Difference between revisions of "Characteristics of muddy coasts"

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Muddy coasts:
 
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*the area exposed to tidal variation is often vegetated by mangrove
 
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*this coast type occurs in tropical climates where rivers supply abundant fine material to coastal zone (CZ)
 
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*wave exposure is normally low to moderate; tidal regime can be any
 
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*connected coast type is often low wetland exposed to flooding
 
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*mangrove constitutes an important part of muddy coast profile, biologically and for stability. Cutting can cause severe problems, decreasing biodiversity and causing erosion and flooding. (p68)
 
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*mixed environments with wave-exposed shores or sandy tidal flats alternating with mud-dominated tidal flats and deeper muddy areas are seen often (and require special management consideration) (p 55-56)
 
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*Silt and clay are not stable in the littoral zone and are washed offshore. If large amounts of fines are supplied, mud flats and mangrove areas may develop (ppt)
 
  
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This article provides a short introduction to and summary of habitats derived from fine sediments suspended in tidal waters.
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Muddy coasts are common in environments that are fairly calm with respect to wave conditions or where there is abundant supply of fine sediments. A global inventory of coasts dominated by fine-grained sedimentary deposits (silts and clays) forming flat surfaces, revealed that 14% of the world’s ice-free coastline is muddy, about 60% of which is located between 25°N and 25°S. The total length of muddy coastlines is estimated at about 90,000 km<ref name=H23>Hulskamp, R., Luijendijk, A., van Maren, B., Moreno-Rodenas, A., Calkoen, F., Kras, E., Lhermitte, S. and Aarninkhof, S. 2023. Global distribution and dynamics of muddy coasts. Nature Communications 14, 8259</ref>.
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==[[Mangroves]]==
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Coastal areas exposed to tides in tropical and subtropical climates are often covered with mangrove forests. This type of coast occurs where rivers bring abundant fine material to the coastal zone. Wave exposure is generally low to moderate, as silt and clay are easily washed offshore by wave action. The tidal regime can be any. Mangrove forests stabilize the muddy subsoil. Mangrove clearing causes erosion and biodiversity loss and increases the flood risk of inland areas, which often consist of low-lying wetlands.
  
 
==Salt marsh areas and intertidal mud flats==
 
==Salt marsh areas and intertidal mud flats==
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Salt marshes and intertidal mud flats act as natural coastal defences against a rising sea level. It is however questionable whether these areas are able to keep track with a changing sea level at the same time as adjusting to various anthropogenic impacts including stress caused by herbicides, nutrient loading etc.  
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[[Image:Saltmarsh usgs.jpg|thumb|Salt marsh. Source: [http://www.usgs.gov/ USGS]]] [[Salt marsh]]es and intertidal mud flats are [[natural shore protecting barriers]] against a rising sea level. It is however questionable whether these areas are able to keep pace with a rising sea level while adjusting to various anthropogenic impacts including stress caused by dredging, reclamation, herbicides, nutrient loading etc.
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Sustainable development of an ecosystem requires adequate anticipation to future developments. In order to predict the response of salt marshes to [[climate change]], process descriptions of the bio-geo-chemical and geo-morphological processes influencing this area are needed as well as an understanding of the present ecosystem vulnerability. The interactions between human impacts and natural changes in the ecosystem include the aspects of biodiversity and global change.
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==State of the art==
 +
===Processes===
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Estuarine areas and coastal lagoons are net sinks for fine-grained sediment. The processes responsible for this net import of sediment to estuaries are well described in the literature. The processes involved include (see e.g., [[Dynamics of mud transport]], [[Estuarine turbidity maximum]]):
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#Settling and scour-lag<ref>van Straaten, L. M. J. U. and Kuenen, Ph. H. 1958. Tidal action as a cause of [[clay]] accumulation. Journal of Sedimentary Petrology 28: 406-413</ref><ref>Postma, H., 1967. Sediment transport and sedimentation in estuarine environment. In: Estuaries. Ed. by G. H. Lauff.  Am. Assn. Adv. Sci., Washington, D. C., 158-179.</ref>;
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#[[Estuarine circulation]] driven by horizontal density gradients;
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#[[Tidal asymmetry and tidal basin morphodynamics|Tidal asymmetry]] resulting from the interaction between estuarine morphology and tidal wave propagation;
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#[[Flocculation cohesive sediments|Aggregation of fine-grained particles]] either by electrochemical or biological processes<ref>van Leussen, W. 1994. Estuarine macroflocs and their role in fine-grained sediment transport. PhD thesis Utrecht University, Netherlands, 488 p.</ref>.  
  
