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硝酸盐在北部湾球形棕囊藻藻华过程中的关键影响作用
吕旭宁
Subtype博士
Thesis Advisor俞志明
2020-05-20
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Degree Name理学博士
Degree Discipline海洋生态学
Keyword北部湾 球形棕囊藻藻华 硝酸盐 偏好吸收 影响因子
Abstract

近年来,在人类活动与气候变化双重压力下,近海富营养化程度不断加剧,导致藻华发生频率不断增加、持续时间不断增长、影响范围不断扩大,已成为全球沿海国家面临的典型生态灾害之一。近十年,我国北部湾海域球形棕囊藻藻华频发,不仅严重影响了当地渔业生产和生态环境,也给滨海核电冷源安全带来了严重隐患,引起广泛关注。本学位论文针对北部湾海域球形棕囊藻藻华,基于精细化的航次调查、现场培养实验和同位素示踪实验,刻画了球形棕囊藻藻华生消全过程中的环境因子变化特征发现了硝酸盐对球形棕囊藻藻华的关键影响作用,揭示了球形棕囊藻囊体对硝酸盐的偏好吸收机制,定量阐述了硝酸盐在不同藻华阶段的关键生物地球化学过程,并判定了化学、物理过程在藻华形成与维持过程中的贡献。主要研究结果如下:

1影响球形棕囊藻藻华生消的环境因子研究 为全面了解球形棕囊藻藻华生消全过程中的环境因子变化,探讨影响藻华生消的重要环境因子,20169月至20178月于北部湾海域开展了9个航次调查(201691112月,以及2017123468月),结果表明:12月发现球形棕囊藻囊体后,其丰度至翌年3月持续升高;4月丰度开始下降,至6月仅少数站发现少量囊体,8月则无囊体发现。研究海域受沿岸水、琼州海峡陆架水、南海陆架深层水与南海陆架混合水4个水团影响,水团的季节变化导致不同环境因子的时空分布各有特点。围绕藻华期间环境因子的时空变化特征,13种环境因子进行了主成分分析,结果表明:硝酸盐、磷酸盐、硅酸盐在第一主成分中的得分系数分别为0.190.210.20,其他因子的得分系数均低于0.17。进一步辨析不同环境因子与藻华生消之间的潜在关系,认为硝酸盐磷酸盐可能对球形棕囊藻藻华的生消具有重要影响作用,水团输运、浮游植物同化吸收和有机物分解是影响硝酸盐磷酸盐时空分布的主要因素。调查期间,硝酸盐磷酸盐的高值区主要出现在琼州海峡邻近海域,整体上表底分布较为一致,但在2月和3月,囊体丰度较高站位的表层硝酸盐磷酸盐浓度明显低于底层,可能受到了囊体的吸收利用。基于硝酸盐氮、氧稳定同位素手段,验证了球形棕囊藻对硝酸盐的同化吸收过程,进一步证实了藻华期间硝化过程对硝酸盐的补充作用。随着藻华的发生,研究海域内硝酸盐同化作用的增强、内部再生过程的减弱和外源输入的减少,降低了硝酸盐浓度,致使4月海域内的无机氮:磷酸盐 < 10硅酸盐:无机氮 > 1发生了相对氮限制,这可能导致了藻华的消亡

2球形棕囊藻囊体对硝酸盐的偏好吸收 为了阐明球形棕囊藻囊体对不同营养盐的利用特征藻华期间(20181月)于广西防城港核电站冷源取水口处收集囊体,开展了不同氮源加富条件下的现场培养实验,并测定了囊体内外溶液中的营养盐浓度和细菌群落结构。结果表明:不同实验组中,硝酸盐、铵盐、磷酸盐、硅酸盐、亚硝酸盐的最大吸收速率分别为7.38 ± 2.06 × 1092.14 ± 0.25 × 1090.14 ± 0.11 × 1090.09 ± 0.03 × 1090.08 ± 0.04 × 109 μmol·h1·cell10–12 h,硝酸盐的平均吸收速率显著高于其他四项营养盐(P < 0.05);且加富条件下,囊内的硝酸盐和铵盐浓度分别在1.5 h3 h出现了升高,表明囊体对硝酸盐具有偏好吸收和较快透过的特性。16S rDNA结果表明,囊体内部与外海水中的细菌群落结构存在差异,且自然状态下,磷酸盐、铵盐和硅酸盐在囊内浓度较高,硝酸盐和亚硝酸盐在囊外浓度较高,认为囊体外被的半透性和囊内的细菌矿化过程、糖异生过程导致了囊体内外营养盐的浓度差异。结合20162017年的现场调查结果,囊体出现站位中囊体细胞丰度高于其他浮游植物,对硝酸盐的利用能力也较强,推测硝酸盐浓度降低是导致球形棕囊藻藻华消亡的主要原因之一。

