Global-scale models of rock-derived nutrient availability often assume that physical erosion drives soils toward an approximate “steady state” over geologic timescales. By definition, steady-state models do not represent landscape age—that is, the time elapsed since soil formation is initiated by major erosional or depositional events. We hypothesize that this steady-state assumption has large consequences on estimates of soil fertility because landscape age can mediate the retention of mobile elements in soil, particularly in low-relief landscapes and humid climates. We quantified the effect of landscape age on soil fertility by estimating Na retention in soils across the United States and explicitly resolving landscape age in regions that experienced significant deposition or glacial retreat after the Last Glacial Maximum (LGM). We then used a simple one-compartment model to simulate soil formation and weathering, comparing predictions that incorporated landscape age with those based on the steady-state assumption. We found that soils formed in LGM deposits in low-relief, humid settings generally retain 10 times more Na than soils formed outside of LGM deposits. Furthermore, the model that accounted for landscape age outperformed a steady-state model across the United States and increased globally averaged estimates of Na retention by 17%. These results reinforce the idea that landscape age is a major control on weathering and should not be ignored in simulations of nutrient cycling.
Bibliographical noteFunding Information:
and listed in the References. A database of code and model outputs derived from this study is stored on Zenodo.org ; doi: 10.5281/zenodo.2653972) and is described in the supporting information. We thank Kyungsoo Yoo and Claire Kouba for providing feedback on a draft of the manuscript and both Ronald Amundson and an anonymous reviewer for helping us to improve the manuscript after submission. E. W. S. received fellowship support from the U.S. National Science Foundation during initial development of this project. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE‐AC52‐07NA27344. Data Availability All data used to parameterize the model are published in sources described in section (Slessarev,
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- Rock-derived nutrients