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Keeping up with the sea level
Featured scientist: Anne Giblin from the Marine Biological Laboratory and the
Plum Island Ecosystems Long-Term Ecological Research site
Research Background:
Salt marshes are ecosystems that occur along much of the coast of New England in the United
States. Salt marshes are very important – they serve as habitat for many species, are a safer
breeding location for many fish, absorb nutrients from fertilizer and sewage coming from land
and prevent them from entering the ocean, and protect the coast from erosion during storms.
Unfortunately, rising sea levels are threatening these important ecosystems. Sea level is the
elevation of the ocean water surface compared to the elevation of the soil surface. Two
processes are causing sea levels to rise. First, as our world gets warmer, ocean waters are
getting warmer too. When water warms, it also expands. This expansion causes ocean water to
take up more space and it will continue to creep higher and higher onto the surrounding coastal
land. Second, freshwater frozen in ice on land, such as glaciers in Antarctica, is now melting
and running into the oceans. Along the New England coast, sea levels have risen by 0.26 cm a
year for the last 80 years, and by 0.4 cm a year for the last 20 years. Because marshes are
such important habitats, scientists want to know whether they can keep up with sea level rise.
When exploring the marsh, Anne, a scientist at the Plum Island Ecosystems Long Term
Ecological Research site, noticed that the salt marsh appeared to be changing over time. One
species of plant, salt marsh cordgrass (Spartina alterniflora), appeared to be increasing in some
areas. At the same time, some areas with another species of plant, salt marsh hay (Spartina
patens), appeared to be dying back. Each of these species of plants is growing in the soil on the
marsh floor and needs to keep its leaves above the surface of the water. As sea levels rise, the
elevation of the marsh soil must rise as well so the plants have ground high enough to keep
A view of salt marsh hay growing in a marsh
Researcher Sam Bond taking Sediment Elevation
Table (SET) measurements in the marsh
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Teacher Copy, Level 3
Name_________________
them above sea level. Basically, it is like a race between the marsh floor and sea level to see
who can stay on top!
Anne and her colleges measured how fast marsh soil elevation was changing near both species
of plants. They set up monitoring points in the marsh using a device called the Sediment
Elevation Table (SET). SET is a pole set deep in the marsh that does not move or change in
elevation. On top of this pole there is an arm with measuring rods that record the height of the
marsh surface. The SETs were set up in 2 sites where there is salt marsh cordgrass and 2 sites
where there is salt marsh hay. Anne has been taking these measurements for more than a
decade. If the marsh surface is rising at the same rate as the sea, perhaps these marshes will
continue to do well in the future.
Scientific Questions: Is marsh elevation rising in the same way where both types of
vegetation live? Is either species keeping up with sea level rise?
Scientific Data:
Use the data below to answer the scientific questions:
Marsh soil
Species
Location Year elevation (cm)
salt marsh cordgrass
1
2002
0
salt marsh cordgrass
1
2003
0.7
salt marsh cordgrass
1
2004
1.68
salt marsh cordgrass
1
2005
2.25
salt marsh cordgrass
1
2006
3.18
salt marsh cordgrass
1
2007
3.81
salt marsh cordgrass
1
2008
4.64
salt marsh cordgrass
1
2009
5.41
salt marsh cordgrass
1
2010
5.92
salt marsh cordgrass
1
2011
6.82
salt marsh cordgrass
1
2012
7.17
salt marsh cordgrass
2
2002
0
salt marsh cordgrass
2
2003
0.43
salt marsh cordgrass
2
2004
1.25
salt marsh cordgrass
2
2005
2.11
salt marsh cordgrass
2
2006
2.92
salt marsh cordgrass
2
2007
3.88
