Issue link: https://wardsworld.wardsci.com/i/1464361
The major environmental problems affecting soil are erosion and pollution. Almost half of American farmland is losing fertile topsoil faster than it can be formed. Most of the erosion results from poor farming practices and overzealous logging, which deplete the soil of plants and root systems that hold the soil in place. Most soil pollution is caused by synthetic chemical pesticides which not only kill the pests but also are absorbed by plants, which are then eaten by people and other animals. Water The amount of water on the Earth's surface is constant and more than enough to supply human needs. Water problems are generally concerned with local supply and its pollution. Serious water shortages in the United States occur in many western states because of increasing populations, as in Phoenix, Las Vegas, and Los Angeles. In areas where surface water supplies are inadequate, fresh- water can commonly be obtained from underground sources. The water occurs in the open spaces between the grains in sedimentary rocks and has accumulated in the rocks over many thousands of years. When this water is withdrawn faster than it is naturally replenished by rain- and snowfall, the underground supply can become seriously depleted, as is occurring today in many western cities. Such depletion is also a serious problem in the heavily irrigated agricultural areas of the central United States, because most irrigation water is drawn from subsurface supplies. Removal of subsurface water can also result in ground subsidence, a serious problem in central California, Houston, and New Orleans. Pollution Most water pollution problems in the United States are caused by synthetic organic compounds and heavy elements released in wastewater discharges, many by the military as well as by chemical plants. Oil refineries are also major polluters. Other sources of pollution include leaking sanitary landfills, pesticides in runoff from farms, and mixtures of sulfuric acid and cyanide from mining operations. Environmental Geology (continued) + ward ' s science Earthquake damage, Northridge, California, USA. (Credit: USGS)