3硝酸盐关键转化过程对球形棕囊藻藻华生消的影响研究 在藻华生消过程中,营养盐再生过程能够为藻华维持提供物质保障,为了进一步量化硝酸盐再生过程对球形棕囊藻藻华不同阶段的影响,根据201811月至20194月期间囊体丰度的变化特点,将藻华划分为起始阶段(11月)、发展阶段(1月)和消亡阶段(2月)。于不同藻华阶段采集相关理化参数,并选取琼州海峡陆架水中的ZN1-6藻华频发海域ZN4-3作为典型站位开展了同位素示踪实验,测定了硝酸盐的同化吸收和硝化速率。结果显示ZN1-6站位的硝化速率分布范围为0.27–0.95 μmol·L1·d1硝酸盐同化速率分布范围为0.62–2.00 μmol·L1·d1,两者平均速率的最大值均出现于发展阶段,最小值均出现于消亡阶段。在藻华发展阶段,ZN4-3站位的硝化速率和同化速率分布范围分别为0.72–1.44 μmol·L1·d11.77–2.34 μmol·L1·d1,各水层的硝化速率和同化速率均高于ZN1-6,表明藻华频发海域的生物地球化学过程更加剧烈。值得注意的是,不同研究海域的硝化速率从表层至底层逐渐升高,同化速率则从表层至底层逐渐降低,分析发现上述规律是分别受温度、铵盐及硝酸盐、Chl a浓度的影响。作为硝酸盐的主要再生途径,与众多国内外研究相比,藻华期间该海域的硝化速率较低,仅为同化速率的43–51%,因此仅依靠硝化过程产生的硝酸盐不能满足浮游植物对其的吸收利用。球形棕囊藻的囊体形成和藻华维持需要大量硝酸盐,琼州海峡陆架水是向研究海域输入硝酸盐的主要水团,对该海域球形棕囊藻藻华发生与维持具有重要作用。

创新点主要体现于:精细刻画了北部湾海域主要环境因子的时空变化特征,在综合分析水文、生物、化学等同步观测指标的基础上,发现并验证了硝酸盐对球形棕囊藻藻华的关键影响作用;球形棕囊藻囊体内外的营养盐浓度和细菌群落结构存在差异,且囊体外被对硝酸盐具有较快透过的特性,揭示了球形棕囊藻囊体对硝酸盐偏好吸收的机制;利用同位素示踪技术定量阐述了不同藻华阶段硝酸盐转化过程,发现各阶段硝酸盐的同化速率均高于硝化速率,阐明了琼州海峡陆架水输入高浓度硝酸盐对该海域球形棕囊藻藻华发生与维持的重要作用。

综上所述,本博士学位论文较为全面的分析了北部湾球形棕囊藻藻华生消过程中主要理化因子的时空变化特征;发现了囊体细胞对硝酸盐的偏好吸收,并探讨了其作用机制,认为硝酸盐对球形棕囊藻藻华的生消具有关键影响作用;定量阐述了硝酸盐关键转化过程及其对球形棕囊藻藻华的影响,认为琼州海峡陆架水对高浓度硝酸盐的输运是藻华形成与维持的重要因素。相关研究结果有助于深入揭示北部湾海域球形棕囊藻藻华的形成机制,为进一步了解该海域的关键生源要素循环和科学防控球形棕囊藻藻华的发生提供了科学参考。

