Radiocarbon age of different photoreactive fractions of freshwater dissolved organic matter

摘要

Dissolved organic carbon (DOC) plays a major role in aquatic carbon cycling. In order to determine if DOC photolability was related to DOC age, we tested the effect of oxidation time using UV irradiation on natural radiocarbon concentrations (Delta C-14) of DOC in six US rivers. The most photo-labile DOC was C-14 youngest. After a 100 min UV irradiation, most DOC (>93%) was oxidized in two out of the six rivers studied. On the other hand, the other four rivers still had a considerable amount (>20%) of DOC resistant to UV oxidation, which showed lower Delta C-14 values than those of bulk DOC. We also found that the concentration and Delta C-14 value of bulk DOC are controlled by the photochemically intermediate fraction. The results suggest that C-14 age of organic matter is not homogeneous within DOC, the degree of which may depend on the characteristics unique to rivers. (C) 2019 Elsevier Ltd. All rights reserved.