Author: Yasuhiko T Yamaguchi,  Researcher (Lake Biwa Environmental Research Institute)

Designation: 

Description:
Degradation of aquatic dissolved organic matter (DOM) is a major process of the global biogeochemical cycles. A strong relationship between molecular sizes and reactivity of DOM has been suggested (the size-reactivity continuum model: Amon & Benner, 1996). Yet, details and mechanisms of the link still remain poorly understood. In this study, we investigated changes of molecular size distribution of dissolved organic carbon (DOC) in a deep meso/oligotrophic lake (Lake Biwa, Japan) and an inflowing river to the lake (Yasu River) by long-term dark incubations (> 200 days) and a custom-made high-performance size-exclusion chromatograph with total organic carbon analyzer (HPSEC-TOC: Shimotori et al. 2016). Two discrete molecular size classes of DOC were identified: high-molecular-weight (HMW) DOC (apparent weight-averaged molecular weights (M_w) ~ 150kDa) and low-molecular-weight (LMW) DOC (apparent M_w ~2kDa). HMW DOC was all degraded within 200 days, while LMW DOC contained semi-labile (LMW SLDOC) and refractory (LMW RDOC) fractions. Thus, the DOM examined in this study can be modeled by mixing of the three components (HMW DOC: ~10%, LMW SLDOC: ~30%, LMW RDOC: ~60%). HMW DOC showed higher degradation rates than LMW SLDOC (k^-d: 0.02-0.04 and 0.01-0.02, respectively). LMW SLDOC and LMW RDOC showed almost the same apparent M_w values. These results suggest that, while DOM reactivity significantly differs depending on its molecular size on a large MW scale (~150kDa vs ~2kDa), this relationship would not be applicable to the finer MW scale (within the LMW fraction).

Category: Scientific Program Abstract > Special Sessions > SS42 The biogeochemistry of dissolved organic matter