裹体的岩相学特征研究表明,包裹体类型主要分为富液相两相包裹体、含CO2、CH4三相包裹体及单相H2O溶液包裹体3种类型,前2类为原生包裹体,与成矿关系密切;富液相两相包裹体均一温度峰值为220~260℃,盐度为0.88％~20.82％ NaCleqv,流体的总密度为0.72~1.06g·cm-3,液相成分主要是水溶液,气相成分含有部分CO2及CH4;含CO2、CH4三相包裹体完全均一温度峰值为260~280℃,盐度为6.63％~15.21％ NaCleqv,流体的总密度为0.60~0.91g·cm-3,气相成分以CO2、CH4为主,次为H2S、N2及少量的H2;液相组分以H2O为主,次为CO2及少量的CH4、H2S。各矿区石英脉型矿石的δ18OH2O为4.02‰~6.32‰,δD为-75.5‰~-42.8‰,均显示出岩浆水的特征。总体而言,石英脉型矿体的初始流体主要来自酸性岩浆热液,为中高温(220~280℃)、中盐度(10％~14％ NaCleqv)、低密度的NaCl-H2O-CO2体系。钨锡成矿与区内加里东期岩浆作用密切相关,石英脉型矿石形成时流体处于不均匀的状态,成矿流体不混溶作用以及温压条件、pH、Eh、fO2、fS2等的变化是石英脉型钨锡矿沉淀的主要原因。 图1 白干湖-戛勒赛钨锡矿带区域地质简图(据刘贵忠等,2007修改) I-塔里木陆块;Ⅱ-柴达木陆块;Ⅲ-昆仑造山带;Ⅲ1-1-北祁漫塔格早古生代岩浆弧;Ⅲ1-2-中昆仑微陆块(早古生代、晚古生代复合岩浆弧);Ⅲ1-3-昆南早古生代增生楔;Ⅲ2-1-南昆仑晚古生代残留弧;Ⅳ-阿尔金早古生代造山带;V-巴颜喀拉晚古生代-中生代浊积盆地褶断带;①-祁漫塔格南缘早古生代构造混杂岩带;②-阿尔金南缘断裂;③-白干湖断裂;④-昆中蛇绿构造混杂岩带;⑤-康西瓦-木孜塔格-阿尼玛卿断裂带.1-第四系;2-新近系;3-侏罗系叶尔羌群;4-侏罗系大煤沟组;5-志留系白干湖组;6-长城系小庙岩组;7-古元古代阿尔金岩群;8-华力西期花岗岩;9-华力西期闪长岩;10-华力西期碱长花岗岩;11-华力西期花岗闪长岩;12-华力西期二长花岗岩;13-华力西期辉长岩;14-加里东期花岗杂岩;15-未确定性质的构造形迹;16-左行扭动构造形迹;17-左行岩石圈断裂;18-左行超岩石圈断裂;19-钨锡矿床 Fig.1 Regional geological map of Baiganhu-Jialesai W-Sn mineralization belts (after Liu et al., 2007)  相似文献   

11.
Constructed wetlands (CWs) are considered important sources of nitrous oxide (N2O). Various reports in the literature indicate that CWs have high N2O emission rates. The release of N2O from CWs treating wastewater emissions range from ?16.7 to 188 mg N2O m?2day?1. N2O in CWs is produced mainly by nitrification, denitrification, nitrifier denitrification, and nitrate-ammonification. Denitrification is considered the major source of N2O under most conditions. In recent years, two main methods of sampling N2O gas in CWs have been employed, including the headspace equilibration technique and the closed static chambers technique. N2O emission may be affected by various operating parameters and environmental conditions. One of the main environmental factors affecting the removal of nitrogen in CWs is dissolved oxygen, which affects nitrification and denitrification processes, thus greatly influencing N2O emission. CW gas dynamics is affected mainly by season and weather conditions, especially temperature and moisture. Aquatic plants, flow regime, oxidation–reduction potential, nitrate concentration, C/N ratio and other factors can affect N2O emission in CWs.  相似文献   

