2010年夏季珠江口海域颗粒有机碳的分布特征及其来源

Abstract

于2010年8月对珠江口海域20个站位的颗粒有机碳 (POC) 进行采样,分析了POC的空间分布特征,讨论了POC与环境因子之间的关系,并利用碳稳定同位素 (δ¹³C) 分析了POC的来源及其贡献率。结果显示,研究区域POC的浓度范围98.5-1929.8 μg/L,平均浓度541.9 μg/L,空间分布总体呈现自北部海域向中部海域逐渐降低,中部海域至南部海域又逐渐升高,底层大于表层的特点。总悬浮颗粒物、叶绿素a、水动力是影响POC空间分布的重要原因。研究区域总悬浮颗粒物δ¹³C值的变化范围-27.05‰-21.03‰,平均为-24.57‰,反映出珠江口海域颗粒有机碳为陆源和水生源混合来源,其分布呈现沿盐度梯度自口门内向口门外逐渐递增,底层高于表层的特点。陆源输入和海洋生物生产是影响δ¹³C值分布的主要原因。运用二元混合模型计算得知,珠江口北部和中部海域POC以陆源有机碳为主,贡献率平均为64%;南部海域POC以水生源有机碳为主,贡献率平均为68%。与20多年前相比,POC的分布特征与来源已经发生了改变,珠江口海域含沙量减少与营养盐含量增加可能是导致POC组成发生变化的主要原因。;Particulate organic carbon (POC) is one of the main forms of carbon and plays an important role in aquatic ecosystems and global carbon cycling. Marine and terrestrial ecosystems are the two important carbon pools for the estuaries on earth, so the investigation on the POC in estuaries is dramatically practical for the research of global carbon cycling. Generally, the POC in estuaries can be classified into two categories by its source (terrestrial input and marine organism production). Stable carbon isotope (δ¹³C) and C/N are the two recommendatory methods for measuring and analyzing the source of organic carbon, and the precision of stable carbon isotope method (δ¹³C) is better than that of C/N method because of the stability of δ¹³C. The present study aimed to investigate the distribution of POC and its sources in the Pearl River Estuary in summer through the POC measurements of 20 sites in August, 2010. The results showed that the concentrations of POC ranged from 98.5 to 1929.8 μg/L (the average of 541.9 μg/L), and the concentrations decreased with the salinity gradient in the northern and middle part of the Pearl River Estuary and then increased from the middle part to the southern part of the Pearl River Estuary, and the concentrations of POC in the bottom waters layers were higher than those in the surface water layers. The total suspended matter (TSM), chlorophyll <em>a</em> and hydrodynamics were the major factors that influenced the POC spatial distribution, and the δ¹³C values of TSM increased with the salinity gradient and varied from -27.05‰ to -21.03‰ (the average of -24.57‰), and the values in the bottom water layers were higher than those in the surface water layers. Our results showed that the terrestrial input and marine phytoplankton production contributed to the POC together in the Pearl River Estuary. According to the analysis of binary mixture model, most POC in the northern and middle part of the Pearl River Estuary was subject to the terrestrial organic carbon, which accounted for 50% to 88% (the average of 64%) of the total POC. In contrast, the marine organic carbon was the main contributor to the POC in the southern part of the Pearl River estuary, and it accounted for 50% to 89% (the average of 68%) of the total POC. Compared with two decades ago, the distribution and source of POC varied significantly, which is mainly due to the decrement of sediment discharge and increment of nutrient inputs into the Pearl River estuary. We predict that the sediment discharge rate of the Pearl River will decrease gradually with the construction of more large reservoirs, and then the contribution of terrestrial organic carbon to the POC in the Pearl River estuary will be decreasingly.