Effects of Acid Deposition

Acid deposition, acid rain, snow, or fog loaded with sulfuric and nitric acid, doesn't hit every ecosystem the same way. Bedrock chemistry decides the outcome. Limestone is calcium carbonate, an alkaline mineral that reacts with acid and neutralizes it, so a lake sitting in a limestone watershed can absorb years of acid deposition and keep a stable pH. Granite is mostly silica, chemically unreactive, so it offers no buffering. Acid passes straight through granite soils into the water, and pH keeps falling year after year.

The damage goes beyond pH itself. As acid percolates through soil, hydrogen ions displace aluminum that is normally locked into clay minerals, freeing it into soil water and runoff. Dissolved aluminum washes into streams and lakes, where it clogs and damages fish gills, interfering with oxygen uptake and ion balance, often killing fish before the acidity alone would. Over decades, the same acid also strips calcium and magnesium, nutrients trees need, out of forest soil, leaching them away faster than weathering can replace them. A forest exposed to acid deposition for 40 years can show thinning canopies and stunted growth even if the trees never visibly touch acid rain, because the problem is nutrient-poor soil, not direct leaf damage.

This connects back to where the acid came from, sulfur dioxide and nitrogen oxides from smokestacks and tailpipes converting to acids in the atmosphere. Because the effects are a slow buildup in soil and bedrock chemistry, fixing symptoms at the lake doesn't fix the system.