Salt Impacts & Our Environment

Excess salt introduced to the environment can change the intricate structure and chemistry of soil and the plants that live in those soils. These physical and chemical changes can have negative consequences on complex ecosystems like inland wetlands, plants, fungal, and wildlife communities. When salt impacts any of these ecosystems there can be direct, or indirect, effects.

 

SOIL & WETLANDS | PLANTS | WHAT CAN BE DONE? | RESOURCES

SOIL & WETLANDS

Chemically, salts are made of two parts, a positive ion (known as a cation) and a negative ion (known as an anion). Like batteries, these opposite charges are attracted to each other to form a chemical bond. The most common salt we are familiar with, and use daily, is sodium chloride (NaCl). When salt dissolves in water it breaks up into a positive, sodium ion (Na⁺) and a negative, chloride ion (Cl^-). In small amounts, these ions are not problematic, but when there are a lot of these ions, they can be. Sodium and chloride ions can have different effects in soils and plants. You can learn more about some of these effects down below.

The Soil Parking Lot – How Salt Changes Soil Chemistry(1,2)

Every soil type has a Cation Exchange Capacity, or CEC. This is a property of the soil that can determine its ability to support plant growth. A cation is a positively charged particle. In Chemistry, particles with positive charges are attracted to negative charges (opposites attract). We can think of a soil’s CEC as a parking lot, where each parking space is an area of negative charge that allows nutrients (positively charged particles) to adsorb – or park! Different soils have a different capacity, or number of spaces, in their parking lot and can hold a different number of nutrients. Nutrients that aren’t parked can be carried away by rain and groundwater.

Sodium (Na⁺) is a cation that forms when salt is dissolved by rain, snow, or ice. Unlike other cations, it is not a plant nutrient – but it can still park in the parking lot. When sodium cations start to build up, or fill in the parking spaces in the soil, it limits the number of parking spots for the plant nutrients.

 

 

 

Figure 1-Example of a parking lot (negatively charged) filled with different nutrients (positively charged) demonstrating the concept of Cation Exchange Capacity. In this image there are a number of empty parking spots still available for other positively charged nutrients. This parking lot contains calcium (Ca²⁺), potassium (K⁺), and magnesium (Mg²⁺).

When soils have an excess of sodium cations, they are called sodic soils.^(2,3) One of the determining factors for whether a soil is sodic is the Exchangeable Sodium Percentage – ESP.⁽⁴⁾ In our parking lot, ESP is the percentage of parking spots that have a sodium cation parked in it. With as little as 6% ESP, soils can begin to physically change, and by the time the ESP is 15%, the soil is considered highly sodic.

 

Here is a parking lot with 6% ESP:

 

 

Figure 2-Example of the parking lot filled with more nutrients. 6% of the parking spots are filled with sodium ions. This parking lot contains calcium (Ca²⁺), potassium (K⁺), magnesium (Mg²⁺), and ammonium (NH₄⁺).

 

Here is a parking lot with 15% ESP:

 

 

Figure 3-Example of a crowded parking lot filled with more sodium ions than other important nutrients like calcium, potassium, magnesium, and ammonium. This parking lot contains calcium (Ca²⁺), potassium (K⁺), magnesium (Mg²⁺), and ammonium (NH₄⁺).

Soil Structure – How Salt Physically Changes Soil

 

Sodic soils have high soil dispersion and decreased water infiltration. Soil dispersion means that individual soil particles, rather than clumping together, spread out across the soil’s surface. Infiltration means the ability for water to flow through the spaces between the soil particles. The opposite of soil dispersion is flocculation. Flocculation is really important because when soil particles clump together, tiny channels are formed that allow water to flow through the soil and plant roots to grow more easily.

 

 

In this cartoon we see an example of what happens when sodic (salty) soil gets wet:

 

Panel 1: Soil with good structure that will allow water and plant roots to grow easily because the soil particles are clumped together. But this soil is also sodic and something interesting happens when sodic soils get wet.

