【作者】 虞中杰；

【导师】 许世远； 王东启；

【作者基本信息】 华东师范大学 ， 自然地理学， 2011， 硕士

【摘要】 氧化亚氮（N20）和甲烷（CH4）是大气中重要的温室气体,其对未来全球气候变化可能会产生巨大的直接和间接影响,然而目前全球N2O、CH4源汇通量清单中还存在很大不确定性。随着全球范围内城市化进程的推进,人类的生存与发展极大地影响了全球的碳、氮循环,使得河流生态系统碳、氮负荷加倍增长,河流富营养化和黑臭等水质污染现象频发,增加了河流生态系统产生和排放N2O、CH4的潜能。在国家自然科学基金青年科学基金项目：“长江三角洲河网水体氧化亚氮产生机制及其排放通量”和国家重大水专项课题：“城市黑臭河道外源阻断、工程修复与原位多级生态净化关键技术研究与示范”等的支持下,本论文选取上海市河网作为研究对象,运用环境地球化学、生物地球化学、自然地理学等多学科综合研究手段,采用野外采样与实验室分析相结合、现场试验与室内培养试验相结合的方法,系统研究上海市河网水体溶存N2O、CH4浓度和饱和度的时空变化特征,探讨环境因子的控制作用和影响,采集市区（SQ）和郊区（QP）典型河流河底沉积物来考察N2O、CH4在沉积物—界面的产生与释放,并最终初步估算出上海市河网水—气界面N2O、CH4排放总量。主要结论包括以下几个方面：（1）河网水体N20和CH4浓度的总体变化范围分别在0.26±0.01～89.91±45.50μg N·L-1和0.74±0.64～1367.68±186.69μg C·L-1之间,溶解饱和度的变化范围分别在108.74+5.75-21355.11±10808.41%和95.95±49.70-64704.78±13886.65%之间,总体均处于饱和至高度过饱和状态；2月和4月水中N20和CH4浓度及饱和度显著高于其他月份；河网内水中N20和CH4浓度及饱和度的高值均出现在SQ、BS、JD等市区或工业集中区域。（2）水体中N20和CH4浓度之间存在显著的正相关；N20和CH4均分别与水温、气温、pH值、ORP和DO含量存在显著负相关,而与NH4+-N、TP、DOC和DIC存在显著正相关；N20与NH4+-N浓度在各个DO含量范围内整体存在一致的正相关关系,其关系可用回归方程：y=0.713015*e0.298754*x （R2=0.430, P<0.001）来描述,而N03-N与N20浓度仅在DO含量处于O～1.2 mg·L-1范围时N20浓度随着N0₃--N浓度的增加显著升高。（3） CART模型分类结果表明,NH4+-N、水温、DO、NO3--N、TP和pH是水中N20浓度的主要分类因子,而NH4+-N、NO3--N、DO、ORP和S042-是cH4浓度的主要分类因子。CART模型在水质较差、N2O、CH4浓度较高区域对N2O、CH4浓度的分类预测效果较好。GAM模型对水中N20总偏差解释率为72.31%,其中NH4+-N贡献率达42.99%,表层水体环境因子通过GAM模型拟合后对水中N20浓度的整体拟合效果较好；GAM模型对CH4浓度总偏差解释率为51.20%,预测效果总体较差。GAM模型在郊区水体较清洁区域可以得到较好的预测效果。（4）QP和SQ水体内部N20产生速率分别为O.10±0.67和0.97±0.65 ng N·h-1,远低于QP和SQ沉积物—水界面N20释放速率的3.86±1.93和12.49±6.25 ngN·h-1；两地沉积物—水界面CH4释放速率分别为0.079±0.0084和7.04±0.48μgC·h-1,上覆水体的氧化作用使得两地水体内部CH4产生速率极低；沉积物是两地表层水体N20和C出的主要来源；QP和SQ沉积物—水界面N20和CH4的释放通量分别为4.02±2.01和13.01±6.51μg N·m-2·h-1以及83.66±11.22和7335.48±495.79μg C·m-2·h-1,沉积物—水界面N20和CH4释放通量的较大差异是造成表层水体N20和CH4浓度空间分异的主要原因之一（5）富氧状态下QP和SQ沉积物的耗氧量均大于贫氧状态；由于沉积物中有机碳含量较高,SQ沉积物在富氧和贫氧状态下的耗氧量均高于QP沉积物,使得上覆水体总体处于缺氧状态；添加了NH4+-N或NH4+-N/NO3--N条件下,QP和SQ沉积物耗氧量明显增加,且随物质添加梯度出现上升趋势；上覆水体中的NH4+-N扩散进入沉积物表层加快了硝化反应速率可能是沉积物—水界面DO消耗加速的主要原因。（6）贫氧条件下QP和SQ沉积物—水界面N20的释放通量总体高于富氧状态；添加NH4+-N和NH4+-N/NO3--N显著增加了QP和SQ沉积物—水界面N20释放通量,其中尤以SQ沉积物更为显著,上覆水体中的DO和NH4+-N浓度是影响沉积物—水界面N20释放最为主要的因素；而上覆水体DO浓度是唯一显著影响QP和SQ沉积物—水界面CH4释放的决定性因素。（7）自然条件下QP和SQ表层O～1cm沉积物孔隙水N20浓度分别在1.02±0.64-2.04±1.45和2.23±0.85～3.40±1.07μg N·L-1之间,高于两地原位表层水体中的N20浓度；贫氧状态以及NH₄+-N和NH4+-N/NO3--N添加明显促进了表层0～1cm内孔隙水中N20的产生；在上覆水体较高的NH4+-N浓度和较低的DO浓度条件下,沉积物表层的硝化作用是N20的主要产生机制。自然条件下QP和SQ表层0～1cm沉积物孔隙水CH4浓度分别在49.48±12.94-54.14±21.48和6941.25±2647.55～7465.17±1234.68μg C·L-1;沉积物表层0～1cm内氧化作用显著降低了孔隙水CH4浓度；QP和SQ沉积物中极高的有机碳含量使得N03--N和S042-添加对CH4的抑制作用并不明显,并使沉积物成为水体中CH4的主要来源。（8）河网水—气界N20和CH4排放通量的总体变化范围分别在0.05±0.003～48.12±6.42 mg N·h-1·m-2和-0.04±0.01～579.25±86.20 mg N·h-1·m-2之间,河网水体总体是大气N20和CH4的源；较高的水温条件对水体N20和CH4排放存在一定的促进作用；SQ、BS和JD等市中心区域以及工业生产区域内水体N20和CH4排放通量显著较高；河网水体N20排放通量略低于长江口海域水体N20排放通量,而CH4排放通量与典型湿地生态系统CH4排放水平相当。（9）上海市河网水体N2O、CH4的年排放总量分别为7.23 Gg N·yr-1和58.22Gg C·yr-1;上海市河网水体N20年排放总量可占全球河流水体N20排放估算量的0.66%,现今对全球河流N20源效应的认识可能存在较大误差；上海市河网水体CH4的年排放量可占全国淡水湿地CH4排放估算量的6.62%,佐证了河流生态系统作为大气CH4排放源的重要性；城市化地区河网是大气N2O、CH4潜在的重要排放源,应当引起更多的关注与重视。更多还原

【Abstract】 Nitrous oxide (N2O) and methane (CH4) are important greenhouse gases, which directly or indirectly influence future climate change. The inventories of global N2O and CH4, however, still left significant uncertainties. With the process of urbanization in the whole global dimension, human being’s living and development extremely affect global carbon and nitrogen cyclings, causing the exponential increases of carbon and nitrogen loads in the river ecosystem and eutrophication and black-odor of river water. Consequently, the potential to produce and emit N2O and CH4 of river ecosystem has been stimulated.This paper was supported by the project of Nitrous oxide production mechanism and emission flux at Yangtze delta river net, funded by State Natural Science Fund and National Water Project:The research and demonstration