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Atmospheric Sciences & Global Change
Research Highlights

February 2018

New Analysis Yields Missing Pieces in Modeling the Global Carbon Cycle

Scientists identified key environmental factors and hydrological processes important for modeling sediment yield and particulate organic carbon yield in Earth system models.

catchments
Analyzing data from catchments around the world, scientists identified strong relationships between sediment yield (the amount of sediment per unit basin area reaching a river basin outlet in a given period) and seismicity, land forest cover, and land management. Enlarge Image.

The Science

Sediment from soil erosion is ubiquitous, and its environmental impacts, such as reduced nutrients and water quality and increased flooding, are well known. However, the impacts of sediment yield on the global carbon cycle remain largely uncertain because Earth system models lack a representation of soil erosion.

Led by scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory, a recent study identified the key environmental factors and hydrological processes that dominate sediment yield and particulate organic carbon yield in different environments around the world. These factors and processes include agriculture, seismicity, heavy storms, and annual peak runoff.

The Impact

Recent studies refuted the traditional view that aquatic ecosystems play a passive role in the global carbon cycle as a "pipe" to transport organic carbon from land to oceans. Increasingly, observational evidence suggests that a considerable fraction of carbon in the aquatic ecosystems is biogeochemically modified on its journey to the oceans. Therefore, estimating the magnitude and timing of carbon fluxes from land to rivers is critical for understanding how the carbon cycle responds to perturbations.

This research establishes the foundation for representing sediment yield, a major source of riverine carbon, in Earth system models.

Summary

Sediment yield is a process that involves soil erosion, sediment transport, and deposition. It is defined by the amount of sediment per unit basin area reaching a river basin outlet during a given period. In riverine biogeochemistry, this is important because the particulate organic carbon yield—the amount of particulate organic carbon detached in erosion and sediment transport—could be as much as 13.5 percent of the global total produced by terrestrial ecosystems.

However, neither sediment yield nor particulate organic carbon yield are represented in most Earth system models because soil erosion and sediment transport processes vary greatly across space and time. Also, existing sediment yield models cannot capture the global variability of sediment yield at scales resolvable by Earth system models.

To remedy this situation, scientists analyzed worldwide sediment yield and organic carbon yield data from 1,081 and 38 catchments, respectively, in the size range of 0.1-200 km2. They identified robust relationships between sediment yield and seismicity, land forest cover, and land management. They also found high sediment yield in areas with intense traditional agriculture, seismicity, heavy storms, and high annual peak runoff.

These findings highlight the need to model sediment yield at event scales to reproduce catastrophic mass transport during episodic events and the importance of accounting for cropland management.

Analyses also revealed that sediment yield dominates the variability of particulate organic carbon yield in small catchments. This study establishes a statistically significant empirical relationship between sediment yield and particulate organic carbon yield as a starting point for representing particulate organic carbon in Earth system models.

Acknowledgments

Sponsors: The U.S. Department of Energy Office of Science, Biological and Environmental Research supported this study as part of the Earth System Modeling program through the Energy Exascale Earth System Modeling (E3SM) project. The German Science Foundation DFG supported J.H.

Research Area: Climate and Earth Systems Science

Research Team: Zeli Tan, L. Ruby Leung, Teklu Tesfa, and Xuesong Zhang, PNNL; Hongyi Li, Montana State University; Matthias Vanmaercke, Université de Liège (Belgium); Jean Poesen, KU Leuven (Belgium); Hui Lu, Tsinghua University (China); and Jens Hartmann, Universität Hamburg (Germany)

Reference: Z. Tan, L.R. Leung, H. Li, T. Tesfa, M. Vanmaercke, J. Poesen, X. Zhang, H. Lu, J. Hartmann, "A Global Data Analysis for Representing Sediment and Particulate Organic Carbon Yield in Earth System Models." Water Resources Research 53 (2017). [DOI: 10.1002/2017WR020806]


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