Panel 2: As water enters the soil, those larger clumps start to break apart into individual soil particles. Sodium ions bonded to the surface of a soil particle, especially clay particles, can cause them to disperse and resist flocculation.

Panel 3: As the water travels down through the soil, those particles do not clump back together. Instead, they spread out away from each other in thin layers.

Panel 4: The spaces between individual particles are much smaller than those between the larger clumps and can lead to tight layers forming in the soil column that don’t allow water or plant roots to pass through. This can lead to existing plants not being able to get water deeper in the soil while also not allowing new plants to get their root system into the soil.

 

Physical changes in soil can negatively impact important ecosystems like wetlands. Wetlands that aren’t influenced by tidal waters are called inland wetlands. By law in Connecticut wetlands are defined by soil type. All floodplain, poorly drained, and very poorly drained soil types are considered wetlands in Connecticut.

 

You might be thinking that it seems like sodic soils would be a good thing because if less water is infiltrating through soil, then that would mean more wetlands. Not exactly!

 

A functioning wetland or watercourse has soils that are able to properly cycle nutrients and allow plants to grow healthy roots. When soil is dispersed it can prevent water and roots from pushing down through the top layer of soil, especially in soils with a lot of clay making it difficult for plants to survive. Even sodic soils that don’t exhibit this dispersion effect can leave plants at a disadvantage with sodium cations outcompeting important nutrients for parking spaces.

Currently, in Connecticut, we are not seeing evidence of widespread sodic soils, however it can take very little sodium to change soil conditions.

 

PLANTS

 

Plants form complex ecosystems that depend on soil, water, and other organisms such as fungi and other animals to survive and thrive. When salt is overused in and around these ecosystems, there can be direct, and indirect, effects. Many effects have been identified and documented in scientific research for over 50 years.⁽⁵⁾

 

How Salt Impacts Plants

 

Salts can directly damage plants both externally and internally. Externally, plant leaves can be damaged by salt spray from traffic or from wind-blown sea water in coastal areas along Long Island Sound. Likewise, plants can be damaged by salty snow piles. Internally, plant tissues can be damaged when plants absorb both sodium and chloride ions from dissolved salts. Chloride ions can accumulate in plant leaves to such levels that interfere with photosynthesis and chlorophyll production leading to leaf burn and die-back. Sodium ions can displace important nutrients in the soil such as potassium, magnesium, and calcium leading to plant nutrient deficiencies. Repeated external and internal damage to plants can cause their health to decline or even die. Plants impacted by other issues, such as disease, infection, or insect infestation, will also be especially sensitive.

 

Salts can also indirectly impact plants. Salts can build up in soils, interfering with the roots of plants and changing soil composition. The change in soil composition can limit the movement of water (because of soil dispersion, as described in Soils & Wetlands) making it harder for native plants to grow and making it easier for other, possibly invasive, plants to grow, such as the invasive giant reed (Phragmites australis), narrow leaved cattails (Typha angusifoliaI), common ragweed (Ambrosia artemisiifolia), and wild carrot (Daucus carota)⁽⁴⁾. As the invasive plants outgrow native plants, animals that were attracted to and assisted with pollinating/spreading the native plants may move on to different areas which further limits the native plants from competing against invasive plants. This cycle can change the diversity of plants in an area which can have ripple effects on wildlife, soil, and water.

While many native Connecticut plants have some salt-sensitivity, there are some Connecticut plant species that are salt tolerant. These salt tolerant species can cope better with salts on their leaves, in the soil, or both. Planting more salt tolerant plants closer to the roadways can mitigate (make less severe) salt effects to other sensitive plants by acting as a physical buffer. You can find more information on coastal planting in the Connecticut Coastal Planting Guide published by UCONN and Sea Grant CT.

