无定河流域碳氮稳定同位素研究

Stable carbon and nitrogen isotopes in the Wudinghe drainage basin

对黄河中游一条很有特点的高悬沙支流——无定河流域进行了碳氮稳定同位素调查,发现该流域植被的碳氮同位素组成分布范围很广,碳同位素组成呈现出明显的双峰特征,说明该流域生态系统属于C3和C4混合植被类型。植物的氮同位素组成与碳同位素组成之间并不存在相关关系。沿河沉积物中的碳氮同位素组成之间存在有弱负相关性。河水悬浮体中碳氮同位素组成显示出良好的负相关关系,反映出该河悬浮体中主要有2种物质来源以及具保守性的物理混合特征。根据无定河流域植被、土壤、沉积物的碳同位素调查结果,估算出该河流颗粒有机质中C3植物碳的贡献可占75%～80%。河水悬浮体中有机质的控制性来源是中下游陆地侵蚀物质,同样也反映了流域植被的同位素特征,C3植物碳的贡献占优势。初步的研究结果已经证明,在研究河流中生源要素的输送通量与降水及径流过程之间的关系和河流物质与陆地生态环境变化之间的关系时碳氮稳定同位素示踪应该是十分有效的手段。

Biogenic elements(mainly carbon and nitrogen)and various pollutants in rivers undergo very complex environmental biogeochemical proc esses,such as transportation,and t ransformation,causing different e cological effects.It has an important scientific and practical significance to op en out their environmental behavior and to elucidate their distribution featu re on a district scale.An investigation of carbon and nitrogen isotope compositions in the Wudinghe drainage basin,whic h is a high turbid distributary in the middle reach of the Yellow River,was conducted.It is found that the values of stable carbon and nitrogen isoto pes of plants in the basin have wide ra nges,the carbon isotope values show bimod al characteristics,but nitrogen is otopes have no relativity to carbon o nes.A weak negative relativity exists between stable carbon and nitrogen isotopes in sediments along the river.St able carbon and nitrogen isotope values i n the suspended matter exhibit a good negative correlation,reflecting t he two main sources of suspended matter in t his river and conservative feature o f physical mixture.Based on the investigation of carbon stable isotopes of plants,soils and sediments f rom the Wudinghe drainage area,the contribution of C 3 plants to riverine particulate organic matter may be calculated to be 75%～80%.The dominating source of suspended orga nic matter in freshwater is eroded ma terial from land around the middle an d lower reaches.It also reflects the i sotopic characteristics of vegetation in this drainage basin,which is t hat the contribution from C 3 plants is predominant.The primary r esults of the investigation have pro ven that the naturally existing carbon and nitrogen isotop ic tracers should be very efficient means in studying the relationship of transportation fluxes of biogenic e lements in rivers with the precipita tion and runoff processes,as well as the relation of riverine substance to changes in t he terrestrial ecosystem environme nts.