Impact of photodegradation on the fate of dissolved organic carbon in tropical peatland canals

Peatland ecosystems tend to export more dissolved organic carbon (DOC) through aquatic pathways compared to other terrestrial ecosystems, contributing ~20% of all DOC export from freshwaters globally. However, the fate of DOC and its susceptibility to photodegradation versus microbial respiration in peatland-draining freshwaters remains poorly constrained. Here we quantified DOC oxidation rates and investigated when photodegradation dominated DOC oxidation in freshwater canals overlying peatlands in West Kalimantan, Indonesia. Field chemistry, hydrology, and meteorology measurements were paired with more than 100 short-term laboratory incubations to quantify and scale DOC oxidation rates throughout the day from photomineralization and microbial respiration. Our results show that photodegradation drives DOC oxidation when ultraviolet and visible photons are absorbed by DOC within a larger portion of the water column from a shallower water column depth or a higher daily photon flux. In contrast, microbial respiration drives DOC oxidation in larger canals with deeper water column depths where photodegradation is restricted to the sunlit water surface. Given that the majority of canals are small with shallow water column depths and have become unshaded from the clearing of peat swamp forests during deforestation, these findings suggest that photodegradation can substantially alter the fate of peatland-exported DOC in freshwaters draining disturbed tropical peatlands.  

Presentation Preference: Oral

Primary Presenter: Jennifer Bowen, Stanford University (bowen.jenniferc@gmail.com)

Authors:

Jennifer Bowen, Stanford University, Scripps Institution of Oceanography  (jcbowen@stanford.edu)

Putri Wahyudio, Tanjungpura University  (pjuliandini@gmail.com)

Desi Silvani P.A.B., Tanjungpura University  (silviani.desi90@gmail.com)

Yulita Andriyani, Tanjungpura University  (yulitaandriyani0@gmail.com)

Erin Dayanti, Tanjungpura University  (erindyt@gmail.com)

Gusti Anshari, Tanjungpura University  (gzanshari@live.untan.ac.id)

Lihini Aluwihare, Scripps Institution of Oceanography  (laluwihare@ucsd.edu)

Alison Hoyt, Stanford University  (ahoyt@stanford.edu)