 

Salt Impacts Microscopic Ecosystems Important to Plant Health

 

Most plants have mutualistic relationships (both partners benefit) with mycorrhizal fungi (fungi) that live on tree roots. In these mutualistic relationships, the plant provides sugars, made during photosynthesis, to the fungi and the fungi pull nutrients from the soil and make them usable to the plants. This relationship is like the relationship between bees and flowers.

 

Not only do these fungi help provide nutrients to plants, but they also help plants tolerate stressful conditions by improving overall nutrition in the plant. The importance of protecting the fungal communities associated with trees is like our need to protect plant pollinators, such as bees, in plant conservation efforts.

 

In this photo, you can see the horizontal seedling root with fungi branches (both the pale and darker brown structures) growing out from the root.

 

These fungi protect plant roots from stressors such as salt stress⁽⁶⁾, pathogens, and heavy metal contamination. However, different fungi have different tolerances to salt stress. Some fungi have been shown to be moderately salt tolerant while others are not as tolerant. Consistent exposure to salt can be toxic to beneficial fungi which can make tree root systems more vulnerable and change the diversity of microscopic ecosystems⁽⁷⁾.

 

Signs of Plant Stress

 

 

High levels of salt concentrations in the environment can cause different symptoms in plants that can look like other problems such as drought, leaf wilt, chemical burn, sun injury, and root diseases. These symptoms include:

• Browning of foliage (leaves),^(8,9)
• Premature defoliation (loss of leaves and needles),^(10,11)
• Suppression of flowers and die back in terminal shoots (tip of plant stem where most plant growth occurs),⁽¹²⁾ and
• Decreased regrowth.⁽¹³⁾

Looking back on the parking lot example, sodium from introduced salts can replace other important soil and plant nutrients such as calcium, magnesium, potassium, and others. When there is excessive salt in the soil that replaces these important nutrients, plants can suffer from malnutrition impairing their ability to grow and spread. Salt can also impair plants’ ability to absorb water through their root systems which is why salt stress symptoms may look like drought symptoms. In many trees, the symptoms can start from the top of the tree downward or from the tips of leaves and needles inward. Some trees may even form “witches-brooms” which is when one branch wilts and shrivels up.

Paying attention to the pattern of symptoms can help determine if the symptoms you are seeing might be associated with salt stress. For example, consistent red discoloration at the bottom few inches of the base of shrubs located along roadways and sidewalks is a hallmark symptom of salt damage caused from salts on sidewalks or salty snow build up. 

 

Connecticut Trees and Plants with Known Salt Sensitivity or Tolerance:

 

Sensitive Species:

• Red Maple (Acer rubrum), Sugar Maple (A. saccharum)
• Boxwood, (Buxus sempervirens)
• Eastern white pine (Pinus strobus) 

Plants with Some Salt Tolerance:

• White oak (Quercus alba), red (Q. rubra), swamp white oaks (Q. bicolor)
• Winterberry (Ilex verticillate)
• Black chokeberry (Aronia melanocarpa)
• Nannyberry (Viburnum lentago)
• Sassafras (Sassafras albidium)
• Inkberry Holly (Ilex glabra)
• eastern red cedar (Juniperus virginiana),
• American Holly (Ilex opaca)
• White cedar (Thuja occidentalis),
• Southern Magnolia (Magnolia grandiflora)
• Common Juniper (Juniperus communis),
• Wax myrtle (Morella cerifera)
• Cherry laurel (Prunus laurocerasus),
• White and Green Ash (Fraxinus americana, F. pennsylvanica)

WHAT CAN BE DONE?

 

What To Do If Your Plants Are Showing Signs of Stress

If any plants on your property are showing signs of stress, it is good practice to check on your soil quality first. To check if your soil may contain excessive salt concentrations, contact the Connecticut Agricultural Experiment Station or your local extension agent for more information on how to collect a soil sample to test for salts. for more information on how to collect a soil sample to test for salts.

