Cinderella in Czechia

Fly ash is formed during combustion in thermoelectric power plants, and it used to be captured in liquid and sedimented in the sedimentation lagoons designed for this purpose. Nowadays, it is possible to capture dry fly ash, which can be used in the construction industry. Consequently, sedimentation lagoons lost their purpose and are being recultivated.

That seems right, but the biodiversity in the sedimentation lagoons has to be studied first to make a correct conclusion. It was discovered that some threatened species of insects found secondary refuge in these lagoons. This very unusual artificially created environment is inhabited by many endangered species whose natural environment, such as sandbanks or fens, has disappeared from the Czech Republic, or was permanently polluted by chemicals and nutrients from the agriculture and fishing industry. The question of whether the fly ash lagoons should be protected arises.

To deepen our understanding of the biodiversity of fly ash deposits, the researchers studied the aquatic ecosystems of sedimentation lagoons. For the first time, they studied the freshwater biodiversity of fish, invertebrates, plants, and phytoplankton (algae, cyanobacteria, and other primary producers) in fly ash lagoons. To assess their conservation potential, they compared their biodiversity with abandoned post-mining ponds which are well known for their rich biodiversity of freshwater organisms, including threatened species.

Fly ash ponds and flooded mining sites - these sites are surprisingly similar in their high biodiversity. Source: original article

And what did they find out? These two types of habitats didn’t differ significantly either in their biodiversity or in their conservation potential. Fly ash lagoons were inhabited by species typical for salt marshes, wetlands, and oligotrophic waters in general (with very low levels of nutrients). Unfortunately, most of these habitats vanished from our landscape due to agricultural pollution. Fifteen threatened species occurred in fly ash lagoons, some of which were even absent in the post-mining ponds. These high abundances suggest that their local populations are viable.

However, how can so many organisms live in fly ash lagoons known for high concentrations of some heavy metals? Scientists explain that heavy metal concentrations are far below the risk limits and these metals are immobile and biologically unavailable. Furthermore, various organisms, such as some invertebrate species, have adaptations to cope with high concentrations of heavy metals. Their concentration can therefore divide organisms into those who can tolerate it and therefore live in the lagoon, and those who cannot.

A common inhabitant of sedimentation basins was, for example, this vulnerable species of caddisfly (Agrypnia pagetana) source: Wikimedia commons

Fly ash lagoons and post-mining ponds differed in their species composition. Heavy metals might affect this distribution, but their higher concentration doesn’t mean that no such habitat can’t be inhabited. Threatened species can be found in such habitats as well.  And what does this suggest for future nature protection? Scientists previously described how terrestrial fly ash deposits should be restored, considering the protection of endangered species and the possible risks to the surrounding environment. Techniques used in the restoration of sedimentation lagoons are similar to the ones used in the restoration of terrestrial deposits of fly ash. Besides other things, wind erosion and leaks of contaminated water into the surroundings must be prevented by ensuring a closed water system. However, ecological restoration is most effective when it’s left to natural processes.

Don’t be mistaken. Just as the hated Cinderella eventually became a princess, initially condemned fly ash from thermoelectric power plants is an important part of our ecosystems at last.

Eliška Leštinová

Kolar V., Chmelová E., Bílková M., Borovec J., Carreira B.M., Černý M., Ditrich T., Horká P., Hrivniak L., Hrubý F., Jan J., Landeira-Dabarca A., Lepšová-Skácelová O., Musilová Z., Otáhalová Š., Poláková M., Polášková V., Sacherová V., Špaček J., Sroka P., Vebrová L., Boukal D.S., Tropek R. (2023) Muddying the unexplored post-industrial waters: Biodiversity and conservation potential of freshwater habitats in fly ash sedimentation lagoons. Science of the Total Environment 900: 165803. https://doi.org/10.1016/j.scitotenv.2023.165803