Chemodiversity of dissolved organic matter in boreal inland waters and links to water history

Recent studies of DOM in inland waters have increasingly highlighted the importance of terrestrial-aquatic links and of hydrological connectivity in shaping both DOM concentration and composition. Here we present a study of large-scale patterns in DOM composition in boreal inland waters where we establish links to hydrologic, watershed and environmental factors.  For this we used ultrahigh-resolution mass spectrometry to analyze the molecular composition of DOM from over 400 sites including lakes, reservoirs, and fluvial systems, encompassing broad geographic, climatic and environmental gradients in Eastern Canada. Rarefaction curves of DOM molecular richness, both overall and by system type, approach asymptotes, indicating good coverage of DOM diversity in our dataset. Lakes had the highest molecular richness and the most distinct DOM composition relative to that of reservoirs and fluvial systems. Redundancy analysis identified deuterium excess (d-excess), an index of water evaporation and an integrator of previous water history, as the strongest driver of DOM variation, with land cover features further contributing to these differences. The low molecular novelty and uniqueness that we observed across system types, combined with the prevalence of ubiquitous molecules, suggests that degradation processes dominate over the production of new DOM along the aquatic continuum. This is further supported by patterns in putative biochemical transformations, quantified by matching mass differences between peaks to known reactions. Transformation rates were highest in lakes and declined with increasing d-excess, suggesting that individual molecules undergo more transformations in evaporatively enriched systems than in other environments. Overall, these results offer new insights on how water history and landscape context shape DOM diversity and transformations across boreal inland waters.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Michaela de Melo, Université du Québec à Montréal (michaelaldemelo@gmail.com)

Authors:

Michaela de Melo, Universitè du Québec à Montréal  (ladeira_de_melo.michaela@uqam.ca)

Masumi Stadler, Université du Québec à Montréal  (mstadlerjpat@gmail.com)

Amir Shahabinia, Université du Québec à Montréal  (amirshahabi66@gmail.com)

Ryan Hutchins, Toronto Metropolitan University  (hutchinsryan@gmail.com)

Paul del Giorgio, Université du Québec à Montréal  (del_giorgio.paul@uqam.ca)