It is important that you discuss your concerns and the purpose of testing your soil with the laboratory so that the laboratory professionals can provide guidance for which tests would best fit your needs. One test to determine soil salinity is an electrical conductivity test, which can provide an overall picture of whether the salt levels are low, moderate, or high. Most labs can do other general tests such as cation exchange capacity (CEC), pH, etc. Additionally, irrigation water can also be tested if it is suspected the groundwater is impacted with salt. Lists of State Certified Laboratories for testing well water and/or groundwater samples are available on the CT DPH webpage.

 

 

Once the laboratory compiles the test results, they may provide guidance and/or recommendations on what nutrients and/or amendments you can make to your soil to improve the soil health if it is impacted by salt. It is possible that adding organic matter (such as compost) into soils can reduce salt damage and improve soil health. Overall improvement of soil health can help mitigate salt stress, for example, improving the texture, drainage, and fertility of the soil.⁽¹⁴⁾

If you’re doing any work in soils or wetlands on your property, check with your municipality for any permits that may be required. Please visit our Inland Wetlands page to find a directory of local Inland Wetlands agents here: Inland Wetlands Citizen Information.

 

Physical Ways to Protect Plants

If you live in a coastal area or have plants near roadways, covering your plants to protect them from salt spray during storms by using wooden barriers or burlap may be a short-term solution for preventing plant damage. To minimize damage from salt spray, rinse plants off as soon as possible after contact when temperatures are above freezing. Be mindful to water your plants during dry periods, as drought-stricken plants may be even more sensitive to salt damage during the winter.

 

Managing the Impacts of Salt to Soils and Plants

 

Let Nature Take Its Course

 

Dilution is part of the solution to salt pollution. In wet years, the rain and snow melt can help flush salt through soil into groundwater before damage can occur to plants. However, as the rain and snow flush the salt out of soil and into groundwater, it can increase the salinity (the amount of dissolved salt) of well water, water reservoirs, aquifers⁽¹⁵⁾, and wildlife habitats.

While dilution is part of the solution, it is out of our control; whereas reduction is within our control.

 

Reducing the Source

 

The best way to mitigate impacts of salt to soils and plants is by reducing the introduction of excess salts to the environment.

 

Here are some quick tips on how to minimize salt impacts to soil and plants on your property:

 

One 12oz coffee cup of salt is enough to treat a 500 sq ft driveway or about 10 sidewalk squares.

• Be conscientious of how much, and where, you use salt in relation to your plants.
• Minimize the amount of salt you use on impervious (impenetrable) surfaces such as walkways, driveways, and other hardscaped spaces that can be washed off into gardens and tree lines.
• Plan where you plow/pile snow, which will likely contain salt, on your property, because areas where snow is piled can create concentrated salt areas.

As Connecticut experiences more extreme weather, including droughts paired with more intense winter weather that could require more salt application (e.g., ice storms), there is a greater risk of salt build-up in our soils. And increased salt concentrations in our soils could increase the amount of sodic soil which can have ripple effects in the greater environment.

This is why reducing our salt use is important. Reducing the amount of salt we use can help prevent these negative impacts and benefit our wetlands, watercourses, and native plants. We can make the difference.

 

Using Alternative Salts

 

Plants are more sensitive to sodium-based salt (NaCl) than alternative de-icers such as calcium chloride (CaCl₂) and magnesium chloride (MgCl₂). However, these alternative de-icing salts are meant to be used in colder temperatures than is typical for most of Connecticut and they contain twice the chloride than traditional rock salt (NaCl), so it is important to carefully consider if using the other types of salt are necessary. Reduction of salt use is more helpful than using different types of salt.

 

Reducing Other Sources of Salt

 

A lesser-known source of salt to soils is found in commercial fertilizers. Fertilizers contain mixtures of salts to add some necessary nutrients back into the soil. Adding too much fertilizer can create a nutrient imbalance by introducing too many salts to the soil which can be harmful to plants, so just as you should carefully apply de-icing salt, it is important to be aware of the amount of fertilizer you are applying. Always follow the application instructions on the packaging.

