- Welcome, everyone, to Wednesday Nite @ the Lab.
I'm Tom Zinnen.
I work at the University of Wisconsin-Madison
Biotechnology Center.
I also work for the Division of Extension, Wisconsin 4-H.
And on behalf of those folks and our other co-organizers,
PBS Wisconsin, the Wisconsin Alumni Association,
and the UW-Madison Science Alliance,
thanks again for coming to Wednesday Nite @ the Lab.
We do this every Wednesday night, 50 times a year.
Tonight, it's my pleasure to introduce to you
Hilary Dugan.
She's a professor
in the Department of Integrative Biology here.
She was born in London, Ontario,
and then went to high school in Woodstock, Ontario.
She studied both biology and geography
at Queen's College in Kingston, Ontario.
Then she got her PhD
at the University of Illinois in Chicago.
In 2014, she came to UW-Madison,
where she's with the Center for Limnology.
Tonight, she's gonna speak with us about the effects of salt
on Wisconsin's freshwaters.
Would you please join me in welcoming Hilary Dugan
to Wednesday Nite @ the Lab?
- Thanks, Tom.
So as a limnologist, I study lakes and water quality,
and there's no better place to do that than Wisconsin.
And today, I'm gonna talk to you about salt
and what salt means for Wisconsin's freshwaters.
So living in Wisconsin,
you can't open a news site in the winter
without reading something about salt.
Whether or not it's talking
about the horrible morning commute
where it took you an hour to get to work
or the fact that road salt is harming our freshwater lakes
and our drinking water.
And we're all familiar with salt, especially road salt.
We see plow trucks with beds full of salt
driving around the streets in the winter.
We see piles of salt on sidewalks and in parking lots.
This is something we've all lived with
for most of our lives.
And what I wanna try and convince you of today
is that when we use salt on a large scale,
the scale at which we're currently using it,
we really need to think of salt as an environmental pollutant.
And it's really no mystery why we see marine organisms
in some of our freshwater rivers.
This is in Toronto, Ontario, Canada,
where they found crabs in a nearby river.
And it's because the river was so salty
from road salt runoff
that these crabs could happily live in that environment.
And so today, I wanna talk about a few things.
First is gonna be about some of the scientific terms we use.
So, what do we mean when we say salinity?
Then we're gonna talk about how much salt we use,
and then what are we seeing in freshwater lakes?
And what does that mean for those ecosystems?
So the word salinity is one we've probably all heard of,
but you might not know how we actually measure it.
So this is a scale of salinity from zero grams per liter
to 35 grams per liter.
And the ocean is considered saline.
It has 35 grams per liter of salt,
whereas freshwater's on the other end of that scale
at about zero to one grams per liter of salt.
And almost all of our surface water in Wisconsin
falls beneath that one gram per liter line.
So we have almost entirely freshwater in this state.
And then everything in between 1 to 35
is considered to be subsaline or brackish water.
So, how do we actually measure salinity?
Well, the term salinity is defined
as the total dissolved ions in water.
So we actually have to go out
and measure all the individual ions and add them up.
So mostly, those are our major cations,
so these are our positively charged ions.
So that's sodium, calcium, magnesium, potassium.
And then our negatively charged ions,
so sulfate, like carbonate and chloride.
And when we add those up,
the total number is equal to the salinity of the water,
or sometimes we use the term total dissolved solids.
And what ions we find in which water bodies
differs based on the water body and where you are.
So the ocean is saline,
35 grams per liter of salt.
Most of that salt is sodium and chloride ions,
so 86% of the ocean.
And that's because these ions are not used
by a lot of biological organisms,
so they stay dissolved in the water.
Whereas if we were to look at the salinity
of lakes and rivers in, say, southern Wisconsin,
what we see is very low total salinities,
and most of that is made up of calcium and bicarbonate.
And that calcium is coming from things like rock weathering.
And to get that total salinity value,
we have to measure all of those ions,
which, unfortunately, is pretty time-consuming.
We have to take a water sample.
We have to bring it back to the lab.
We have to measure all of those individual ions
on pretty sophisticated machinery
to get that total salinity value.