12.
In this study rates of oxygen, ammonium (NH4 +), nitrate (NO3 −), nitrite (NO2 −), and nitrous oxide (N2O) fluxes, nitrogen (N) fixation, nitrification, and denitrification were compared between two intertidal sites for which there is an abundant global literature, muddy and sandy sediments, and two sites representing the rocky intertidal zone where biogeochemical processes have scarcely been investigated. In almost all sites oxygen production rates greatly exceeded oxygen consumption rates. During daylight, NH4 + and NO3 − uptake rates together with ammonification could supply the different N requirements of the primary producer communities at all four sites; N assimilation by benthic or epilithic primary producers was the major process of dissolved inorganic nitrogen (DIN) removal; N fixation, nitrification, and denitrification were minor processes in the overall light DIN cycle. At night, distinct DIN cycling processes took place in the four environments, denitrification rates ranged from 9 ± 2 to 360 ± 30 μmol N2 m−2 h−1, accounting for 10–48% of the water column NO3 − uptake; nitrification rates varied from 0 to 1712 ± 666 μmol NH4 + m−2 h−1. A conceptual model of N cycle dynamics showed major differences between intertidal sediment and rocky sites in terms of the mean rates of DIN net fluxes and the processes involved, with rocky biofilm showing generally higher fluxes. Of particular significance, the intertidal rocky biofilms released 10 times the amount of N2O produced in intertidal sediments (up to 17 ± 6 μmol N2O m−2 h−1), representing the highest N2O release rates ever recorded for marine systems. The biogeochemical contributions of intertidal rocky substrata to estuarine and coastal processes warrant future detailed investigation.  相似文献   

13.
Filter-feeding bivalves, like oysters, couple pelagic primary production with benthic microbial processes by consuming plankton from the water column and depositing unassimilated material on sediment. Conceptual models suggest that at low to moderate oyster densities, this deposition can stimulate benthic denitrification by providing denitrifying bacteria with organic carbon and nitrogen (N). While enhanced denitrification has been found at oyster reefs, data from oyster aquaculture are limited and equivocal. This study measured seasonal rates of denitrification, as well as dissimilatory nitrate reduction to ammonium (DNRA), and dissolved inorganic N fluxes at a rack and bag eastern oyster (Crassostrea virginica) aquaculture farm. Consistent with models, denitrification was enhanced within the farm, with an average annual increase of 350% compared to a reference site. However, absolute denitrification rates were low relative to other coastal systems, reaching a maximum of 19.2 μmol m?2 h?1. Denitrification appeared to be nitrate (NO3 ?) limited, likely due to inhibited nitrification caused by sediment anoxia. Denitrification may also have been limited by competition for NO3 ? with DNRA, which accounted for an average of 76% of NO3 ? reduction. Consequently, direct release of ammonium (NH4 +) from mineralization to the water column was the most significant benthic N pathway, with seasonal rates exceeding 900 μmol m?2 h?1 within the farm. The enhanced N processes were spatially limited however, with significantly higher rates directly under oysters, compared to in between oyster racks. For commercial aquaculture farms like this, with moderate oyster densities (100–200 oysters m?2), denitrification may be enhanced, but nonetheless limited by biodeposition-induced sediment anoxia. The resulting shift in the sediment N balance toward processes that regenerate reactive N to the water column rather than remove N is an important consideration for water quality.  相似文献   

14.
Nitrous oxide supersaturation was measured in the Bothnian Bay, Bothnian Sea and four depth zones of the Baltic proper along with O2, NO?3, NO?2 and other parameters useful in interpreting the sources of the N2O. In the Baltic Sea supersaturation of N2O (123%) was found in the surface water of 0 to 0.5 m. The supersaturation resulted in a flux of N2O to the atmosphere of 2.8 × 10?2Tg N · yr?1 which was 5% of the estimated total nitrogen loss for the Baltic. For the entire photic zone (0 to 20 m) the N2O saturation was 135%. The source of the N2O is not clear, as the nitrification and denitrification were ruled out as sources. The N2O saturation was the lowest (118%) in the intermediate zone. Nitrification appears to be the likely N2O sorce in this region. At the halocline zone, an increasing oversaturation of N2O (200 to 300%) correlated with decreasing O2 concentrations and increasing NO?3 concentrations, indications of nitrification. Of the NH+4 that was oxidized to NO?3, 0.56% was produced as N2O. In the deep water zone, the supersaturation of N2O remained very high (150 to 200%). Sufficient O2, high NO?3 and the presence of nitrifying activity suggested nitrification as most likely source, however in deeper waters of this zone where oxygen was less than 2% saturation the N2O production could be due to denitrification. In anoxic waters the N2O concentrations rapidly decreased to zero suggesting N2O consumption by denitrification, further evidenced by a developing nitrate anomaly.  相似文献   

