20.4: Soil and Water Conservation
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Biodiversity is also important for global soil and water protection. Terrestrial vegetation in forests and other upland habitats maintain water quality and quantity, and controls soil erosion.
In watersheds where vegetation has been removed, flooding prevails in the wet season and drought in the dry season. Soil erosion is also more intense and rapid, causing a double effect: removing nutrient-rich topsoil and leading to siltation in downstream riverine and ultimately oceanic environments. This siltation harms riverine and coastal fisheries as well as damaging coral reefs (Turner and Rabalais 1994; van Katwijk et al. 1993).
One of the most productive ecosystems on earth, wetlands have water present at or near the surface of the soil or within the root zone, all year or for a period of time during the year, and the vegetation there is adapted to these conditions. Wetlands are instrumental for the maintenance of clean water and erosion control. Microbes and plants in wetlands absorb nutrients and in the process filter and purify water of pollutants before they can enter coastal or other aquatic ecosystems.
Wetlands also reduce flood, wave, and wind damage. They retard the flow of floodwaters and accumulate sediments that would otherwise be carried downstream or into coastal areas. Wetlands also serve as breeding grounds and nurseries for fish and support thousands of bird and other animal species.