 

 

RESOURCES

1. Minnesota Stormwater Manual. Environmental impacts of road salt and other de-icing chemicals. Environmental impacts of road salt and other de-icing chemicals - Minnesota Stormwater Manual (state.mn.us)
2. Walker, S.E., Robbins, G., Helton, A.M., Lawrence, B.A. 2021. Road salt inputs alter biogeochemistry but not plant community composition in exurban forested wetlands. Ecosphere 12:1-20. https://doi.org/10.1002/ecs2.3814.
3. North Dakota State University. Saline and sodic soils. 2014. Saline-and-Sodic-Soils-2-2.pdf (ndsu.edu)
4. University of Georgia Cooperative Extension: Soil Salinity Testing, Data Interpretation and Recommendations
5. Kelting, D.L., Laxson, C.L. 2010. Review of effects and costs of road de-icing with recommendations for winter road management in the Adirondack Park. Adirondack Watershed Institute Report # AWI 2010-01. Review of Effects and Costs of Road De-icing with Recommendations for Winter Road Management in the Adirondack Park — Adirondack Watershed Institute (adkwatershed.org)
6. Guerrero-Galán, C., Calvo-Polanco, M., Zimmerman, S.D. 2019. Ectomycorrhizal symbiosis helps plants to challenge salt stress conditions. Mycorrhiza 29:291-301. https://doi.org/10.1007/s00572-019-00894-2.
7. Ke, C., Zhouyuan, L., Yingmei, L., Wanqiang, T., Mengchan, D. 2013. Impacts of chloride de-icing salt on bulk soils, fungi, and bacterial populations surrounding the plant rhizosphere. Applied Soil Ecology 72:69-78. https://doi.org/10.1016/j.apsoil.2013.06.003
8. Hofstra, G., Hall, R. 1971. Injury on roadside trees: leafy injury on pine and white cedar in relation to foliar levels of sodium and chloride. Canadian J. of Botany 49:613-622. https://doi.org/10.1139/b71-097
9. Hall, R., Hofstra, G., Lumis, G.P. 1972. Effects of de-icing salt on easter white pine: foliar injury, growth suppression, and seasonal change in foliar concentration of sodium and chloride. Canadian J. of Forest Research. 2:244-249. https://doi.org/10.1139/x72-040
10. Lacasse, N.L., Rich, A.E. 1964. Maple decline in New Hampshire. Phytopathology 54:1071-1075. cabidigitallibrary.org/doi/full/10.5555/19650303967
11. Viskari, E., Karenlampi, L. 2000. Roadside scots pine as an indicator of de-icing salt use-a comparative study from two consecutive winters. Water, Air, and Soil Pollut. 122:405-419. https://doi.org/10.1023/A:1005235422943
12. Hofstra, G., Lumis, G.P. 1975. Levels of de-icing salt producing injury on apple trees. Canadian J. of Plant Science 55:113-115. https://doi.org/10.4141/cjps75-016
13. Fleck, A.M., Lacki, M.J., Sutherland, J. 1988. Response by White Birch (Betula papyrifera) to road salt application at Cascade Lakes, New York. J. of Environmental Management 27:369-377. cabidigitallibrary.org/doi/full/10.5555/19890631210
14. University of California Agriculture & Natural Resources: Nutrient and Mineral Excesses, Salinity, and Salt Toxicity
15. Walker, S., Robbins, G., Helton, A., Lawrence, B. Quantifying road salt impacts on forested wetland structure and function in eastern Connecticut. Final Report to Connecticut Institute of Water Resources, United States Geological Survey FY2018-19 104 B Program. B-314-CTIWR-Lawrence.pdf (uconn.edu)

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