【作者】 于海燕；

【导师】 俞志明； 宋秀贤；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 环境科学， 2012， 博士

【摘要】 本论文以稳定氮同位素(δ¹⁵N)技术为基础，对长江口海域氮的同位素特征及其环境意义进行了研究。以前人建立的一套完整的水体中氮的稳定同位素分析预处理方法为基础，通过一系列物理、化学改性处理制备选取了更适于水中溶解态硝酸盐δ¹⁵N预处理的国产沸石。运用该方法对2009年和2010年长江口海域表层和断面水体中的溶解态硝酸盐和悬浮颗粒物的δ¹⁵N特征进行分析，根据不同季节、不同区域内δ¹⁵N的特征研究水体中氮的迁移、转化等生物地球化学过程，揭示其环境行为，从而对该海域的氮循环机制进行探索。主要结果如下：为选取更适于水中溶解态硝酸盐δ¹⁵N预处理的沸石，通过多种改性方法（重力筛选、钠改性、酸改性、微波改性和超声波改性等）对几种天然沸石进行改性处理，提高其酸性条件下对低浓度铵氮吸附率。改性处理后，几种沸石在酸性条件下对低浓度铵氮吸附率达90%以上，氮同位素分馏系数为-0.8‰^-0.4‰，制备出符合海水硝酸盐氮同位素预处理的沸石材料。将选取好的沸石应用于本实验室前期确立了的水体氮的稳定同位素分析预处理方法，对2009年和2010年2、5、8、11月份长江口海域表层溶解态硝酸盐δ¹⁵N值(δ¹⁵NO₃)以及2010年2、5、8、11月份长江口海域断面水体15NO₃进行分析。研究发现，长江口海域表层和断面水体中15NO₃组成具有明显的时空分布特点，反映了不同区域受不同的物理、生物地球化学作用影响。口门内，15NO₃值的变化与浓度相一致，且离散程度较小，说明长江径流输入在该区域影响明显；通过河道δ¹⁵NO₃值的变化可反映出排污口的排污影响。最大浑浊带，表层水域和底部水域各季节所受到影响作用复杂，5月份表层水体主要受同化吸收作用影响，外海区下层水体受固氮作用影响；8月份底部水体主要受硝化作用影响，表层在上升流作用下，受硝化作用和同化吸收的影响；11月份底层水体主要受硝化作用影响，表层受同化吸收和反硝化作用影响。外海区，底部水体主要受硝化作用影响，表层除受硝化作用影响外，还受同化吸收作用及反硝化作用的影响。同时，本文对长江口海域硝化反应的主要影响因子（温度、盐度、DO、可利用营养盐、硝化细菌等）进行探讨，并对硝化反应的同位素分馏效应进行了评估，利用瑞利公式计算得出长江口海域11月份水体中硝化作用的分馏系数为-8‰。发现低氧水体中由矿化作用和硝化作用再生而来的氮是长江口海域水体富营养化的一个重要来源。此外，本文对2009年和2010年2、5、8、11月份长江口海域表层悬浮颗粒物的δ¹⁵N(δ¹⁵Np以及2010年2、5、8、11月份长江口海域断面水体δ¹⁵Np进行研究。发现长江口海域2009年和2010年表层和断面水体中δ¹⁵Np组成具有明显的时空分布特点，说明长江口海域不同区域受不同的物理、生物地球化学作用影响。口门内，δ¹⁵Np值的变化受长江径流输入影响明显，通过δ¹⁵Np值特征反映出长江径流输入的氮2月份和5月份主要来源于农业化肥和大气沉降，8月份和11月份主要来源于工业与生活污水。同时，不同河道排污口附近的δ¹⁵Np值不同，说明土地的利用方式可通过δ¹⁵Np特征反映出来。口门外海域，不同深度水体发生的生物地球化学过程不同。一般来说，底部水体δ¹⁵Np较高，发生了含氮有机物的矿化分解作用；2010年11月底部水体较低的δ¹⁵Np是由生物的矿化分解作用和硝化作用、同化吸收作用共同造成的。除2月份外，各季节表层海水均发生了生物的同化吸收作用。2月份长江口海域δ¹⁵Np分布受陆源海源物理混合和矿化作用共同影响。长江口海域水体中溶解态硝酸盐和悬浮颗粒有机氮之间存在相互转化，二者之间δ¹⁵N的变化及其相互关系反映了一定的生物地球化学变化和环境信息。总体而言，长江口海域表层15NO₃的分布水平较δ¹⁵Np略低，二者之间的分馏总体平均值偏正向。其中，15NO₃与δ¹⁵Np的最低值均出现在2月份，该季节水体中溶解态硝酸盐和悬浮颗粒有机氮主要受长江径流的外源输入影响，同时还受同化吸收作用和矿化作用的影响；5月份水体中氮的生物地球化学作用程度明显升高，δ¹⁵Np与15NO₃之间呈现明显的线性负相关，二者之间的分馏偏负，表明微藻的同化吸收作用在该季节作用明显，同时，外海区东部海域发生了颗粒物的矿化分解反应和硝化反应；8月份，δ¹⁵NO₃与δ¹⁵Np之间分馏为正，且底层水体比表层更大，说明8月份长江口海域中表层与底部水体生物地球化学过程不同，表层主要受生物的同化吸收和硝化作用影响，底部水体受颗粒物的矿化分解和硝化作用影响；11月份，除外海区表层有几个负值外，其余海区均为正值，且呈现出自表层向底层递增的趋势，表层主要受生物的同化吸收和硝化作用影响，底部水体受颗粒物的矿化分解和硝化作用影响。更多还原