So it takes a lot of time and money
to actually measure the salinity of water.
So it'd be really nice if we had an easier way
to measure salinity, and luckily we do.
We use what we call electrical conductivity of water
to tell us something about salinity.
So because all of those individual ions are charged,
the more ions you have in water,
the better able water is to conduct an electrical flow.
And so we're actually just able to measure this
using a sensor.
And so we can take a sensor out to a lake,
put it in the water,
and measure the electrical conductivity.
This is a picture of us
using an electrical conductivity meter on Lake Mendota.
So we can just stick that sensor right into the lake.
And in this example,
the lake is 506 microsiemens per centimeter,
that's the unit for conductivity, on this day.
And so if we see that number increasing,
we know the lake is getting saltier.
We don't actually know which ion is causing that.
It could be calcium, it could be sodium,
it could be magnesium.
We just know that there's more ions in the lake.
So this is nice
'cause we can go around to any body of water,
use these sensors, and get a sense of what the salinity is.
You'll also see limnologists talking about chloride.
So chloride is just one ion that makes up total salinity.
But chloride is unique because in Wisconsin waters,
the background concentration is actually very, very low,
about zero to two milligrams per liter of chloride.
So if we go out and we measure chloride
and see it at higher concentrations,
we know that that's probably being caused
by human pollution.
And so instead of measuring that whole suite of ions,
we go out and we measure just chloride
'cause that can tell us something
about chloride contamination.
And so these terms,
salinity, electrical conductivity, chloride,
they're all ways that we measure salinity
and track salinity changes over time.
So why is salt such a pervasive pollutant?
Well, there's three main reasons.
One is it's really effective.
So salt works by depressing the freezing point of water,
and it works really well between the temperature
15 degrees Fahrenheit and 30 degrees Fahrenheit.
And so if we put it on our roads
in, say, 25-degree Fahrenheit weather,
instead of water freezing into ice,
it's gonna stay liquid.
And so we use this as a way of making our roads safer.
We've all seen it in action.
Really effective.
Salt is also relatively cheap.
You can go to the hardware store
and buy a bag of salt for $5, not breaking the bank.
The state can buy a ton of salt for about $80.
There's not very many substances
you can go and buy a ton of for $80.
And that price has actually gone up
pretty drastically over time,
so we are spending a lot more money on salt,
but for the quantity we buy,
it's still relatively inexpensive.
And then the third reason is salt is natural.
We eat salt every day.
We have sodium chloride on our dinner tables.
And so how can it be bad if we are eating it?
Well, just like us consuming salt,
when we have too much, it causes problems.
And so salt isn't bad at low quantities;
it's when we start using a lot
that it becomes an environmental pollutant.
And this is kind of like coal.
It's effective.
It's really good at heating.
It's relatively cheap, we can mine it pretty easily.
And it's natural.
And coal was not a problem
when we used it in little quantities.
But when we started using it at an industrial scale,
it's caused some
pretty catastrophic environmental damages.
So, what's the downside?
Well, every ounce of road salt that we use
ends up in our environments.
No one's going up and picking up the salt that we put down.
So every ounce we put on the ground ends up in our soils
and in our rivers and lakes.
And that's a problem because the United States puts down
over 23 million tons of road salt a year.
And that number is just at the state scale.
It's not accounting for sort of other sources of salt
beyond road salt.
And we need freshwater.
As humans, we need freshwater to drink.
We also need it for industrial applications
and food processing.
And aquatic organisms also need freshwater to survive.
Freshwater organisms have evolved
to live in freshwater habitats, and as we start adding salt,
some of those organisms are gonna die.
And so if we keep increasing the salinity
of our freshwaters,
we're gonna have some pretty catastrophic consequences
to both organisms and human health.
So because of that,
the government has some ecotoxicity regulations
on what they think are the important limits
for freshwater habitats.
So this is a scale of chloride, showing zero chloride
all the way up to ocean concentrations.
So the ocean has about 19,000 milligrams per liter
of chloride.
And the EPA has set the chronic aquatic toxicity threshold
at 230 milligrams per liter.
