A September 10 Baltimore Sun article discussed a recent series of studies that were published in a special issue of the journal Biochemistry which examined how urban development affects water and stream quality over time.  Several key findings of the studies related to increasing salt and calcium levels in nearby waterways.  The studies looked at a diverse cross-section of United States cities, including Baltimore, Boston, and San Juan.  From the article:

If current trends continue, Marylanders may not have to go “down-y oshun” in future to dip their toes in salt water. Thanks to liberal de-icing of our roads in winter and chronic sewage leaks, salinity levels are rising in Baltimore area streams  – with at least one already a third as tangy as Ocean City surf. …

Urbanization increases the saltiness of streams flowing through it. In addition to runoff of road salt, salinity is raised by cracked sewage pipes leaking chloride-laden waste – from humans’ salt-heavy diet.

Urban streams also have elevated calcium levels, a byproduct of rainfall and weather dissolving concrete frequently made with limestone.  Researchers dubbed the proliferation of such concrete a new geologic formation – “urban karst.”