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Sustainable development of an ecosystem requires the system to be fully understood and the future development to be adequately anticipated in order to make the right basis for management In order to predict the future development of salt marshes under a changing climate, process descriptions of the bio-geo-chemical and geo-morphological processes influencing this area are needed as well as an understanding of the present ecosystem vulnerability. The interactions between human impacts and natural changes in the ecosystem include the aspects of bio-diversity and global change.
 
  
 +
These processes together have the effect of accumulating fine-grained sediments in shallow coastal lagoons. In most estuaries and coastal lagoons, accretion of fine sediments is currently keeping pace with the local sea level rise<ref>Nichols, M.  M. 1989. Sediment accumulation rates and relative sea level rise in lagoons. Marine Geology. Vol. 88, 201-219.</ref>. A large spatial variation in accumulation rates is often observed, with the highest rates in the inner parts of the lagoons and the lowest rates close to the tidal inlet and in deeper parts of the area<ref>Pejrup, M,. Larsen, M. and Edelvang K. 1997. A fine-grained sediment budget for the Sylt-Rømø tidal basin. Helgoländer Meeresuntersuchungen. 51: 253-268.</ref>. Therefore, where accommodation space is available, salt marsh areas develop, especially fringing the inner parts of estuarine areas. The global mud coast inventory<ref name=H23/> found that in the period 1984-2016, about 1/3 of the muddy shorelines worldwide were about stable, about 1/3 were accreting and about 1/3 were eroding.
  
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==State of the art==
 
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Estuarine areas and coastal lagoons are sinks for fine-grained sediment on an annual time scale. The processes responsible for this net import of sediment to estuaries are well described in literature. The processes involved include I) settling and scour-lag<ref>van Straaten, L. M. J. U. and Kuenen, Ph. H. (1958) Tidal action as a cause of clay accumulation. Journal of Sedimentary Petrology. Vol. 28, 406-413.</ref><ref>Postma, H., 1967. Sediment transport and sedimentation in estuarine environment. In: Estuaries. Ed. by G. H. Lauff.  Am. Assn. Adv. Sci., Washington, D. C., 158-179.</ref>'''II) estuarine circulation driven by horizontal density gradients, III''') shoaling of the tidal wave causing an asymmetric distribution of the velocity and sediment concentration, IV) the aggregation of fine-grained particles either by electrochemical or biological processes<ref>van Leussen, W. (1994) Estuarine macroflocs and their role in fine-grained sediment transport. Proefschrift from university of Utrecht, Holland. 488 p.</ref>. These processes together have the effect of accumulating fine-grained sediments in shallow coastal lagoons, generally keeping pace with the magnitude of the local rise in sea level<ref>Nichols, M.  M. (1989) Sediment accumulation rates and relative sea level rise in lagoons. Marine Geology. Vol. 88, 201-219.</ref>. However, there is large spatial variation in accumulation rates with the highest rates in the inner parts of the lagoons and the lowest rates close to the tidal inlet and in deeper parts of the area (Ref.6). Therefore, where accommodation space is available, salt marsh areas develop, especially fringing the inner parts of estuarine areas.
 