Other Abstract

In recent years, under the dual pressures of human activities and climate change, the level of eutrophication in coastal waters has intensified. The frequency of Harmful Algal Blooms (HABs) has increased, the duration of HABs has increased, and the influence scope of HABs has expanded. HABs have become typical ecological disasters in coastal countries around the world. Phaeocystis globosa blooms in the Beibu Gulf in China has not only seriously affected the local fishery production and ecological security, but also brought serious hidden dangers to the safety of nuclear power sources in the past ten years, which had caused widespread concern. Based on refined voyage surveys, field experiment and isotope tracer experiment, the characteristics of environmental factors during the entire P. globosa blooms were revealed, and the key effect of nitrate on P. globosa blooms was found. The uptake strategy of nitrate by P. globosa was revealed. The biogeochemical process of nitrate in typical sea areas were quantified and its role in the process of blooms was analyzed. The main findings are as follows:

(1) Study on environmental factors affecting the initiation and disappearance of P. globosa blooms In order to fully understand the changes in environmental factors during generation and elimination of P. globosa blooms and explore the key factors affecting blooms, 9 voyage surveys from September 2016 to August 2017 (September 2016, November 2016, December 2016, January 2017, February 2017, March 2017, April 2017, June 2017, August 2017) were conducted in the Beibu Gulf. P. globosa colony appeared in December, and the abundance of colony increasing to March of the following year. The abundance began to decline in April. Only a few colonies were found in little stations in June, and no colony were found in August. The study area was controlled by 4 water masses: Coastal Water, Qiongzhou Strait Shelf Water, South China Sea Bottom Shelf Water, and South China Sea Mixed Shelf Water. Affected by seasonal changes of water masses, the spatial and temporal distribution of different environmental factors had their own characteristics. Based on these characteristics, 13 physical and chemical factors during blooms were preliminarily screened using principal component analysis. The results showed that the score coefficients of nitrate, phosphate, and silicate in the first principal component were 0.19, 0.21, and 0.20, respectively and the score coefficients of other factors are all lower than 0.17. The potential relationship between different environmental factors and blooms was further identified. It was suggested that nitrate and phosphate might be key factors affecting P. globosa blooms. Water mass transport, phytoplankton assimilation and organic matter decomposition were the main factors affecting the spatial and temporal distribution of nitrate and phosphate. High-value areas of nitrate and phosphate mainly appeared in the adjacent waters of the Qiongzhou Strait. Overall the distribution of nitrate and phosphate in surface and bottom layers was relatively consistent. At sites with higher colony abundance in February and March, the concentrations of nitrate and phosphate in surface layer were significantly lower than those in bottom layer. The loss of nitrate and phosphate in surface layer may be uptaked by colonies. Based on the nitrate nitrogen and oxygen stable isotope method, the assimilation process of nitrate by P. globosa was verified, and the supplementary effect of nitrification on nitrate during blooms was confirmed. With blooms going on, the enhancement of nitrate assimilation, the weakeness of the internal regeneration process, and the reduction of external input reduced the concentration of nitrate. These processes led to relative nitrogen limitation (DIN:phosphate < 10 and silicate:DIN > 1), which may cause the extinction of blooms.

(2) The preferential uptake of nitrate by P. globosa colony In order to clarify the uptake characteristics of different nutrients by P. globosa colony, the colonies were collected at the cold water intake of Fangchenggang Nuclear Power Station in Guangxi during P. globosa blooms in January 2018 to conduct field experiment under different enrichment conditions of nitrogen sources. The nutrient concentrations and bacterial community structure were measured during the experiment. In different experimental groups, the maximum uptake rates of nitrate, ammonia, phosphate, silicate, nitrite were 7.38 ± 2.06 × 109, 2.14 ± 0.25 × 109, 0.14 ± 0.11 × 109, 0.09 ± 0.03 × 109, 0.08 ± 0.04 × 109 μmol·h1·cell1 (0–12 h) and the average uptake rate of nitrate was significantly higher than the other four nutrients (P < 0.05). Under enrichment conditions, the concentrations of nitrate and ammonia in the colony increased at 1.5 h and 3 h, respectively. These phenomena indicated that the colony had the characteristics of preferential uptake and faster transmission of nitrate. 16S rDNA technology confirmed that there were differences in bacterial community between the inside and outside of colony. Under natural conditions, the concentrations of phosphate, ammonia and silicate were higher in the colony, and nitrate, nitrite have higher concentrations outside the colony. It was believed that the semi-permeability of the colony envelope and the bacterial mineralization process, the gluconeogenesis process in the colony led to differences of nutrient concentrations in and out of colony. Based on the field survey results from 2016 to 2017, the abundance of colony cell was much higher than that of other phytoplankton at stations with colony, and its ability of uptaking nitrate was also stronger than other phytoplankton. It was speculated that the decrease of nitrate concentration cause the extinction of P. globosa blooms.

