The history of human influence on soil erosion can be described as occurring in three epochs. From 5000 BC to about AD 1500, early farmers extended cultivation from valley bottoms upslope and into the surrounding forestlands. In the last 500 years, extensive conversion of grasslands to croplands has occurred on all continents; most of it in semiarid regions with soils developed directly as a result of concomitant plant community development, the loss of which caused soils not prone to erosion to become highly susceptible to erosion. Abundant food production over the course of the last 5000 years has led to improved human nutrition, health, sanitation, a rapidly increasing human population, and, ironically, the most recent epoch of soil erosion. Within the last 50 years, extensive conversion of ecological sites heretofore unsuited for crop production has taken place, made possible with the advent of commercial fertilizer and genetically manipulated (breeding) crops ofincreased hardiness, production, and resistance to diseases and pests. From these sites, soil erosion alone has more than offset the conservation gains made in countries where agricultural abundance has led to cultures of soil and water conservation.
Ancient civilizations were likely more aware of soil fertility declines, than in the magnitude of soil lost through wind or water erosion, due to decreases in crop production. The earliest and still commonly used remedy for lost productivity was abandonment of depleted sites for, literally, greener fields. However, archeological evidence of terraced cropland exists globally where hunter-gatherers settled into agricultural, crop-producing societies, dating to 2000 BC. Recognition of depleted soil resources and soil loss, despite efforts to slow or reverse the processes, has not always saved early civilizations from decline concomitant with the decline of their soil resource, as evidenced by the rise and fall of the Mediterranean and Mesoamerican societies.
Sediment is the primary pollutant from farm, range, and forest lands. Soil lost from these uplands results in local decreased biomass productivity and impaired hydrologic conditions, which in turn leads to a deterioration of the soil biotic community and further decrease in soil fertility. Concentrated and delivered to a stream, sediment degrades water quality and in-stream habitat, reforms channel morphology, and increases transportation costs through shipping channel maintenance. Finally, deposition can bury human communities, croplands, or native plant communities, and it adds to the costs of infrastructure by filling irrigation canals and hydropower and irrigation reservoirs. Siltation can affect commercial and recreational fisheries and result in destruction of otherwise appealing water-recreation sites. One of the few positive effects of soil loss from productive uplands occurs where storm flows are allowed to cover bottomlands and create deposits of rich, fertile soil.
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