Freshwater acidification might turn out to be a trivial problem but we don’t know how much danger aquatic life is in unless we can track down more data

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IN 2003, a scary phrase made its debut in the scientific literature. In a paper in Nature, a couple of scientists at the Lawrence Livermore National Laboratory in California cautioned that, over the coming centuries, carbon dioxide released from burning fossil fuels would dissolve in the ocean and make it significantly less alkaline. They called this phenomenon “ocean acidification” and warned that it might have consequences for marine life – while admitting that there was a “paucity of relevant observations”.

Fast forward 15 years and we are now sure that ocean acidification will have major impacts on marine biology, especially corals. We also have another new scary phenomenon to contend with: freshwater acidification (see “Lakes of Acid”). This is the ocean problem applied to rivers and lakes. It, too, may have serious effects on aquatic life, though at this early stage there is another paucity of relevant data.

Indeed, “paucity” is a word that cautious scientists and climate change deniers alike may use about the evidence for freshwater acidification. Right now, the evidence that it is happening at all is limited to just four reservoirs in the Ruhr region of Germany. Scientists in other places, notably the UK’s Lake District, haven’t seen any sign of it. This could be confirmation of a long-held consensus that, for a variety of complex reasons, fresh water isn’t as susceptible as seawater to acidification by CO 2 .


If so, that would be good news. Planet Earth has enough environmental problems as it is. And while a new one could provide fresh impetus to campaigns, the acidification of a few reservoirs in Germany is not going to make anyone change their ways.

“The reservoir research is a wake-up call that something might be wrong, perhaps badly so”

But ignoring freshwater acidification on the grounds of limited data would be dangerously complacent. The German researchers were fortunate to have access to continuous records going back to 1981, allowing them to discern long-term trends. It will only be possible to dismiss what they found as an outlier after examining similar data sets from elsewhere. Do these even exist? We don’t know. Limnologists need to find out. Failing that, they need new and clever ways of measuring historical pH levels in fresh water, perhaps from lake bed sediments.

There is another caveat that must be considered. The acidity of the reservoirs is nowhere near the levels that were seen in many lakes during the acid rain crisis of the 1970s and 80s. We know from that episode what constitutes dangerous acidification. At current rates, it will take many decades for dissolved CO 2 to push fresh water that far. So maybe the problem is trivial.

Nonetheless, the research is a wake-up call that something might be wrong, perhaps badly so. The process of scientific discovery has to start somewhere and usually starts small.

And even if freshwater acidification turns out to be a minor or localised issue, that doesn’t detract from the urgent need to tackle its cause. It is beyond doubt that CO 2 pollution is driving climate change and ocean acidification. Either of these alone is reason to act.

This article appeared in print under the headline “Yet another CO2 problem?”