Biodegradability of riverine dissolved organic carbon in a Dry-hot Valley Region: Initial trophic controls and variations in chemical composition

摘要

Aquatic carbon (C) loss is mostly driven by in-situ mineralization of dissolved organic carbon (DOC) and leads to autonomous carbon dioxide (CO2) emissions to the atmosphere. However, limited studies have examined the biodegradability of riverine DOC, especially for the initial trophic controls of DOC biodegradation (%BDOC) and variations in dissolved organic matter (DOM) chemical composition. In this study, we employed a laboratory incubation experiment to determine the riverine %BDOC, temperature sensitivity (Q(10) value), nutrients and DOM optical properties in a subtropical river in the Dry-hot Valley Region. We observed the %BDOC at 30 degrees C (52 +/- 19.8%) was significantly higher than that at 20 degrees C (34 19.9%) with an average Qio value of 2 +/- 1.7. Decreases in a(254), a(350) values indicated that the aromatic and lignin fractions were decomposed, while increases in E2:E3 and decreases in E4:46 values suggested that large molecular DOMs were incompletely degraded and accumulated after 56-day incubations. The %BDOC was negatively correlated with the DOC:TDP ratio, which suggested that P availability was a dominant control in aquatic microbial respiration. Our results conclude that temperature and trophic status regulate biodegradability of DOC, and also stimulate the incomplete degradation of recalcitrant fraction in DOMs.