Editing Salt marsh (section)

===Upstream agriculture===
Cultivation of land upstream from the salt marsh can introduce increased silt inputs and raise the rate of primary sediment accretion on the tidal flats, so that pioneer species can spread further onto the flats and grow rapidly upwards out of the level of tidal inundation. As a result, marsh surfaces in this regime may have an extensive cliff at their seaward edge.<ref name="ranwell">Ranwell, D. S. (1972). ''Ecology of salt marshes and sand dunes''. Chapman and Hall Ltd, London.</ref> At the Plum Island estuary, Massachusetts (U.S.), stratigraphic cores revealed that during the 18th and 19th century the marsh prograded over subtidal and mudflat environments to increase in area from 6&nbsp;km<sup>2</sup> to 9&nbsp;km<sup>2</sup> after European settlers [[deforestation|deforested]] the land upstream and increased the rate of sediment supply.<ref name="kirwan">{{Cite journal |last=Kirwan |first=Matthew L. |last2=Murray |first2=A. Brad |last3=Donnelly |first3=Jeffrey P. |last4=Corbett |first4=D. Reide |date=2011-05-01 |title=Rapid wetland expansion during European settlement and its implication for marsh survival under modern sediment delivery rates |url=http://pubs.geoscienceworld.org/geology/article/39/5/507/130567/Rapid-wetland-expansion-during-European-settlement |journal=Geology |language=en |volume=39 |issue=5 |pages=507–510 |doi=10.1130/G31789.1 |issn=1943-2682|url-access=subscription }}</ref>