大沽河流域有机质来源、保存及影响因素分析

Sources,preservation,and influencing factors of organic carbon from the Dagu River Basin

于2022年的干季(5月)和湿季(9月)在山东半岛大沽河流域采集表层水体､悬浮颗粒物和沉积物,进行环境参数､总有机碳氮､稳定碳同位素(δ13C)、生物标志物以及矿物学参数测定.结果显示,大沽河表层湿季与干季悬浮颗粒物有机质来源有较大差异,湿季悬浮颗粒物有负的δ13C(–29.1‰)和低的颗粒有机碳氮比(POC/PN,6.3),其有机质主要来自河流浮游植物;干季表层悬浮颗粒物有更正的δ13C(–26.8‰)和更高的POC/PN(8.8),其有机质除了来自河流浮游植物,还有河流对土壤的侵蚀带来的C3植物和C4植物;沉积物有机质则来源较为复杂,除河流浮游植物,C3植物､C4植物外,还包括海洋浮游植物､污水源的混合.基于δ13C二端元模型显示沉积物陆源有机质相对贡献自上游到下游从58%下降至0%.主成分分析表明,高含量溶解无机氮(DIN)的存在导致河流浮游植物大量繁殖,对应了高含量的POC､叶绿素-a和短链烷烃.河口段较细的沉积物粒径和较大的比表面积导致其吸附了较多有机质,有机碳含量显著高于河流段.从河流上游至下游沉积物有机碳载荷量(TOC/SSA)从1.4mg/m^(2)下降至0.2mg/m^(2),表明有机质在运输途中经历了不断的再悬浮过程,较长的氧暴露时间导致约85%陆源有机质在运输中被微生物分解为CO_(2).研究结果为认识中小河流有机质的来源和保存特征提供了数据支撑和参考依据.

In this study,surface water,suspended particulate matters and sediments were collected in the Dagu River of Shandong Peninsula during the dry(May)and wet(September)seasons in 2022 for the determination of total organic carbon(TOC)and nitrogen(TN),stable carbon isotopes(δ13C),biomarkers,and mineralogical parameters.The results showed that the sources of organic matter in the surface suspended particulate matter in the Dagu River in the wet and dry seasons were quite different.The surface suspended particulate matter in the wet season had a negativeδ13C(–29.1‰)and a low POC/PN(6.3),and its organic matter mainly came from river phytoplankton;the surface suspended particulate matter in the dry season had a more positiveδ13C(–26.8‰)and a higher POC/PN(8.8),and its organic matter were derived from river phytoplankton as well as from C3and C4plants brought in by riverine erosion of the soil,and the source of organic matter in surface sediments were more complicated,in addition to river phytoplankton,the contribution of C3 plants,C4 plants,marine phytoplankton,and sewage source were also mixed.The relative contribution of the terrestrial organic matter in river sediments based on the two-end member model ofδ13C decreases from 58%to 0%from upstream to downstream.Principal component analysis showed that the presence of dissolved inorganic nitrogen(DIN)led to phytoplankton blooms in the river corresponding to high levels of POC,chlorophyll-a and short-chain alkanes.The sediments in the estuarine section could absorb more organic matters due to fine grain size and large specific surface area,thus resulting higher TOC content than that in the riverine section.Comparison of the TOC loading in riverine and estuarine sediments showed that the organic matters underwent resuspension during transportation,and the longer oxygen exposure time resulted in the microbial decomposition of about 85%of the terrestrial organic matter into CO_(2).The results of this study provide data support and references for understanding the source and conservation characteristics of organic matters in small and medium-sized rivers.