So that means that if a water body is above 230,
it has sort of a threatened habitat.
Now, this is a feature of environmental governance
where we wanna set a threshold,
saying that anything below that threshold's okay,
anything above that threshold's a problem,
which is not really true in reality.
There's some organisms
that are harmed at really low concentrations
and there's other organisms that are pretty fine
at quite high concentrations.
The problem being that the organisms that have evolved
to freshwater environments in Wisconsin,
so our native organisms,
are the ones that are usually more susceptible
to higher salt concentrations.
Invasive species like zebra mussels
don't care about higher salt concentrations.
And so these environmental governance thresholds
are really treating water as sort of a sink for salt.
How much salt can we put into the river,
flush it downstream before it becomes a problem?
So 230 milligrams per liter, that is a number
that doesn't really have any relevance to us, right?
We don't really think about concentrations of salt.
So let's think about what that looks like.
So if we have a five-gallon bucket,
and this is full of pure water, so just H2O,
think about how much salt
we might have to add to this bucket
to produce a concentration of 230 milligrams per liter.
So think about that for a second.
If you were to dump salt in here,
when would it hit that EPA chronic toxicity threshold?
Well, it only takes about a teaspoon of salt, shockingly.
Not very much salt to produce 230 milligrams per liter.
So it shows you that it's really easy
to pollute water with salt.
Usually, we see those five-gallon buckets
just full of road salt.
And you can think about how easily it would be
to pollute, say, a shallow lake or a stream.
So, how much salt are we using?
What are we talking about?
Well, Wisconsin doesn't have a total budget
for how much salt the state uses,
but someone in Minnesota did this a few years ago
for the state of Minnesota.
And Minnesota is pretty comparable.
We have very similar populations,
we have similar density of roads,
lots of similar land use
in terms of agriculture in the south
and forest in the north.
And most of the salt that's used by the state is road salt.
So road salt is by far the biggest salt source
in Wisconsin and Minnesota,
but there's other sources as well.
One of that is water softeners.
So when you put salts in your water softener,
that effluent is sent to the sewage treatment plant
or your septic, and that salt is not removed.
So there's no economically feasible way
to remove salt from water.
And so the wastewater treatment plant
is just gonna be sending that salt downstream
wherever the effluent is discharged,
so probably your local river.
And then we also see salt coming from agriculture.
So there's salt in livestock manure, excretion,
and also some salts in fertilizer use.
So potassium chloride is a popular one.
And so all of these add up to be environmental pollutants.
All of these salt sources are not being removed
from the environment.
The only way they're removed
is sort of eventually flushing downstream.
So think about Wisconsin.
We have 34,000 lane miles of roads
and we apply about half a million tons
of road salt per year.
And that differs a lot year to year.
Depends on how snowy the winter is,
how long the winter is.
But in general, we spend about $80 million
in total annual expenditures on road salt.
So this is an environmental problem,
but it's also an economic problem.
If we can use less salt, we also save a lot of money,
and we can put that money towards things
like fixing potholes.
And salt is expensive
because Wisconsin doesn't have any natural salt supplies.
We actually have to import all of the salt we use.
And so these are pictures
from the Milwaukee Harbor last year,
offloading salt into piles
that will eventually be either put on trains or trucks
and delivered around the state.
And the result is that we see
really high salt concentrations in our rivers and lakes.
So this is data from Milwaukee.
These are three rivers, urban rivers in Milwaukee,
the Kinnickinnic, the Menomonee, and the Milwaukee River.
And what we see is really large swings
in chloride concentrations
depending on the time of the year.
And so this data shows these big annual swings
where we see very high concentrations in the winter.
So that makes sense,
we're applying road salt in the winter, that melts,
flushes into our rivers, and then in the summer,
it goes back to lower concentrations.
And on this graph, you can see two dashed lines,
and these are the EPA toxicity thresholds.
So 230 milligrams per liter is the lower one,
and that acute toxicity threshold of 860.
And you can see that this river routinely surpasses
those thresholds in the winter,
going upwards of 1,000, 2,000 milligrams per liter of salt.
