Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope
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摘要: 为了解珠江口氮循环过程及氮污染主要来源,于2020年7月在珠江口近岸海域(伶仃洋西部、磨刀门和黄茅海)系统采集了40个站位的海水样品,耦合水化学基本参数与硝酸盐氮氧稳定同位素示踪技术,定量解析
${\mathrm{NO}}_3^- $ 污染的主要来源,揭示其空间梯度变化与迁移转化机制。结果表明,珠江口近岸海域${\mathrm{NO}}_3^- $ 平均浓度为44.05 ± 27.85 μmol/L,δ15N-${\mathrm{NO}}_3^- $ 和δ18O-${\mathrm{NO}}_3^- $ 值分别为10.8 ± 2.6‰ 和6.1 ± 4.5‰。三个海域的${\mathrm{NO}}_3^- $ 、δ15N-${\mathrm{NO}}_3^- $ 和δ18O-${\mathrm{NO}}_3^- $ 均不遵循保守混合特征,δ18O-${\mathrm{NO}}_3^- $ 和δ15N-${\mathrm{NO}}_3^- $ 的回归斜率表明,浮游植物同化作用和硝化作用是珠江口硝酸盐同位素组成变化的主要调控过程,而无机氮(Dissolved Inorganic Nitrogen,DIN)的显著去除则表现出沉积物反硝化作用对珠江口氮储库的影响。贝叶斯模型溯源结果进一步揭示生活污水是三个海域${\mathrm{NO}}_3^- $ 的最大来源,平均占比达到51.97%,水产养殖是磨刀门和黄茅海${\mathrm{NO}}_3^- $ 第二大主要来源,这可能与珠江口西岸城市较高的水产养殖面积有关。本研究结果可为近岸海域氮污染综合治理提供科学依据。-
关键词:
- 硝酸盐氮氧同位素组成 /
- 氮循环 /
- 溯源 /
- 珠江口
Abstract: To elucidate nitrogen cycling processes and identify dominant nitrogen pollution sources in the Pearl River Estuary (PRE), seawater samples were systematically collected from 40 stations in coastal waters (the western of Lingdingyang, Modaomen and Huangmaohai) during July 2020. By integrating hydrochemistry parameters and nitrogen-oxygen dual stable isotope (δ15N-${\mathrm{NO}}_3^- $ and δ18O-${\mathrm{NO}}_3^- $ ), we quantitatively analyzed the main sources of nitrate pollution and elucidated spatial gradient variation and transformation mechanism. The results showed an average nitrate concentration of 44.05 ± 27.85 μmol/L in the PRE, with the nitrogen-oxygen isotope value of 10.8 ± 2.6‰ and 6.1 ± 4.5‰, respectively.${\mathrm{NO}}_3^- $ , δ15N-${\mathrm{NO}}_3^- $ and δ18O-${\mathrm{NO}}_3^- $ values in the three areas deviated from conservative mixing behavior, with regression slopes between δ15N-${\mathrm{NO}}_3^- $ and δ18O-${\mathrm{NO}}_3^- $ indicating phytoplankton assimilation and nitrification are the dominant processes governing isotopic variations in the PRE. Additionally, incomplete sedimentary denitrification also significantly contributes to nitrogen reservoir dynamics. The Bayesian mixing model results revealed that domestic sewage represents the largest nitrate source in Lingdingyang, Modaomen and Huangmaohai, accounting for an average of 51.97% + 25.1%. Aquaculture emerged as the secondary source, which may linked to extensive aquaculture activities along the Pearl River Delta (PRD). These findings provide scientific basis for integrated nitrogen pollution control and water quality management in coastal ecosystems. -
图 3 珠江口近岸海域 (a)
