Editing Soil erosion (section)

==Human activities that aid soil erosion==

===Agricultural practices===
{{see also|agricultural pollution|overgrazing}}
[[File:Soil erosion at Hill Farm - geograph.org.uk - 1287527.jpg|thumb|Tilled farmland such as this is very susceptible to erosion from rainfall, due to the destruction of vegetative cover and the loosening of the soil during plowing.]]
Unsustainable agricultural practices increase rates of erosion by one to two [[Order of magnitude|orders of magnitude]] over the natural rate and far exceed replacement by soil production.<ref>{{cite journal |last1=Montgomery |first1=D. R. |title=Soil erosion and agricultural sustainability |journal=Proceedings of the National Academy of Sciences |date=8 August 2007 |volume=104 |issue=33 |pages=13268–13272 |doi=10.1073/pnas.0611508104|pmid=17686990 |pmc=1948917 |bibcode=2007PNAS..10413268M |doi-access=free }}</ref><ref>{{Cite journal|last1=Wuepper|first1=David|last2=Borrelli|first2=Pasquale|last3=Finger|first3=Robert|date=January 2020|title=Countries and the global rate of soil erosion|url=https://www.nature.com/articles/s41893-019-0438-4|journal=Nature Sustainability|language=en|volume=3|issue=1|pages=51–55|doi=10.1038/s41893-019-0438-4|s2cid=208539010|issn=2398-9629}}</ref> The [[tillage]] of agricultural lands, which breaks up soil into finer particles, is one of the primary factors. The problem has been exacerbated in modern times, due to mechanized agricultural equipment that allows for [[deep plowing]], which severely increases the amount of soil that is available for transport by water erosion. Others include [[monocropping]], farming on steep slopes, [[pesticide]] and [[chemical fertilizer]] usage (which kill organisms that bind soil together), row-cropping, and the use of [[surface irrigation]].<ref>{{cite book|author=Blanco, Humberto|author2=Lal, Rattan|name-list-style=amp|chapter=Tillage erosion|title=Principles of Soil Conservation and Management|publisher=Springer|year=2010|isbn=978-90-481-8529-0|chapter-url=https://books.google.com/books?id=Wj3690PbDY0C&pg=PA109}}</ref><ref>{{cite book|author=Lobb, D.A.|chapter=Soil movement by tillage and other agricultural activities|editor=Jorgenson, Sven E.|title=Applications in Ecological Engineering|publisher=Academic Press|year=2009|isbn=978-0-444-53448-4|chapter-url=https://books.google.com/books?id=aRKO6ZazC8UC&pg=PA247}}</ref> A complex overall situation with respect to defining nutrient losses from soils, could arise as a result of the size selective nature of soil erosion events. Loss of total [[phosphorus]], for instance, in the finer eroded fraction is greater relative to the whole soil.<ref>{{cite journal |title=Bioavailable phosphorus in fine-sized sediments transported from agricultural fields |author= Poirier, S.-C. |author2=Whalen, J.K. |author3=Michaud, A.R. |year= 2012|volume=76|issue=1|pages=258–267|doi= 10.2136/sssaj2010.0441
|journal= Soil Science Society of America Journal |bibcode=2012SSASJ..76..258P}}</ref> Extrapolating this evidence to predict subsequent behaviour within receiving aquatic systems, the reason is that this more easily transported material may support a lower solution P concentration compared to coarser sized fractions.<ref>{{cite journal |title= Phosphorus loss in overfertilized soils: The selective P partitioning and redistribution between particle size separates |author= Scalenghe, R. |author2= Edwards, A.C. |author3= Barberis, E. |name-list-style= amp|year= 2007|volume=27|issue=11|pages=72–80|doi= 10.1016/j.eja.2007.02.002|journal= European Journal of Agronomy}}</ref> Tillage also increases wind erosion rates, by dehydrating the soil and breaking it up into smaller particles that can be picked up by the wind. Exacerbating this is the fact that most of the trees are generally removed from agricultural fields, allowing winds to have long, open runs to travel over at higher speeds.<ref>{{cite book|author=Whitford, Walter G.|chapter=Wind and water processes|title=Ecology of Desert Systems|publisher=Academic Press|year=2002|isbn=978-0-12-747261-4|page=65|chapter-url=https://books.google.com/books?id=OZ4hZbXS8IcC&pg=PA65}}</ref> Heavy [[grazing]] reduces vegetative cover and causes severe soil compaction, both of which increase erosion rates.<ref>{{cite book|author=Imeson, Anton|chapter=Human impact on degradation processes|title=Desertification, Land Degradation and Sustainability|publisher=John Wiley & Sons|year=2012|isbn=978-1-119-97776-6|page=165|chapter-url=https://books.google.com/books?id=BjJQY-i7kNsC&pg=PA165}}</ref>