And so if you're an aquatic organism
trying to live in this river,
you're constantly having your habitat change salinity,
and so you're being stressed out part of the year.
If you think about species trying to evolve to this,
it's hard to evolve to a system that just keeps changing.
This is data from the city of Madison.
This is a urban sub-watershed
that drains directly into Lake Mendota.
And this is conductivity data from USGS.
And this is measured in microsiemens per centimeter.
But these concentrations that we see in the winter
are about halfway to being ocean salinity.
So the ocean's about 50,000 microsiemens,
we're hitting 20,000 in some of this urban runoff
in the winter.
So a very salty environment.
This is the same watershed in 2022.
And we can see that there's a few days in February
where it hits 30,000 microsiemens per centimeter.
So again, almost halfway to being ocean salinity
in these urban environments
that are draining right into a freshwater lake.
And so you can think about the lake diluting that,
but that habitat right where the river enters the lake
is gonna be a really hard environment to live in.
And so what does that mean over time?
Well, over time we're seeing the concentrations of salt
increase in our lakes.
So this is data from three lakes in Madison, Wisconsin,
Lake Mendota, Lake Monona, and Lake Wingra.
And since the 1940s,
which is kind of when we started using road salt,
we've seen this steady increase in salinity.
And this data set's unique because we actually have data
that goes back to before we started using road salt.
And we know the chloride concentrations in these lakes
sometimes were about one or two milligrams per liter.
It's rare to have data that goes this far back in time.
And we can see that that is just continually increased
through time.
There's been a few times where it seems to level off
and then continuing its pace.
And the size of the lake matters too.
So in this graph,
Lake Wingra is the smallest lake,
so it's the most easy to pollute,
so it has the highest salt concentrations.
Lake Mendota is the largest lake,
has the lowest concentrations
because it just takes more salt to pollute it.
And we can look at data across the state of Wisconsin
and across the Midwest.
So this is data from Michigan, Wisconsin, Minnesota,
and we can see urban hotspots standing out as places
with really problematic chloride concentrations.
So the dots that are in sort of the green to yellow color
are ones where we see really high chloride.
And we can see the Detroit metro area stand out.
We can see Milwaukee, Madison, Twin Cities
as places where you can routinely get
really high salt concentrations in our freshwaters.
And then if we go to the Northwoods,
we see a lot lower concentrations.
That makes sense, there's less roads.
Often it's too cold for road salt to be effective,
and so we're still seeing sort of
natural background concentrations in many places
in the northern regions of these states.
That being said,
it's not like it's immune to problems.
There's certainly cases of lakes
or rivers right beside a road that have high concentrations.
There's been instances
where people's shallow groundwater wells
have also been polluted with salt.
And groundwater is not immune either.
So as we put salt onto the surface,
some of that's gonna percolate down into our groundwater,
and that's scary when we think about freshwater
for drinking.
So this is data from the City of Madison
where they track chloride concentrations
in their high-capacity groundwater wells,
and they're seeing some of their wells
increasing in chloride over time.
And this is a direct result
of road salt runoff of the surface,
sort of draining down into these aquifers.
And these are really deep wells,
these are high-capacity municipal wells,
but if you have a shallow well,
you're even more at risk of having chloride contamination
in your groundwater.
And the University of Wisconsin-Stevens Point
actually has a great groundwater well viewer
that you can look up online
and see private well data for chloride across the state.
And there's a huge variability
because it's really spatially different.
If you happen to be by a road,
you happen to have groundwater flowing a certain direction,
you might have a saline well
versus someone on the other side of the street,
their well might not be affected at all.
So, how widespread of a problem is this?
Well, there's been a lot of studies done.
This is one that we did a few years ago
where we tried to look at long-term data sets
of lakes across North America,
and what we found is that lakes in urban environments
were all increasing in salt,
and lakes in sort of rural, forested environments
were staying about the same.
So it was very clear that this sort of urban land use
is what's leading to salinization.
We also looked at the Lake Michigan water basin.
So we had a postdoc here at the Center of Limnology
who drove around Lake Michigan,
sampling every stream that flows into Lake Michigan,
measuring water quality.
