黄土高原泾河小流域泥沙碳、氮同位素与生态环境示踪

Organic Carbon and Nitrogen Isotopes of the River Sediments and Ecological Environment Tracer in Jinghe Basin of Loess Plateau

以泾河(陕西彬县境内)4条支流表层沉积物为研究对象,对其有机质的稳定碳、氮同位素组成进行测定和研究。结果表明,4条河流表层沉积物有机质的碳同位素(δ13C)值变化范围为(-29.1‰)～(-20.4‰),平均值为-25.4‰。其δ13C值从上游到下游都有逐渐偏正的趋势,表明从上游到下游植被覆盖类型的变化影响了沿河表层沉积物有机质的δ13C值。4条河流表层沉积物有机质的氮同位素(δ15 N)值和碳氮比(C/N)的变化范围分别为0～4.6‰和1.4～17.2,平均值分别为2.8‰和7.3。从上游到下游其δ15 N值逐渐偏正,表明沿岸进入河中的泥沙比例越来越大,人类活动等对自然环境的影响增强。徐家河和拜家河下游采样点表层沉积物有机质的δ15 N值有偏负趋势,可能与下游煤炭开采,煤等有机质进入河流表层沉积物有关。因此,对河流表层沉积物中有机质的碳、氮同位素组成特征和变化研究可以揭示流域土壤侵蚀状态和生态环境的变化。

Stable carbon and nitrogen isotopic compositions were used as indicators affected to monitor changes of vegetation and environment.This paper analyzed carbon and nitrogen isotopic signatures of river surface sediment in four tributaries of the Jinghe(Binxian,Shaanxi)river basin and revealed the vegetation and environmental changes in this region.Results showed that,in river catchment,from the water sources to their confluence,(1) δ13 C values of organic matter in surface sediments varied from-29.1‰to-20.4‰ with the average value as-25.4‰.The δ13C values gradually increased from upstream to downstream,indicated that δ13C values was negative in forest areas,and positive in C4 grassland and agricultural areas.(2)The δ15 N values and C/N ratios of organic matter in surface sediments ranged from 0to 4.6‰and 1.4 to 17.2,respectively. δ15 N values gradually increased along the rivers,maybe due to increasing soil erosion and human activities effect.In addition,the δ15 N values of surface sediments had a tendency to negative in the downstream areas at Xujia river and Baijia river,which was probably impacted by the coal and other organic matter.Therefore,the carbon and nitrogen isotopic signatures of river sediments could be used as indicators for the soil erosion status and ecological changes in rivers catchment.