Abstract
Riverine transport of silt and clay particles—or mud—builds continental landscapes and dominates the fluxes of sediment and organic carbon across Earth’s surface. Compared with fluxes of sand-sized grains, mud fluxes are difficult to predict. Yet, understanding the fate of muddy river sediment is fundamental to the global carbon cycle, coastal landscape resilience to sea-level rise, river restoration and river–floodplain morphodynamics on Earth and Mars. Mechanistic theories exist for suspended sand transport, but mud in rivers is often thought to constitute washload—sediment with settling velocities so slow that it does not interact with the bed, such that it depends only on upstream supply and is impossible to predict from local hydraulics. To test this hypothesis, we compiled sediment concentration profiles from the literature from eight rivers and used an inversion technique to determine settling rates of suspended mud. We found that mud in rivers is largely flocculated in aggregates that have near-constant settling velocities, independent of grain size, of approximately 0.34 mm s−1, which is 100-fold faster than rates for individual particles. Our findings indicate that flocculated mud is part of suspended bed-material load, not washload, and thus can be physically described by bed-material entrainment theory.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Rent or buy this article
Prices vary by article type
from$1.95
to$39.95
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Parker, G. 1D Sediment Transport Morphodynamics With Applications to Rivers and Turbidity Currents http://hydrolab.illinois.edu/people/parkerg/powerpoint_lectures.htm (2009).
Church, M. Bed material transport and the morhology of alluvial river channels. Annu. Rev. Earth Planet. Sci. 34, 325–354 (2006).
Wright, S. & Parker, G. Flow resistance and suspended load in sand-bed rivers: simplified stratification model. J. Hydraul. Eng. 130, 796–805 (2004).
Einstein, H. A. & Johnson, J. W. in Applied Sedimentation (ed. Trask, P. D.) 62–71 (John Wiley & Sons, 1950).
Syvitski, J. P. M. & Milliman, J. D. Geology, geography, and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean. J. Geol. 115, 1–19 (2007).
Wang, J. et al. Controls on fluvial evacuation of sediment from earthquake-triggered landslides. Geology 43, 115–118 (2015).
Pizzuto, J. E. Long-term storage and transport length scale of fine sediment: analysis of a mercury release into a river. Geophys. Res. Lett. 41, 5875–5882 (2014).
Aalto, R., Lauer, J. W. & Dietrich, W. E. Spatial and temporal dynamics of sediment accumulation and exchange along Strickland River floodplains (Papua New Guinea) over decadal-to-centennial timescales. J. Geophys. Res. Earth Surf. 113, F01S04 (2008).
Adams, P. N., Slingerland, R. L. & Smith, N. D. Variations in natural levee morphology in anastomosed channel flood plain complexes. Geomorphology 61, 127–142 (2004).
Hajek, E. A. & Wolinsky, M. A. Simplified process modeling of river avulsion and alluvial architecture: connecting models and field data. Sediment. Geol. 257-260, 1–30 (2012).
Bouchez, J. et al. Prediction of depth-integrated fluxes of suspended sediment in the Amazon River: particle aggregation as a complicating factor. Hydrol. Process. 25, 778–794 (2011).
Droppo, I. G. Rethinking what constitutes suspended sediment. Hydrol. Process. 15, 1551–1564 (2001).
Hill, P. S., Milligan, T. G. & Geyer, W. R. Controls on effective settling velocity of suspended sediment in the Eel River flood plume. Cont. Shelf Res. 20, 2095–2111 (2000).
Sutherland, B. R., Barrett, K. J. & Gingras, M. K. Clay settling in fresh and salt water. Environ. Fluid Mech. 15, 147–160 (2014).
Dyer, K. R. Sediment processes in estuaries: future research requirements. J. Geophys. Res. 94, 14327 (1989).
Winterwerp, J. C. On the flocculation and settling velocity of estuarine mud. Cont. Shelf Res. 22, 1339–1360 (2002).
Nicholas, A. P. & Walling, D. E. The significance of particle aggregation in the overbank deposition of suspended sediment on river floodplains. J. Hydrol. 186, 275–293 (1996).
Bungartz, H. & Wanner, S. C. Significance of particle interaction to the modelling of cohesive sediment transport in rivers. Hydrol. Process. 18, 1685–1702 (2004).
Rouse, H. R. Modern conceptions of the mechanics of turbulence. Trans. Am. Soc. Civ. Eng. 102, 463–543 (1937).
de Leeuw, J. et al. Entrainment and suspension of sand and gravel. Earth Surf. Dynam. 8, 485–504 (2020).
Kranenburg, C. The fractal structure of cohesive sediment aggregates. Estuar. Coast. Shelf Sci. 39, 451–460 (1994).
Winterwerp, J. C. A simple model for turbulence induced flocculation of cohesive sediment. J. Hydraul. Eng. 36, 309–326 (1998).
Strom, K. & Keyvani, A. An explicit full-range settling velocity equation for mud flocs. J. Sediment. Res. 81, 921–934 (2011).
Wendling, V. et al. Using an optical settling column to assess suspension characteristics within the free, flocculation, and hindered settling regimes. J. Soils Sediments 15, 1991–2003 (2015).
Beckett, R. & Le, N. P. The role of organic matter and ionic composition in determining the surface charge of suspended particle in natural waters. Colloids Surf. 44, 35–49 (1990).
Grangeon, T., Droppo, I. G., Legout, C. & Esteves, M. From soil aggregates to riverine flocs: a laboratory experiment assessing the respective effects of soil type and flow shear stress on particles characteristics. Hydrol. Process. 28, 4141–4155 (2014).
