Bogs self-restore after reduction in power plant emissions

Lütt-Witt Moor in Henstedt-Ulzburg, Germany. Image credit, Jan van der Crabben

A new study in Estonia finds that reductions in power plant emissions can allow degraded bogs to naturally self-restore.

Bogs are types of wetlands typically found in cold climates. The study looked at raised bogs which are fed entirely from precipitation and form  as a result of the continuous accumulation and decay of Sphagnum mosses creating acidic peat. While these ecosystems are very important as carbon sinks and sources of biodiversity, they are also extremely sensitive to atmospheric pollution.

Since the 1950s power plants in northeast Estonia have emitted thousands of tons of calcium-rich fly ash along with other atmospheric pollutants. These emissions have caused substantial pH increases in bogs and the addition of various chemicals leading to a widespread disappearance of Sphagnum mosses in favor of other plants adapted to neutral or alkaline soil conditions.

In recent years developments such as improved dust catching filters and cutbacks in electricity have reduced power plants emissions. Jaanus Paal and fellow researchers sought to understand the bogs’ self-restoration capabilities after these reductions. They published their results in the journal Restoration Ecology.

Niinsaare bog in Estonia. Image credit, Edgar Karofeld.The team looked at current and historic conditions at 13 bogs including two reference sites with varying distances to power plants. They found that sites with lower levels of pollution and greater distances from the power plants had vegetation that more closely resembled natural bogs - i.e they had a greater proportion of bog-specific bryophyte species and lower percentage of vascular plants.

In comparing current conditions to historical records, they found evidence that the situation has improved since the 1990's reductions in emissions. For example, In the mid-1980s only 9 Sphagnum species were recorded in LiivJarve and Niinsaare bogs, but in 2007 the team recorded 14 species. This could be possibly due to the 2-4 time decrease in ash content found in the moss layers. The pH of water also decreased after the 1990s, becoming closer to the more typical values expected for bogs.

The return of the Sphagnum vegetation is part of an overall process of self-restoration. The authors write,

"Once they have reappeared, Sphagnum species themselves cause the lowering of bog water pH toward the level that is characteristic for natural bogs, and facilitate the establishment of other typical bog species."

Though power plants continue to emit high concentrations of pollutants each year, this study suggests that modest reductions are allowing degraded bogs to naturally recover. These results are promising for bogs in other countries of Europe where pollution is causing similar degradation.  Despite the, improvements in Estonia, the researchers warn that,

“..bogs located close to power plants still exceed their threshold of environmental buffering capacity, and that these bogs are subject to an ongoing risk of large-scale changes in ecosystem quality and vegetation structure.” 

--Reviewed by Evyan Borgnis

Paal, J., Vellak, K., Liira, J., & Karofeld, E. (2009). Bog Recovery in Northeastern Estonia after the Reduction of Atmospheric Pollutant Input Restoration Ecology DOI: 10.1111/j.1526-100X.2009.00608.x