State of the Planet

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You Asked About River Salinity and Water Pollution

Got a burning question about climate change? “You Asked” is a series where Earth Institute experts tackle reader questions on science and sustainability. To submit a question, drop a comment below, message us on Instagram, or email us here.

Paulina Concha Larrauri is a staff associate at the Columbia Water Center.

Today’s questions come from our Earth Month Q&A on Instagram. Both answers are by Paulina Concha Larrauri, staff associate at the Columbia Water Center. She has a masters degree in environmental engineering.

How does climate variability affect the salinity of rivers like the Mississippi?

The process of salinization, or the buildup of salts, varies in each place and it can be naturally occurring or influenced by human activities. Natural salinization can occur in arid places that have low aquifer recharge rates, or in basins that have naturally saline rocks that erode over time, for example.

As for human influence, increases in soil salinity due to agriculture play a significant role in increasing salinity in rivers and aquifers, as salt gets mobilized to the water bodies.

More than climate variability, salinization in aquifers mostly occurs when there is excessive pumping. For example, in coastal areas, decreasing groundwater levels can lead to salt water intrusion from oceans; agricultural groundwater use for irrigation can also increase salinity as salt gets concentrated.

Climate variability in this case plays a role in the demand for water; in the event of a drought there may be more water being pumped for irrigation or water supply. As we have seen recently, extreme events like droughts are becoming much more frequent and long-lasting due to climate change. Other causes that can impact salinity in rivers—both of which are subject to influence from climate variability—are sea level rise and dams.

How are we going to clean up all of the air and water pollution? The problem seems so overwhelming.

This is a very general question, and one that scientists and policy makers continue to work on. My expertise lies in the water pollution area, so I’ll focus on that.

I think one important part is to first attack the sources of pollution by enforcing treatment and controlling discharges through regulations and enforcement. For example, the way we produce our food has a great impact in water quality (all the fertilizers, pesticides, and animal waste that enter the water systems), so we need to find solutions to reduce these discharges.

We also need to measure and collect data about water quality parameters, because without that, we can’t understand the problem and the scale of the mitigation efforts that are needed. It is a complex question and we need to take action on many fronts.


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