of the application of extraneous sources interdiction, engineering restoration, and in-situ multilevel ecological purification technology in urban black-odorous river. The whole river network of Shanghai was selected as the research object and multi-disciplinary synthetic study methods were used in this study, including environmental geochemistry, biogeochemistry, physical geography and so on. Based on field samplings, laboratory analysis, in situ measurements and incubation experiments, this paper was aimed to systematically study the spatial and temporal variabilities of solube N2O and CH4 concentrations and saturations, gas production and exchange across sediment-water inferface, the effects of primary environmental factors on gas concentrations and the preliminary calculation of N2O and CH4 total emission across air-water interface of Shanghai river network. Main conclusions were as followings.(1) The total variation ranges of N2O and CH4 concentrations in river water were 0.26±0.01～89.91±45.50μg N·L-1 and 0.74±0.64～1367.68±186.69μg C·L respectively. The total variation ranges of N2O and CH4 saturations in river water were 108.74±5.75～21355.11±10808.41% and 95.95±49.70～64704.78±13886.65%, and the surface water had a overall high saturation; In February and April, the N2O, CH4 concentrations and saturations were significantly higher than those in other months; the highest concentrations and saturations of N2O and CH4 in river network appeared at downtown area and industrial area, like SQ, BS and JD.(2) N2O and CH4 concentrations in river water were significantly correlated with each other; Both N2O and CH4 concentrations had significant negative correlations with water temperature, air temperature, pH, ORP and DO respectively, and had significant positive correlations with NH4+-N, TP, DOC and DIC respectively; N2O concentration had a uniform positive correlation under different DO concentration, and this positive correlation could be described by regression formula:y 0.713015*e0298754*x (R2=0.430, P<0.001). However, the rapid increase of N2O concentration with N03--N could only be observed under low DO concentration ranging from 0～1.2 mg·L(3) The results of CART model indicated that NH4+-N, water temperature, DO, N03--N, TP and pH were primary environmental that could be used to classify N2O concentration in river water, and NH4+-N, N03--N, DO, ORP and SO42-correspondently were the classification factors of CH4 concentrations. CART model functioned ideally under the poor-quality water condition and high N2O, CH4 concentrations to classify N2O and CH4. GAM model could explain 72.31% of total variation of N2O concentration in which NH4+-N was attribute to 42.99% so that primary environmental factors could be used by GAM model to well fit N2O concentration in river water; However, GAM model could only explain 51.20% of total variation of CH4 concentration which unable GAM model to exactly fit or predict CH4 in river water. Generally, GAM model was effective under the good-quality water condition.(4) N2O production rate in water body of QP and SQ were 0.10±0.67 ng N·h-1 and 0.97±0.65 ng N·h-1, respectively, and were significantly lower than N2O emission rate across sediment-water interface, which were 3.86±1.93 ng N·h-1 and 12.49±6.25 ng N·h-1. CH4 emission rate across sediment-water interface of QP and SQ were 0.079±0.0084μg C·h-1 and 7.04±0.48μg C·h-1, respectively. The oxidation effect of oxygenic overlying water made the CH4 production rate extremely low. Sediments were main sources of N2O and CH4 in overlying water of QP and SQ. The emission flux of N2O and CH4 in QP and SQ were 4.02±2.01μg N·m-2·h-1 and 13.01±6.51μg N·m-2·h-1, and 83.66±11.22μg C·m-2·h-1 and 7335.48±495.79μg C·m-2·h-1, respectively. The significant differences of N2O and CH4 emission flux across sediment-water interface were one of the primary reasons that could explain spatial variations of N2O and CH4 concentrations in river network.