长江口海域氮的同位素特征及其环境意义

IOCAS-IR > 海洋环流与波动重点实验室

	长江口海域氮的同位素特征及其环境意义
其他题名	Study on the Variability of Nitrogen Isotope in the Yangtze River (Changjiang) Estuary, China and Its Environmental Implications
	刘秀娟
学位类型	博士
导师	俞志明
	2009-05-27
学位授予单位	中国科学院海洋研究所
学位授予地点	海洋研究所
学位专业	海洋化学
关键词	稳定氮同位素预处理方法溶解态硝酸盐悬浮颗粒物生物地球化学过程长江口海域长江干流
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。确立了一套完整的水体中氮的稳定同位素分析预处理方法，并运用该方法对2006年长江干流以及长江口海域表层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、不同区域内其δ15N值的变化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：稳定氮同位素的分析准确与否，预处理过程是关键。不同形态、不同水体中氮的预处理方法不同。本文以传统的蒸馏法为基础，对适合海水中溶解态硝酸盐的氮同位素分析预处理方法进行研究并改进，并进行了不同实验条件的验证，效果较好。此外，对淡水体系中溶解态硝酸盐的氮同位素分析预处理方法以及悬浮颗粒物的氮同位素分析方法也进行了研究，确立了一套完整的水体中氮的稳定同位素分析方法，对δ15N技术在河口氮循环研究中的广泛应用提供了基础。依据上述方法，对2006年2、5、8、11月份长江口海域表层水体中的溶解态硝酸盐δ15N值（δ15N-NO3-）进行分析。研究发现，δ15N-NO3-分布范围在0.4‰到6.5‰之间，平均为3.5‰，具有明显的时空分布特点，在不同季节不同区域内所受的物理、生物地球化学作用不同。口门内，δ15N-NO3-的季节变化主要受长江径流输入影响，来源单一。最大浑浊带，δ15N-NO3-的分布规律不明显，保守混合行为较差，说明该区域的影响作用复杂，不同季节水体中发生的生物地球化学作用存在差异。外海区，δ15N-NO3-的季节变化明显，春季>秋季>夏季>冬季，与生物对硝酸盐的吸收程度变化相一致，反映了生物作用在该区域的影响显著。同样在2006年2、5、8、11月份本文对长江口海域表层水体中悬浮颗粒物的δ15N（δ15Np）组成进行了研究。δ15Np值分布在0.6-8.2‰之间，同样具有明显的时空分布特点，其变化趋势与陆源输入和水体中氮的生物地球化学过程有关。口门内，表层水体中δ15Np的变化主要受长江径流的陆源输入影响，生物地球化学作用影响较弱；最大浑浊带，水体中的悬浮颗粒有机氮受微生物的降解活动影响明显，各季节均存在不同程度的颗粒物分解作用；外海区，陆源输入减弱，悬浮颗粒物的δ15Np值主要受微藻的同化吸收作用以及一定程度的颗粒物分解作用影响。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重要的相互转化作用，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，长江口海域表层水体中δ15N-NO3-的分布水平较δ15Np略低，二者之间的分馏ε总体偏正。其中，δ15N-NO3-与δ15Np的最低值均出现在2月份，说明该季节水体溶解态硝酸盐和悬浮颗粒物都可能受到一致的外源输入影响，其内部生物地球化学作用较弱。5月份和11月份水体中的δ15N-NO3-值和δ15Np值均各自水平相近，说明在这两个季节溶解态硝酸盐和悬浮颗粒物都可能受到程度相近的外源输入或生物吸收作用的影响，分馏ε偏负程度较大。8月份δ15N-NO3-值较低而δ15Np值较高，分馏ε在四个季节中最大，可能是该季节程度较大的颗粒物分解作用影响所致。 2006年长江干流表层水体中溶解态硝酸盐及悬浮颗粒物的δ15N组成也具有明显的时空分布特点，二者季节变化规律相近，丰水期（5、8月份）δ15N值较高，而枯水期（2、11月份）较低。δ15N-NO3-与δ15Np之间呈现明显的正向相关关系，其空间分布趋势相同，自长江上游至下游δ15N值逐渐升高，说明二者均受到相似的氮来源影响；长江上游氮的来源均以大气沉降和农业源（无机化肥和土壤有机氮）为主，而中、下游水体氮的来源则都偏重于工业及生活排污的贡献，随着人类活动程度以及工业化、城市化程度的升高，硝酸盐及悬浮颗粒有机氮的来源发生变化，其δ15N值相应增加。
其他摘要	Based on the analysis of stable nitrogen isotope (δ15N), variability of nitrogen isotope in the Yangtze River (Changjiang) estuary and its environmental implications were studied. The comprehensive preparation method for stable nitrogen isotopic analysis in waters was given. δ15N of dissolved nitrate (NO3-) and suspended particulate matters (SPM) in surface water of the Yangtze River mainstream and its estuary were analyzed by using the preparation method in 2006. According to the variations of δ15N in different seasons and geographical regions, the biogeochemical processing of nitrogen transformation was studied and its environmental implications were also revealed. In this sense, the mechanism of nitrogen cycle was explored in the Yangtze River estuary. The main results are as follows: The preparation method of water samples is critical to identify both inaccurate and accurate analysis of δ15N in seawater. The method varies with different nitrogen form and water bodies. In this paper, based on the traditional distillation, a suitable method for the preparation of dissolved nitrate samples in seawater for nitrogen isotopic analysis was studied and improved. Some tests of the method were conducted and good effect on analysis was found. Additionally, both the preparation method of dissolved nitrate in freshwater and the method of nitrogen isotopic analysis for SPM were studied. The comprehensive preparation method for stable nitrogen isotopic analysis in waters was given, which can supply basic information for wide application of δ15N in study of estuarine nitrogen cycle. The δ15N values of dissolved nitrate (δ15N-NO3-) in surface water of the Yangtze River estuary were analyzed