Abstract

Abstract. Suspended sediment plays a vital role in the regional and global cycling of carbon and nutrients by carrying carbon and nutrients from headwaters into lowland rivers and the oceans. Sediment transport through river systems is often fundamentally modified by human activities such as reservoir management. However, a physically based representation of sediment transport is still missing in most existing Earth system models (ESMs), which are essential tools for modeling and predicting Earth system changes. Here, we introduce a multi-process river sediment module for ESMs, which includes (1) hillslope soil erosion and sediment discharge into streams, (2) sediment transport processes through river networks, (3) reservoir operation based on the inflows from upstream areas and water demand from downstream areas, and (4) sediment trapping by reservoirs. All model parameters are estimated a priori without calibration. We apply this new sediment modeling framework to the contiguous United States and validate it against historical observations of monthly streamflow and sediment discharges at 35 river gauges. The model reasonably well captures the long-term balance and seasonal variations of suspended sediment in large river systems. Furthermore, our model results show that suspended sediment discharge in managed rivers is affected more by reservoirs' direct trapping of sediment particles than by their flow regulation. This new sediment module enables future modeling of the transportation and transformation of carbon and nutrients carried by the fine sediment along the river–ocean continuum to close the global carbon and nutrient cycles.

Highlights

  • Fluvial suspended sediment is fine-grained particles that may be diffused throughout the vertical column of rivers via turbulence and transported along rivers (Garcia, 2008)

  • While understanding the global carbon and nutrient cycling has been one of the primary goals of Earth system models (ESMs), few ESMs have incorporated the representation of suspended sediment and the associated carbon and nutrient fluxes, e.g., particulate organic and inorganic carbon, nitrogen, and phosphorous

  • These 35 United States Geological Survey (USGS) gauges are selected based on three criteria: (1) a no more than 20 % difference between the actual upstream drainage area and the area represented within a grid-based river network, (2) at least 5 years of both monthly streamflow and suspended sediment observations in our study period 1990–2012, and (3) relative bias of Model for Scale Adaptive River Transport (MOSART)-water streamflow simulation of no more than 50 % in 1990–2012

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Summary

Introduction

Fluvial suspended sediment (referred to as suspended sediment) is fine-grained particles that may be diffused throughout the vertical column of rivers via turbulence and transported along rivers (Garcia, 2008). The inherent empiricism of BQART/WBMsed limits its scalability (from large to small rivers) and, in its current formulation, the models do not explicitly account for erosion processes on the landscape and within the channel systems. This empiricism is a hurdle to studying the individual impacts of the first-order processes and their driving factors, such as the various human activities such as land and water management.

Modeling framework
MOSART-water
MOSART-sediment
Hillslope sediment processes
Riverine sediment processes
Reservoir sediment processes
Study area
Inputs and parameters
Numerical experiments
Model validation
Model structure uncertainty
Model parameter uncertainty
Impacts of reservoirs on suspended sediment discharge to the coasts
Findings
Summary and conclusion
Full Text
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