The National Academy of Sciences has a new study out on “freshwater salinization syndrome“. If I understand it correctly, it goes something like this: Air pollution and acid rain leach minerals like calcium out of all the concrete we use for pavement and buildings. All the road salt we apply leaches minerals like calcium out of soil and replaces it with sodium. The result is a lot more minerals like calcium in freshwater, which changes its alkalinity, or in high school science terms, its pH and ability to resist changes in pH.

Salt pollution and human-accelerated weathering are shifting the chemical composition of major ions in fresh water and increasing salinization and alkalinization across North America. We propose a concept, the freshwater salinization syndrome, which links salinization and alkalinization processes. This syndrome manifests as concurrent trends in specific conductance, pH, alkalinity, and base cations. Although individual trends can vary in strength, changes in salinization and alkalinization have affected 37% and 90%, respectively, of the drainage area of the contiguous United States over the past century. Across 232 United States Geological Survey (USGS) monitoring sites, 66% of stream and river sites showed a statistical increase in pH, which often began decades before acid rain regulations. The syndrome is most prominent in the densely populated eastern and midwestern United States, where salinity and alkalinity have increased most rapidly. The syndrome is caused by salt pollution (e.g., road deicers, irrigation runoff, sewage, potash), accelerated weathering and soil cation exchange, mining and resource extraction, and the presence of easily weathered minerals used in agriculture (lime) and urbanization (concrete). Increasing salts with strong bases and carbonates elevate acid neutralizing capacity and pH, and increasing sodium from salt pollution eventually displaces base cations on soil exchange sites, which further increases pH and alkalinization. Symptoms of the syndrome can include: infrastructure corrosion, contaminant mobilization, and variations in coastal ocean acidification caused by increasingly alkaline river inputs. Unless regulated and managed, the freshwater salinization syndrome can have significant impacts on ecosystem services such as safe drinking water, contaminant retention, and biodiversity.

It’s a little ironic that this is happening to fresh water at the same time we are worried about ocean acidification. There is also a larger context to me though – even if our waters meet numerical standards we set for water quality, they just don’t have the same chemistry, biology, or links to the land that they used to. This would still happen even if we were able to eliminate all pollution that is directly toxic to aquatic life.