夏季大亚湾悬浮颗粒有机物碳、氮同位素组成及其物源指示

Stable carbon and nitrogen isotopes as tracers of sources of suspended particulate organic matter in the Daya Bay in summer

2015年夏季开展了大亚湾悬浮颗粒有机物碳(POC)、氮含量(PN)及其同位素组成的研究,结果表明,δ^(13)CPOC和δ^(15) NPN的变化范围分别为-25.7‰^-17.4‰和-6.3‰~10.4‰,平均值分别为-20.2‰和8.2‰。大亚湾悬浮颗粒有机物含量及其碳氮同位素组成的空间变化反映了不同有机质来源的影响:喜洲岛附近海域表现出高POC、PN、δ^(13)CPOC和δ^(15)NPN的特征,指征着浮游植物水华的主导贡献;东北部范和港附近海域具有高POC、PN、低δ^(13)CPOC和高δ^(15)NPN的特征,反映了河流/河口水生有机物的影响;湾顶白寿湾附近海域的δ^(13)CPOC和δ^(15)NPN出现低值,体现了陆源有机质和人类污水排放的影响。借助δ^(13)CPOC和δ^(15)NPN的三端元混合模型,定量出海洋自生有机质、陆源有机质、河流/河口水生有机质等3个来源的贡献平均分别为70%、13%和17%,其中海洋自生有机质是夏季大亚湾悬浮颗粒有机物的最主要来源。从这3种来源颗粒有机物含量的空间变化看,海洋自生有机质含量由湾内向湾外减少,与初级生产力的空间变化相对应;河流/河口水生有机质含量在大亚湾东北部出现高值;陆源有机质含量在表、底层出现不同态势,表层陆源有机物含量在湾中部海域最低,而底层则呈现出自湾内向湾口增加的趋势,主要受控于离岸距离和珠江冲淡水、粤东沿岸上升流输送的影响。

Stable carbon and nitrogen isotopes were used to distinguish sources of suspended particulate organic mat ter in the Daya Bay in summer 2015. Our results showed that the values of δ^13 CPOC and δ^15 NPN ranged from -25.7‰ to -17.4‰ and from -6.3 to 10.4‰, with averages of -20.2‰ and 8.2‰, respectively. The spatial variation of δ^13 CPOC： and δ^ NPN reflected the effect of different sources of organic matter. The high POC, PN, δ^13CPOC and δ^15NPN were observed around Xizhou Island, indicating a phytoplankton bloom. The high POC, PN, δ^15Npn, but low δ^13 CPOC： occurred around the Fanhe Habour in the northeastern bay, pointing to the contribution of riverine/estuarine organic matter. Meanwhile, the low values of δ^13 CPOC and δ^15 NPN were observed in the north coastal areas, reflecting the input of terrigenous organic matter and anthropogenic wastes. Based on the mass bal ance of δ^13CPOC,- and δ^15 NPN, the contribution of autochthonous, terrigenous and riverine/estuarine organic matter were estimated as 70%, 13% and 17% respectively. The particulate organic matter in the Daya Bay in summer was dominated by marine autochthonous source. The contents of autochthonous organic matter showed a decrease from the inner to the mouth of the bay, corresponding to the decrease of primary productivity. The riverine/estu- arine organic matter showed high contents in the northeastern bay. However, distribution of terrigenous organic matter showed different patterns in the surface and bottom layers. The low contents of terrigenous organic matter in surface waters were observed in the central bay, while they increased from the inner to the mouth of the bay in the bottom. The spatial distribution of terrigenous organic matter in the Daya Bay was regulated by the offshore distance, the Pearl river diluted water and the coastal upwelling along the eastern part of Guangdong province.