Editing Salt marsh (section)

==Sediment trapping, accretion, and the role of tidal creeks==
[[Image:BloodyMarsh2008.jpg|right|thumb|[[Bloody Marsh]] in Georgia, US]]

The factors and processes that influence the rate and spatial distribution of sediment accretion within the salt marsh are numerous. Sediment deposition can occur when marsh species provide a surface for the sediment to adhere to, followed by deposition onto the marsh surface when the sediment flakes off at low tide.<ref name="pethick"/> The amount of sediment adhering to salt marsh species is dependent on the type of marsh species, the proximity of the species to the sediment supply, the amount of plant biomass, and the elevation of the species.<ref name="li">{{Cite journal |last=Li |first=H. |last2=Yang |first2=S. L. |date=2009-07-01 |title=Trapping Effect of Tidal Marsh Vegetation on Suspended Sediment, Yangtze Delta |url=http://www.bioone.org/doi/abs/10.2112/08-1010.1 |journal=Journal of Coastal Research |language=en |volume=254 |pages=915–924 |doi=10.2112/08-1010.1 |issn=0749-0208|url-access=subscription }}</ref> For example, in a study of the Eastern [[Chongming Island]] and [[Jiuduansha Island]] tidal marshes at the mouth of the [[Yangtze River]], China, the amount of sediment adhering to the species ''[[Spartina alterniflora]]'', ''[[Phragmites australis]]'', and ''[[Scirpus]] mariqueter'' decreased with distance from the highest levels of suspended sediment concentrations (found at the marsh edge bordering tidal creeks or the mudflats); decreased with those species at the highest elevations, which experienced the lowest frequency and depth of tidal inundations; and increased with increasing plant biomass. ''Spartina alterniflora'', which had the most sediment adhering to it, may contribute >10% of the total marsh surface sediment accretion by this process.<ref name="li"/>

Salt marsh species also facilitate sediment accretion by decreasing current velocities and encouraging sediment to settle out of suspension.<ref name="pethick"/> Current velocities can be reduced as the stems of tall marsh species induce hydraulic drag, with the effect of minimising re-suspension of sediment and encouraging deposition.<ref name="shi">{{Cite journal |last=Shi |first=Z. |last2=Hamilton |first2=L. J. |last3=Wolanski |first3=E. |date=2000 |title=Near-Bed Currents and Suspended Sediment Transport in Saltmarsh Canopies |url=https://www.jstor.org/stable/4300101 |journal=Journal of Coastal Research |volume=16 |issue=3 |pages=909–914 |issn=0749-0208}}</ref> Measured concentrations of suspended sediment in the water column have been shown to decrease from the open water or [[tidal creek]]s adjacent to the marsh edge, to the marsh interior,<ref name="li"/><ref name="shi"/><ref name="reed">{{Cite journal |last=Reed |first=Denise J. |last2=Spencer |first2=Thomas |last3=Murray |first3=Anne L. |last4=French |first4=Jonathan R. |last5=Leonard |first5=Lynn |date=1999-03-01 |title=Marsh surface sediment deposition and the role of tidal creeks: Implications for created and managed coastal marshes |url=http://link.springer.com/10.1007/BF02802742 |journal=Journal of Coastal Conservation |language=en |volume=5 |issue=1 |pages=81–90 |doi=10.1007/BF02802742 |issn=1400-0350|url-access=subscription }}</ref> probably as a result of direct settling to the marsh surface by the influence of the marsh canopy.<ref name="shi"/><ref name="reed"/>

Inundation and sediment deposition on the marsh surface is also assisted by tidal creeks<ref name="reed"/> which are a common feature of salt marshes.<ref name="chapman"/><ref name="pethick"/><ref name="bird"/><ref name="reed"/><ref name="wood">{{Cite journal |last=Wood |first=Nathan |last2=Hine |first2=Albert C. |date=2007-07-01 |title=Spatial Trends in Marsh Sediment Deposition Within a Microtidal Creek System, Waccasassa Bay, Florida |url=https://bioone.org/doi/abs/10.2112/04-0243.1 |journal=Journal of Coastal Research |language=en |volume=23 |issue=4 |pages=823–833 |doi=10.2112/04-0243.1 |issn=0749-0208|url-access=subscription }}</ref> Their typically dendritic and [[meander]]ing forms provide avenues for the tide to rise and flood the marsh surface, as well as to drain water,<ref name="bird"/> and they may facilitate higher amounts of sediment deposition than salt marsh bordering open ocean.<ref name="wood"/> Sediment deposition is correlated with sediment size: coarser sediments will deposit at higher elevations (closer to the creek) than finer sediments (further from the creek). Sediment size is also often correlated with particular trace metals, and thus tidal creeks can affect metal distributions and concentrations in salt marshes, in turn affecting the biota.<ref>{{Cite journal|last1=Chen|first1=Si|last2=Torres|first2=Raymond|date=2012-03-21|title=Effects of Geomorphology on the Distribution of Metal Abundance in Salt Marsh Sediment|journal=Estuaries and Coasts|language=en|volume=35|issue=4|pages=1018–1027|doi=10.1007/s12237-012-9494-y|bibcode=2012EstCo..35.1018C |s2cid=129721804|issn=1559-2723}}</ref> Salt marshes do not however require tidal creeks to facilitate sediment flux over their surface<ref name="shi"/> although salt marshes with this morphology seem to be rarely studied.

The elevation of marsh species is important; those species at lower elevations experience longer and more frequent tidal floods and therefore have the opportunity for more sediment deposition to occur.<ref name="li"/><ref name="cahoon">{{Cite journal |last=Cahoon |first=Donald R. |last2=White |first2=David A. |last3=Lynch |first3=James C. |date=2011-08-15 |title=Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta |url=https://linkinghub.elsevier.com/retrieve/pii/S0169555X10005234 |journal=Geomorphology |language=en |volume=131 |issue=3-4 |pages=57–68 |doi=10.1016/j.geomorph.2010.12.002|url-access=subscription }}</ref> Species at higher elevations can benefit from a greater chance of inundation at the highest tides when increased water depths and marsh surface flows can penetrate into the marsh interior.<ref name="reed"/>