Stream carbon fluxes are one of the major components in the global C cycle, yet the discrimination of the various sources of stream carbon remains to a large extent unclear and less is known about the biogeochemical transformations that accompany the transfer of C from soils to streams. Here, we used patterns in stream water and groundwater δ¹³C values in a small forested tropical headwater catchment to investigate the source and contribution from the soil carbon pools to stream organic and inorganic carbon behavior over seasonal scales. Stream organic carbon (DOC and POC) comes mainly from the upper rich soil organic carbon horizons and derived from total organic carbon (TOC) of biogenic source. The isotopic compositions δ¹³C_TOC, δ¹³C_DOC and δ¹³C_POC of these carbon species were very close (− 30‰ to − 26‰) and typical of the forested C3 vegetation. The relationship observed between DOC and log pCO₂ and δ¹³C_DIC indicated that besides the considerable CO₂ evasion that occurs as DIC is transported from soils to streams, there were also other processes affecting the stream DIC pool. In-stream mineralization of DOC and mixing of atmospheric carbon had a significant influence on the δ¹³C_DIC values. These processes which varied seasonally with hydrological changes represent the main control on DOC and DIC cycling in the wet tropical milieu. The rapid turnover of carbon on hillside soils, the transformation of TOC to DOC in wetland soils and further mineralization of stream DOC to DIC favor the evasion of C, making the zone a source of carbon to the atmosphere.

溪流碳通量是全球碳循环的主要组成部分之一，然而，对溪流碳各种来源的区分在很大程度上仍不清楚，并且对伴随碳从土壤向溪流转移的生物地球化学转化了解甚少。在这里，我们使用在流水和地下水δ图案^13个C值在一个小森林热带水源集水调查从土壤碳库的源极和贡献超过季节性秤到流有机和无机碳的行为。河流有机碳（DOC和POC）主要来自上层富裕的土壤有机碳层，并来源于生物源的总有机碳（TOC）。同位素组成δ ¹³ Ç _TOC，δ ¹³Ç _DOC和δ ¹³ Ç _POC这些碳物质的非常接近（ - 30‰至- 26‰）和典型的森林C3植被。DOC之间观察到的关系并登录的pCO ₂和δ ¹³ Ç _DIC表示，除了相当大的CO ₂作为DIC从土壤运送到流发生逃逸，也有影响流DIC池的其它过程。插播DOC和大气中的碳的混合的矿化对的一个δ影响显著¹³ Ç _DIC价值观。这些随水文变化而季节性变化的过程代表了热带湿润环境中DOC和DIC循环的主要控制。碳在山坡土壤上的快速周转，湿地土壤中TOC向DOC的转化以及DOC向DIC的进一步矿化有利于C的逃逸，使该区域成为大气中的碳源。