15.
Measurements of15N/14N in dissolved molecular nitrogen (N2), nitrate (NO 3 − ) and nitrous oxide (N2O) and18O/16O in N2O [expressed as δ15N and δ18O, relative to atmospheric N2 and oxygen (O2), respectively] have been made in water column at several locations in the Arabian Sea, a region with one of the thickest and most intense O2 minima observed in the open ocean. Microbially-mediated reduction of NO 3 − to N2 (denitrification) in the oxygen minimum zone (OMZ) appears to greatly affect the natural isotopic abundances. The δ15N of NO 3 − increases from 6‰ in deep waters (2500 m) to 15‰ within the core of the denitrifying layer (250–350 m); the δ15N of N2 concurrently decreases from 0.6‰ to 0.20‰ Values of the isotopic fractionation factor (ε) during denitrification estimated using simple advection-reaction and diffusion-reaction models are 22‰ and 25‰, respectively. A strong decrease in δ15N of NO 3 − is observed from ∼ 200m (> 11‰) to 80m (∼ 6‰); this is attributed to the input of isotopically light nitrogen through nitrogen fixation. Isotopic analysis of N2O reveals extremely large enrichments of both15N and18O within the OMZ, presumably due to the preferential reduction of lighter N2O to N2. However, isotopically light N2O is observed to accumulate in high concentrations above the OMZ indicating that the N2O emitted to the atmosphere from this region cannot be very heavy. The isotope data from the intense upwelling zone off the southwest coast of India, where some of the highest concentrations of N2O ever found at the sea surface are observed, show moderate depletion of15N, but slight enrichment of18O relative to air. These results suggest that the ocean-atmosphere exchange cannot counter inputs of heavier isotopes (particularly18O) associated with the stratospheric back flux, as proposed by previous workers. This calls for additional sources and/or sinks of N2O in the atmosphere. Also, the N2O isotope data cannot be explained by production through either nitrification or denitrification, suggesting a possible coupling between the two processes as an important mechanism of N2O production.  相似文献   

16.
The biological and physical controls on microbial processes that produce and consume N2O in soils are highly complex. Isotopomer ratios of N2O, with abundance of 14N15N16O, 15N14N16O, and 14N14N18O relative to 14N14N16O, are promising for elucidation of N2O biogeochemistry in an intact ecosystem. Site preference, the nitrogen isotope ratio of the central nitrogen atom minus that of the terminal nitrogen atom, is useful to distinguish between N2O via hydroxylamine oxidation and N2O via nitrite reduction.We applied this isotopomer analysis to a groundwater system in a temperate coniferous-forested ecosystem. Results of a previous study at this location showed that the N2O concentration in groundwater varied greatly according to groundwater chemistry, i.e. NO3−, DOC, and DO, although apportionment of N2O production to nitrification or denitrification was ambiguous. Our isotopic analysis (δ15N and δ18O) of NO3− and N2O implies that denitrification is the dominant production process of N2O, but definitive information is not derived from δ15N and δ18O analysis because of large variations in isotopic fractionations during production and consumption of N2O. However, the N2O site preference and the difference in δ15N between NO3− and N2O indicate that nitrification contributes to total N2O production and that most measured N2O has been subjected to further N2O reduction to N2. The implications of N2O biogeochemistry derived from isotope and isotopomer data differ entirely from those derived from conventional concentration data of DO, NO3−, and N2O. That difference underscores the need to reconsider our understanding of the N cycle in the oxic-anoxic interface.  相似文献   

17.
Sediment denitrification was monthly evaluated in two tropical coastal lagoons with different trophic states using the 15N isotope pairing technique. Denitrification rates were very low in both environments, always <5.0 μmol N2 m?2 h?1 and were not significantly different between them. Oxygen consumption varied from 426 to 4248 μmol O2 m?2 h?1 and was generally three times higher in the meso-eutrophic than the oligotrophic lagoon. The low denitrification activity was ascribed to both low water NO3 ? concentrations (<2.0 μM) and little nitrate supply from nitrification. There was no correlation of denitrification with nitrate or ammonium fluxes. Sediments in temperate environments with similar oxygen consumption rates usually presented a higher proportion of nitrification–denitrification rates. Sediment oxygen consumption was a good predictor of sediment denitrification in both studied lagoons.  相似文献   

18.
The stable isotope nitrogen-15 (15N) is a robust indicator of nitrogen (N) source, and the joint use of δ15N and δ18O–NO3 ? values can provide more useful information about nitrate source discrimination and N cycle process. The δ15N and δ18O–NO3 ? values, as well as major ion tracers, from Taihu Lake in east China were investigated to identify the primary nitrate sources and assess nitrate biogeochemical process in the present study. The results show that the nitrate concentration in West Taihu Lake (WTL) was generally higher than those in East Taihu Lake (ETL) and its upstream inflow rivers. The NO3 ?/Cl? value combined with mapping of δ15N–NO3 ? and NO3 ? concentration suggest that the mixing process should play a major effect in WTL, and denitrification was the dominant N transformation process in WTL. A linear relationship of close to ~1: 2 was observed between δ15N–NO3 ? and δ18O–NO3 ? values in WTL, confirming the occurrence of denitrification in WTL. The δ15N–NO3 ? data imply that sewage and manure were the principal nitrate sources in WTL and its feeder rivers, while the nitrate in ETL might derive from soil organic nitrogen and atmospheric deposition. The δ18O–NO3 ? data indicate most of nitrate from microbial nitrification of organic nitrogen matter possibly make a significant contribution to the lake.  相似文献   

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