The Trade-off of Salting Winter Roads: Human Safety vs. Plant Survival

The Trade-off of Salting Winter Roads: Human Safety vs. Plant Survival

A Practical Experiment of Determining Anthropogenic Salting Impacts on Local Plant Species

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When it comes to salting icy, dangerous winter roads, most people would not consider any other effects of salt, other than its extremely useful ability to melt ice, break bonds of ice to paved roads, and lower the freezing temperature of water to prevent re-freezing.  Some studies have even shown that the sooner salt can be applied to winter roads after a snow storm, the lower the number of vehicular fatalities that would occur, which is of course a paramount concern ("Mobility and Safety Impacts of Winter Storm Events in a Freeway Environment " by Keith Knapp from February 2000).  However, an article sponsored by the Salt Institute itself flatly states that “all materials used in winter maintenance have the potential to harm the natural environment,” which especially includes many local species of roadside plant-life that play a specific function in helping to structure natural ecosystems (http://www.saltinstitute.org/content/download/480/2980).  This statement may invoke questions like: Are there alternatives to salt? Is too much salt being used on roads? Why should we care about roadside plants in winter when human safety or normal economic trade may be at risk?  These big picture questions were the primary motivators for our Plant Ecology class (BL 435/535) at John Carroll University to perform an experiment on four local roadside plant species (the Black-Eyed Susan, the Mexican Aster, the Shasta Daisy, and the Purple Coneflower, arranged in order below) in relation to their tolerance to differing salt concentrations that may arise from the casual build-up of salt (NaCl) in soils over time, a direct consequence of winter road management.

 

Black-Eyed Susan
commons.wikimedia.org

Mexican Aster
www.discoverlife.org

Shasta Daisy
www.riverssourcebotanicals.com

Purple Coneflower
www.missouribotanicalgarden.org

               Why care about roadside plants? Generally speaking, plants provide a number of functions such as producing oxygen and removing carbon dioxide from the atmosphere, increasing organic matter in soils that biota can consume for cycling nutrients through soil, providing habitats for invertebrates and bacteria, and locking soil molecules together in roots to prevent erosion, not to mention the aesthetic value of a beautiful landscape.  Roadside plants play a particularly unique role because they create a barrier between a less disturbed, natural habitat for other flora and fauna to reside and the highly disturbed, human altered terrain that may cause increasing levels of tension or risk to natural systems.  But, as a result of being this barrier, unwanted mineralization from salting roads can flow right into roadside soils and plants, causing adverse effects like blocking other mineral acquisition, burning plant tissues with high concentrations, slowing physiological growth by impeding water uptake or causing too much water accumulation, etc (Parida and Das, 2005).  While the Salt Institute and the Ohio Department of Transportation both indicate that alternative methods of melting ice on winter roads do exist and are being further studied, there has been little work done to investigate harmful effects of salt on roadside plants in the recent capacity of salt use(http://www.dot.state.oh.us/Services/Documents/ODOT_Road_Salt_Market_and_Price_Analysis_12-15-08.pdf).  For more information regarding salt as it affects natural environments of plants and rivers, visit the Cleveland blog (http://blog.cleveland.com/metro/2010/02/road_salt_on_highways_saves_li.html).

For the purpose of our class experiment, we wanted to examine the effects of salt concentrations (0, 50, 100 mM) on plant biomass accumulation and physiological growth of the four species of plants previously mentioned, the Mexican Aster (Cosmos bipinnatus), the Shasta Daisy (Chrysantheum maximum), the Purple Coneflower (Echinacea purpurea), and the Black-Eyed Susan (Rudbeckia hirta).

The Experiment:

           The first step in setting up the experiment included transferring the soil and plants to empty pots.  First, we lined the pots with a piece of plastic mesh that allowed for proper filtration of water in the soil.

 

Angelica and Alex are implanting the plastic mesh in their pots before adding the soil mixture.

 

The soil composition was an equal mix of sand and clay. 

These buckets are filled with sand and fritted clay used to put in the pots for transplanting.

We then planted three individual plants of each of the four species into separate pots designed for one of each of the salt concentrated mixtures, which were color coded (0 mM: white; 50 mM: green; 100 mM: red).  Next, the pots were labeled by group and organized in a completely random placement of both salt concentration and species.

 

Maria and Jay are in the process of transplanting plants into pots and labeling the pots for correct salt concentration treatment.

Katie and Jared are also transplanting their plants into pots. Every group in the class provided one block of plants to be treated in the experiment.

 

Dr. Drenovsky is overseeing that the plastic mesh in the bottom of the pots is holding the soil, while helping Maria transplant.

 

 

This picture represents one of the five blocks of the experiment (one block done by each lab group), where colors clearly indicate which plants get which salt concentration.

After planting was completed, all species from all salt treatment groups were watered with 0 mM salt, as a control.  The concentration of 0 mM lacked salt and contained only water and 1/10th Hoagland’s fertilizer solution, which is a solution that contains all macro- and micro- nutrients needed for plant growth cycles. 

 

Jaylan is watering the completed block of planted plants with 0 mM concentrated solution.

The second step of the experiment was then to produce the higher salt concentrations to be used in the experiment after the initial fertilizing of the newly transplanted plants.  Higher salt concentrations of 50 mM and 100 mM will gradually be given to those treatment groups of plants over time in varying amounts until 50 mM and 100 mM is reached.  For example, for the concentration of 50 mM, plants will receive 12.5 mM NaCl, then 25 mM NaCl, and then 37.5 mM NaCl for two weeks, before reaching the full amount for the duration of the experiment. (For 100 mM NaCl, amounts of 25 mM NaCl, 50 mM NaCl, and 75 mM NaCl will be applied for two weeks before reaching 100 mM NaCl).

For the making of solutions, each of the sodium chloride concentrations were mixed with 1/10^th Hoagland’s solution and the appropriate volume of water.

 

Step 1: Natalie is filling the container with water to mix the solution.

 

Step 2: Meghan is adding the chemical components of Hoagland’s solution to the container with a micropipette.

 

Step 3: Lindsay and Alex are weighing NaCl, so that the correct amount can be added to each container.

Step 4: Although not depicted, this step involves the final filling of the containers with water to the appropriate volume, allowing the avoidance of crystal formation.

                When transplanting and solution mixing were completed, the five experimental blocks were assembled together to facilitate ease of water for the coming weeks.

 

Angelica, Natalie, Josh, and Alex are displaying all of the five blocks compiled together on a table in the greenhouse at John Carroll University.

Finally, insulation was applied to the plant blocks in order to keep the temperature constant for all experimental plants for the duration of our trial.  Without the insulation, the plants on the outside of the arranged pots would have a higher temperature than the plants that were more centralized.

Josh and Jaylan are placing the pieces of insulation around the plant beds.

 

Alex, Jaylan, Meghan, and Natalie are fitting the final pieces of insulation together.

In completing the experimental set up, a group effort was needed to clean the greenhouse for other student work.

 

Danny is washing tools that were used for transferring soil and plants into pots.

 

           Over eight weeks, the salt solutions will be applied to the treatment groups, and the plants will be measured for growth, as well as examined for relative health.  For example, discoloration, dying leaves, spots, etc. may be indications that the plant is struggling to survive in the relative salt concentration used. At the end of this data collection, the plants will also be weighed. Stay tuned for results!

  Jay and Jared are making notations in their field notes about personal observations made in setting up the experiment.

 

Works Cited

Parida, A. K. and A. B. Das. 2005. Salt tolerance and salinity effects on plants: a review. Ectotoxicology and Environmental Safety 60: 324-349.