And we measured chloride in all of those samples,
trying to predict what was gonna happen to the Great Lakes.
And what we found was that, again,
these urban environments
had really high salt concentrations.
So especially around the Milwaukee area,
Chicagoland, Green Bay,
and then the northern part of the watershed
had really low concentrations.
And so what we're seeing in the Great Lakes
is that there's been sort of a slow increase
in chloride over time, but it's relatively low
because the Great Lakes are just a huge body of water
that to actually increase the salinity
of Lake Michigan, in this case, just takes a lot of salt.
So luckily, the Great Lakes are staying relatively fresh,
even though they are increasing slightly in chloride.
So if we look across the Midwest and Northeast,
this is a region that uses a lot of road salt.
This is a climate belt where we have those temperatures
between 20 and 30 degrees Fahrenheit a lot in the winter,
and road salt is really effective.
And so we've become dependent on using road salt in the winter
to keep our roads safe.
So we spend about $370 million for materials, so buying salt,
and we spend over a billion dollars for actual application.
So that includes trucks and people hours
to actually keep our roads
clear of snow and ice in the winter.
So this is a very costly enterprise.
This is also a region with a lot of freshwater.
A lot of regions in the United States have water scarcity,
and luckily the Midwest and Northeast is not one of those.
And so this is a region where we have to balance
being dependent on road salt,
but also protecting our freshwater environments.
So we've done some work looking
at how many lakes might be at risk,
and so we were able to find a lot of data
from certain states.
There's also other states
that don't have a lot of water quality monitoring
for chloride.
And we were able to build a predictive map
where we actually could pinpoint
what lakes we thought were at risk.
And so there's a number of lakes
where we saw pretty high chloride concentrations
and lots of lakes where we predicted
that they would have high chloride concentrations.
So we were able to predict this for about 50,000 lakes.
And this helps managers go out and assess lakes
that they might be responsible for
and where they should be monitoring,
and then potentially implement some better management practices
for protecting those environments.
So we've learned about what salinity is,
how much salt we're using,
what we're seeing in lakes and rivers,
but what does this actually mean for lakes themselves?
So I'm gonna hit on three points.
We're gonna talk about physics, chemistry, and biology.
So chemistry is kind of inherent.
We're adding chemicals to our lake,
salt is a chemical,
but what does that mean for lake physics?
Well, lakes in Wisconsin, so especially deep lakes,
go through this really interesting
sort of annual cycle of mixing.
So when the lake ice comes off in the spring,
the lake is all about the same temperature,
and the wind sort of easily mixes the water body.
And this mixing of the water body
is really important for the lake habitat
'cause it sort of redistributes nutrients and gases
throughout the whole lake.
So nutrients are brought up from the bottom,
mixed to the surface.
Oxygen from the surface is brought down to the bottom,
and it's sort of this reset in the spring.
Then in the summer what happens
is as the surface waters start to warm,
that warming water is actually less dense.
And so warm water will sort of float on top
of colder, denser water in the bottom.
And the lake actually stratifies into two layers,
and we call this stratification.
And so those two layers don't really mix.
And what happens is we see buildup of nutrients
in the bottom of lakes,
but sometimes the bottom of lakes also lose oxygen
because they're not able to get new oxygen from the surface.
And then in the fall when the lakes cool,
what happens is the lake's losing heat,
the water becomes all the same density,
and it mixes in the fall.
And again, that mixing is really important.
It's bringing nutrients from the bottom back to the surface,
those nutrients feed phytoplankton and zooplankton,
and then gases are brought back to the bottom.
So we want our lakes to have oxygen,
we want that mixing to take place.
And then the lakes actually stratify again in the winter
under ice.
And so we call these lakes dimictic,
they mix twice a year.
And this is an annual pattern
that we see in all deep lakes in Wisconsin.
Shallow lakes tend to mix just kind of all the time.
And so this mixing process is sort of crucial
for lake chemistry and also lake biology.
But what happens when you add salt?
Well, when you add salt to water,
it actually becomes more dense.
And so saline water is denser than freshwater.
So if we add salty, inflowing water into a lake,
it's gonna want to pool at the bottom of the lake
'cause it's denser.
