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Acidification of inland waters

This article belongs to Ambio’s 50th Anniversary Collection. Theme: Acidification

Acidification was one of the most recognized environmental concerns of the late twentieth century. The industrial revolution and its rapid increase in the combustion of coal and oil resulted in emissions to the atmosphere of oxides of sulfur and nitrogen, followed by deposition on land and waters. The effects are manifold. Soils get acidified and forest growth is impaired, metals are mobilized as the groundwater gets acidic; this results in increased metal concentrations in drinking water wells, corrosion is accelerated, and our cultural heritage is degraded as statues and other constructions from stones with calcium carbonate dissolve.

Being the recipients of water that runs off the surrounding landscape, inland waters—streams, rivers, and lakes—are particularly vulnerable. Lakes integrate processes in the surrounding watershed. Hence, many of the natural and anthropogenic conditions of lakes are the function of processes at much larger scales, including, e.g., natural flow with gravity of organic and inorganic matter, and agricultural fertilizers and chemicals, and they also respond to altered export of matter from their watersheds due to changing land use, temperature, and precipitation. Accordingly, lakes are not only valuable ecosystems and natural resources per se, but also sentinels of environmental change beyond their own boundaries (Williamson et al. 2008). This applies also to acidification—acids are deposited on land and water, transported downstream along with other chemical species that are mobilized from soils due to increased acidity, with subsequent consequences for aquatic life. Scandinavia and northeastern United States have in common that regional industrial areas, up to more than 1000 km away, affect the chemistry of local precipitation. Moreover, the geological conditions of these areas result in poorly buffered soils and waters, which make them vulnerable to acidification. Hence, in hindsight, it is not surprising that it is in the lakes and streams of these regions that acidification was first recognized.

Here, we highlight several influential papers published in Ambio that were important for the early discovery and understanding of acidification of inland waters (Almer et al. 1974; Schofield 1976; Henriksen et al. 1988). The authors of two of the pioneering Ambio articles give their personal views and behind the paper stories (Almer and Dickson 2021; Brakke 2021), and two other scientists who were highly influential in the recognition of acidification present their reflections on those papers and their importance (Likens 2021; Rosseland 2021). Together, these documents provide an exciting window into the history of the science of acidification of lakes and rivers.

There is currently a broad consensus on the causes and consequences of anthropogenic acidification. However, similar to other environmental issues, not the least global warming, to reach acceptance and political action in line with the scientific evidence is not trivial. Industry and governments were long reluctant to accept the facts on acidification. In their book Merchants of Doubt, Oreskes and Conway (2010) highlight acidification along with several other cases of politicized denial of scientific evidence, including health effects of tobacco, global warming, and ozone depletion; the two latter also subject to highly influential papers that will be recognized in forthcoming issues of the Ambio 50 year celebrations. The success in making governments and industry to act against acidification depended on solid scientific evidence, but also on scientists reaching out to policy makers and the public. This was very much the case during the era of acidification research highlighted here. Both authors of the original papers and those who provide the peer reflections below have acted outside of the ivory tower. An exceptional case is by Gene Likens, who played a central role in advocating the importance of combatting acidification during the Reagan administration in the USA in the 1980s (Oreskes and Conway 2010).

Today, more than half a century after the discovery of widespread acidification by fossil fuel combustion, there has been substantial progress in the reduction of emissions of acidifying sulfur and nitrogen oxides, and gradual recovery of the chemistry and biology of inland waters. Liming to restore pH and acid neutralizing capacity has been successful in protecting populations of fish and other organisms. The early reports in Ambio were important steps towards these successes. Importantly, it should be noted that the successful combat of acidification is not global. The emissions of sulfur and nitrogen from fossil fuel combustion are falling in Europe and North America, but the trend is opposite in the highly populated regions of Asia (Aas et al. 2019). The imminent drastic decrease in the use of fossil fuel that is crucial to address the momentous issue of global warming will also benefit recovery from acidification worldwide.



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Correspondence to Lars J. Tranvik.

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Tranvik, L.J. Acidification of inland waters. Ambio 50, 261–265 (2021).

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