Overview of Shortwave — "The world’s freshwater is getting saltier. Why?"
This NPR Shortwave episode (hosted by Emily Kwong, reporting with Burley McCoy) explains a growing, global problem: freshwater in lakes, rivers and groundwater is becoming saltier. The show uses Madison, Wisconsin as a case study to illustrate causes, ecological and human impacts, and practical steps communities are taking to slow the trend.
Key points and takeaways
- Freshwater salinity is rising worldwide; researchers only started tracking it seriously in recent decades.
- Major causes: road salt (sodium chloride), runoff from agriculture and mining, seawater intrusion from overpumping aquifers, and concentration effects from climate-driven evaporation.
- Salt is persistent in the environment; decades of application (1970s–1980s onward) continue to affect water today.
- Higher salinity is ecological pollution — it can kill or stress aquatic plants and animals and favor invasive species.
- Treating salty drinking water (distillation or reverse osmosis) is possible but expensive and energy‑intensive.
- Local, low‑cost interventions (calibrating spreaders, pre-wetting roads with brine, cleaning excess salt) can substantially reduce salt use — Madison reduced salt use by about 40%.
Causes of freshwater salinization
- Road salt: In cold regions, millions of tons of salt are applied for deicing; much of it runs off into nearby water bodies.
- Runoff from fertilizer and mining: These activities introduce salts and chloride to surface and groundwater.
- Seawater intrusion: Excessive groundwater pumping near coasts can allow ocean water to move into aquifers.
- Climate change: Increased evaporation concentrates existing salts in remaining freshwater.
Case study — Madison, Wisconsin
- Madison sits between two large lakes and has a strong cultural tie to its lakes; thus salt impacts are visible and meaningful locally.
- Before road salt usage, local lakes had virtually no salt. Lake Wingra now measures over 100 mg/L chloride — still “freshwater” by some definitions but near levels that affect taste and aquatic life.
- Some municipal wells have rising chloride (e.g., one well passed 120 mg/L in 2014), with similar trends observed in wells across multiple U.S. states.
- A 2017 study found about half of hundreds of lakes in the northern U.S. and Canada have increased salinity.
Environmental and human impacts
- Ecology: Elevated chloride is toxic to fish, snails, zooplankton and can shift community composition toward salt-tolerant invasive species. Even sublethal salinity causes physiological stress.
- Human health: Increased sodium in drinking water adds to dietary sodium exposure — a concern for people on low-sodium diets.
- Economic/social: Some households in affected areas buy bottled water; in one reported case, a family sold dairy cows because of saline groundwater impacts on livestock needs.
Solutions and mitigation (what works)
- Reduce salt use — the simplest and most effective long-term solution:
- Calibrate spreaders and train operators so they apply appropriate amounts (pavement temperature matters).
- Pre-wet roads with liquid brine before storms: brine sticks to pavement, reduces bounce-off and total salt needed, and acts faster.
- Clean up excess salt and avoid over-salting sidewalks and driveways.
- Community programs and trainings (e.g., SaltWise) to change practices across municipalities and private contractors.
- Technology/engineering remedies:
- Desalinating drinking water via reverse osmosis or distillation is possible but costly and energy-intensive; not a scalable solution for all affected rural wells.
- Grassroots innovation: Examples include contractors building small brine systems and walk-behind brine applicators for sidewalks — practical, local reductions can add up.
Notable quotes
- “We’re now talking 70 plus years of road salt use… the salinity kind of steadily increasing year after year.” — Hilary Dugan (UW‑Madison)
- “Because chloride is a persistent chemical… we are still getting the legacy of salt use from 1970s and 1980s.” — Kyung Do‑han (postdoc)
- “If I was going to tell people we need to stop using salt, I would be laughed out of the room.” — Allison Madison (SaltWise), illustrating social and operational realities of deicing policy change
Practical actions for listeners
- If you live in a snowy area: avoid over-salting driveways/sidewalks; hire contractors who use calibrated spreaders or brine.
- Test private wells for chloride if you suspect contamination.
- Support local salt‑reduction programs and policies (training, pre‑wetting/brine adoption, measurement and reporting).
- Advocate for municipal monitoring of chloride levels in surface water and groundwater.
Credits / episode context
- NPR Shortwave episode produced by Burley McCoy, Emily Kwong (host), with reporting focused on Madison, WI. The episode is part of Shortwave’s water series and highlights both science and community-driven mitigation efforts.