【Abstract】 Stable nitrogen isotope (δ¹⁵N) can be used as fingerprints to study sources andsinks of nitrogen in aquatic environments. To reveal nitrogen dynamics in theChangjiang River estuary, variability of nitrogen isotope and its environmentalimplications were studied. Natural zeolites were modified to enhance theirperformances in acid environments for stable nitrogen isotopic analysis in waters. Theδ¹⁵N of dissolved nitrate (δ¹⁵NO₃) and suspended particulate matters (δ¹⁵Np) in thesurface and transect water columns of the Changjiang River estuary were analyzed bythis method in2009and2010. According to the seasonal and spatial variations of15N, fate of nitrogen as well as the biogeochemical processing involved were studiedand its environmental implications were also discussed. Accordingly, the nitrogencycle and its evolution process were explored in the Changjiang River estuary.The main conclusions were listed below:Several Chinese natural zeolites were modified with multiple methods toincrease their ammonium adsorption efficiency for nitrogen isotope analyses. Beingtreated by gravity screen, sodium chloride, hydrochloric acid, microwave andultrasonic wave, their ammonium adsorption efficiency under acid conditions wereimproved even at low concentrations. The nitrogen isotope fraction factor of newlymodified zeolite was small and the modified zeolite is proper for nitrogen isotopeanalysis of nitrate in seawater.The15NO₃in surface and transect water of the Changjiang River estuary wereanalyzed in February, May, August and November of2009and2010. The distributionof15NO₃varied both spatially and temporally, which reflected that different physicaland biogeochemical processes might affect the15NO₃signatures in differentgeographic regions. In the inner estuary,15NO₃was mainly affected by the riverineinput from the Changjiang River. The15NO₃feature in the channel may reflect thedifferent pollution resources from drain outlets. In the Turbidity Maximum zone,complicated biogeochemical processes were found in different seasons. Assimilation was found in both surface and transects waters in May. Nitrification was found in thedeep waters in August. With upwelling current, surface water was influenced bynitrification and assimilation in August. In November, nitrification was found in thedeep waters while assimilation and denitrification was found in the surface water. Inthe adjacent marine area, deep waters were mainly controlled by nitrification, whilesurface waters were influenced by nitrification, assimilation and denitrification.Meanwhile, influence of environmental factors such as temperature, salinity,dissolved oxygen, nutrients of nitrification were discussed. The nitrogen isotopicfactor of nitrification was evaluated to be-8‰using Rayleigh equation. It is inferredthat newly regenerated nitrogen from mineralization and nitrification is an importantsource of eutrophication in the Changjiang River estuary.Meanwhile, theδ¹⁵Npin surface and transect water of the Changjiang Riverestuary were analyzed in February, May, August and November of2009and2010. Itwas observed that the distribution ofδ¹⁵Npvaried seasonally in different regions,which reflected that different physical and biogeochemical processes affected theδ¹⁵Npsignatures. In the inner estuary,δ¹⁵Npwas mainly affected by riverine inputfrom the Changjiang River. Chemical fertilizer and atmospheric precipitation wasbelieved to be the main source of nitrogen from the Changjiang River in February andMay, while industrial and domestic sewage were the main source of nitrogen from theChangjiang River in August and November. In the turbidity maximum zone and theadjacent marine area, different biogeochemical processes were found in the surfaceand deep waters. Normally,δ¹⁵Npvalues were high in the deep waters, whichindicated that mineralization occurred in deep waters. However, in November of2010,δ¹⁵Npvalues were low in the deep waters. Mineralization, nitrification andassimilation occurred in the deep waters and caused the lowδ¹⁵Npvalues.Assimilation was found in the surface waters throughout the whole year except inFebruary. The distribution ofδ¹⁵Npin February was influenced mainly bymineralization and mixing between river and ocean. The reciprocal transformation of dissolved nitrate and suspended particulatematters was observed in the Changjiang River estuary. The correlations betweenδ⁽15NO₃andδ¹⁵Npreflected biogeochemical processing and evolution of nitrogen. Ingeneral,15NO₃was slightly lower thanδ¹⁵Npin the surface waters. The nitrogenfractionation （） between them was positive in average. The lowest values of15NO₃andδ¹⁵Npwere both observed in February. Dissolved nitrate and suspendedparticulate materials were mainly influenced by riverine input from the ChangjiangRiver. The15N distributions were also affected by assimilation and mineralization. InMay, biogeochemical processes were significantly increased. Negative correlationswere found between15NO₃and15Np, and values were mainly negative.Assimilation contributed greatly in this season, while mineralization and nitrificationwere also found in the east area of the adjacent marine area. In August, values weremainly positive; and were higher in the deep waters than those in the surface waters.The results indicated different biogeochemical processes between surface and deepwaters. Assimilation and nitrification dominated in the surface waters whilemineralization and nitrification played important roles in the deep waters. InNovember, values were mainly positive expect some negative values in the adjacentmarine area. values increased from surface to deep layers. Surface waters weremainly influenced by assimilation and nitrification, while mineralization andnitrification were found in the deep waters.更多还原