惠州白盆珠水库沉积物营养元素时空变化特征及源解析

Spatial and Temporal Variations of Sediment Nutrients and Relevant Sources Identification in Baipenzhu Reservoir,Guangdong Province

为了探究自然过程和人类活动对水库水环境演变过程的影响,采集广东惠州白盆珠水库表层沉积物和沉积柱样品,测定表层沉积物总氮(TN)、总磷(TP)和总有机碳(TOC)含量,将水库划分为入库区、中部区和近坝区,分析表层沉积物的营养元素空间分布特征;利用放射性核素(210Pb)和稳定初始放射性通量(CIC)模式为长度为27 cm的沉积柱建立年代序列,测定沉积柱TN、TP、TOC含量,碳稳定同位素(δ13C)值和粒径垂向分布特征,分析营养元素时间分布特征及来源。结果表明:表层沉积物TN、TP和TOC含量分别在水库3个区域间无显著性差异(P>0.05),营养物质污染程度低;沉积柱沉积历史约53年,平均沉积速率为0.5 cm·a-1;沉积柱TN、TP和TOC含量垂向分布特征可分为3个阶段:1983年之前含量均保持相对稳定,1984-2004年受人类活动影响而逐渐增加,2005-2018年呈先减小后逐渐增加趋势;沉积柱的总有机碳与总氮比值(C/N)和δ13C指示沉积物中的有机质为陆源和内源的混合来源,由于白盆珠水库具有供水功能,以及流域内水土流失控制措施,陆源有机质占比与珠江三角洲其他水库相比较低,约占50%。

To investigate the impact of natural processes and human activities on the evolution of a reservoir water environment,surface sediment samples and several sediment cores were collected from Baipenzhu Reservoir,Huizhou,Guangdong Province.The total nitrogen(TN),total phosphorus(TP)and total organic carbon(TOC)contents of the surface sediment samples were measured.Three areas were categorized,i.e.,the entrance area,central area and near dam area,to investigate the spatial patterns of nutrients in the surface sediment.210Pb dating was carried out in a core sample of approximately 27 cm in depth to establish a sediment chronology by using the constant initial concentration(CIC)method.On the other hand,vertical distributions of TN,TP,TOC,stable carbon isotope(δ13C)value and granularity in the sediment core were analyzed,reflecting the temporal change in nutrient elements and relevant sources.The results showed that TN,TP and TOC contents in surface sediment samples were not significantly different(P>0.05)among the three areas,and the nutrient level was low in the whole reservoir according to one Canadian assessment standard.The history of the sediment core was estimated to be approximately 53 years,yielding an average annual deposition rate of 0.5 cm.The vertical distributions of TN,TP and TOC contents in the sediment core showed that they could be separated into three stages.,i.e.,a relatively stable before 1983,a gradually increasing from 1984 to 2004 due to the impact of human activities,and a decreasing and then increasing from 2005 to 2018.The organic matter in the sediment core was found to be a mix of terrestrial and endogenous sources by using the C/N ratio andδ13C.Because of the water supply function and relevant water and soil conservation measures in the whole basin of Baipenzhu,the terrestrial organic matter accounted for a relatively low amount of approximately 50%,compared with that in the other reservoirs in the delta area of the Pearl River.