So it's gonna flow in and pool at the bottom.
And this becomes a problem
for that mixing phenomenon in the spring.
So because there's really dense water in the bottom,
it takes a lot of energy
to be able to sort of mix that salt out.
And sometimes if you have enough salt
at the bottom of the lake, it just won't mix;
you don't have enough wind energy to really mix that salt
back to the surface.
And there's examples of lakes in Michigan
where they've had so much road salt runoff come in
that they've stopped mixing.
We call these lakes meromictic; they just don't mix.
And that causes consequences for chemistry
because you lose oxygen
and you have different chemical feedbacks.
And it also has a huge problem for biology,
because if you're creating these layers
that don't have oxygen,
you can't have any organisms living there.
And so what we see is that
in between this sort of mixing to no mixing stage,
we're gonna go through a phase where we delay spring mixing.
So again, going back to our normal mixing patterns
where we have a freshwater lake,
when the lake ice comes off in the spring,
we're usually gonna mix that lake right away.
So this is data that some students collected
in Lake Monona in Madison, Wisconsin.
They put sensors in the lake, measuring temperature
and also conductivity.
So they were able to measure both temperature
and say something about salinity.
And what they saw was that the bottom of Lake Monona
gets pretty salty in the winter.
And when the lake ice comes off in the spring,
they actually didn't find that the lake was mixing.
They saw there was a 20-day delay in that spring mixing.
And so that's important.
That salt at the bottom of the lake
is delaying that spring mixing,
which then has feedbacks for things
like the spring algal bloom and zooplankton populations,
which then are important fish foods.
So we have sort of food web effects
from this changing lake physics
because these lakes are getting saltier.
So there's a lot of really interesting feedbacks
that sort of go beyond salt just being toxic to organisms.
But salt is toxic to organisms, so it will change biodiversity.
So one of the fears
is that we're not gonna kill all the organisms in a lake,
but we're gonna change what communities are present.
And so we're gonna change our phytoplankton communities.
So we might shift towards more cyanobacteria
instead of green algae.
And cyanobacteria are a problem because they're the ones
that cause these harmful algal blooms with toxins.
They're also not as tasty to zooplankton.
And we also might change our zooplankton populations.
So there's a lot of research going on right now
thinking about how community dynamics are gonna change
as we increase salinity.
And this is gonna differ between lakes and rivers.
Going back to that data that I showed earlier,
lakes are sort of slowly increasing in salinity,
and there's some thought
that actually some of these short-lived organisms
might be evolving to withstand some of those changes.
But if you think about that river data,
that salinity was sort of going up and down
throughout the year to really high concentrations.
And so you've gotta be an organism
that's able to withstand these really big swings.
And so we're gonna see different pressures
based on the environment that these organisms are living in.
So as I said,
there's lots of research going on in this area.
So this was a study that was conducted with daphnia.
So daphnia are zooplankton.
They're sort of the middle of the food chain.
We consider them keystone species.
They're really important for grazing on algae.
And this study looked at daphnia in a soft water culture medium,
and they added chloride to different sort of tanks
to see what would happen to the zooplankton populations.
And what they saw was that there was a big decrease
in daphnia, the number of daphnia,
at chloride concentrations
between 5 and 40 milligrams per liter.
So why this is important
is that EPA chloride toxicity threshold
is 230 milligrams per liter.
So the EPA says that water bodies are fine
if they're below 230 milligrams per liter,
even though the natural background concentrations
in Wisconsin are 0 to 10 milligrams per liter.
So what this study shows
is that these thresholds might be way too high
to protect certain organisms.
In this case,
concentrations as low as 40 milligrams per liter,
we're seeing big shifts in the food web,
and so we might actually be really overestimating damages
based on these thresholds.
So this study was recreated using water
from 16 different lakes around the world.
So they were interested in,
is this result transferable to other systems?
Because all lakes have different background concentrations
of ions.
And what they found was that pretty consistently
in these 16 lakes,
you took water from that lake and added chloride,
you would see declines in zooplankton populations.
But at the same time,
you would see increases in algal populations.
