U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

A new approach to represent multi-consumer, multi-species soil biogeochemical reactions for Earth System Models

William J. Riley
Lawrence Berkeley National Laboratory

Highlight

5 September 2017
A new kinetics formulation (SUPECA) scales mixed reaction networks

The Science
Environmental biogeochemistry emerges from microbially mediated redox reactions in a complex web of consumers and substrates. The two dominant approaches to represent these reactions, Monod and Synthesizing Unit (SU), are unable to scale consistently across complex reaction networks and fail to include substrate limitations, respectively. The authors here extend these approaches (termed SUPECA) to general redox reaction networks to improve terrestrial ecosystem biogeochemical modeling. The authors also applied the SUPECA approach to analyze the soil moisture constraint on soil organic matter decomposition and compared to a benchmark dataset to show our approach accurately represents this constraint across a wide range of soil moisture conditions. The SUPECA approach is being applied in NGEE-Arctic modeling analyses and in DOE’s Earth System Model (E3SM) Land Model (ELM).

The Impact
The authors demonstrate that (1) existing Monod and Synthesizing Unit kinetics are scaling inconsistent; (2) the new SUPECA kinetics rectifies these problems; and (3) that SUPECA is well-suited to trait-based modeling approaches. The authors also show that SUPECA kinetics enables mechanistic modeling of soil moisture effects on organic matter decomposition.

Summary
Soil organic matter decomposition occurs in an extremely complex network of reactions, substrates, and consumers. To address this problem in a manner amenable to land model representation (e.g., E3SM’s ELM), the authors extended the Equilibrium Chemistry Approximation approach to generic biogeochemical networks that include redox reactions (termed the SUPECA (Synthesizing Unit plus ECA) kinetics). The authors demonstrated that SUPECA consistently scales from single Monod type and redox reactions to a reaction network, while the popular dual Monod kinetics and Synthesizing Unit kinetics fail to do so. It is also demonstrated that SUPECA kinetics is superior to dual Monod kinetics in modeling substrate competition in the presence of substrate-mineral interactions. By applying SUPECA to soil organic matter decomposition, the authors showed that soil aggregates have significant impacts and illustrate potential flaws in current ESM land model approaches. The authors are applying the SUPECA approach in NGEE-Arctic modeling analyses and in DOE’s ELM.

Contacts (BER PM)
Daniel Stover and Dorothy Koch
daniel.stover@science.doe.gov (301-903-0289) and Dorothy.Koch@science.doc.gov (301-903-0105)

(PI Contact)
William J. Riley
Lawrence Berkeley National Lab
wjriley@lbl.gov

Funding
DE-AC02-05CH11231 as part of NGEE-Arctic project and Accelerated Climate Modeling for Energy (ACME) project.

Publications
Tang, J.-Y. and Riley, W. J.: SUPECA kinetics for scaling redox reactions in networks of mixed substrates and consumers and an example application to aerobic soil respiration, Geosci. Model Dev., 10, 3277-3295, https://doi.org/10.5194/gmd-10-3277-2017, 2017.

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