Effects on Ecosystem - Air pollutants
The effects of pollutants on ecosystem become visible after a long period of exposure. In highly industrialised countries the vegetation has been exposed to pollutants for several years. Consequently their devastating effects on terrestrial and aquatic ecosystem has long been observed. These are mainly due to wet (acids like sulphuric and nitric acid dissolved in water) or dry (gases affecting directly vegetation and soil) deposition of acid in combination with other air pollutants such as 03, hydrogen flouride (HF) and particulates. Acid rain is defined as the precipitation of water in the form of rain or snow that possesses a pH between 3.7 and 3.0.
Some of the trees are covered with lichens and the fruiting bodies of decomposers. The condition of trees is quite frightening. The forest floor is covered with dry brittle, pealing branches of uprooted trees. Trees such as spruce, pine, birch, ash, alder, maple and oak are among the dead. In 1985, the cost of forest death in Germany was estimated at $1 billion. A long-term reduction in radial growth of many kinds of trees is observed in United States. The most severely affected forests were located on the windward slope of mountains enshrouded in cloud or fog and had been under stress for some time. The damage caused are due to ozone and other photochemical oxidants, sulphur dioxide, deposition of nitrogen compounds, acid precipitation, heavy metal deposition and organic chemicals. In the previous section we have already explained how air pollutants affect plants directly or indirectly by changing nutrient status of the soil. However, our understanding of the acid rain phenomena and its ecological effect is fragmentary. Acid rain affects yield, resistance and species diversity of terrestrial ecosystem.