Because if you have less zooplankton,
they're not gonna be eating the algae,
so the algae can grow better.
And that's a problem.
We don't want our lakes to be full of algal blooms.
Zooplanktons are our friends,
we'd like them to be healthy, eating algae.
And so this study shows that as you increase salinity,
you might actually risk having more algal blooms on lakes.
So let's think about what's next,
how can we solve this problem?
My philosophy is this is a problem we can solve.
There's a lot of environmental problems
that are really tricky to manage.
We think about things like mercury in our lakes.
Well, mercury is bound up in organisms,
it stays in the food web, it's really hard to get rid of.
We think of things like PFAS, these forever chemicals.
How do we get rid of them?
Well, salt is very easy.
Salt stays dissolved in water, it will flow downstream,
eventually reaching the ocean where it's not a problem.
So, what do we need to do?
We need to use less salt.
We need to put less salt into our lakes
and our lakes and rivers over time
will eventually become healthier again.
So, how do we do that?
So we have to think about management practices
and education.
So for a long time, we haven't thought about salt
as a pollutant.
You can go to the store, buy a bag,
throw it in your driveway, there's no consequences.
But there are consequences.
There's consequences to the environment,
there's consequences to infrastructure.
Our cars all get rusty.
So, how do we manage that?
Well, the state and some municipalities
are starting to undergo trainings.
They're starting to calibrate their salt application,
and a lot of private applicators are gonna be trained as well.
So there's lots of different levels
at which you can start using less salt.
You can start using less salt at your house.
If you're a business owner,
you can request your applicators to use less salt.
And a lot of this goes back to just education.
We have to start thinking about salt as a pollutant.
We can use a lot less and still maintain safe roads.
So one thing that the state of Wisconsin is doing
is they're really investing in liquid brine application.
So instead of filling a truck up with salt,
so solid minerals of sodium chloride,
instead they take that salt and they dissolve it in water
and they create a really salty, briny solution
that then they spray on roads.
And that brine solution is about 23% salt.
So it's still much saltier than ocean water,
it's very salty,
but because it can be sprayed on,
you can actually use a lot less salt.
And so one way of maintaining good road safety
and using less salt is this liquid application.
So this is a map of the state of Wisconsin,
county by county.
So different counties take care of their own roads
in Wisconsin.
And this is from the 2021 Department of Transportation
Annual Report.
And on the left, we see a heat map of how much brine,
so liquid application, different counties are using.
So the counties in blue use a lot of liquid application
and the counties in red use very little.
So those counties in red are still using
that traditional rock salt.
And on the right is a graph of how much salt
that county used that year
versus the five-year, long-term average.
So this is actually a pretty dry year.
So overall, most counties used less salt than average,
but we see the biggest reductions
in those counties that are using liquid application.
And so we see counties
like Jefferson County in the southeast,
it's a blue county for brine,
but it's also a blue county for its salt reduction.
So Jefferson County uses a lot of liquid brine
and they've actually been able to reduce their salt use
by about 50% to 60%.
So this is a major shift in how much salt we're using.
And if we think about how much salt
the state of Wisconsin is using every year,
so 500,000 tons of salt at $80 a ton,
if we can reduce salt use by 50%,
the state can save millions of dollars
and we can also protect our freshwater rivers and lakes.
So there's lots of incentive to reduce our salt use.
There's also a lot of effort on the legislation side
to try to pass limited liability legislation
to protect people who use best salting practices
from things like slip and fall lawsuits.
If you're using best management practices,
you shouldn't be able to be sued as a landowner.
So there's lots of effort in the state
going towards trying to reduce salt use
and trying to protect people
who make environmentally informed decisions
when it comes to salt.
So, what can you do to reduce your salt use?
Well, here's a great video made by Wisconsin Sea Grant
on UW-Madison's campus,
focused on how you can reduce your salt use.
We apply de-icer
over a lot of the different impervious surfaces
in the winter, so parking lots, roads, sidewalks.
And as soon as that salt usually is hit with water,
it dissolves and it goes anywhere the water goes.
So in this case, it runs into storm sewers
and straight into our lakes.
