Acid rain has wide-ranging environmental and societal impacts, altering ecosystems, damaging infrastructure, and threatening human health. Understanding these consequences is essential for evaluating sustainability and policy responses.

Impacts on Soils

Acid deposition affects soil chemistry in multiple ways, reducing fertility and destabilising nutrient balances.

• Leaching of nutrients: Essential ions such as calcium, magnesium, and potassium are washed out, lowering soil productivity.

• Mobilisation of metals: Toxic metals like aluminium and heavy metals become more soluble in acidic conditions, contaminating groundwater and harming plant roots.

• Reduced microbial activity: Soil bacteria and fungi are sensitive to pH changes, slowing down decomposition and nutrient cycling.

This soil degradation diminishes agricultural yields and weakens natural vegetation growth, especially in sensitive forest ecosystems.

Effects on Vegetation

Plants suffer both direct and indirect damage from acid deposition.

• Leaf injury: Acidic droplets can damage the waxy cuticle of leaves, reducing photosynthesis efficiency.

• Root toxicity: Increased solubility of aluminium inhibits root development and nutrient uptake.

• Forest decline: Long-term exposure leads to weakened trees, particularly at higher altitudes where acid rain concentrations are greater.

Crops may also experience reduced productivity, affecting food security in regions exposed to prolonged acid rain.

Dead conifers alongside regenerating trees illustrate forest decline associated with acid deposition and nutrient depletion. Visual cues include extensive canopy loss and standing dead trunks in a high-elevation setting. The photograph shows impact patterns rather than specific chemical pathways (for example aluminium mobilisation). Source.

Impacts on Freshwater Ecosystems

Aquatic environments are especially vulnerable to acidification.

• pH reduction in lakes and rivers: Many fish species cannot survive below pH 5, leading to biodiversity loss.

This graph shows the pH tolerances of common aquatic organisms and the loss of species as waters acidify. It supports the link between acid deposition, lower pH, and biodiversity decline in lakes and streams. Although aluminium mobilisation is discussed in the text, this figure focuses on pH tolerance rather than metal toxicity. Source.

• Mobilisation of aluminium: Toxic aluminium ions enter waterways, clogging fish gills and causing suffocation.

• Food web disruption: Acidification reduces plankton populations, destabilising food chains and reducing fishery yields.

In Scandinavia and North America, entire lake ecosystems have been devastated, demonstrating the severity of long-term acidification.

Damage to Buildings and Materials

Urban and cultural heritage sites are at risk from acid deposition.

• Stone erosion: Limestone and marble, composed of calcium carbonate, react with sulphuric acid to form gypsum, which crumbles easily.

Acid deposition dissolves calcite in limestone and marble, smoothing edges and removing fine sculptural details. The roughened, pitted surface is typical of carbonate stone exposed to sulphuric and nitric acids. This visual complements the description of gypsum formation and accelerated weathering of monuments. Source.

• Metal corrosion: Acid rain accelerates rusting of steel and iron, weakening bridges and infrastructure.

• Cultural loss: Historic monuments and statues experience accelerated decay, particularly in regions with high industrial emissions.

This damage imposes significant economic costs for restoration and maintenance.

Human Health Impacts

While acid rain itself does not directly burn human skin, it contributes indirectly to health risks.

• Respiratory issues: Acid rain forms from sulphur dioxide (SO₂) and nitrogen oxides (NOx), which also generate fine particulates. Inhalation increases risks of asthma, bronchitis, and lung cancer.

• Drinking water contamination: Mobilised aluminium and heavy metals enter water supplies, increasing neurological and developmental risks in humans.

• Ecosystem services decline: Reduced forest cover and soil fertility limit natural filtration of air and water, indirectly reducing health protections.

Thus, acid deposition worsens air quality, particularly in urban-industrial areas.

Global and Regional Variations

The severity of impacts depends on local geology, industrialisation, and atmospheric conditions.

• Regions with thin soils (e.g., Scandinavia, Canada) are more sensitive, as they lack buffering capacity.

• Industrial regions (e.g., China, India) face higher deposition rates due to coal combustion.

• Transboundary pollution: Winds carry SO₂ and NOx across national borders, making acid rain an international issue.

These variations highlight the interconnected nature of atmospheric pollution and the need for global cooperation.

Societal and Economic Costs

Beyond ecology and health, acid rain imposes significant financial burdens.

• Loss of timber productivity in forestry.

• Decline in fish stocks affecting commercial fishing.

• Increased expenditure on repairing damaged infrastructure and monuments.

• Higher healthcare costs linked to respiratory illnesses.

These costs highlight why acid rain is both an environmental and economic challenge, requiring integrated management strategies.