Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: Acid Rain Effects on Ecosystems
Acid rain is one of the most visible and damaging consequences of air pollution. It occurs when pollutants in the atmosphere mix with water droplets and fall to Earth as precipitation with higher acidity than normal. This seemingly simple change in rainwater chemistry can have devastating effects on ecosystems, from lakes and rivers to forests and soil systems.
Key Definitions:
Acid rain forms when sulphur dioxide (SO2) and nitrogen oxides (NOx) are released into the air, primarily from:
These gases react with water, oxygen and other chemicals in the atmosphere to form sulphuric and nitric acids. These acids then fall to Earth in rain, snow, fog, or even as dry particles.
Acid rain is not evenly distributed across the globe. It tends to be worst in:
Prevailing winds can carry pollutants hundreds of kilometres, meaning acid rain often falls far from the original pollution source, creating international environmental problems.
Water bodies are particularly vulnerable to acid rain because many lakes and streams don't have natural buffering capabilities to neutralise acids.
When acid rain falls into lakes and rivers, it can dramatically alter their chemistry:
As water becomes more acidic (pH below 6), fish eggs cannot hatch properly. At pH 5.5, many adult fish die. Below pH 5, most fish species disappear entirely. Acid-sensitive species like salmon, trout and minnows are the first to vanish.
Acidification reduces the diversity of aquatic plants. Acid-tolerant species like Sphagnum moss may thrive, while many other species disappear. This disrupts the food web and habitat structure for many organisms.
Acidic water leaches aluminium from soils into lakes and streams. This aluminium is toxic to fish, causing them to produce excess mucus that clogs their gills, leading to suffocation. Other toxic metals like mercury may also become more bioavailable.
Sweden has been particularly affected by acid rain, with thousands of lakes damaged. By the 1980s, approximately 14,000 Swedish lakes had become acidified. The country implemented a massive liming programme, adding limestone to lakes to neutralise acidity. While this helped restore some lakes, it requires ongoing treatment and doesn't address the root cause of the problem.
The acidification led to the loss of sensitive fish species like brown trout and roach in many lakes, disrupting traditional fishing and local ecosystems. Sweden's experience demonstrates how acid rain can be a transboundary issue, as much of the pollution originated in other European countries.
Forests are major victims of acid rain, with damage often visible in the form of thinning tree canopies and dying trees.
Acid rain can damage plants directly by:
Scientists have identified a condition called "forest decline syndrome" or "Waldsterben" (forest death) linked to acid rain. Symptoms include:
Germany's Black Forest (Schwarzwald) became an iconic example of acid rain damage in the 1980s. Nearly half of the forest showed signs of damage, with spruce and fir trees particularly affected. The forest's decline became a powerful symbol that helped drive environmental policy changes in Europe.
Researchers found that acid rain had leached calcium and magnesium from the soil while increasing toxic aluminium levels. This nutrient imbalance weakened trees and made them vulnerable to bark beetle infestations and fungal diseases. After emissions controls were implemented, the forest has shown signs of recovery, though the process is slow.
Soil is the foundation of terrestrial ecosystems and acid rain can fundamentally alter soil chemistry and function.
When acid rain infiltrates soil, it triggers a cascade of chemical changes:
Acid rain leaches essential nutrients like calcium, magnesium and potassium from the soil. These nutrients are washed away before plants can use them, leading to nutrient deficiencies. This is especially problematic in areas with thin soils like mountain regions.
As soil becomes more acidic, aluminium and other potentially toxic metals become more soluble. These metals can damage plant roots and interfere with water uptake. When washed into waterways, they harm aquatic life as well.
Soil microorganisms that decompose organic matter and recycle nutrients are sensitive to pH changes. Acidification can reduce their diversity and activity, slowing decomposition and nutrient cycling processes that are vital for ecosystem health.
Scientists use several methods to track acid rain and its effects:
Addressing acid rain requires both preventing its formation and mitigating its effects on ecosystems.
The 1990 Clean Air Act Amendments in the United States established a cap-and-trade programme for sulphur dioxide emissions. This market-based approach allowed companies to buy and sell emissions permits, creating financial incentives to reduce pollution. The result was dramatic:
This success demonstrates that with proper policies, environmental recovery from acid rain is possible, though full ecosystem restoration takes decades.
Acid rain demonstrates how air pollution can have far-reaching consequences for entire ecosystems. The damage follows a connected path:
Understanding these connections helps us recognise why addressing air pollution is essential for protecting the health of our natural environments.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.