In Wisconsin, we have a lot of freshwater.
And as we start to have salt runoff from de-icers
pollute those lakes,
the concentration of salt starts increasing.
And you can think of it like you think of yourself.
If you eat too much salt, it's bad for you.
We need freshwater to drink and to survive,
and so do the organisms that live in the lake.
So as we start increasing those salt concentrations,
it starts hurting anything that lives
and has evolved to live in freshwater.
And the problem for humans really
is that the lake is connected to our groundwater
and we're seeing our groundwater concentrations of salt
increase as well,
which means our drinking water is getting saltier.
So the good thing about chloride
and sort of salt pollution in general
is that it's definitely a solvable problem.
It dissolves in water, and so as the lake flushes out,
the concentrations will decrease.
And so for us to lower the concentration
of salt in our water,
all we need to do is stop putting it in.
It's really that simple.
- The key to keeping sidewalks clear in the winter
is to manually remove as much snow and ice as you can
using shovels and brooms
before you think about applying salt.
Using salt on top of snow just creates ice or slush,
which you'll have to clean up later.
Another challenge is clearing snow
during a snowfall or snowstorm.
When people walk on the sidewalks,
the snow can become compacted and is harder to remove.
The trick is to start mechanical snow removal early,
right when it starts snowing, then work all through the storm.
Clearing snow throughout the storm
will stop snow from compacting.
Temperatures usually drop after a storm,
and sidewalks can become so cold that salt cannot work properly.
Using more salt when it is cold isn't going to work.
If you need to clear compacted snow or ice,
use an ice chisel or an ice scraper.
- So often, if we get out early,
we can shovel and remove ice
and that takes care of a lot of the problem.
Obviously, salt is necessary in certain circumstances,
when it's really icy out,
but a little salt goes a long way.
- So, how much salt should you use?
Here's a simple way to look at it.
A coffee mug of salt is enough to treat
an entire 20-foot driveway or 10 sidewalk squares.
So if your area is about five sidewalk squares,
use a half a coffee cup.
If it is more like 20 sidewalk squares,
use two coffee cups of salt.
If you can't estimate the size of a certain space,
make sure that you are spreading the salt
so that there are no overlapping pieces.
The pieces should be no more than three inches apart.
You rarely need the salt spread more densely than this.
A little salt goes a long way,
so you only need to reapply in special circumstances,
such as when snow is continually melting and refreezing.
Other weather conditions will affect
how and when you apply salt.
If it's a warm day and the sidewalk or steps look wet,
you don't need to apply salt
because the sun is doing the melting.
If it is an average winter day, salt will work fine to melt ice.
But on a very cold, below-zero day,
salt may not work.
To decide what salt to use,
you need to consider the temperature of the air
and the temperature of the pavement.
Sodium chloride or rock salt works for an average day,
but will not melt the ice
if it is below 15 degrees Fahrenheit.
Magnesium or calcium chloride works at colder temperatures,
but won't work below negative five degrees Fahrenheit.
If you are using a blended de-icer,
you will need to read the bag for application instructions.
Wisconsin Salt Wise provides
an easy-to-use application calculator
that allows you to enter the pavement temperature
and the type of salt you are using.
Then it'll tell you how much to use.
Make sure to keep the salt fresh and spreadable.
Store it in a tightly covered container
because many de-icers attract moisture
and turn into a solid lump if we keep them uncovered.
If you have applied too much salt or if you spilled some,
take a minute and sweep it up
and reapply it to a different slippery area.
- This problem of chloride pollution into water
is really at this nexus of trying to maintain public safety
while at the same time
being really environmentally friendly.
And so there's probably some middle ground
where we can use a lot less salt and maintain public safety
while still trying to protect our freshwater resources.
[gentle music]
So I hope you enjoyed that video.
And if you wanna learn more
about how you can do things at home to reduce your salt use,
I would recommend checking out wisconsinsaltwise.com.
It's a statewide organization aimed at reducing salt use
and there's lots of great information on their website.
So thank you for listening to my talk today,
and I hope you learned something interesting.
And your Wisconsin lakes and rivers thank you.