${\mathrm{NO}}_3^- $ ,(b) DIN,(c) δ15N-${\mathrm{NO}}_3^- $ ,(d) δ18O-${\mathrm{NO}}_3^- $ 与盐度关系图(浅蓝色五角星表示两端元,两端元间的浅蓝色虚线表示保守混合线)Fig. 3 Relationship between (a)
${\mathrm{NO}}_3^- $ and (b) DIN and (c) δ15N-${\mathrm{NO}}_3^- $ and (d) δ18O-${\mathrm{NO}}_3^- $ versus salinity in the Pearl River Estuary (light blue star represent the two end-members, the light blue dotted line indicate the conservative mixing lines of two end-members)图 4 (a, b) 珠江口近岸海域 Δδ15N-
${\mathrm{NO}}_3^- $ 、Δδ18O-${\mathrm{NO}}_3^- $ 与 Δ[${\mathrm{NO}}_3^- $ ] 关系图;(c) Δδ15N-${\mathrm{NO}}_3^- $ 与 Δδ18O-${\mathrm{NO}}_3^- $ 关系图;(d) Δ[$ {\mathrm{NH}}_4^+ $ ] 与 Δ[${\mathrm{NO}}_2^- $ ] 关系图Fig. 4 (a, b) Scatter plots for Δδ15N-
${\mathrm{NO}}_3^- $ and Δδ18O-${\mathrm{NO}}_3^- $ versus Δ[${\mathrm{NO}}_3^- $ ]; (c) Relationship between Δδ15N-${\mathrm{NO}}_3^- $ versus Δδ18O-${\mathrm{NO}}_3^- $ in the Pearl River Estuary; (d) Scatter plots for Δ[${\mathrm{NH}}_4^+ $ ] versus Δ[${\mathrm{NO}}_2^- $ ]图 6 (a) 不同硝酸盐来源的δ15N-
${\mathrm{NO}}_3^- $ 和δ18O-${\mathrm{NO}}_3^- $ 值典型范围示意图(虚线方框表示以往研究中采用的硝酸盐来源的δ15N-${\mathrm{NO}}_3^- $ 和δ18O-${\mathrm{NO}}_3^- $ 典型范围值[9, 23],十字表示珠三角地区实测的不同硝酸盐来源的平均值和标准差);(b) 利用SIAR模型计算的4种端元对于珠江口近岸海域不同区域硝酸盐的贡献比例(数字百分比表示不同端元的贡献)Fig. 6 (a) Schematic showing typical ranges of δ15N-
${\mathrm{NO}}_3^- $ and δ18O-${\mathrm{NO}}_3^- $ in various sources. The boxes bordered by dotted lines delineate the typical ranges of δ15N-${\mathrm{NO}}_3^- $ and δ18O-${\mathrm{NO}}_3^- $ values for nitrate sources adopted from previous studies[9, 23]. The cross represents the means and standard deviations measured in the site-specific nitrate sources in the Pearl River region; (b) Proportion of the contribution of the four${\mathrm{NO}}_3^- $ sources in the Pearl River Estuary calculated using the SIAR model (The percentage of figures indicates the contribution of different sources)表 1 两端元盐度、
${\mathrm{NO}}_3^- $ 浓度和同位素组成特征值Tab. 1 Characteristics of riverine and marine end-members
端元 站位 盐度 / psu ${\mathrm{NO}}_3^- $/μmol/L δ15N-${\mathrm{NO}}_3^- $/‰ δ18O-${\mathrm{NO}}_3^- $/‰ 河水 S62 - 64 0.84 114.99 7.1 2.7 海水 S39 32.71 2.90 13.0 16.8 注: S62-64站位布设于鸡啼门和磨刀门上游。 表 2 不同端元硝酸盐来源的氮氧同位素特征值
Tab. 2 Isotopic compositions of nitrogen and oxygen in nitrate from different sources
硝酸盐来源 δ15N-${\mathrm{NO}}_3^- $/‰ δ18O-${\mathrm{NO}}_3^- $/‰ 样品数量 / 个 生活污水 10.9 ± 4.1 3.0 ± 2.6 n = 22 化肥 3.1 ± 6.8 13.7 ± 5.6 n = 8 水产养殖 6.0 ± 4.5 1.1 ± 0.9 n = 13 外海水 9.1 ± 6.1 13.7 ± 4.1 n = 6 -
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