Pristine peat swamp forests in SE Asia act as carbon sinks and store organic matter. However, when drained and logged, carbon may remobilize into aquatic bodies and the coastal ocean. The effects of land use change on the flux of dissolved organic matter (DOM) and its fate (i.e., oceanic sequestration vs. atmospheric release), are largely unknown. Here, we assess the flux and potential fate of DOM in 3 peat-draining rivers in the Sarawak region of Malaysia, representing varying levels of catchment disturbance due to logging and agriculture. We sampled a pristine (Maludam), moderately disturbed (Sebuyau), and disturbed (Simunjan) river system along a fresh to seawater gradient for greenhouse gases, nutrients, DOC, DOM composition (via FT-ICR-MS). Oxygen consumption and nutrient and methane concentrations of the disturbed rivers were higher than those of the pristine Maludam, implying agricultural nutrient input, greenhouse gas emissions, and differences in respiration in these more disturbed systems. However, the DOC concentrations were higher in the Maludam than the disturbed rivers and there were distinctions in DOM composition between sites: the DOM from the Maludam had the highest molecular richness, diversity, and fractions of labile (calculated with a molecular lability boundary) and refractory (identified as CRAM) molecular formulae of the 3 river systems. These results suggest that DOM from the disturbed rivers is less molecularly diverse and contains fewer labile and refractory molecular formulae, which would alter its bioavailability and potential for carbon sequestration.  

Primary Presenter: Sarah Bercovici, National Oceanography Centre (sarah.bercovici@noc.ac.uk)

Authors:

Sarah Bercovici,   (sarah.bercovici@noc.ac.uk)

Mourad Harir,   ()

Manuela Hartmann,   ()

Annette Burden,   ()

Joost Brandsma,   ()

Daniel Mayor,   ()

Philippe Schmitt-Kopplin,   ()

Boris Koch,   ()

Christopher Evans,   ()

Patrick Martin,   ()

Aazani Mujahid,   ()

Moritz Mueller,   ()

Richard Sanders,   ()

Claire Evans,   (clevans@noc.ac.uk)