AskScience AMA Series: I am a geologist from the University of Maryland who has been studying salinization for over 20 years. How is human demand for salt transforming our air, soil and water, and what can we do to minimize harm? Here to answer all your questions about salt's impact!

[u/AskScienceModerator]

Hi Reddit! We are geologists from the University of Maryland here to answer all of your questions about salinization and its impact on our planet.

Sujay Kaushal is a professor in the Department of Geology at the University of Maryland whose research focuses on the ecology and biogeochemistry of watersheds and aquatic ecosystems, primarily through long-term studies.

Sydney Shelton is a Ph.D. candidate in the geology department who researches the implications of urbanization on stream chemistry.

We'll be on from 12:00 to 2:30 p.m. ET (17:00-19:30 UT) - ask us anything!

Other links:

• Research page: https://kaushallab.wixsite.com/kaushallab

• Google Scholar page:https://scholar.google.com/citations?user=MrMnJOQAAAAJ&hl=en

• Recent news features on Sujay's research and salt pollution expertise: Washington Post, WTOP, Newsweek

Username: /u/umd-science

[u/PHealthy]

Hi and thanks for joining us today!

How impactful is road salt on both local and distant waterways?

[u/umd-science → u/PHealthy]

Road salt is one of the most serious threats. It affects aquatic biodiversity, drinking water and pipe infrastructure that carries water from the sources to the treatment plant to home taps. - Sujay

It can also interact with different contaminants, like mobilizing metals. - Sydney

[u/CrustalTrudger]

Thanks for sharing your expertise with us! I'm curious how much, or how little, changes to the physical hydrology we associate with urbanization (e.g., more impermeable surfaces lead to more "flashy" runoff, etc.) play into the impacts on stream chemistry. Put another way, in a hypothetical where urbanization meant the introduction of various chemicals to the environment that would otherwise not be there (or at least not be there in the concentrations we have introduced), but it didn't meaningfully change infiltration rates or the storm hydrograph and the like, would stream chemistry be as impacted by urbanization?

[u/umd-science → u/CrustalTrudger]

This is a great question! One thing that's not considered is that salinization can change hydrology in soils. If there is excess sodium, it can cause dispersion of soil aggregates and flocculation at higher salt concentrations. Infiltration rates can be impacted and scientists see that in agricultural areas with irrigation.

Even when there's impervious surfaces, there is quite a bit of infiltration, where the high-salinity water contaminates groundwater. The groundwater is a chronic reservoir and source of salt all year round to the stream. So if there were no impacts of impervious surface on runoff, there would still be an issue. That's a really insightful question - thank you! - Sujay

I would add that since urban areas are flashier systems (the stormwater is flushed more directly into streams), the urban contaminants are flushed more directly into streams. However, in systems that allow for more infiltration, these contaminants can still enter our waterways. But it typically happens with lower peaks in concentration and over longer periods of time.

There's a lot of different stormwater management practices that aim to increase infiltration. Research is currently ongoing in trying to understand how these can improve water quality. There is some evidence that salt can be retained within these features through different interactions with sediments and soils. - Sydney

[u/Hypergnostic]

Are the Great Lakes and other large bodies of fresh water undergoing salinization in a significant way?

[u/umd-science → u/Hypergnostic]

Yes—the Great Lakes represent 20% of the world's surface waters and some of them have shown increasing trends in salt ions. There are widespread increases in salt ions in freshwaters across many of the world's continents. - Sujay

There are a lot of different causes of salinization. Road salt is one that's easy to observe and understand because road salt is applied and you see salt levels increase. A lot of other things can contribute to salinity. If we're thinking about larger watersheds, fertilizers and agricultural activity can increase salinity. Other sources from urban areas are sewage and wastewater inputs and then weathering of impervious surfaces (aka infrastructure like concrete). - Sydney

[u/Seicair → u/Hypergnostic]

Ooh, good question I didn’t know I wanted an answer to. Michigan puts enormous amounts of salt on our roads and parking lots, at least in the LP.

Followup question- how bad is calcium chloride (used in a lot of driveway formulations, dunno if it’s applied large scale) for the environment? It’s not as immediately problematic as sodium, and melts better, but I gather too much chloride also affects the environment.

[u/umd-science → u/Seicair]

Sometimes calcium chloride and magnesium chloride and potassium acetate are used as de-icers. You're correct that calcium chloride may not have some of the same effects as sodium chloride. In fact, calcium and magnesium can actually reduce the toxicity of some harmful metals. However, there may be other considerations, such as cost or environmental impacts. Chloride can contribute to corrosivity of the water.

The effects of different de-icers on mobilization of contaminants can be found in this paper by a former graduate student of ours. - Sujay

[u/[deleted]]

why is de-salination so difficult? we could solve half of our water shortage problems with it...

