How does acid rain affect biodiversity in freshwater ecosystems?

Acid rain significantly degrades biodiversity in freshwater ecosystems by altering water chemistry and mobilizing toxic substances. When acidic precipitation enters lakes and streams—particularly those with low buffering capacity—it lowers the pH, which can be lethal to many aquatic organisms.12

The primary impacts on biodiversity include:

• Direct Toxicity: Increased acidity and the mobilization of aluminum from soils can damage fish gills, impairing respiration and leading to population declines. Research in the Adirondack Mountains has demonstrated a direct correlation between lower pH levels and a reduction in the number of fish species present.12
• Disruption of Food Webs: Acidification negatively affects various organisms, including crayfish, clams, and plankton. As these populations decline, the effects ripple throughout the food chain, reducing overall plant and animal diversity.2
• Bioaccumulation of Toxins: High acidity can accelerate the conversion of mercury into methyl mercury, a potent neurological toxin. This substance bioaccumulates as it moves up the food chain, reaching levels in top predators that can be harmful to both wildlife and humans.2
• Episodic Stress: Rapid pulses of acidic meltwater during spring snowmelt can be particularly deadly, causing sudden, acute stress to acid-sensitive species.2