Soil degradation has been defined as a process that leads to decline in the fertility or future productive capacity of soil as a result of human activity (United Nations Environment Programme, 1993).It occurs whenever the natural balances in the landscape are changed by human activity through misuse or overuse of soil. Degraded soils which result in poor or no production are also called problem soils.
Waste lands are those which for one or the other reason have poor life sustaining property. Out of 100 per cent potentially active lands only 44 per cent are available for cultivation and 56 per cent of land are non-available for cultivation.
The wasteland can be made useful by increasing productivity of land by using some useful methods as afforestation or by using bio-fertilizers. Soil degradation is a complex phenomenon derived by interaction between natural and socio economic factors.
The degradation or deterioration of soil may be caused by the following factors:
1. Physical factors, e.g. loss of fertile top soil due to water or wind erosion.
2. Chemical factors e.g. depletion of nutrients or the toxicity due to acidity or alkalinity (salinization) or water logging.
3. Biological factors which affect the micro-flora and reduce the microbial activity of the soil. These factors reduce the yield.
Eutrophication arises from the oversupply of nutrients, which induces explosive growth of plants and algae which, when such organisms die, consume the oxygen in the body of water, thereby creating the state of hypoxia.
According to Ullmann's Encyclopedia, "the primary limiting factor for eutrophication is phosphate." The availability of phosphorus generally promotes excessive plant growth and decay, favouring simple algae and plankton over other more complicated plants, and causes a severe reduction in water quality. Phosphorus is a necessary nutrient for plants to live, and is the limiting factor for plant growth in many freshwater ecosystems. Phosphate adheres tightly to soil, so it is mainly transported by erosion. Once translocated to lakes, the extraction of phosphate into water is slow, hence the difficulty of reversing the effects of eutrophication.
The source of this excess phosphate are detergents, industrial/domestic run-off, and fertilizers. With the phasing out of phosphate-containing detergents in the 1970s, industrial/domestic run-off and agriculture have emerged as the dominant contributors to eutrophication.
Sodium triphosphate, once a component of many detergents, was a major contributor to eutrophication.
When algae die, they decompose and the nutrients contained in that organic matter are converted into inorganic form by microorganisms. This decomposition process consumes oxygen, which reduces the concentration of dissolved oxygen. The depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity. Nutrients may become concentrated in an anoxic zone and may only be made available again during autumn turn-over or in conditions of turbulent flow.
Enhanced growth of aquatic vegetation or phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen needed for fish and shellfish to survive. The water becomes cloudy, typically coloured a shade of green, yellow, brown, or red. Eutrophication also decreases the value of rivers, lakes and aesthetic enjoyment. Health problems can occur where eutrophic conditions interfere with drinking water treatment.
Thermal pollution is the degradation of water quality by any process that changes ambient water temperature. Many industries use high temperature furnace and boilers in their manufacturing processes. The resulting hot effluents are directly released in to a nearby water source. This is called thermal pollution. It destroys the aquatic life due to the thermal shock. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature decreases oxygensupply and affects ecosystem composition. Urban runoff–stormwater discharged to surface waters from roads and parking lots–can also be a source of elevated water temperatures.
When a power plant first opens or shuts down for repair or other causes, fish and other organisms adapted to particular temperature range can be killed by the abrupt change in water temperature known as "thermal shock."