Water and Land Pollution

Water covers 70% of the earth’s surface. Only 3% of this is freshwater, which is indispensable in sustaining plant and animal life. The amount of freshwater is maintained constant by the hydrological cycle. This cycle involves evaporation from oceans and inland waters, transpiration from plants, precipitation, infiltration into the soil, and runoff of surface water into lakes and rivers. The infiltrated water is used for plant growth and recharges groundwater reserves. Although the global supply of available freshwater is sufficient to maintain life, the worldwide distribution of freshwater is not even. In some areas the supply is limited because of climatic conditions or cannot meet the demands of high population density. In other places, although there is no shortage of freshwater, the water supply is contaminated with industrial chemicals and is thus unfit for human use. Moreover, fish and other aquatic species living in chemically contaminated water become unfit for human consumption. Thus, water pollution deprives us and other species of two essential ingredients for survival: water and food. An example of hydrologic changes caused by urbanization is given in Figure 11.1. Conditions before and after urbanization were measured in Ontario, Canada, by the Organization for Economic Cooperation and Development (1). In the urban setting, pervious areas are replaced with impervious ones (such as streets, parking lots, and shopping centers). Groundwater replenishment is greatly reduced and runoff is considerably increased by these changes. Thus, urbanization not only contributes to water pollution; it also increases the possibility of floods. Nitrogen is an important element for sustenance of life. However, in order to be incorporated into living matter it has to be converted into an assimilative form—an oxide or ammonia. Until the beginning of the twentieth century most of the atmospheric nitrogen was converted into assimilative form by soil microorganisms and by lightning. Nitrogen compounds which were not utilized by living matter did not accumulate because the denitrifying bacteria decomposed them to elemental nitrogen which was then released back into the atmosphere. In this way the nitrogen cycle was completed.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.