===Deforestation===
[[File:BURNED CLEAR-CUT AREA OF OLYMPIC NATIONAL TIMBERLAND WASHINGTON. NEAR OLYMPIC NATIONAL PARK - NARA - 555088.tif|thumb|In this [[clearcut]], almost all of the vegetation has been stripped from the surface of steep slopes, in an area with very heavy rains. Severe erosion occurs in cases such as this, causing stream [[sedimentation]] and the loss of nutrient-rich [[topsoil]].]]

In an undisturbed [[forest]], the mineral soil is protected by a layer of ''[[leaf litter]]'' and an ''[[humus]]'' that cover the forest floor. These two layers form a protective mat over the soil that absorbs the impact of rain drops. They are [[porosity|porous]] and highly [[Permeability (Earth sciences)|permeable]] to rainfall, and allow rainwater to slow [[percolate]] into the soil below, instead of flowing over the surface as [[surface runoff|runoff]].<ref name="Sands-2005-pp74-75">{{cite book|author=Sands, Roger|chapter=The environmental value of forests|title=Forestry in a Global Context|publisher=CABI|year=2005|isbn=978-0-85199-089-7|pages=74–75|chapter-url=https://books.google.com/books?id=UO1DAI60IQEC&pg=PA74}}</ref> The roots of the trees and plants<ref>The [[Mycelium|mycelia]] of forest [[Fungus|fungi]] also play a major role in binding soil particles together.</ref> hold together soil particles, preventing them from being washed away.<ref name="Sands-2005-pp74-75" /> The vegetative cover acts to reduce the velocity of the raindrops that strike the foliage and stems before hitting the ground, reducing their [[kinetic energy]].<ref name="Goudie-2000-p188" /> However it is the forest floor, more than the canopy, that prevents surface erosion. The [[terminal velocity]] of rain drops is reached in about {{convert|8|m|ft|abbr=off}}. Because forest canopies are usually higher than this, rain drops can often regain terminal velocity even after striking the canopy. However, the [[intact forest landscape|intact forest]] floor, with its layers of leaf litter and organic matter, is still able to absorb the impact of the rainfall.<ref name="Goudie-2000-p188">{{Cite book|author=Goudie, Andrew|chapter=The human impact on the soil|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|page=[https://archive.org/details/humanimpactonn00goud/page/188 188]|chapter-url=https://books.google.com/books?id=r8l-DMj3XTgC&pg=PA188|url=https://archive.org/details/humanimpactonn00goud/page/188}}</ref><ref>{{cite journal|author=Stuart, Gordon W.|author2=Edwards, Pamela J.|name-list-style=amp|title=Concepts about forests and water|journal=Northern Journal of Applied Forestry|volume=23|issue=1|pages=11–19|year=2006|url=http://treesearch.fs.fed.us/pubs/14744|doi=10.1093/njaf/23.1.11|doi-access=free|access-date=2015-10-05|archive-date=2017-07-01|archive-url=https://web.archive.org/web/20170701142057/https://www.treesearch.fs.fed.us/pubs/14744|url-status=dead}}</ref>

[[Deforestation]] causes increased erosion rates due to exposure of [[mineral]] [[soil]] by removing the humus and litter layers from the soil surface, removing the vegetative cover that binds soil together, and causing heavy [[soil compaction]] from logging equipment. Once trees have been removed by fire or logging, infiltration rates become high and erosion low to the degree the forest floor remains intact. Severe fires can lead to significant further erosion if followed by heavy rainfall.<ref>{{Cite book|author=Goudie, Andrew|chapter=The human impact on the soil|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|pages=[https://archive.org/details/humanimpactonn00goud/page/196 196–197]|chapter-url=https://books.google.com/books?id=r8l-DMj3XTgC&pg=PA196|url=https://archive.org/details/humanimpactonn00goud/page/196}}</ref>

