Metabolic control analysis of biogeochemical systems

Abstract Many reactive systems involve processes operating at different scales, such as hydrodynamic transport and diffusion, abiotic chemical reactions, microbial metabolism, and population dynamics. Determining the influence of these processes on system dynamics is critical for model design and for prioritizing parameter estimation efforts. Metabolic control analysis is a framework for quantifying the role of enzymes in cellular biochemical networks, but its applicability to biogeochemical and other reactive systems remains unexplored. Here I show how the core concepts of metabolic control analysis can be generalized to much more complex reactive systems, enabling insight into the roles of physical transport, population dynamics, and chemical kinetics at organismal to planetary scales. I demonstrate the power of this framework for two systems of importance to ocean biogeochemistry: A simplified (mostly didactic) model for the sulfate methane transition zone in Black Sea sediments, and a more comprehensive model for the oxygen minimum zone in Saanich Inlet near steady state. I find that physical transport is by far the greatest rate-limiting factor for sulfate-driven methane oxidation in the first system and for fixed nitrogen loss in the second system.