Wendling, V., Legout, C., Gratiot, N., Michallet, H. & Grangeon, T. Dynamics of soil aggregate size in turbulent flow: respective effect of soil type and suspended concentration. CATENA 141, 66–72 (2016).
Tang, F. H. M. & Maggi, F. A mesocosm experiment of suspended particulate matter dynamics in nutrient- and biomass-affected waters. Water Res. 89, 76–86 (2016).
Furukawa, Y., Reed, A. H. & Zhang, G. Effect of organic matter on estuarine flocculation: a laboratory study using montmorillonite, humic acid, xanthan gum, guar gum and natural estuarine flocs. Geochem. Trans. 15, 1 (2014).
Dietrich, W. E. Settling velocity of natural particles. Water Resour. Res. 18, 1615–1626 (1982).
Einstein, H. A. & Chien, N. Can the rate of wash load be predicted from the bed-load function? Trans. Am. Geophys. Union 34, 876–882 (1953).
He, Q. & Walling, D. E. Spatial variability of the particle size composition of overbank floodplain deposits. Water Air Soil Pollut. 99, 71–80 (1997).
Edmonds, D. A. & Slingerland, R. L. Significant effect of sediment cohesion on delta morphology. Nat. Geosci. 3, 105–109 (2010).
Torres, M. A. et al. Model predictions of long-lived storage of organic carbon in river deposits. Earth Surf. Dynam. 5, 711–730 (2017).
Lapôtre, M. G. A., Ielpi, A., Lamb, M. P., Williams, R. M. E. & Knoll, A. H. Model for the formation of single-thread rivers in barren landscapes and implications for pre-Silurian and Martian fluvial deposits. J. Geophys. Res. Earth Surf. 124, 2757–2777 (2019).
Peakall, J., Ashworth, P. J. & Best, J. L. Meander-bend evolution, alluvial architecture, and the role of cohesion in sinuous river channels: a flume study. J. Sediment. Res. 77, 197–212 (2007).
Leithold, E. L., Blair, N. E. & Wegmann, K. W. Source-to-sink sedimentary systems and global carbon burial: a river runs through it. Earth Sci. Rev. 153, 30–42 (2016).
Lupker, M. et al. A Rouse-based method to integrate the chemical composition of river sediments: application to the Ganga basin. J. Geophys. Res. Earth Surf. 116, F04012 (2011).
Ferguson, R. I. & Church, M. A simple universal equation for grain settling velocity. J. Sediment. Res. 74, 933–937 (2004).
Jordan, P. R. Fluvial Sediment of the Mississippi River at St. Louis, Missouri Water Supply Paper No. 1802 (USGS, 1965); https://doi.org/10.3133/wsp180
Nittrouer, J. A., Mohrig, D., Allison, M. A. & Peyret, A.-P. B. The lowermost Mississippi River: a mixed bedrock-alluvial channel. Sedimentology 58, 1914–1934 (2011).
Colby, B. R. & Hembree, C. H. Computations of Total Sediment Discharge, Niobrara River near Cody, Nebraska Water Supply Paper No. 1357 (USGS, 1955); https://doi.org/10.3133/wsp1357
Nordin, C. F. & Dempster, G. R. Vertical Distribution of Velocity and Suspended Sediment, Middle Rio Grande, New Mexico (USGS, 1963).
Hubbell, D. W. & Matejka, D. Q. Investigations of Sediment Transportation, Middle Loup River at Dunning, Nebraska: With Application of Data from Turbulence Flume Water Supply Paper No.1476 (USGS, 1959); https://doi.org/10.3133/wsp1476
Haught, D., Venditti, J. G. & Wright, S. A. Calculation of in situ acoustic sediment attenuation using off-the-shelf horizontal ADCPs in low concentration settings. Water Resour. Res. 53, 5017–5037 (2017).
Moodie, A. J. Yellow River Kenli Lijin Station Survey. Zenodo https://doi.org/10.5281/zenodo.3457639 (2019).
Vanoni, V. A. Transportation of suspended sediment by water. Trans. Am. Soc. Civ. Eng. 111, 67–102 (1946).
Acknowledgements
This research was sponsored by a National Science Foundation grant (number EAR 1427262) to M.P.L., J.A.N. and G.P., and a Caltech Discovery grant to M.P.L. and W.W.F.
Author information
Authors and Affiliations
Contributions
M.P.L., W.W.F. and G.P. designed the study. M.P.L. and J.d.L. analysed data. A.J.M., J.G.V., J.A.N. and D.H. contributed data. M.P.L. led the writing of the manuscript with contributions from all authors.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Peer review information Primary Handling Editor: Tamara Goldin.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data
Extended Data Fig. 1 Mud abundances in sand-bedded rivers.
Fraction of mud measured in the bed material and that measured from the total suspended sediment in the water column when depth averaged from the field data in our database (Table S1). Except for the Loup River, mud typically constitutes > 70% of the suspended sediment, but generally < 10% of the bed material (with the exception of the Yellow River).
Rights and permissions
About this article
Cite this article
Lamb, M.P., de Leeuw, J., Fischer, W.W. et al. Mud in rivers transported as flocculated and suspended bed material. Nat. Geosci. 13, 566–570 (2020). https://doi.org/10.1038/s41561-020-0602-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41561-020-0602-5
This article is cited by
-
Biophysical flocculation reduces variability of cohesive sediment settling velocity
Communications Earth & Environment (2023)
-
Preface: understanding fine sediment dynamics in aquatic systems
Journal of Soils and Sediments (2023)
-
Competing effects of vegetation density on sedimentation in deltaic marshes
Nature Communications (2022)
-
Bedform segregation and locking increase storage of natural and synthetic particles in rivers
Nature Communications (2021)