in February, May, August and November of 2006 by using above method. It was indicated that the distribution of δ15N-NO3- varied with seasons and geographic regions, with an average of 3.5‰ (ranging from 0.4‰ to 6.5‰). Different physical and biogeochemical processes affected the δ15N-NO3- signatures in different geographic regions. In the inner estuary, δ15N-NO3- was affected mainly by riverine input from the Yangtze River with single nitrogen source. In the Turbidity Maximum zone, irregular distribution and non-conservative mixing behaviour of δ15N-NO3- were investigated, indicating complex processing of NO3-. In the adjacent sea, seasonal variations of δ15N-NO3- were consistent with those of nitrate uptake rates in phytoplankton as a result of biological processing. At the same time, the δ15N values of SPM (δ15Np) in surface water of the Yangtze River estuary were studied in February, May, August and November of 2006. The spatial and temporal variations were also observed in δ15Np with a range between 0.6‰ and 8.2‰, as the result of different influence of terrigenous inputs and nitrogen biogeochemical processing. In the inner estuary, δ15Np was affected mainly by riverine inputs from the Yangtze River. In the Turbidity Maximum zone, SPOM was affected by microbial degradation obviously, indicating the control of the decomposition processing of SPOM in δ15Np during four seasons. In adjacent marine sea, the influence of terrigenous inputs weakened and δ15Np was controlled by inorganic nitrogen assimilation by phytoplankton and the decomposition of SPOM. The important mutual transformation of dissolved nitrate and SPM was found in the Yangtze River estuary. The variations and correlations between δ15N-NO3- and δ15Np reflected some biogeochemical processing and environmental implications. In general, δ15N-NO3- was slightly lower than δ15Np. The nitrogen fractionation (ε) between them was positive in average. The lowest δ15N-NO3- and δ15Np were both investigated in February, indicating consistent influence from external nitrogen inputs and weakened biogeochemical processing in waters. In May, the δ15N-NO3- and δ15Np values were close to those in November, respectively. And the fractionation (ε) of δ15N-NO3- and δ15Np was seriously negative in general. It was shown that the dissolved nitrate and SPM were probably affected by similar influence from external inputs or biological assimilation. In August, the fractionation (ε) of high δ15N-NO3- and low δ15Np was most positive in four seasons, probably caused by intense decomposition of particulate matters. Obvious spatial and temporal variations were also observed in δ15N of dissolved nitrate and SPM from the Yangtze River mainstream in 2006. The seasonal variations of δ15N-NO3- and δ15Np were similar, with high δ15N values in wet season (in May and August) and low δ15N values in dry season (in February and November). There was obvious positive correlation between δ15N-NO3- and δ15Np. The uniform spatial distribution of δ15N-NO3- and δ15Np was also found, with an increase from the upper reaches to the lower reaches of the Yangtze River. It was considered that dissolved nitrate and SPM were influenced by similar nitrogen inputs. In the upper reaches, the main nitrogen inputs were from atmosphere deposition and agricultural sources. In the middle and lower reaches, nitrogen sources varied and the δ15N values of dissolved nitrate and SPM increased with human activity, industrialization and urbanization.
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1513
专题	海洋环流与波动重点实验室文献信息中心
推荐引用方式 GB/T 7714	刘秀娟. 长江口海域氮的同位素特征及其环境意义[D]. 海洋研究所. 中国科学院海洋研究所,2009.

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