Acid rain may remove soil nutrients such as calcium and magnesium from soils in high elevation forests and cause damage to needles of Red Spruce. Acid rain may also help weaken natural defenses of some trees, making them more vulnerable to some diseases and pests. Acid rain deposits nitrates that can lead to increases in nitrogen in forests. Nitrogen is an important plant nutrient, but some forest systems may not be able to take use all they receive, leading to nitrogen saturation. In the Eastern United States, there is evidence of nitrogen saturation in some forests.
Nitrates can remove additional calcium and magnesium from the soils.
Continued nitrogen deposition may alter other aspects of the nutrient balance in sensitive forest ecosystems and alter the chemistry of nearby lakes and streams. This may lead to unwanted growth of algae and other nuisance plants. Table I shows estimates of the percentage of nitrogen deposition which comes from the atmosphere. Acid rain can react with aluminum in the soil. Trees can not absorb naturally occurring aluminum, but acid rain may convert it to aluminum sulfate or aluminum nitrate.