Editing Sediment (section)

==Environmental issues==
{{see also|Sediment transport#Applications}}

===Erosion and agricultural sediment delivery to rivers===
One cause of high sediment loads is [[slash and burn]] and [[shifting cultivation]] of [[tropical]] forests. When the ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of a country have become erodible. For example, on the [[Madagascar]] high central [[plateau]], which constitutes approximately ten percent of that country's land area, most of the land area is devegetated, and gullies have eroded into the underlying soil to form distinctive gulleys called ''[[lavaka]]s''. These are typically {{convert|40|m||sp=us}} wide, {{convert|80|m||sp=us}} long and {{convert|15|m||sp=us}} deep.<ref>{{cite web |last1=Sawe |first1=Benjamin Elisha |title=Erosion Landforms: What Is A Lavaka? |date=25 April 2017 |url=https://www.worldatlas.com/articles/erosion-landforms-what-is-a-lavaka.html |publisher=WorldAtlas |access-date=24 September 2021}}</ref> Some areas have as many as 150 lavakas/square kilometer,<ref>{{cite journal |last1=Voarintsoa |first1=N. R. G. |last2=Cox |first2=R. |last3=Razanatseheno |first3=M.O.M.|last4=Rakotondrazafy |first4=A.F.M. |title=Relation Between Bedrock Geology, Topography and Lavaka Distribution in Madagascar |journal=South African Journal of Geology |date=1 June 2012 |volume=115 |issue=2 |pages=225–250 |doi=10.2113/gssajg.115.225|bibcode=2012SAJG..115..225V }}</ref> and lavakas may account for 84% of all sediments carried off by rivers.<ref>{{cite journal |last1=Cox |first1=Rónadh |last2=Bierman |first2=Paul |last3=Jungers |first3=Matthew C.|last4=Rakotondrazafy |first4=A.F. Michel|title=Erosion Rates and Sediment Sources in Madagascar Inferred from 10 Be Analysis of Lavaka, Slope, and River Sediment |journal=The Journal of Geology |date=July 2009 |volume=117 |issue=4 |pages=363–376 |doi=10.1086/598945|bibcode=2009JG....117..363C |s2cid=55543845 }}</ref> This [[siltation]] results in discoloration of rivers to a dark red brown color and leads to fish kills. In addition, sedimentation of river basins  implies sediment management and siltation costs. The cost of removing an estimated 135 million m<sup>3</sup> of accumulated sediments due to water erosion only is likely exceeding 2.3 billion euro (€) annually in the EU and UK, with large regional differences between countries.<ref>{{Cite journal |last1=Panagos |first1=Panos |last2=Matthews |first2=Francis |last3=Patault |first3=Edouard |last4=De Michele |first4=Carlo |last5=Quaranta |first5=Emanuele |last6=Bezak |first6=Nejc |last7=Kaffas |first7=Konstantinos |last8=Patro |first8=Epari Ritesh |last9=Auel |first9=Christian |last10=Schleiss |first10=Anton J. |last11=Fendrich |first11=Arthur |last12=Liakos |first12=Leonidas |last13=Van Eynde |first13=Elise |last14=Vieira |first14=Diana |last15=Borrelli |first15=Pasquale |date=January 2024 |title=Understanding the cost of soil erosion: An assessment of the sediment removal costs from the reservoirs of the European Union |url=https://linkinghub.elsevier.com/retrieve/pii/S095965262304341X |journal=Journal of Cleaner Production |language=en |volume=434 |pages=140183 |doi=10.1016/j.jclepro.2023.140183|bibcode=2024JCPro.43440183P }}</ref>

Erosion is also an issue in areas of modern farming, where the removal of native vegetation for the cultivation and harvesting of a single type of crop has left the soil unsupported.<ref>{{cite journal |last1=Ketcheson |first1=J. W. |title=Long-Range Effects of Intensive Cultivation and Monoculture on the Quality of Southern Ontario Soils |journal=Canadian Journal of Soil Science |date=1 March 1980 |volume=60 |issue=3 |pages=403–410 |doi=10.4141/cjss80-045}}</ref> Many of these regions are near rivers and drainages. Loss of soil due to erosion removes useful farmland, adds to sediment loads, and can help transport anthropogenic fertilizers into the river system, which leads to [[eutrophication]].<ref>{{cite book |last1=Ohlsson |first1=Thomas |editor1-last=Motarjemi |editor1-first=Yasmine |editor2-last=Lelieveld |editor2-first=Hubb |title=Food safety management: a practical guide for the food industry |date=2014 |publisher=Elsevier |isbn=9780128056820 |chapter-url=https://books.google.com/books?id=sCR3DAAAQBAJ&dq=%22Monoculture+agriculture%22+%22eutrophication%22&pg=PP6 |access-date=24 September 2021 |chapter=Sustainability and Food Production}}</ref>