Globally one of the largest contributors to erosive soil loss in the year 2006 is the [[slash and burn]] treatment of [[tropical]] [[forest]]s. In a number of regions of the earth, entire sectors of a country have been rendered unproductive. For example, on the [[Madagascar]] high central [[plateau]], comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of [[vegetation]], with gully erosive furrows typically in excess of {{convert|50|m|ft}} deep and {{convert|1|km|mi|abbr=off|1}} wide. [[Shifting cultivation]] is a farming system which sometimes incorporates the [[slash and burn]] method in some regions of the world. This degrades the soil and causes the soil to become less and less fertile.<ref>{{Cite thesis|title=Shifting cultivation in the upland secondary forests of the Philippines: biodiversity and carbon stock assessment, and ecosystem services trade-offs in land-use decisions|publisher=University of Queensland Library|first=Sharif Ahmed|last=Mukul|year=2016 |doi=10.14264/uql.2016.222}}</ref>

===Roads and human impact===
[[File:Erosion pollution.jpg|thumb|Erosion polluted the Kasoa highway after downpour in Ghana.]]
[[Human impact on the environment|Human Impact]] has major effects on erosion processes—first by denuding the land of vegetative cover, altering drainage patterns, and compacting the soil during construction; and next by covering the land in an impermeable layer of asphalt or concrete that increases the amount of surface runoff and increases surface wind speeds.<ref>{{cite book|author=Nîr, Dov|title=Man, a Geomorphological Agent: An Introduction to Anthropic Geomorphology|publisher=Springer|year=1983|isbn=978-90-277-1401-5|pages=121–122|url=https://books.google.com/books?id=3HSCQvZ7U2kC&pg=PA121}}</ref> Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals.<ref>{{cite book|author=Randhir, Timothy O.|title=Watershed Management: Issues and Approaches|publisher=IWA Publishing|year=2007|isbn=978-1-84339-109-8|page=56|url=https://books.google.com/books?id=PNBlSPdu0JAC&pg=PA56}}</ref> This increased runoff, in addition to eroding and degrading the land that it flows over, also causes major disruption to surrounding watersheds by altering the volume and rate of water that flows through them, and filling them with chemically polluted sedimentation. The increased flow of water through local waterways also causes a large increase in the rate of bank erosion.<ref>{{cite book|author=James, William|chapter=Channel and habitat change downstream of urbanization|editor=Herricks, Edwin E.|editor2=Jenkins, Jackie R.|title=Stormwater Runoff and Receiving Systems: Impact, Monitoring, and Assessment|publisher=CRC Press|year=1995|isbn=978-1-56670-159-4|page=105|chapter-url=https://books.google.com/books?id=X0xt9HZbyToC&pg=PA105}}</ref>

