南流江口陆源物质输送的季节性差异及其影响

Seasonal differences of terrigenous material transport in Nanliu Estuary and their effects.

通过对南流江丰水期(2015年7月)、枯水期(2016年4月)河口表层沉积物中有机质含量和同位素组成的变化来揭示陆源入海物质输送的季节性差异,评估其对近海环境的影响.结果表明,枯水期水体悬浮颗粒物(SPM)含量自河口向外随水深增加逐步降低(平均值为0.030g/L),丰水期洪水前SPM含量较低(平均值为0.020g/L),洪水后SPM含量显著增高(平均值为0.047g/L),证明枯水期浪、潮对表层沉积物扰动较大使颗粒物大量悬浮,而丰水期浪、潮的影响较小,以洪水控制为主.不同季节沉积物中总有机碳(TOC)、总氮(TN)平均含量相当,TOC平均含量均接近0.46%,丰水期和平水期TN含量分别为0.054%和0.062%,但空间分布差异明显,丰水期在河口东侧半封闭海湾中有机质含量较高,枯水期有机质呈斑块状分布.根据同位素组成特征来看,丰水期陆源有机质自河口向外输送,沿河口向南形成高陆源有机质沉积带,半封闭海湾中以海源有机质为主;而枯水期陆源有机质贡献呈现明显的自河口向外快速降低趋势.丰水期颗粒物自河口向外输送后快速堆积,枯水期在浪、潮作用下使区域内物质强烈混合,这是该区域中沉积环境的主要特征,也是导致周边海域水体环境质量呈现明显的季节性差异的原因之一,后期水体环境治理过程中应充分考虑如何有效的进行季节性调控.

The variations of organic matter content and isotopic composition in the surface sediments of the Nanliu River estuary during the wet season(July 2015)and the dry season(April 2016)were investigated to reveal the seasonal differences of terrestrial materials transported into the sea,and to evaluate their influences on the offshore environment.The results showed that the content of suspended particulate matter(SPM)decreased gradually with the increase of water depth in the dry season(average value:0.030g/L).In the wet season,the content of SPM was lower before the flood(average value:0.020g/L),and significantly increased after the flood(average value:0.047g/L).It is indicated that waves and tides in dry seasons have greater disturbance to the surface sediments,resulting in a large amount of SPM,while waves and tides in wet seasons have less influence,and SPM content is mainly controlled by flood.The average contents of total organic carbon(TOC)and total nitrogen(TN)in sediments in different seasons were similar,and the average TOC content was close to 0.46%.The TN content in wet season and normal season was 0.054%and 0.062%,respectively,but the spatial distribution was significantly different.The content of organic matter is higher in the semi-closed bay east of the estuary in the wet season,and the distribution of organic matter is patchy in the dry season.According to the characteristics of isotopic compositions,terrigenous organic matter was transported outward from the mouth of the river during the wet period,and sedimentary zone with high terrigenous organic matter was formed southward along the estuary,and marine organic matter was the main source in the semi-closed bay.In dry season,the contribution of terrigenous organic matter decreased rapidly from estuarine outward.In the study area,the sedimentary environment was mainly characterized by rapid sediments accumulation after being transported outward from the estuary in wet seasons,and strong mixing under the action of waves and tides in dry seasons,which contributes to the obvious seasonal differences in the environmental quality of surrounding sea waters.Therefore,it is necessary to fully consider how to effectively carry out seasonal regulation in the future water environment treatment process.