Global-Scale Trait-Based Ecology of Organic Matter Thermodynamics

Abstract:

River corridors are fundamental elements of natural ecosystems that link processes across terrestrial and aquatic systems. Metabolism of organic matter (OM) in river corridors plays a critical role in global biogeochemical cycles. Recent studies have emphasized the importance of OM thermodynamics, calculated using metrics derived from high-resolution OM characterization, on both aerobic and anaerobic river corridor biogeochemistry. These studies highlight the need to move beyond analytical methods and model structures that focus on optical profiles, and pools defined only by bulk chemical properties. Despite the biogeochemical relevance of OM thermodynamics, there have been no evaluations of how thermodynamics of OM vary across river corridors. In addition, we lack systematic comparisons between OM thermodynamics in surface water and those in associated sediments. Here use a trait-based approach to help understand variation in sediment and water OM thermodynamics from globally-distributed river corridors. We use a newly developed metric of OM thermodynamics as our focal trait (λ). The parameter λ implies the number of catabolic reactions needed to synthesize biomass, therefore serving as an indicator of thermodynamic efficiency of OM. It is calculated from the stoichiometry of individual OM compounds and can be applied to highly diverse OM pools with 10,000+ measured compounds. The outcomes of this study provide an opportunity to inform substrate-explicit models through probabilistic sampling of λ distributions that take into account the full diversity of OM chemistries in sediments and water pools.