Human activities that increase soil erosion
Agricultural practices
Unsustainable agricultural practices are the largest contributor to the global increase in erosion rates. Tillage of agricultural land, which breaks the soil into finer particles, is one of the main 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 available for transport by water erosion. Others include monoculture, farming on steep slopes, the use of pesticides and chemical fertilizers (which kill soil-binding organisms), row crops, and the use of surface irrigation. A complex global situation regarding the definition of soil nutrient losses could arise as a result of the size-selective nature of soil erosion events. The loss of total phosphorus, for example, in the finer eroded fraction is greater relative to the entire soil. Extrapolating this evidence to predict subsequent behavior within receiving aquatic systems, the reason is that this more easily transported material can support a lower concentration of P compared to the coarser size fractions. Tillage also increases wind erosion rates, dehydrating the soil and breaking it down into smaller particles that can be picked up by the wind. This is compounded by the fact that most trees are usually removed from agricultural fields, allowing the winds to have long, open runs to travel at higher speeds. Heavy grazing reduces vegetation cover and causes strong soil compaction, which increases erosion rates.
Deforestation
In an undisturbed forest, the mineral soil is protected by a layer of leaf litter and humus that covers the forest floor. These two layers form a protective mat on the floor that absorbs the impact of raindrops. They are porous and highly permeable to precipitation, allowing rainwater to reduce infiltration into the soil, rather than flowing over the surface as runoff. The roots of trees and plants hold soil particles together, preventing them from being carried away by water. The canopy acts to slow down raindrops that hit the foliage and stems before hitting the ground, reducing their kinetic energy. However, it is the forest floor, rather than the canopy, that prevents surface erosion. The final velocity of the raindrops is reached at approximately 8 meters (26 feet). Because tree crowns are generally taller than these, raindrops can often regain terminal velocity even after hitting the canopy. However, the intact forest floor, with its layers of leaf litter and organic matter, can still absorb the impact of rain.
Deforestation causes increased erosion rates due to exposure of mineral soil by removing layers of humus and leaf litter from the soil surface, removing the vegetative cover that binds the soil, and causing soil compaction from logging equipment. Once trees have been removed by fire or logging, infiltration rates become high and erosion decreases as long as the forest floor remains intact. Severe fires can lead to further erosion if accompanied by heavy rain.
Globally, one of the largest contributors to erosive soil loss in 2006 is slash-and-burn treatment of tropical forests. In various regions of the earth, entire sectors of a country have become unproductive. For example, on the high central plateau of Madagascar, which comprises approximately ten percent of that country's land area, virtually the entire landscape is barren of vegetation, with erosion grooves typically exceeding 50 meters (160 ft) deep and 1 kilometer (1 kilometer) wide. Shifting agriculture is an agricultural system that 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.
Streets and urbanization
Urbanization has important effects on erosion processes: first, by stripping the land of vegetation cover, altering drainage patterns, and compacting the soil during construction; and then covering the land in an impermeable layer of asphalt or concrete which increases the amount of surface runoff and increases surface wind speed. Much of the sediment transported in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals. This increased runoff, in addition to eroding and degrading the land over which it flows, also causes major disruption to surrounding watersheds by altering the volume and rate of water flowing through them and filling them with chemically contaminated sedimentation. The increased flow of water through local waterways also causes a large increase in the rate of bank erosion.
Climate change
The warmer atmospheric temperatures observed over recent decades are expected to lead to a more vigorous hydrological cycle, including more extreme precipitation events. The rise in sea levels that has occurred as a result of climate change has also greatly increased rates of coastal erosion.
Studies on soil erosion suggest that increasing rainfall amounts and intensities will lead to higher rates of soil erosion. Therefore, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase unless ameliorative 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 rain. Other reasons include: a) changes in the plant canopy caused by changes in plant biomass production associated with moisture regime; b) changes in soil litter cover caused by changes in plant residue decomposition rates as a result of temperature- and humidity-dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to changing precipitation regimes and evapotranspiration rates, which changes infiltration and runoff rates; d) changes in soil erosion due to decreased soil organic matter concentrations in soils leading to soil structure more susceptible to erosion and increased runoff due to increased sealing and crusting of the soil surface; e) a shift of winter precipitation from non-erosive snow to erosive rain due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) changes in land use necessary to accommodate new climate regimes.
