Lake Acidification: Causes, Consequences, and Mitigation

What Is Lake Acidification and What Causes It? 

Lake acidification refers to changes in a lake’s water chemistry that lowers its pH levels. A low pH level means more acidic water, which can be harmful to some of the marine life in the ecosystem and beneficial to others, such as some types of algae. 

Even small changes to a lake’s pH level can have a major impact on acidity. According to the National Oceanic and Atmospheric Administration (NOAA), the ocean’s pH levels have only dropped by 0.1 pH in the past 200 years, but this is a “30 percent increase in acidity” due to the measurement’s logarithmic scale. 

Although ocean acidification differs from freshwater acidification, the causes are largely the same: excess CO2 in the atmosphere gets absorbed into the surface water, turning into carbonic acid (H2CO3) and then hydrogen (H+) and bicarbonate (HCO3-) ions. 

Linda Weiss, a biologist at Ruhr University in Germany, found that in some lakes and reservoirs, pH levels had fallen by 0.3, a faster rate than ocean acidification. Similar rates have been detected in Ontario, Canada, and other parts of North America. 

How Does Carbon Dioxide in the Atmosphere Contribute to Lake Acidification? 

Lake acidification occurs when acidic compounds such as sulfur oxides (SOx), nitrogen oxides (NOx), and carbonic acid get into freshwater systems. This transfer can happen in one of several different ways, including acid deposition, or acid rain, which causes these compounds to move from the atmosphere into surface water systems. 

Although acid rain isn’t the major threat that it once was, not all lake acidification is due to precipitation. Higher concentrations of carbon dioxide in the atmosphere mean that more CO2 is absorbed into the surface of the water, even without rain. 

Other causes of lake acidification include the weathering of rocks, and soil runoff and leaching from areas with high carbon dioxide concentrations. 

What Are the Consequences of Lake Acidification on Aquatic Ecosystems? 

Freshwater systems have more variable pH levels than seawater does, and freshwater biota, or plant and animal species, can tolerate a greater degree of pH variability. In fact, some lakes release more carbon dioxide into the atmosphere than they absorb, so the impact of increased acidity on a lake’s ecology isn’t always clear-cut. 

In general, the acidification of lakes affects the ecosystem in a few different ways. The first is that some forms of life may be unable to survive in a lake with high acidity levels. For example, crustaceans rely on calcium carbonate to produce shells, and a low pH level means that less carbonate is available for them.  

In contrast, other forms of life may thrive in a more acidic environment. NOAA explains that acidification is linked to a rise in algae blooms in the Great Lakes. This can lead to a reduction in sunlight reaching other plants and animals below the surface, as well as an increase in algae-related toxins that can kill fish and animals that eat them. 

How Does Lake Acidification Affect Fish Populations and Overall Biodiversity? 

Lake acidification reduces biodiversity by impacting some species directly, and others indirectly by disrupting the food chain and other natural cycles. 

As far back as 1976, Canadian researchers found that the acidification of lakes resulted in reduced fish populations as female fish failed to spawn and “maintain normal serum calcium levels.” In 1993, researchers in the USA found that up to 19% of lakes they surveyed had “lost one or more fish populations as a result of acidification,” and that individual trout and minnow populations had declined by 11% and 19%. 

Some fish species are especially sensitive to low pH levels, increasing the mortality rates of eggs and adult fish alike, while others face reduced food sources as algae blooms, phytoplankton, zooplankton, and amphibians compete for resources. 

Acidic lakes may also have high levels of other harmful substances, such as heavy metals, and lower levels of nutrients like phosphorus and nitrogen. According to the New Hampshire Department of Environmental Services, “an acid-stressed lake is typically very clear, with filamentous algae along the bottom.” 

What Strategies Are Available to Mitigate the Impacts of Lake Acidification? 

There are several ways to mitigate the effects of lake acidification. The first is to reduce fossil fuel emissions and other types of atmospheric pollution. The response to acid rain is an environmental success story, and taking steps to reduce the amount of CO2 and other pollutants in the atmosphere would mitigate lake acidification. 

For lakes that are already experiencing the negative effects of acidification, there are several mitigation options. One solution is a practice called “liming.” This refers to the addition of calcium carbonate (CaCO3) in the form of limestone into the water system. Limestone counteracts the acidity and increases the pH level of the lake, potentially allowing fish populations to bounce back and the lake’s ecosystem to thrive. 

Liming isn’t a permanent solution to lake acidification, and it may not be enough to bring the lake back into balance. Adding nutrients like phosphorus and nitrogen may help to reestablish the food chain, but it introduces the risk of eutrophication — or having too many nutrients in the water system to sustain a balanced ecosystem. 

How Effective Are Calcium Carbonate Applications in Mitigating Lake Acidification? 

Adding calcium carbonate to lakes and rivers can be an effective method for addressing acidification, but it’s not a surefire solution. According to Environmental Pollution, “liming increased the abundance and richness of acid-sensitive invertebrates and increased overall fish abundance, but benefits were variable and not guaranteed.” 

Scientists need to take the total environment into account when determining which of these mitigation strategies will be most effective for a particular water system. Some parts of North America, like New Hampshire, have lower levels of key elements like calcium and magnesium that serve as a “buffer” against acidity. 

Advances in limnology — a branch of environmental sciences that focuses on inland water systems — may provide more mitigation solutions in the years to come. 

Are There Any Natural Processes that Can Help Counteract Lake Acidification? 

Lake acidification isn’t just a matter of what goes on in the water system. By expanding our scope to consider the entire watershed, we can support natural processes that help keep a lake’s pH levels in balance. In Europe, the U.K. Forestry Commission explains how better forest management can reduce surface water acidification: 

“The primary mechanism is the ability of tree canopies to capture … pollutants from the atmosphere…. Tree planting can [also] influence acidification by the scavenging of acid deposition, base cation uptake, the scavenging and concentration of sea salts, soil drying and the formation of an acid litter layer at the soil surface.” 

In other words, improved land use and forest management practices can go a long way toward improving water quality in nearby rivers and lakes. Another option to counteract lake acidification is to aerate the lake by pumping oxygen into it. This makes the lake less hospitable to anaerobic bacteria and supports healthy fish populations. 

How Does Lake Acidification Affect Drinking Water Quality? 

Many municipal water systems in the U.S. get their drinking water from surface water sources, including lakes and rivers. Although the water treatment and filtration process involves adjusting pH levels, watersheds experiencing acidification may have higher levels of organic carbon, sediments, and other total dissolved solids (TDS). 

Acidic water can leach metals like copper and aluminum out of the soil and contaminate both surface and groundwater resources. And according to Scientific American, climate change has been linked to “increasing concentrations of dissolved rare earth elements in mountain streams,” especially in areas with a history of mining. 

The U.S. Environmental Protection Agency (EPA) sets national drinking water quality standards, but doesn’t yet have regulations in place for some of these elements. 

What Can Individuals Do to Protect Themselves From Lake Acidification? 

Like ocean acidification, the acidification of lakes and other surface water sources is a complex problem, driven by high concentrations of carbon dioxide in the atmosphere. Along with reducing atmospheric pollution and runoff into rivers and streams, we can pursue mitigation strategies like liming and aeration to improve water quality. 

Individuals can reach out to local environmental protection agencies to find out what steps they’re taking to mitigate lake acidification. For example, in the Great Lakes region, local high school students worked with the Thunder Bay National Marine Sanctuary to monitor freshwater acidification. 

When swimming recreationally, pay attention to warnings from your local environmental authorities about harmful algal blooms, and consider installing a water filter at home to remove any potential contaminants from your tap water.