  
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Tidal currents and waves dominate the local hydrodynamics and thus determine the physical, morphological and biological characteristics of a mudflat.  The degree of wave activity depends upon both the fetch and the nature of the prevailing wind, and can vary significantly within an estuary.  It is well known that even small waves are able to erode large amounts of surface sediment; this material can be carried shoreward with the advancing tide<ref>Christie, M. and Dyer, K. R. (1998) Measurements of the turbid tidal edge over the Skeffling mudflats. In: Sedimentary Processes in the Intertidal Zone (Eds: Black, Paterson and Cramp). Geolgical Soc. Lon. Vol. 139, 45-55.</ref>.  The level of wave attack at a point on the mudflat is the result of wave attenuation and the relationship between the mudflat slope and the water level and is thus sensitive both to rise in sea level and storm frequency. The mudflat profile will change in response to different forcing, altering the feedback between the morphology and hydrodynamics, whilst evolving to reach some new equilibrium.  
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===Local hydrodynamics===
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Tidal currents and waves dominate the local hydrodynamics and thus determine the physical, morphological and biological characteristics of a [[mudflat]].  The degree of wave activity depends upon both the [[fetch]] and the strength of the prevailing wind, and can vary significantly within an estuary.  Even small waves are able to erode large amounts of surface sediment which is subsequently transported by tidal currents<ref>Christie, M. and Dyer, K. R. 1998. Measurements of the turbid tidal edge over the Skeffling mudflats. In: Sedimentary Processes in the Intertidal Zone (Eds: Black, Paterson and Cramp). Geolgical Soc. Lon. 139: 45-55</ref>.  Wave action on the mudflat depends on the relationship between the mudflat slope and the water level and is thus sensitive both to rise in sea level and storm frequency. [[Tidal channel meandering and marsh erosion|Tidal channel morphodynamics]] also play an important role in the morphological evolution of mudflats.
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===Eco-morphology of muddy coasts===
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[[Image:Mud shrimp-USGS.png|thumb|Mud shrimp. Source: [http://pubs.usgs.gov/of/2000/of00-304/htmldocs/chap11/index.htm USGS]]]
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Biological processes such as the effect of the macrofauna living in the mud and algae growing on the sediment surface producing EPS (Extracellular Polymeric Substances) are of prime importance for mudflat stability and erodibility<ref>Holland, A.F., Zingmark, R.G. & Dean, J.M. 1974. Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms. Marine Biology 27: 191-196</ref><ref>Nowell, A.R.M., Jumars, P.A. & Eckman, J.E. 1981. Effects of biological activity on the entrainment of marine sediments. Marine Geology. 42, 133-153.</ref>. The net effect of these processes on erosion and deposition on the intertidal mudflats is only partly understood. Furthermore, there is a gap in knowledge about how a changing climate will affect key species of the intertidal ecosystem in particular<ref>Asmus, H. and Asmus, R. 1998. The role of macrobenthic communities for sediment-water material exchange in the Sylt-Rømø tidal basin. Senckengergiana Maritima 29: 111-119.</ref>. The biological, sedimentary and physical processes are closely inter-connected, and complex relationships control the nature and movement of surface sediment across the intertidal zone. Therefore, alterations in the activity of key species on the tidal flats due to climate change may lead to significant changes in salt marsh development. See [[Biogeomorphology of coastal systems]] for further details.
  
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Biological processes such as the effect of the macrofauna living in the mud and algae growing on the sediment surface producing EPS (Extracellular Polymeric Substances) are of prime importance for mudflat stability and erodibility<ref>Holland, A.F., Zingmark, R.G. & Dean, J.M. 1974. Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms. Marine Biology, 27, 191-196.</ref><ref>Nowell, A.R.M., Jumars, P.A. & Eckman, J.E. 1981. Effects of biological activity on the entrainment of marine sediments. Marine Geology. 42, 133-153.</ref>. The net effect of these processes on erosion and deposition on the intertidal mudflats is only partly understood. Furthermore, there is a gap in knowledge about how a changing climate will affect key species of the intertidal ecosystem in particular<ref>Asmus, H. and Asmus, R. (1998) the role of macrobenthic communities for sediment-water material exchange in the Sylt-Rømø tidal basin. Senckengergiana Maritima. Vol. 29, 111-119.</ref>. The biological, sedimentary and physical processes are closely inter-connected, and complex relationships control the nature and movement of surface sediment across the intertidal zone. Therefore, alterations in the activity of key species on the tidal flats due to climate change may lead to significant changes in salt marsh development.  
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===Effect of storm events===
 +
The altering processes of inundation and drying are on an average believed to establish a steady state situation with salt marshes being both eroded and fed during the inundation events. Therefore, it is not a straightforward problem to foresee what will happen to a specific salt marsh area if the storm frequency increases or if mean sea level rises faster than it has up till now<ref>Dyer, K. R. 1994. Estuarine sediment transport and deposition. In: Sediment transport and depositional processes. (Ed: Pye, K.). Blackwell sci. Pub. 193-215. </ref>. Salt marsh areas build up vertically when inundated by turbid estuarine waters. This means that episodic events like storm surges and extreme high water levels are important and one storm event may substantially alter the net annual sedimentation<ref>Andersen, T.J. and Pejrup, M. 2001. Suspended sediment transport on a temperate, microtidal mudflat, the Danish Wadden Sea. Marine Geology 173: 69-85</ref>. The timing and frequency of such events are likely to be very different in warmer climates than in colder climates with important implications for the stability of the system.
  