salt marsh cordgrass
2
2008
4.68
salt marsh cordgrass
2
2009
5.41
salt marsh cordgrass
2
2010
6
salt marsh cordgrass
2
2011
7.17
salt marsh cordgrass
2
2012
7.77
Marsh soil
Species
Location Year elevation (cm)
salt marsh hay
1
2002
0
salt marsh hay
1
2003
0.99
salt marsh hay
1
2004
0.22
salt marsh hay
1
2005
0.99
salt marsh hay
1
2006
0.98
salt marsh hay
1
2007
1.22
salt marsh hay
1
2008
1.72
salt marsh hay
1
2009
1.71
salt marsh hay
1
2010
1.42
salt marsh hay
1
2011
1.83
salt marsh hay
1
2012
1.57
salt marsh hay
2
2002
0
salt marsh hay
2
2003
0.02
salt marsh hay
2
2004
0.53
salt marsh hay
2
2005
0.84
salt marsh hay
2
2006
1.55
salt marsh hay
2
2007
1.97
salt marsh hay
2
2008
1.97
salt marsh hay
2
2009
2.35
salt marsh hay
2
2010
2.49
salt marsh hay
2
2011
2.69
salt marsh hay
2
2012
2.81
Data Nuggets developed by Michigan State University fellows in the NSF BEACON and GK-12 programs
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Teacher Copy, Level 3
Rate of marsh soil elevation rise =
total elevation gained (cm)
time (years)
Calculate the rate of marsh soil elevation rise based on the equation above:
Salt marsh cordgrass 1
7.17 – 0
Rate of marsh soil elevation rise =
2012 – 2002
=
7.17
10
= 0.717 cm/year
=
7.77
10
= 0.777 cm/year
=
1.57
10
= 0.157 cm/year
=
2.81
10
= 0.281 cm/year
Salt marsh cordgrass 2
7.77 – 0
Rate of marsh soil elevation rise =
2012 – 2002
Salt marsh hay 1
1.57 – 0
Rate of marsh soil elevation rise =
2012 – 2002
Salt marsh hay 2
2.81 – 0
Rate of marsh soil elevation rise =
2012 – 2002
Teacher Note: The tables give marsh soil elevation over time for 2 salt marsh cordgrass
sites and 2 salt marsh hay sites. Students should use the data to calculate the rate of soil
elevation rise for each of the 4 sites. The slope of the line drawn through the points
(regression line) is the rate that the elevation is increasing per year. Students can
calculate the rate of soil elevation change per year between 2002 and 2014 for each site
by determining the total gain in marsh soil elevation, divided by the number of years.
Students then compare this value to the sea level rise values we have for New England,
found in the Background section. Remember, along the New England coast, sea levels
have risen by 0.26 cm a year for the last 80 years, and by 0.4 cm a year for the last 20
years.
What data will you graph to answer the questions?
Independent variables: year and type of vegetation (salt
marsh hay or salt marsh cordgrass)
Dependent variable: salt marsh elevation (cm)
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Teacher Copy, Level 3
Draw your graph below:
Marsh Soil Elevation (cm)
9
8
7
6
5
cordgrass 1
4
cordgrass 2
3
hay 1
hay 2
2
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
0
2002
1
Year
Interpret the data:
What trends, changes, or differences do you see in the table or on the graph?
There is a positive trend on the graph. Over time there is a
change in elevation – elevation is going up under both Spartina
species. There is a difference between the two species – the
positive trend is steeper for sites with salt marsh cordgrass
than it is for salt marsh hay sites.
What is the relationship between the dependent and independent variables? What does
the relationship between the variables mean?
There is a positive relationship between the continuous
independent variable (time) and continuous dependent variable
(salt marsh elevation). This means that over the years, the salt
marsh elevation is going up. There is also a difference based on
the independent variable (Spartina species). The slope is
steeper under salt marsh cordgrass, meaning that the elevation
is going up faster under this species.
Data Nuggets developed by Michigan State University fellows in the NSF BEACON and GK-12 programs
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Teacher Copy, Level 3
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Make a claim that answers each of the scientific questions.
