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Can A Salt Marsh Recover After Restoration?
Featured scientists: NOAA, Liz Duff from Mass Audubon, and Bob Allia & 7th graders
from Rockport Middle School. Written by: Bob Allia, Cindy Richmond, & Dave Young
Research Background:
In the 1990s, it was clear that the Saratoga Creek Salt Marsh in Rockport, MA was in trouble.
The invasive plant, Phragmites australis, covered large areas of the marsh. The thick patches of
Phragmites crowded out native plants and reduced the number of animals, especially migrating
birds, because it was too thick to land in. Salt marshes are wetland habitats near ocean coasts
that have mostly water-loving, salt-tolerant grasses. Human activity was having a huge effect on
the health of the Saratoga Creek Salt Marsh by lowering the salinity, or salt concentrations in
the water. Drains built by humans to keep water from rainstorms off the roads changed how
water moved through the marsh. The storm drains added a lot of runoff, or freshwater and
sediments from the surrounding land, into the marsh after rainstorms. Adding more freshwater
to the marsh lowers salinity. The extra sediment that washed into the marsh raised soil levels
along the road. If the soil levels get too high, the salty ocean water does not make it into the
marsh during high tide. Perhaps these storm drains
were changing the salinity of the marshes in a way
that helped Phragmites because it grows best when
salinity levels are low.
In 1998, scientists, including members of the Rockport
Conservation Commission and students from the
Rockport Middle School science club, began to look at
the problem. They wanted to look at whether
freshwater runoff from storm drains may be the reason
Phragmites was taking over the marsh. They were
curious whether the salinity would increase if they
made the storm water drain away from the marsh.
They also thought this would stop the runoff sediments
from raising soil levels. If so, this could be one way to
restore the health of the salt marsh and reduce the
amount of Phragmites.
In 1999, a ditch was dug alongside the road to collect
runoff from storm drains before it could enter the
marsh. A layer of sediment was also removed from the
marsh so ocean water could reach the marsh once
again. Students set up transects, specific areas
chosen to observe and record data. Then they
measured the growth and abundances of Phragmites
Students collecting salinity data at a
transect point. The tall tan grass is
Phragmites.
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found in these transects. They also measured water salinity levels. Transects were 25 meters
long and data were collected every meter. The students decided to compare Phragmites data
from before 1999 and after 1999 to see if diverting the water away from the marsh made a
difference. They predicted that the number and height of Phragmites in the marsh would go
down after freshwater runoff was reduced after restoration.
Students in Phragmites portion of marsh.
Student using a refractometer to measure salinity.
Scientific Question: How did diverting freshwater runoff away from the marsh change
the number and height of Phragmites plants in the salt marsh?
What is the hypothesis? Find the hypothesis in the Research Background and underline
it. A hypothesis is a proposed explanation for an observation, which can then be tested
with experimentation or other types of studies.
View of Saratoga Creek Salt Marsh several years after restoration,
showing location of one of the transects. Native grasses are growing in the foreground.
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Scientific Data:
Use the data below to answer the scientific question:
1998
Average
Phragmites
Height (cm)
(no data)
Frequency of
Phragmites
(%)*
36%
1999
2000
280.3
196
36%
32%
2001
183
(no data)
2002
2003
177.5
200.5
32%
40%
2004
173.2
44%
2005
2006
165.8
193
44%
40%
2007
155.7
44%
2008
2009
183
186.1
60%
48%
2010
127.8
32%
2011
2012
128.6
115.7
44%
32%
2013
97.5
8%
2014
2015
116.5
0
8%
0%
Year
(After Ditch)
*Frequency of Phragmites means percent of locations Phragmites were present in
along a 25 meter transect.
What data will you graph to answer the question?
Predictor variable: Year (before or after the ditch was installed)
Response variables: (1) Average Phragmites Height (cm)
(2) Frequency of Phragmites (%)
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300
After Ditch
250
200
150
100
2008
2009
2010
2011
2012
2013
2014
2015
2008
2009
2010
2011
2012
2013
2014
2015
2007
2006
2005
2004
2003
2002
2001
2000
0
1999
50
1998
Average Phragmites Height (cm)
Draw your graphs below:
Year
After Ditch
60%
50%
40%
30%
20%
2007
2006
2005
2004
2003
2002
2001
2000
0%
1999
10%
1998
Frequency of Phragmites (%)
70%
Year
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Interpret the data: Based on this evidence, write a statement that helps answer the
scientific question. Connect the pattern in the data to a pattern in the natural world.
Justify your reasoning using data.
Based on this data, it appears the restoration was successful
after some time (over a decade). Overall, we can see a decline
in Phragmites after the ditch was installed and extra sediment
was removed. In all years after 1999, Phragmites is shorter than
before 1999. Before 1999, it was 280.3 cm tall, and after the
tallest it ever got was 200.5 cm. This height data supports the
hypothesis that Phragmites was benefitting from lowered salinity
and increased sediments caused by runoff.
The frequency of Phragmites data is a little more difficult to
interpret. Before 1999, Phragmites was present at 36% of the
transect points. After the 1999 restoration, Phragmites numbers
rose to being present at 60% of transect points by 2008. This
would make it seem that the restoration was unsuccessful and
Phragmites was increasing in numbers. However, after 2008
numbers began to fall and by 2015 there was no Phragmites
detected along the transect. Assuming that all change in
Phragmites over the course of 15 years was caused by the
restoration, it would appear that though Phragmites did better
immediately following the restoration, eventually the
restoration was successful and their numbers were reduced
greatly.
TEACHER NOTE: Have a discussion with your students about what it
means to have only one data point for Phragmites height before
the restoration, and only two for Phragmites frequency (good
lead-in for the “Next Steps” section below). Is 1-2 years of
data before restoration enough to show a clear pattern before
and after restoration? Are you convinced that the restoration is
the force driving the patterns seen in the data? What data could
you collect to strengthen support for the hypothesis? More years
of data before the restoration would be helpful, or data from
other similar restorations would give replication beyond just
one site. With data from just one site and for only 1-2 years,
other factors could be changing the performance of Phragmites
(ex. weather or other human activities).
Your next step as a scientist: Science is an ongoing process. Did this study fully answer
your original question? What new questions do you think should be investigated? What
future data should be collected to answer them?
•
Why do you think the frequency of Phragmites increased
following restoration? One possibility is that removing
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•
•
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sediment caused a disturbance that temporarily favored
Phragmites, though once salinity levels began to go up and
there was no new sediment entering the system, Phragmites
numbers then dropped as expected. There is a lot of
scientific evidence that invasive species, like Phragmites,
benefit more from disturbance than do native plant species.
Students have now noticed that Phragmites has spread to
another part of the marsh near houses built near the marsh
area. Discuss why this might be happening and how you could
test your hypotheses.
Another question to look into is whether the native plants
have returned to take back land that was previously
occupied by Phragmites. Similar methods could be used to
measure the height and presence of native plants along the
same transects.
Additional teacher resources related to this Data Nugget:
Salt Marsh Science Website: for more information on the project and datasets
http://www.massaudubon.org/get-outdoors/wildlife-sanctuaries/endicott/salt-marsh-project
Data Nuggets developed by Michigan State University fellows in the NSF BEACON and GK-12 programs
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