How Does Acid Rain Affect Lakes?

Acid rain is a product of the burning of fossil fuels and poses a threat to the ecosystems of streams and lakes. In particular, when certain levels of acidity are reached, fish and other aquatic life will die. Since all flora and fauna in a given ecosystem are interdependent, the effects of acidic water are far-reaching. Acid rain is worse in areas with dense populations and heavy industry, particularly the eastern United States.

Acid Rain

Atmospheric pollutants, particularly nitrogen oxide and sulfur dioxide from the burning of fossil fuels, cause precipitation to become acidic. These gases mix with water vapor and oxygen in the atmosphere to form nitric and sulfuric acids, which cause acid rain. This acidic precipitation lowers the pH level of water in streams and lakes, creating adverse effects. Acidic waters will also more readily absorb aluminum leeched from soil runoff, and the combination of aluminum and acidic water is especially harmful to many aquatic species.

Lakes and Acidity

Water pH is the amount of free hydrogen ions in a given sample, and the scale ranges from 0 to 14, with numbers below 7 being acidic. Each level down the scale represents a tenfold increase in hydrogen ions, so a pH of 5 has ten times more ions than a pH of 6. Normally, lakes will be neutral, pH levels between 6 and 8, but lakes with pH below 5 are considered acidic. In addition to acid rain, acidic rainfall leeching through soils that lack acid-buffering capability will eventually wind up in streams and lakes. Normally, lake water contains bicarbonates and other compounds that have the ability to buffer their pH levels, but acid rain in particular disrupts this ability.

Acid Rain and Aquatic Life

When an influx of acid rain reaches a certain threshold in a lake, it overcomes the lake’s ability to buffer acids. The lower pH levels in the water have a direct and primary effect on many of the various creatures that live within the lake ecosystem. Many species of fish, shellfish and other lake species such as snails and salamanders are adversely affected by acidic water. For example, a pH of 5 will kill fish eggs, and lower levels will kill adult fish. Not only does the low pH affect aquatic life, but it also affects the lives of terrestrial species and birds that feed on aquatic life.

Most Sensitive Regions

Given the adverse effects of acid rain on lake ecosystems, it is important to understand which areas are most at risk. Lakes in the northeast United States, Appalachian highlands, upper Midwest and the mountains of western North America are most prone to having pH levels below 5. In 2006, the National Atmospheric Deposition Program noted that acidic precipitation lower than pH 5 falls downwind of heavy industrial areas, and it is worst in the Ohio River Valley region of the upper Midwest. The pH of precipitation in this region can be at dangerously low levels below 4.3. The entire region east of the Mississippi River in the United States is especially vulnerable.