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Abstract

Although the loss of organic carbon and nutrients from land to rivers by soil erosion is well documented, the spatial and temporal variability of this carbon and nutrient loss and its role in the global carbon and nutrient cycles are poorly understood. To fill this knowledge gap, we integrated a well-validated sediment yield model based on the improved Morgan model into the DOE Energy Exascale Earth System Model (E3SM) to investigate the spatial and temporal variability of terrestrial organic carbon and nutrient loss in the conterminous U.S. The modeled yield of sediment and particulate organic carbon in large river basins is consistent with previous reports. Our simulations showed that soil erosion causes substantial loss of terrestrial organic carbon and nutrients from the conterminous United States to the coastal zone. More importantly, this loss is only a small fraction of the amounts of terrestrial organic carbon and nutrients disturbed by soil erosion. Although the carbon and nutrient loss is controlled mainly by the rate of soil loss, the abundance of organic carbon and nutrients in soils is also an important factor. The Mississippi River Basin contributes the most organic carbon and nutrient loss by soil erosion in the conterminous U.S., with the majority of the loss occurring in its Ohio and Missouri sub-basins where the temporal variability of the loss is closely correlated with the land hydrology. The model showed that large carbon sequestration can be achieved in well-managed croplands that are under wet forest climate. In contrast, little carbon sequestration can be achieved in croplands that are under dry forest climate when compared with natural vegetations. The simulations also showed that by increasing the rate of soil erosion wildfires and landslides elevate the loss of terrestrial organic carbon and nutrients. Our study highlights the large impacts of soil erosion on terrestrial, aquatic and coastal ecosystems.

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