===Climate change===
{{Main|Land degradation}}

The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.<ref>{{cite web|author=Intergovernmental Panel on Climate Change (IPCC)|year=1995|title=Second Assessment Synthesis of Scientific-Technical Information relevant to interpreting Article 2 of the UN Framework Convention on Climate Change|page=5|url=http://www.ipcc.ch/pdf/climate-changes-1995/2nd-assessment-synthesis.pdf|access-date=2015-10-05|archive-url=https://web.archive.org/web/20130309040926/http://www.ipcc.ch/pdf/climate-changes-1995/2nd-assessment-synthesis.pdf|archive-date=2013-03-09|url-status=dead}}</ref> The [[rise in sea levels]] that has occurred as a result of climate change has also greatly increased coastal erosion rates.<ref>{{cite book|editor=Bicknell, Jane|display-editors=etal|title=Adapting Cities to Climate Change: Understanding and Addressing the Development Challenges|publisher=Earthscan|year=2009|isbn=978-1-84407-745-8|page=114|url=https://books.google.com/books?id=77Kmhw6sVOMC&pg=PA114}}</ref><ref>For an overview of other human activities that have increased coastal erosion rates, see: {{cite book|author=Goudie, Andrew|chapter=Accelerated coastal erosion|title=The Human Impact on the Natural Environment|publisher=MIT Press|year=2000|isbn=978-0-262-57138-8|page=[https://archive.org/details/humanimpactonn00goud/page/311 311]|chapter-url=https://books.google.com/books?id=r8l-DMj3XTgC&pg=PA311|url=https://archive.org/details/humanimpactonn00goud/page/311}}</ref>
[[File:Ghana Flooding 2.jpg|thumb|Most part of Accra mostly flooded during rainy season, causing environmental crisis in Ghana]]
Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of soil erosion. Thus, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase, unless amelioration measures are taken. Soil erosion rates are expected to change in response to changes in climate for a variety of reasons. The most direct is the change in the erosive power of rainfall. Other reasons include: a) changes in plant canopy caused by shifts in plant biomass production associated with moisture regime; b) changes in litter cover on the ground caused by changes in both plant residue decomposition rates driven by temperature and moisture dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to shifting precipitation regimes and evapo-transpiration rates, which changes infiltration and runoff ratios; d) soil [[erodibility]] changes due to decrease in [[soil organic matter]] concentrations in soils that lead to a soil structure that is more susceptible to erosion and increased runoff due to increased [[soil surface sealing]] and crusting; e) a shift of winter precipitation from non-erosive snow to erosive rainfall due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) shifts in land use made necessary to accommodate new climatic regimes.<ref>{{Cite journal|last1=Klik|first1=A.|last2=Eitzinger|first2=J.|date=October 2010|title=Impact of climate change on soil erosion and the efficiency of soil conservation practices in Austria|url=https://www.cambridge.org/core/product/identifier/S0021859610000158/type/journal_article|journal=The Journal of Agricultural Science|language=en|volume=148|issue=5|pages=529–541|doi=10.1017/S0021859610000158|bibcode=2010EGUGA..12.5412K|s2cid=86550618|issn=0021-8596}}</ref>

Studies by Pruski and Nearing indicated that, other factors such as land use unconsidered, it is reasonable to expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change.<ref>{{cite journal |last1=Pruski |first1=F. F. |first2=M. A. |last2=Nearing |year=2002 |title=Runoff and soil loss responses to changes in precipitation: a computer simulation study |journal=Journal of Soil and Water Conservation |volume=57 |issue=1 |pages=7–16 |url=http://www.jswconline.org/content/57/1/7.abstract }}</ref> In recent studies, there are predicted increases of rainfall erosivity by 17% in the United States,<ref>{{Cite journal|last1=Nearing|first1=M. A.|last2=Pruski|first2=F. F.|last3=O'Neal|first3=M. R.|date=2004-01-01|title=Expected climate change impacts on soil erosion rates: A review|url=http://www.jswconline.org/content/59/1/43|journal=Journal of Soil and Water Conservation|language=en|volume=59|issue=1|pages=43–50|issn=0022-4561}}</ref> by 18% in Europe,<ref>{{Cite journal|last1=Panagos|first1=Panos|last2=Ballabio|first2=Cristiano|last3=Meusburger|first3=Katrin|last4=Spinoni|first4=Jonathan|last5=Alewell|first5=Christine|last6=Borrelli|first6=Pasquale|title=Towards estimates of future rainfall erosivity in Europe based on REDES and WorldClim datasets|journal=Journal of Hydrology|volume=548|pages=251–262|doi=10.1016/j.jhydrol.2017.03.006|pmid=28649140|pmc=5473165|year=2017|bibcode=2017JHyd..548..251P}}</ref> and globally 30 to 66%<ref name="auto">{{Cite journal|last1=Borrelli|first1=Pasquale|last2=Robinson|first2=David A.|last3=Panagos|first3=Panos|last4=Lugato|first4=Emanuele|last5=Yang|first5=Jae E.|last6=Alewell|first6=Christine|last7=Wuepper|first7=David|last8=Montanarella|first8=Luca|last9=Ballabio|first9=Cristiano|date=2020-09-08|title=Land use and climate change impacts on global soil erosion by water (2015-2070)|journal=Proceedings of the National Academy of Sciences|language=en|volume=117|issue=36|pages=21994–22001|doi=10.1073/pnas.2001403117|issn=0027-8424|pmid=32839306|pmc=7486701|bibcode=2020PNAS..11721994B|doi-access=free}}</ref>