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The altering processes of inundation and drying are on an average believed to establish a steady state situation with salt marshes being both eroded and fed during the inundation events. Therefore, it is not a straightforward problem to foresee what will happen to a specific salt marsh area if the storm frequency increases or if mean sea level rises faster than it has up till now<ref>Dyer, K. R. (1994) Estuarine sediment transport and deposition. In: Sediment transport and depositional processes. (Ed: Pye, K.). Blackwell sci. Pub. 193-215.  </ref>. Salt marsh areas build up vertically when inundated by turbid estuarine waters. This means that episodic events like storm surges and extreme high water levels are important and one storm event (as on 3rd December 2000) may substantially contribute to the annual sedimentation rate. The timing and frequency of such events are likely to be very different in warmer climates than in colder climates with important implications for the stability of the system.
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==Related articles==
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:[[Mud]]
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:[[Salt marsh]]
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:[[Mangroves]]
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:[[Fluid mud]]
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:[[Flocculation cohesive sediments]]
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:[[Estuarine turbidity maximum]]
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:[[Coastal mud belt]]
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:[[Dynamics of mud transport]]
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:[[Coastal and marine sediments]]
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:[[Dynamics, threats and management of salt marshes]]
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:[[Sediment deposition and erosion processes]]
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:[[Estuarine circulation]]
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:[[Tidal channel meandering and marsh erosion]]
  
  
 
==References==
 
==References==
 
<references/>
 
<references/>
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{{author
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|AuthorID=11539
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|AuthorFullName=Edelvang, Karen
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|AuthorName=Karen Edelvang}}
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[[Category:Physical coastal and marine processes]]
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[[Category:Sediment]]

Latest revision as of 16:54, 21 August 2025

This article provides a short introduction to and summary of habitats derived from fine sediments suspended in tidal waters.

Muddy coasts are common in environments that are fairly calm with respect to wave conditions or where there is abundant supply of fine sediments. A global inventory of coasts dominated by fine-grained sedimentary deposits (silts and clays) forming flat surfaces, revealed that 14% of the world’s ice-free coastline is muddy, about 60% of which is located between 25°N and 25°S. The total length of muddy coastlines is estimated at about 90,000 km[1].


Mangroves

Coastal areas exposed to tides in tropical and subtropical climates are often covered with mangrove forests. This type of coast occurs where rivers bring abundant fine material to the coastal zone. Wave exposure is generally low to moderate, as silt and clay are easily washed offshore by wave action. The tidal regime can be any. Mangrove forests stabilize the muddy subsoil. Mangrove clearing causes erosion and biodiversity loss and increases the flood risk of inland areas, which often consist of low-lying wetlands.

Salt marsh areas and intertidal mud flats

Salt marsh. Source: USGS
Salt marshes and intertidal mud flats are natural shore protecting barriers against a rising sea level. It is however questionable whether these areas are able to keep pace with a rising sea level while adjusting to various anthropogenic impacts including stress caused by dredging, reclamation, herbicides, nutrient loading etc.

Sustainable development of an ecosystem requires adequate anticipation to future developments. In order to predict the response of salt marshes to climate change, process descriptions of the bio-geo-chemical and geo-morphological processes influencing this area are needed as well as an understanding of the present ecosystem vulnerability. The interactions between human impacts and natural changes in the ecosystem include the aspects of biodiversity and global change.

State of the art

Processes

Estuarine areas and coastal lagoons are net sinks for fine-grained sediment. The processes responsible for this net import of sediment to estuaries are well described in the literature. The processes involved include (see e.g., Dynamics of mud transport, Estuarine turbidity maximum):

  1. Settling and scour-lag[2][3];
  2. Estuarine circulation driven by horizontal density gradients;
  3. Tidal asymmetry resulting from the interaction between estuarine morphology and tidal wave propagation;
  4. Aggregation of fine-grained particles either by electrochemical or biological processes[4].


These processes together have the effect of accumulating fine-grained sediments in shallow coastal lagoons. In most estuaries and coastal lagoons, accretion of fine sediments is currently keeping pace with the local sea level rise[5]. A large spatial variation in accumulation rates is often observed, with the highest rates in the inner parts of the lagoons and the lowest rates close to the tidal inlet and in deeper parts of the area[6]. Therefore, where accommodation space is available, salt marsh areas develop, especially fringing the inner parts of estuarine areas. The global mud coast inventory[1] found that in the period 1984-2016, about 1/3 of the muddy shorelines worldwide were about stable, about 1/3 were accreting and about 1/3 were eroding.


Local hydrodynamics

Tidal currents and waves dominate the local hydrodynamics and thus determine the physical, morphological and biological characteristics of a mudflat. The degree of wave activity depends upon both the fetch and the strength of the prevailing wind, and can vary significantly within an estuary. Even small waves are able to erode large amounts of surface sediment which is subsequently transported by tidal currents[7]. Wave action on the mudflat depends on the relationship between the mudflat slope and the water level and is thus sensitive both to rise in sea level and storm frequency. Tidal channel morphodynamics also play an important role in the morphological evolution of mudflats.