Pruski and Nearing's studies indicated that, without considering other factors, such as land use, it is reasonable to expect a change of approximately 1.7% in soil erosion for every 1% change in total precipitation under climate change. In recent studies, rainfall erosion is projected to increase by 17% in the United States and 18% in Europe.
Due to the severity of its ecological effects and the scale on which it is occurring, erosion constitutes one of the most important global environmental problems we face today.
Land degradation
Water and wind erosion are now the two main causes of land degradation; Combined, they are responsible for 84% of the degraded surface.
Every year, about 75 billion tons of soil are eroded from the earth, a rate that is about 13-40 times faster than the rate of natural erosion. Approximately 40% of the world's agricultural land is seriously degraded. According to the United Nations, an area of fertile soil the size of Ukraine is lost every year due to drought, deforestation and climate change. In Africa, if current land degradation trends continue, the continent could feed only 25% of its population by 2025, according to UNU's Africa Natural Resources Institute based in Ghana.
Recent modeling developments have quantified rainfall erosion on a global scale using high temporal resolution (<30 min) and high-fidelity rainfall recordings. The result is an extensive global data collection effort that produced the Global Rainfall Erosivity (GloREDa) database that includes rainfall erosion for 3,625 stations and covers 63 countries. This first global rainfall erosion database was used to develop a 30 arcsecond (~1 km) global erosivity map based on a sophisticated geostatistical process. According to a new study published in Nature Communications, nearly 36 billion tons of land are lost to water each year, and deforestation and other land-use changes are making the problem worse. The study investigates the global dynamics of soil erosion using spatially distributed high-resolution models (approximately 250 × 250 m cell size). The geostatistical approach allows, for the first time, the incorporation into a global model of land use erosion and land use changes, the extent, types, spatial distribution of global croplands and the effects of different regional cropping systems.
The loss of soil fertility due to erosion is even more problematic because the response is often to apply chemical fertilizers, leading to further water and soil pollution, rather than allowing the land to regenerate.
Sedimentation of aquatic ecosystems
Soil erosion (especially from agricultural activity) is considered the world's leading cause of diffuse water pollution, due to the effects of excess sediment flowing into the world's waterways. The sediments themselves act as pollutants, in addition to being carriers of other pollutants, such as attached pesticide molecules or heavy metals.
The effect of increased sediment loads on aquatic ecosystems can be catastrophic. Mud can smother spawning fish beds by filling the space between gravel in the stream bed. It also reduces food supply and causes significant respiratory problems as sediment enters its gills. The biodiversity of aquatic plants and algae life is reduced, and invertebrates are also unable to survive and reproduce. While the sedimentation event itself might be relatively short-lived, the ecological disturbance caused by the dying mass often persists into the future.
One of the most serious and long-lasting water erosion problems worldwide is in the People's Republic of China, in the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, more than 1.6 billion tons of sediment flows into the ocean each year. The sediment originates mainly from water erosion in the Loess Plateau region in the northwest.
Dust pollution in the air
Soil particles collected during wind soil erosion are a major source of air pollution, in the form of airborne particles, "dust". These airborne soil particles are often contaminated with toxic chemicals, such as pesticides or petroleum fuels, posing ecological and public health risks when they land or are inhaled/ingested.
Dust from erosion acts to suppress precipitation and changes the color of the sky from blue to white, leading to an increase in red sunsets. Dust events have been linked to a decline in the health of coral reefs throughout the Caribbean and Florida, primarily since the 1970s. Similar dust plumes originate in the Gobi Desert, which combined with pollutants, extends great distances downwind, or eastward, toward North America.