The marsh is not rising at the same rate near the two species –
the soil is gaining elevation at a much quicker rate near salt
marsh cordgrass compared to salt marsh hay (almost 3 times
faster!). The sites where salt marsh cordgrass lives are keeping
up with sea level rise, while the marsh where salt marsh hay
lives are not.
Support your claims using data as evidence. Reference specific parts of the table or
graph.
Soil is rising at a rate of 0.717 cm/year at site 1 and 0.777
cm/year at site 2 near salt marsh cordgrass. Soil is rising at a
rate of 0.157 cm/year at site 1 and 0.281 cm/year at site 2 near
salt marsh hay. Along the New England coast, sea level has been
rising by 0.4 cm a year for the last 20 years.
Explain your reasoning and how the data supports your claim. Connect the rates of
marsh elevation rise under each Spartina species and what we know about the rate of
sea level rise in New England.
Because sea level has been rising by 0.4 cm/year for the last 20
years, the data shows that the habitat near one species of grass
is keeping up with sea level rise - salt marsh cordgrass. The
gain in elevation of 0.7 cm near this species is more than
enough to keep up with the current rate of sea level rise. The
rate of soil elevation rise near Spartina patens is below that
of the current rate of sea level rise, meaning those sites are
not keeping up. Gaining between 0.157 and 0.281 cm/year is not
enough to keep this species alive with sea levels rising at 0.4
cm/year. These findings support the observations made by the
scientists that populations of salt marsh cordgrass are
increasing in the marsh over time while salt marsh hay seems to
be dying back.
Your next steps as a scientist:
Science is an ongoing process. Did this study fully answer Anne’s original questions?
More sites could be added to see if this pattern holds true
across the range of both Spartina grass species (data from 2
sites were reported here, more sites would increase
replication). Are there places that salt marsh hay appears to be
doing well? Perhaps in those areas of the marsh, soil is rising
in elevation more quickly near this species.
Data Nuggets developed by Michigan State University fellows in the NSF BEACON and GK-12 programs
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What new questions do you think should be investigated?
What causes soil elevation to rise over time, and what explains
the difference between soil elevation rise near the two Spartina
species?
What hypothesis would you like to test? A hypothesis is a proposed explanation for an
observation, which can then be tested with experimentation or other types of studies.
As water flows by the stems and leaves of plants growing in the
marsh, it slows down and sediments fall out of the water column
and raise the elevation of the soil. Perhaps the elevation of
the soil around salt marsh cordgrass was increasing at a faster
rate because it is closer to the creeks, so much of the
sediments fall out before it reaches the salt marsh hay, and
because salt marsh cordgrass is at a lower elevation so it is
flooded more frequently.
What future data should be collected to test your hypothesis?
Independent variable(s): type of vegetation at the site (salt
marsh cordgrass or salt marsh hay)
Dependent variable(s): Elevation of the plants and amount of
sediment deposited at each site
For each variable, explain why you included it and how it could be measured.
I would want to know if sites with the two different species
were at different elevations because this would tell me if one
species is flooded more often than the other. Remember not all
tides are equally high. To measure this I could coat some dowels
or lath with Elmer’s glue dyed with food coloring. Let it dry.
Put the stakes into the marsh soil at the sites with each plant
species at low tide. Mark the level of the soil. Come back and
collect the stakes at the next low tide and measure the distance
between the sediment and the maximum height of the water.
Because Elmer’s glue is water soluble, you will see this is the
area where the glue and color is gone.
To see if more sediment is deposited I would take 10 rough tiles
and place them out on the marsh surface for a few weeks, 5 in
each vegetation type. I would carefully collect the tiles and
compare how much sediment is on them. I would then scrape all of
the sediment off into a pre-weighted petri dish and dry it, or
wash it onto a pre-weighted piece of filter paper and dry it.
Data Nuggets developed by Michigan State University fellows in the NSF BEACON and GK-12 programs
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