基于碳稳定同位素示踪的金水河颗粒有机碳来源辨析

Identifying sources of particle organic carbon in surface water based on stable isotope tracing in the Jinshui River

颗粒有机碳(Particle Organic Carbon,POC)在河流碳循环中占重要地位,并能提供流域内自然及人类活动的记录。通过采集和测定汉江上游金水河流域河岸带土壤和植物及河流中藻类和悬浮颗粒有机碳(POC)的季节性碳稳定同位素值和C/N比值,对河流水体中悬浮颗粒有机碳的浓度的季节性变化特征以及来源及其贡献进行了研究。结果表明,金水河流域水体中颗粒有机碳(POC)的浓度值存在明显的季节性变化特征,夏季>春季>秋季>冬季。河流上游轻度干扰区的POC浓度值明显低于中下游中度干扰区和严重干扰区。河流中POC主要来源于土壤有机质、C3植物和藻类3个端元,而来源于浮游生物和C4植物碎屑的贡献很小。各季节之间具体的来源及其贡献有所差异,且POC的来源及其贡献具有空间差异。因此,金水河水体中颗粒有机碳(POC)的来源及其贡献受到季节变化和人为干扰程度的影响。

Particle organic carbon （POC） in riverine systems is a critical component in the global carbon cycle, and it could provide information on human activities in particular land use in their representative drainage areas. In present study, soil and plant in the riparian zone and algae and POC in river waters were sampled in the Jinshui River Basin. Stable carbon isotopes analysis and elemental C/N ratios measure were applied to investigate the seasonal change of concentration, sources and their contributions of POC in river. The results showed that the POC concentration in river had remarked seasonal variations in the Jinshui River, in a decrease order of summer, spring, autumn, and winter. Larger quantity of soil organic matters and plant debris were washed into the river in spring and summer due to intensive rainfalls, and higher temperature was in favor of algal growing and which could produce more endogenous POC. Additionally, the POC concentration in slightly disturbed zone （ i.e., upstreams） was obviously lower than that of moderately disturbed zone and intensely disturbed zone （i.e., middle reach and downstreams）. These showed that seasonal change and human disturbance such as change of land use had a great influence on the concentration of POC in the Jinshui River. Qualitative analysis using stable carbon isotope （δ^13C） , elemental C/N ratios and the relational graph indicated that the major sources of POC in river were soil organic matter, C3 plants, and algae, and contribution from plankton and C4 plants were minimal. Ternary analysis model further revealed tempo-spatial variabilities of the sources and their contribution of POC in river. The results showed that the sources and their contribution of POC in river had remarked seasonal variations in the Jinshui River. But, the contribution of POC in river from endogenous （ i.e., algae） was obviously lower than that from exogenous （ i.e., soil organic matter and C3 plants） .At the same time, the sources and their contribution of POC in river also showed differences between different zones. The POC in slightly disturbed zone and in moderately disturbed zone （i.e., upstreams and middle reach） mainly came from soil organic matter and C3 plants, and they were soil organic matter and algae in intensely disturbed zone （e.g., downstream）. Therefore, human disturbance had a great influence on the sources and their contribution of POC in the Jinshui River.