Learn why lakes are browning and what this means for lake health.
Photo by Jonathan Stetler
Lakes around the world are turning brown. This is both good and bad. Browning is a sign of recovery from acid rain, but it’s also a symptom of climate change and development. Read on to discover why lakes are browning, consequences for lake health, and how you can help monitor water quality and contribute to global datasets. You can also download this information as a brochure.
Plant matter and pollutants from the landscape flow into lakes. Since lakes are often the lowest point in the watershed, they are reliable indicators of watershed health. Landscapes that are heavily forested deliver high amounts of dissolved organic matter (DOM) from decaying leaf litter and soil. Agricultural runoff contributes excess nutrients which fuel algal growth. As landscapes change, so does water clarity and lake chemistry. Monitoring lakes can provide early warning of broader changes across the landscape.
Lakes turn brown due to an increase in dissolved organic matter. DOM is transported from the watershed and soil into lakes. As the land recovers from acidification, more organic material is released in the soil and flows into lakes. Browning can also occur due to climate change; increased precipitation and storms can increase DOM runoff into lakes.
Browner lakes are less clear, which impacts many lake features. Light penetrates shallower in brown waters, so surface waters heat up faster in browner lakes. Reduced water clarity can depress oxygen levels and algal productivity, with implications for aquatic organisms and the lake food web.
Browning is both good and bad. It is a sign of recovery from acid rain, but it’s also a result of our activities, like development and climate change. Perceptions of browning are also mixed. Life returning to lakes and watersheds is good, but many people prefer to recreate in clear lakes. And lakes that are used for drinking water may be at risk due to changes in lake processes caused by browning. Understanding these effects can inform smart lake management.
Decades of industrial pollution and acid rain caused water bodies in the northeastern US to become strongly acidic. Through national policies like the 1990 Clean Air Act Amendments, industrial polluters were forced to clean up their act. Due to reduced air pollution, both rain and lakes became less acidic. As a result, lake pH increased.
Acid rain caused many lakes to become clear. This is because acidic conditions kill phytoplankton, which float in the water column and reduce clarity. As lakes and the landscape recover and become less acidic, more organisms can survive and more dissolved plant matter flows through the watershed into lakes. Organic matter is brown, which is why lake browning is associated with acid rain recovery.
Water clarity is an important indicator of lake health. The most common way to measure water clarity is with a Secchi disk (pictured below/above), a tool that has been used for over a century. Watch this video to learn how you can create your own Secchi disk, contribute data to lake research, and help protect lakes for future generations.
Dr. Jonathan Stetler email@example.com // firstname.lastname@example.org
Jonathan Stetler, now a lecturer at RPI, produced this brochure while working as an NSF intern with Cary's Chris Solomon and the Cary Communications Office.
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Funding for this work was provided by the National Science Foundation (grant #1754265).