Compositional and hydrological drivers of DOM degradability across land-water continua of boreal watersheds

Recent studies showed efficient depletion and transformation of the terrestrial C pool from land to water, yet the strength and shape of this pattern vary geographically and the underlying drivers remain unclear. We assessed how DOM intrinsic degradability and watershed hydrology shape broad-scale DOM patterns by measuring biological and photochemical DOM degradability in terrestrial (upland, riparian) and aquatic (stream, lake) compartments of 26 headwaters across boreal and subarctic Quebec, Canada, spanning 48.9–59.1°N; 63.2–76.2°W. We linked degradability with DOM fluorescence and water stable isotopes (d-excess) as proxies of DOM composition and cumulative exposure to degradation processes, respectively. Fulvic-like and protein-like pools showed strong and preferential losses under photochemical and biological experiment, respectively. Reactivity potential also tended to decrease from land to water and with lower d-excess (denoting longer water transit times), indicating a progressive mineralization of bio- and photodegradable substances occurred during transit. However, the loss of biodegradability potential with rising d-excess was expressed mainly in riparian zones whereas photodegradability losses were concentrated in streams and lakes. Despite regional variation, DOC losses (x̄=53%) were greatest from riparian to stream, driven by protein-like depletion (x̄=85%). Thus, DOM intrinsic degradability and watershed hydrology jointly shape broad-scale DOM patterns with implication for C budgets as both aspects will likely respond to different facets of global change.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Adrien Simonet, Université de Montréal, Groupe de Recherche Interuniversitaire en Limnologie (GRIL) (adrien.simonet@umontreal.ca)

Authors:

Adrien Simonet, Université de Montréal, Groupe de Recherche Interuniversitaire en Limnologie (GRIL)  (adrien.simonet@umontreal.ca)

François Guillemette, Université du Québec à Trois-Rivières, Groupe de Recherche Interuniversitaire en Limnologie (GRIL)  (Francois.Guillemette3@uqtr.ca)

Jean François Lapierre, Université de Montréal, Groupe de Recherche Interuniversitaire en Limnologie (GRIL)  (jean-francois.lapierre.1@umontreal.ca)