(3) Study on the effects of key nitrate transformation process on the initiation and disappearance of P. globosa blooms Nutrient regeneration process can provide nutrition foundation for the maintenance of blooms. In order to further quantify the effect of the regeneration process of nitrate on different stages of P. globosa blooms, the blooms was divided into initiation stage (November), development stage (January) and disappearance stage (February) based on the changing characteristics of colony abundance from November 2018 to April 2019. Relevant physical and chemical parameters were collected in different stages. ZN1-6 in the strait shelf water and ZN4-3 in the frequent blooms area were selected as the experimental station to conduct isotope tracer experiment and assimilation and nitrification rate of nitrate were determined. The isotope tracer experiments in different stages showed that the nitration rate of ZN1-6 station ranged from 0.27–0.95 μmol·L−1·d−1 and nitrate assimilation rate of ZN1-6 station ranged from 0.62–2.00 μmol·L−1·d−1. The maximum value of two rates appeared in development stage, and the minimum value appeared in disappearance stage. In development stage, the nitrification rate and assimilation rate of ZN4-3 station ranged from 0.72–1.44μmol·L−1·d−1 and 1.77–2.34 μmol·L−1·d−1, respectively. The nitrification and assimilation rate of each layer at ZN4-3 were higher than ZN1-6. The above results indicated that there were stronger biogeochemical processes in the frequent blooms area. It was worth noting that nitrification rate gradually increased from the surface layer to the bottom layer in different sea areas, while assimilation rate gradually decreased from the surface layer to the bottom layer. The analysis showed that the above rules were caused by the effects of temperature, ammonia and nitrate, Chl a respectively. The nitrification process was the main way to produce nitrate in seawater. Compared with many domestic and foreign studies, the nitrification rate in this sea area during blooms was low, which was only 43–51% of the assimilation rate. Therefore, the nitrate produced by nitrification alone cannot satisfy the absorption of phytoplankton. The formation of P. globosa colony and the maintenance of P. globosa blooms require a large amount of nitrate. Qiongzhou Strait Shelf Water is the main water mass that inputs nitrate to the study area, which plays an important role in the occurrence and maintenance of P. globosa blooms.

The innovations of this dissertation are as follows: The characteristics of the spatiotemporal changes of the main environmental factors in the Beibu Gulf were carefully described. Based on the comprehensive analysis of hydrological, biological, chemical and other synchronous observation indicators, the key effects of nitrate on P. globosa blooms were discovered and verified; The concentration of nutrients and the bacterial community inside and outside of P. globosa colony were different, and the colony envelope had the characteristics of faster penetration of nitrate, which reveals the mechanism of preferential uptake of nitrate by P. globosa colony; The isotope tracing technique was used to quantitatively explain the conversion process of nitrate in different stages, and it was found that the uptake rate of nitrate in each stage was higher than the nitrification rate. The important role of high nitrate concentration input of Qiongzhou Strait Shelf Water on the occurrence and maintenance of P. globosa blooms was clarified.

In conclusion, this dissertation analyzed the spatiotemporal characteristics of main physicochemical factors in the Beibu Gulf. The preferential uptake of nitrate by colony cells was found and its mechanism was explored. It was considered that nitrate had key effects on the occurrence and the extinction of P. globosa blooms. The key transformation processes of nitrate were quantitatively expounded and the effects of these processes during P. globosa blooms were revealed. It speculated the high transport of nitrate from Qiongzhou Strait Shelf Water was an important factor for the formation and maintenance of P. globosa blooms. Relevant research results laid a foundation for further revealing the formation mechanism of P. globosa blooms in the Beibu Gulf. It also provided a scientific reference for further understanding the key elements cycle and scientific prevention and control of P. globosa blooms in this sea area.

