26 August 2019

Representing Nitrogen, Phosphorus, and Carbon Interactions in the E3SM Land Model: Development and Global Benchmarking

Robust representation of carbon-nutrient feedbacks in E3SM.

Science

Terrestrial ecosystem carbon (C), nitrogen (N), and phosphorus (P) cycling processes are strongly modulated by the climate and they also generate significant feedbacks to the climate system and play important roles in the changing climate.

Impact

Modeling C/N/P dynamics is an important step towards better prediction and understanding of future climate. In this study, we present a new land model integrated in E3SM that mechanistically simulates terrestrial ecosystem C/N/P processes and evaluate the model against multiple large-scale datasets. We demonstrate the novelty of the model and show that the model significantly outperforms its predecessor versions.

Summary

Over the past several decades, the land modeling community has recognized the importance of nutrient regulation of the global terrestrial carbon cycle. Implementations of nutrient limitation in land models are diverse, varying from applying simple empirical down-regulation of potential Gross Primary Productivity (GPP) under nutrient deficit conditions to more mechanistic treatments. In this study, we introduce a new approach to model multi-nutrient (nitrogen (N), phosphorus (P)) limitations in the Energy Exascale Earth System Model (E3SM) Land Model version 1 (ELMv1-ECA). The development is grounded on (1) advances in representing multiple-consumer, multiple-nutrient competition; (2) a generic dynamic allocation scheme based on water, N, P, and light availability; (3) flexible plant CNP stoichiometry; (4) prognostic treatment of N and P constraints on several carbon cycle processes; and (5) global datasets of plant physiological traits. Through benchmarking the model against best knowledge of global plant and soil carbon pools and fluxes, we show that our implementation of nutrient constraints on the present-day carbon cycle is robust at the global scale. Compared with predecessor versions, ELMv1-ECA better predicts global-scale gross primary productivity, ecosystem respiration, leaf area index, vegetation biomass, soil carbon stocks, evapotranspiration, N2O emissions, and NO3- leaching. Factorial experiments indicate that representing the phosphorus cycle improves modeled carbon fluxes while considering dynamic allocation improves modeled carbon stock density. We also highlight the value of using the International Land Model Benchmarking package (ILAMB) to evaluate and document performance during model development.

Contact
William J. Riley
Lawrence Berkeley National Laboratory
Publications
Zhu, Q, W Riley, J Tang, N Collier, F Hoffman, X Yang, and G Bisht.  2019.  "Representing Nitrogen, Phosphorus, and Carbon Interactions in the E3SM Land Model: Development and Global Benchmarking."  Journal of Advances in Modeling Earth Systems.  https://doi.org/10.1029/2018ms001571.