Eco-morphology of muddy coasts

Mud shrimp. Source: USGS

Biological processes such as the effect of the macrofauna living in the mud and algae growing on the sediment surface producing EPS (Extracellular Polymeric Substances) are of prime importance for mudflat stability and erodibility[8][9]. The net effect of these processes on erosion and deposition on the intertidal mudflats is only partly understood. Furthermore, there is a gap in knowledge about how a changing climate will affect key species of the intertidal ecosystem in particular[10]. The biological, sedimentary and physical processes are closely inter-connected, and complex relationships control the nature and movement of surface sediment across the intertidal zone. Therefore, alterations in the activity of key species on the tidal flats due to climate change may lead to significant changes in salt marsh development. See Biogeomorphology of coastal systems for further details.

Effect of storm events

The altering processes of inundation and drying are on an average believed to establish a steady state situation with salt marshes being both eroded and fed during the inundation events. Therefore, it is not a straightforward problem to foresee what will happen to a specific salt marsh area if the storm frequency increases or if mean sea level rises faster than it has up till now[11]. Salt marsh areas build up vertically when inundated by turbid estuarine waters. This means that episodic events like storm surges and extreme high water levels are important and one storm event may substantially alter the net annual sedimentation[12]. The timing and frequency of such events are likely to be very different in warmer climates than in colder climates with important implications for the stability of the system.

Related articles

Mud
Salt marsh
Mangroves
Fluid mud
Flocculation cohesive sediments
Estuarine turbidity maximum
Coastal mud belt
Dynamics of mud transport
Coastal and marine sediments
Dynamics, threats and management of salt marshes
Sediment deposition and erosion processes
Estuarine circulation
Tidal channel meandering and marsh erosion


References

  1. ↑ 1.0 1.1 Hulskamp, R., Luijendijk, A., van Maren, B., Moreno-Rodenas, A., Calkoen, F., Kras, E., Lhermitte, S. and Aarninkhof, S. 2023. Global distribution and dynamics of muddy coasts. Nature Communications 14, 8259
  2. ↑ van Straaten, L. M. J. U. and Kuenen, Ph. H. 1958. Tidal action as a cause of clay accumulation. Journal of Sedimentary Petrology 28: 406-413
  3. ↑ Postma, H., 1967. Sediment transport and sedimentation in estuarine environment. In: Estuaries. Ed. by G. H. Lauff. Am. Assn. Adv. Sci., Washington, D. C., 158-179.
  4. ↑ van Leussen, W. 1994. Estuarine macroflocs and their role in fine-grained sediment transport. PhD thesis Utrecht University, Netherlands, 488 p.
  5. ↑ Nichols, M. M. 1989. Sediment accumulation rates and relative sea level rise in lagoons. Marine Geology. Vol. 88, 201-219.
  6. ↑ Pejrup, M,. Larsen, M. and Edelvang K. 1997. A fine-grained sediment budget for the Sylt-Rømø tidal basin. Helgoländer Meeresuntersuchungen. 51: 253-268.
  7. ↑ Christie, M. and Dyer, K. R. 1998. Measurements of the turbid tidal edge over the Skeffling mudflats. In: Sedimentary Processes in the Intertidal Zone (Eds: Black, Paterson and Cramp). Geolgical Soc. Lon. 139: 45-55
  8. ↑ Holland, A.F., Zingmark, R.G. & Dean, J.M. 1974. Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms. Marine Biology 27: 191-196
  9. ↑ Nowell, A.R.M., Jumars, P.A. & Eckman, J.E. 1981. Effects of biological activity on the entrainment of marine sediments. Marine Geology. 42, 133-153.
  10. ↑ Asmus, H. and Asmus, R. 1998. The role of macrobenthic communities for sediment-water material exchange in the Sylt-Rømø tidal basin. Senckengergiana Maritima 29: 111-119.
  11. ↑ Dyer, K. R. 1994. Estuarine sediment transport and deposition. In: Sediment transport and depositional processes. (Ed: Pye, K.). Blackwell sci. Pub. 193-215.
  12. ↑ Andersen, T.J. and Pejrup, M. 2001. Suspended sediment transport on a temperate, microtidal mudflat, the Danish Wadden Sea. Marine Geology 173: 69-85


The main author of this article is Edelvang, Karen
Please note that others may also have edited the contents of this article.
Citation: Edelvang, Karen (2025): Characteristics of muddy coasts. Available from http://www.coastalwiki.org/wiki/Characteristics_of_muddy_coasts [accessed on 5-12-2025]
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