 

Language中文
Table of Contents缩略词说明 XV 第1章 绪论 1 1.1 球形棕囊藻藻华及其危害 1 1.2 不同环境因子对球形棕囊藻生长的影响 6 1.2.1 物理因子对球形棕囊藻生长的影响 6 1.2.2 化学因子对球形棕囊藻生长的影响 7 1.2.3 生物因子对球形棕囊藻生长的影响 9 1.3 北部湾环境特点及球形棕囊藻藻华发生概况 10 1.4 硝酸盐氮稳定同位素在海洋研究中的应用 12 1.4.1 海洋中的关键氮循环过程 12 1.4.2 氮稳定同位素对氮循环过程的指示作用 15 1.4.3 氮稳定同位素在海洋氮循环研究中的应用 18 1.5 本论文的研究目标及内容 20 1.5.1 研究目标 20 1.5.2 研究内容 20 1.5.3 拟解决的主要科学问题 21 第2章 影响球形棕囊藻藻华生消的环境因子研究 23 2.1 前言 23 2.2 样品采集及分析方法 25 2.2.1 站位设置及样品采集 25 2.2.2 样品分析测定 27 2.2.3 数据来源 28 2.2.4 数据处理与统计分析 28 2.3 结果 29 2.3.1 北部湾海域囊体丰度和水文环境的时空变化 29 2.3.2 北部湾海域主要营养盐的时空变化 33 2.3.3 北部湾海域硝酸盐氮、氧稳定同位素的时空变化 41 2.4 讨论 45 2.4.1 影响球形棕囊藻藻华生消的重要因子 45 2.4.2 影响重要因子分布的主要因素 49 2.4.3 氮、氧稳定同位素对氮营养盐循环关键过程的指示 54 2.5 小结 59 第3章 球形棕囊藻囊体对硝酸盐的偏好吸收 61 3.1 前言 61 3.2 材料与方法 61 3.2.1 球形棕囊藻囊体收集与培养 61 3.2.2 实验设计 62 3.2.3 样品分析测定 63 3.2.4 数据处理与统计分析 63 3.3 结果 64 3.3.1 无机氮源中硝酸盐的偏好吸收 64 3.3.2 囊体细胞对硝酸盐和铵盐的吸收特点 65 3.3.3 囊体内外营养盐和细菌的分布特点 67 3.3.4 球形棕囊藻藻华过程中无机营养盐的浓度变化 69 3.4 讨论 70 3.4.1 囊体偏好吸收硝酸盐的机制探讨 70 3.4.2 囊体内部可能发生的生化过程 71 3.4.3 硝酸盐在球形棕囊藻藻华过程中的作用 73 3.5 小结 74 第4章 硝酸盐关键转化过程对球形棕囊藻藻华生消的影响研究 77 4.1 前言 77 4.2 样品采集及分析方法 78 4.2.1 站位设置及样品采集 78 4.2.2 测定关键氮循环过程速率的实验方法 79 4.2.3 样品分析测定 80 4.2.4 数据来源 80 4.2.5 数据处理与统计分析 81 4.3 结果 82 4.3.1 不同藻华阶段的囊体分布特点与水文特征 82 4.3.2 不同藻华阶段主要营养盐及硝酸盐氮、氧稳定同位素分布特征 87 4.3.3 不同藻华阶段硝酸盐同化速率与硝化速率变化特点 94 4.4 讨论 95 4.4.1 硝酸盐供给与球形棕囊藻藻华发生的关系 95 4.4.2 氮、氧稳定同位素对硝酸盐关键转化过程的指示 101 4.4.3 硝酸盐关键转化过程的影响因素 105 4.4.4 硝酸盐关键转化过程对球形棕囊藻藻华的影响 107 4.5 小结 110 第5章 结论与展望 113 5.1 结论 113 5.2 创新点 114 5.3 不足与展望 114 参考文献 117 致 谢 135 作者简历及攻读学位期间发表的学术论文与研究成果 137
Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/164715
Collection海洋生态与环境科学重点实验室
Recommended Citation
GB/T 7714
吕旭宁. 硝酸盐在北部湾球形棕囊藻藻华过程中的关键影响作用[D]. 中国科学院海洋研究所. 中国科学院大学,2020.
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