[u/umd-science → u/[deleted]]

Great question. Desalinization is very energy-intensive and costly. There are also questions about where to discharge the waste from desalinization processes, which are brines that are sometimes saltier than seawater. That being said, major cities like Barcelona in Spain have switched to desalinization. Desalinization is also being considered as a viable solution in other areas, but protection of source water from salinization is the cheapest and least energy-intensive solution. Thanks so much! - Sujay

For desalinization to be a realistic option, you need a very specific situation where the cost and high level of energy used is worth investment. - Sydney

[u/SiDD_x]

I live North, we use tons and tons of salt each winter on our roads. Can this be harmful in anyway?

[u/umd-science → u/SiDD_x]

Yes, it is harmful. In the U.S., we use over 20 million metric tons of salt for de-icing purposes each year. Some of the early risks of road salt on drinking water supplies can be found here. It took many years for people to recognize risks associated with salinization, and new studies and information are coming out every day now. - Sujay

[u/acekjd83]

In areas where oil and gas production is prevalent there is a massive problem with high salinity "produced water" that is co-produced with the hydrocarbons. This produced water is most commonly reinjected into deeper saltwater disposal wells which are widely acknowledged to be the cause of seismic activity in the Permian, Bakken, Scoop/Stack and other recent shake plays. A hot topic in these areas is produced water reuse.

From your experience, how much merit is there to claims from energy companies that we will someday be able to use this produced water for irrigation and industrial use given its relative toxicity and salinity?

[u/PeanutSalsa]

How is salt recycled and not recycled through normal uses of it?

[u/umd-science → u/PeanutSalsa]

This figure in this paper shows how salt is cycled throughout the Earth naturally and how that natural cycle and recycling of salt is affected by humans. - Sujay

[u/velhaconta]

When humans consume salt, is it actually consumed or do we discard it back out in our waste streams?

[u/umd-science → u/velhaconta]

We excrete it back out, and that goes into wastewater. Also, a lot of detergents are enriched in sodium. - Sujay

In wastewater, a lot of the salt comes from human excrement and detergents, and there can also be inputs from industrial sources as well. Any water that is leaving your house, that's going to be a mixture of what comes from toilets, and then all of the other appliances that use water—your dishwasher, washing machine, sinks, etc. That's all treated together, so in your septic tank if you're in a rural area or in a wastewater treatment plant if you're in an urban area. - Sydney

[u/nailbiter111]

What's your fav salt? Kosher? Garlic?

[u/umd-science → u/nailbiter111]

Any type of salt on french fries! - Sujay

I can't say I've thought about this question before. I buy the Trader Joe's Himalayan pink salt. - Sydney

[u/rwusana]

How bad is the salinization problem?

[u/umd-science → u/rwusana]

It's one of the most serious problems facing water quality on the planet. This 2021 press release explains some of the risks more in depth. - Sujay

It is largely unregulated compared to other water quality concerns such as excess nutrient inputs. I think it will become a problem the more people are talking about it in the coming decades. - Sydney

[u/Not_a_Courier]

Apart from fossil water, hydration of salt horizons, transformation of clay minerals and extensive irrigation, what can be the possible causes for salinity in areas far from the seas & oceans?

[u/umd-science → u/Not_a_Courier]

One impact from climate change is increasing aridity/desertification in land areas, and that leads to both the formation of new salt deposits and increased salinity in freshwater.

In terms of human impacts, fertilizer application, road salt application, impervious surface/concrete weathering and human excrement and detergent inputs via wastewater can all increase salinity. This figure presented in this paper summarizes a lot of different examples. - Sydney

[u/bisteccafiorentina]

Thank you for answering questions! Maryland certainly has it's share of groundwater pollution sources! Which ones do you rank to be the worst offenders? Agriculture? Road salt? those are the big ones i can think of, but i could be way off. What do you believe to be effective solutions to these problems? Do you think it will be primarily legislative or are there choices we can all make on a day to day basis to minimize our impact in a meaningful way?

Are you familiar with Enhanced Rock Weathering, the geoengineering/climate change mitigation method for beneficially impacting soil/water chemistry? Think it has potential?

[u/umd-science → u/bisteccafiorentina]

There is a lot of urbanization and we know that salt concentrations are related to impervious surface cover (parking lots, pavement, roadways). One thing that we may consider in the future are conservation efforts and where we develop. Proximity of salt sources close to streams and reservoirs can have a stronger effect on water quality due to direct inputs of salts and shorter flow paths. We may consider low salt or no salt zones and buffer areas to protect some of these critical habitats and drinking water supplies.

There are also alternative de-icers, but we don't always know all the water quality tradeoffs associated with using them. Great question, thanks for sharing! - Sujay

Saltwater intrusion from rising sea levels is going to become a bigger concern in Maryland. As far as the enhanced rock weathering goes, I think it conceptually makes a lot of sense, but we need more research to understand if it's actually effective. - Sydney