2021年夏季珠江口颗粒有机碳空间分布特征及其影响因素

Spatial Distributions and Controlling Factors of Particulate Organic Carbon in the Pearl River Estuary in the Summer of 2021

颗粒有机碳(POC)是河口碳循环的关键变量之一,厘清其空间分布特征及影响因素是开展河口碳循环研究的重要基础。本文研究了2021年7月(珠江丰水期)珠江口大范围区域和不同水层POC浓度空间分布,探究了盐度、悬浮颗粒物浓度(SPM)和浮游植物类脂生物标志物总浓度(ΣPB,包含菜籽甾醇、甲藻甾醇和C 37长链烯酮)等因素对POC空间分布的影响。结果表明,研究区域POC浓度为0.05~0.85 mg/L,均值(0.29±0.19)mg/L,总体呈现近岸浓度高、河口外部区域浓度低的分布趋势,高值区集中在磨刀门近岸海域和香港地区南部海域。垂直分布上,POC平均浓度随着深度的增加先减小再增加,但不同断面间存在差异。A断面(黄茅海-珠江口外侧)POC浓度最大值出现在近岸及叶绿素最大层,B断面(磨刀门-珠江口外侧)POC浓度最大值出现在表层,C断面(伶仃洋-珠江口外侧)大部分站位垂直分布较均匀。POC空间分布受到多种环境和生物因素的显著影响。在某些海域和水层,温度、浊度、溶解氧、营养盐浓度、SPM以及ΣPB等参数与POC浓度具有显著正相关,而盐度与POC浓度具有显著负相关。盐度与POC浓度在整个研究区域具有极显著负相关,这与高盐度引起悬浮物絮凝沉降、海水稀释作用以及陆源输入等因素有关。SPM与POC浓度在底层水和伶仃洋海域显著正相关,表明表层沉积物再悬浮作用对POC空间分布有着直接影响。ΣPB与POC浓度在整个研究区域极显著正相关,表明浮游植物生物量是影响POC空间分布的主要因素。研究结果为丰富珠江口有机碳研究资料、深入研究河口碳循环过程与机制提供重要基础。

Particulate organic carbon(POC)is one of the key variables in estuarine carbon cycle.Illustrating the spatial distribution characteristics and controlling factors of POC is an important basis for the study of estuarine carbon cycle.In this paper,we studied spatial distribution of POC concentrations in different water layers across large areas of the Pearl River Estuary(PRE)in July 2021(Pearl River wet season),and explored the effects of multiple factors such as salinity,suspended particulate matter(SPM)concentrations and total concentrations of phytoplankton lipid biomarkers(ΣPB,It contains brassicasterol,dinosterol and C 37 long alkenone)on POC spatial distributions.The results show that the concentration of POC range between 0.05 and 0.85 mg/L,with an average(±SD)of(0.29±0.19)mg/L.POC concentrations decreased seaward,showing high values at a few stations,off Modaomen and south of Hong Kong.Vertically,the average concentration of POC first decreased and then increased with the increase in depth,but there were differences between different sections.POC concentrations were highest in nearshore areas and at deep chlorophyll maximum(DCM)layer along A section(Huangmaohai-outer esturary)and at the surface layer along B section(Modaomen-outer esturary),while the vertical distributions of POC were relatively uniform at most stations along C section(Lingdingyang-outer esturary).The distribution of POC concentrations was strongly affected by multiple biological and chemical factors.In some sea areas and water layers,parameters such as temperature,turbidity,dissolved oxygen,nutrient concentrations,SPM andΣPB showed significant positive correlations with POC concentrations,while salinity had a significant negative correlation with POC concentrations.Across the whole study area,there was a highly significant negative correlation between salinity and POC concentrations,which is related to factors such as flocculation and sedimentation of suspended solids caused by high salinity,seawater dilution and terrigenous input.The significant positive correlations between SPM and POC concentrations,at the bottom layer and in Lingdingyang,indicate that the resuspension of surface sediments had a direct impact on the spatial distribution of POC.ΣPB and POC concentrations showed a highly significant positive correlation across the whole study area,suggesting that phytoplankton biomass was the main factor controlling POC distribution.Our results provide an important basis for further studies on organic carbon in the PER,as well as on the processes and mechanisms of estuarine carbon cycle.