28 JAN 2026 (WED) 14:35 - 15:05

Dissolved Organic Matter and Greenhouse Gas Emissions from Headwater Streams

Miss LIU Jiao 

( Supervisor: Prof Lishan Ran )

Abstract:

Dissolved organic matter (DOM) serves as a critical link between terrestrial and aquatic systems. However, the regulatory mechanisms by which DOM composition and properties influence greenhouse gases (GHG) emissions remains largely unclear, especially under the context of global warming. This thesis addresses two central scientific questions: what are the molecular characteristics of DOM in headwater streams, and what is the subsequent role of these characteristics in regulating GHG dynamics within headwater river networks? The primary hypothesis posits that elevated temperatures accelerate DOM transformation processes, leading to an increased proportion of labile DOM. This labile DOM, in turn, enhances microbial greenhouse gases production and emissions by providing abundant substrates and fostering conditions conducive to active microbial metabolism, potentially leading to the development of anaerobic environments. Conversely, I hypothesize that a higher contribution of geological-derived DOM in karst regions results in an environment less favorable for microbial GHG production. To test these hypotheses, I select headwater streams located in diverse climatic zones, namely, the alpine Qinghai-Tibet Plateau and subtropical regions characterized by contrasting lithologies (karst and siliciclastic areas). The main objectives of this thesis are to (1) identify the sources and characterize the molecular properties of DOM across different climate zones, (2) elucidate the mechanistic linkages between DOM molecular characteristics and GHG emissions, and (3) develop a predictive model for GHG emissions from headwater streams by integrating DOM molecular signatures, microbial community data, and GHG fluxes. Ultimately, the findings will not only shed light on the underlying mechanisms of GHG emissions from headwater streams, particularly the vital role of DOM molecular characteristics, but also provide scientific guidance for water management strategies under a changing climate.