The Sediment Delivery Ratio (SDR) is fraction of gross erosion (interill, rill, gully and stream erosion) that is expected to be delivered to the outlet of the river.<ref>{{Cite journal|last1=Fernandez|first1=C.|last2=Wu|first2=J. Q.|last3=McCool|first3=D. K.|last4=Stöckle|first4=C. O.|date=2003-05-01|title=Estimating water erosion and sediment yield with GIS, RUSLE, and SEDD|url=http://www.jswconline.org/content/58/3/128|journal=Journal of Soil and Water Conservation|language=en|volume=58|issue=3|pages=128–136|issn=0022-4561}}</ref> The sediment transfer and deposition can be modelled with sediment distribution models such as WaTEM/SEDEM.<ref>{{Cite journal|last1=Van Rompaey|first1=Anton J. J.|last2=Verstraeten|first2=Gert|last3=Van Oost|first3=Kristof|last4=Govers|first4=Gerard|last5=Poesen|first5=Jean|date=2001-10-01|title=Modelling mean annual sediment yield using a distributed approach|journal=Earth Surface Processes and Landforms|language=en|volume=26|issue=11|pages=1221–1236|doi=10.1002/esp.275|issn=1096-9837|url=https://lirias.kuleuven.be/handle/123456789/76728|bibcode=2001ESPL...26.1221V|s2cid=128689971|url-access=subscription}}</ref> In Europe, according to WaTEM/SEDEM model estimates the Sediment Delivery Ratio is about 15%.<ref>{{Cite journal|date=2018-02-01|title=A step towards a holistic assessment of soil degradation in Europe: Coupling on-site erosion with sediment transfer and carbon fluxes|journal=Environmental Research|language=en|volume=161|pages=291–298|doi=10.1016/j.envres.2017.11.009|pmid=29175727|pmc=5773246|issn=0013-9351|last1=Borrelli|first1=P.|last2=Van Oost|first2=K.|last3=Meusburger|first3=K.|last4=Alewell|first4=C.|last5=Lugato|first5=E.|last6=Panagos|first6=P.|bibcode=2018ER....161..291B}}</ref>

===Coastal development and sedimentation near coral reefs===

Watershed development near coral reefs is a primary cause of sediment-related coral stress. The stripping of natural vegetation in the watershed for development exposes soil to increased wind and rainfall and, as a result, can cause exposed sediment to become more susceptible to erosion and delivery to the marine environment during rainfall events. Sediment can negatively affect corals in many ways, such as by physically smothering them, abrading their surfaces, causing corals to expend energy during sediment removal, and causing algal blooms that can ultimately lead to less space on the seafloor where juvenile corals (polyps) can settle.

When sediments are introduced into the coastal regions of the ocean, the proportion of land, marine, and organic-derived sediment that characterizes the seafloor near sources of sediment output is altered. In addition, because the source of sediment (i.e., land, ocean, or organically) is often correlated with how coarse or fine sediment grain sizes that characterize an area are on average, grain size distribution of sediment will shift according to the relative input of land (typically fine), marine (typically coarse), and organically-derived (variable with age) sediment.  These alterations in marine sediment characterize the amount of sediment suspended in the water column at any given time and sediment-related coral stress.
<ref>{{cite journal |last1=Risk |first1=Michael J |title=Assessing the effects of sediments and nutrients on coral reefs |journal=Current Opinion in Environmental Sustainability |date=April 2014 |volume=7 |pages=108–117 |doi=10.1016/j.cosust.2014.01.003|bibcode=2014COES....7..108R }}</ref>

===Biological considerations===
In July 2020, [[Marine biology|marine biologists]] reported that [[Aerobic organism|aerobic]] [[microorganism]]s (mainly), in "[[Suspended animation|quasi-suspended animation]]", were found in organically-poor sediments, up to 101.5 million years old, 250 feet below the [[Seabed|seafloor]] in the [[South Pacific Gyre]] (SPG) ("the deadest spot in the ocean"), and could be the [[List of longest-living organisms|longest-living life forms]] ever found.<ref name="NYT-2200728">{{cite news |last=Wu |first=Katherine J. |title=These Microbes May Have Survived 100 Million Years Beneath the Seafloor - Rescued from their cold, cramped and nutrient-poor homes, the bacteria awoke in the lab and grew. |work=The New York Times |url=https://www.nytimes.com/2020/07/28/science/microbes-100-million-years-old.html |date=28 July 2020 |access-date=31 July 2020 }}</ref><ref name="NC-20200728">{{cite journal |author=Morono, Yuki |display-authors=et al. |title=Aerobic microbial life persists in oxic marine sediment as old as 101.5 million years |date=28 July 2020 |journal=[[Nature Communications]] |volume=11 |number=3626 |page=3626 |doi=10.1038/s41467-020-17330-1 |pmid=32724059 |pmc=7387439 |bibcode=2020NatCo..11.3626M }}</ref>