Acid rain Acid rain Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulphur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Some governments have made efforts since the 1970s to reduce the release of sulphur dioxide and nitrogen oxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes, and sulphur dioxide
Lichens and nitrogen cycling and decrease the growth of the lichen. If the lichen cannot increase its photobiont growth, high nitrogen uptake may result in a higher concentration than it physiologically requires which will negatively affect the lichen and it's host plant as the other nutrients are too limiting. Lichen’s response to nutrient enrichment is both species-specific and dependent its environmental factors e.g. nutrient concentration, light availability and water supply. Lichen is nitrogen sensitive and change in nitrogen availability can affect its health greatly. Two main nitrogen stress factors for lichens are nitrogen deficiency and high nitrogen deposition. Both types of nitrogen stress result