(5) Oxygen comsuption of both QP and SQ were higher under oxygen-rich condition than those under oxygen-poor condition; because of the high organic matter concentration, oxygen comsuption of SQ sediment were higher than those of QP sediment under both oxygen-rich and oxygen-poor conditions, which made the overlying water in persistant oxygen-deficit condition; under the condition of NH4+-N or NH4+-N/NO3--N addition, oxygen comsuption of both QP and SQ sediment increased evidently, and also increased with addition gradient; the acceleration of nitrification process in surface sediment layer caused by NH4+-N diffusion from overlying water might be the main reason to explain the increase of oxygen comsuption across the sediment-water interface.(6) Under oxygen-poor condition, both N2O emission fluxes across sediment-water interface of QP and SQ were higher than those under oxygen-rich condition; NH4+-N and NH4+-N/NO3--N addition significantly increased N2O emission fluxes across sediment-water interface of QP and SQ sediments. DO and NH4+-N concentration in overlying water were most important factors that could influence N2O emission across sediment-water interface; DO was the only factor that could affect CH4 emission fluxes across sediment-water interface of QP and SQ sediments.(7) Under natural condition N2O concentrations of sediment core water in top 0-1 cm of QP and SQ sediments ranged from 1.02±0.64～2.04±1.45μg N·L-1 and 2.23±0.85～3.40±1.07μg N·L-1, and both of them were higher than N2O concentrations in QP and SQ surface water; Oxygen-poor condition, NH4+-N addition and NH4+-N/NO3--N addition significantly stimulated N2O production in top sediment; Under high NH4+-N and low DO condition, nitrification processing at the surface layer of sediment was the main mechanism for producing N2O. Under natural condition CH4 concentrations of sediment core water in top 0～1 cm of QP and SQ sediments ranged from 49.48±12.94～54.14±21.48μg N·L-1 and 6941.25±2647.55～7465.17±1234.68μg C·L-1; oxidation effect in top 0～1 cm of sediment significantly decreased CH4 concentration in sediment core water; the extremely high organic matter concentration of QP and SQ sediments disabled the inhibiting effect of sulfate-reduction and nitrate-reduction on CH4 formation, and made sediments the main sources of CH4 in overlying water.(8) N2O and CH4 emission fluxes across water-air interface of river network ranged from 0.05±0.003～48.12±6.42 mg N·h·m-2 and -0.04±0.01～579.25±86.20 mg N·h-1·m-2, respectively. Generally, river network is the source of atmospheric N2O and CH4; High water temperature promoted N2O and CH4 emission; N2O and CH4 emission fluxes in urban and industrial areas like SQ, BS, JD were significantly higher; N2O emission flux of river network was slightly lower than that in sea water of Yangtze estuary, and CH4 emission flux of river network was equivalent to those of presentative wetland ecosystems.(9) The year total N2O and CH4 emissions of Shanghai river network were 7.23 Gg N·yr-1 and 58.22 Gg C·yr-1, respectively; year total N2O emission accounted for 0.66% of the global N2O emission from river ecosystem,indicating the inaccuracy in current estimation on global N2O emission from river ecosystem; year total CH4 emission of river network accounted for 6.62% of CH4 emission from freshwater wetland nationwide,corrobating the importance of river ecosystem as the source of atomsperic CH4; the river network in urbanized area was the potential important source of atomsperic N2O and CH4, and deserved more concerns and attentions.更多还原