Glossary of Environmental Science - D

D

• DDT - a chlorinated hydrocarbon used as a pesticide that is a persistent organic pollutant.
• debt-for-Nature Swap - a financial transaction in which a portion of a developing nation's foreign debt is forgiven in exchange for local investments in conservation measures.
• decomposers – consumers, mostly microbial, that change dead organic matter into minerals and heat.
• deforestation - the conversion of forested areas to non-forest land for agriculture, urban use, development, or wasteland.
• dematerialisation – decreasing the consumption of materials and resources while maintaining quality of life.
• desalination producing potable or recyclable water by removing salts from salty or brackish water. This is done by three methods: distillation/freezing; reverse osmosis using membranes and electrodialysis; ion exchange. At present, all these methods are energy intensive.
• desert – an area that receives an average annual precipitation of less than 250 mm (9.8 in) or an area in which more water is lost than falls as precipitation.
• desertification - the degradation of land in arid, semi arid and dry sub-humid areas resulting from various climatic variations, but primarily from human activities.
• detritivore (detritus feeder) - animals and plants that consume detritus (decomposing organic material), and in doing so contribute to decomposition and the recycling of nutrients.
• detritus - non-living particulate organic material (as opposed to dissolved organic material).
• developing countries – development of a country is measured using a mix of economic factors (income per capita, GDP, degree of modern infrastructure (both physical and institutional), degree of industrialisation, proportion of economy devoted to agriculture and natural resource extraction) and social factors (life expectancy, the rate of literacy, poverty). The UN-produced Human Development Index (HDI) is a compound indicator of the above statistics. There is a strong correlation between low income and high population growth, both within and between countries. In developing countries, there is low per capita income, widespread poverty, and low capital formation. In developed countries there is continuous economic growth and a relatively high standard of living. The term is value-laden and prescriptive, as it implies a natural transition from "undeveloped" to "developed" when such transitions can instead be imposed. Although poverty and physical deprivation are clearly undesirable, it does not follow that it is therefore desirable for "undeveloped" economies to move towards affluent Western-style "developed" free market economies. The terms "industrialised" and "non-industrialised" are no different in this assumption.
• dfE – design for the environment; dfE considers 'cradle to grave' costs and benefits associated with material acquisition, manufacture, use, and disposal.
• dfM – design for manufacturing; designing products in such a way that they are easy to manufacture.
• dfS – design for sustainability; an integrated design approach aiming to achieve both environmental quality and economic efficiency through the redesign of industrial systems.
• dfX – design for assembly/disassembly, re-use. recycle.
• dieback – (arboriculture) a condition in trees or woody plants in which peripheral parts are killed, either by parasites or due to conditions such as acid rain.
• dietary energy supply – food available for human consumption, usually expressed in kilocalories per person per day.
• dioxin - any one of a number of chemical compounds that are persistent organic pollutants and are carcinogenic.
• distributed water – (water management) purchased water supplied to a user; this is usually through a reticulated mains system (but also through pipes and open channels, irrigation systems supplied to farms).
• diversion rate – (waste disposal) the proportion of a potentially recyclable material that has been diverted out of the waste disposal stream and therefore not directed to landfill.
• divertible resource – (water management) the proportion of water runoff and recharge that can be accessed for human use.
• downcycling – (waste management) recycling in which the quality of an item is diminished with each recycling.
• downstream – those processes occurring after a particular activity e.g. the transport of a manufactured product from a factory to the wholesale or retail outlet cf. upstream.
• drainage – (water management) that part of irrigation or rainfall that runs off an area or is lost to deep percolation.
• drawdown – (water management) drop in water level, generally applied to wells or bores.
• dredging - (water management) the repositioning of soil from an aquatic environment, using specialized equipment, in order to initiate infrastructural and/or ecological improvements.
• drift net - a type of fishing net used in oceans, coastal seas and freshwater lakes.
• drinking water – (potable water) – water fit for human consumption in accordance with World Health Organisation guidelines.
• drip irrigation – (water management) a drip hose placed near the plant roots so minimising deep percolation and evaporation.
• driver – (ecology) any natural or human-induced factor that directly or indirectly causes a change in an ecosystem. A direct driver is one that unequivocally influences ecosystem processes and that can be measured.
• drop-off centre – (waste management) a location where discarded materials can be left for recycling.
• drought – an acute water shortage relative to availability, supply and demand in a particular region. An extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation.
• dryland salinity - (water management) accumulation of salts in soils, soil water and ground water; may be natural or induced by land clearing