Study of algae shows lake’s recovery from man-made acid damage

The results are positive, but scientists also warn climate change may slow the lakes’ recovery

Lakes at a US national park known for its beauty are recovering from man-made acidification thanks to environmental regulations, new research shows.

Research from the 1990s showed that human-caused atmospheric pollution in the 20th century caused the acidification of lakes across eastern North America, starting in the 1940s. Acidification of lakes causes the decrease of dissolved organic carbon in lakes, which impacts lake ecology and makes the water appear clearer.

Now researchers from the University of Maine and the National Park Service have discovered the northeastern United States has received significantly less atmospheric acid depositions since the Clean Air Act Amendments were federally enacted in 1990.

But scientists also warn climate change may slow the lakes’ recovery.

In an article published in the Journal of Paleolimnology, scientists reconstructed historical pigment records of algae and diatoms — a particular type of algae with a silica shell, which is usually negatively impacted by acidification — from two lakes in Acadia National Park, Jordan Pond and Seal Cove Pond, in Maine.

Despite being close geographically, the two lakes are very different. Jordan Pond is considered a ‘clear-water’ or oligotrophic lake, meaning its waters are relatively low in plant nutrients with abundant oxygen at its depths. Seal Cove Pond is a ‘brown-water’ or mesotrophic lake with a moderate amount of nutrients.

Rachel Fowler, the principal investigator of the project, said: “Recovery from acidification is partially dependent on water clarity, which is impacted by climate change.

“Across North America and northern and central Europe, there is an ongoing trend toward ‘brownification’ of lakes.

“Several studies have described ecological changes in clear- vs. brown-water lakes in response to reductions in acid deposition and browning, and our paleolimnological study provides long-term context for interpreting those changes.”

The researchers took sediment cores from the deepest parts of both ponds and analysed the concentrations of different types of algae and the way they varied over time.

The results showed the algae in the lakes responded differently over time to acidification. Despite their differences, both ecosystems are recovering since environmental regulations have reduced the amount of atmospheric sulphur in the area, with many types of algae returning where they had once been pushed out by acidification.

“An exciting takeaway is that this study illustrates the effectiveness of the Clean Air Act Amendments,” Ms Fowler said.

“We can see signs of recovery from acid deposition using the remains of algae preserved in the sediments of Jordan Pond and Seal Cove Pond.”

However, the results also suggested that clear-water lakes like Jordan Pond are more sensitive to climate warming than brown-water lakes like Seal Cove Pond. Recovery of the algal ecosystem has been slower for Jordan Pond, and may continue to be hampered by the effects of climate change.