1. How sea level rise will affect Dublin’s wetlands
Case study: Portmarnock Saltmarsh
MAY 8, 2015
JUSTIN DONAGHY
11125993
2. 1
Introduction
In the I.P.C.C fifth assessment report on climate change by Working group 1 they concluded
“it is very likely that in the 21st century and beyond , sea level will have a strong regional
pattern, with some places experiencing significant deviations of local and regional change
from the global mean change” (I.P.C.C, 2013). There is no doubt that sea level is rising, the
problem now is to see how much and at what rate. Ireland as a small Island will no doubt be
affected by these changes but we must look at how we must cope with these changes.
Macrophytes such as seagrass found in Saltmarshes around Ireland are critical components of
estuarine ecology. They are part of the food chain, help improve water quality and control the
flow of sediments. This may lead to a die-back of less salt tolerant plant species and the
wildlife that depends on them (Department of Investment and investment fisheries, 2011).
There is a wide consensus in the scientific community that saltmarshes in Ireland are under
threat from rising sea level. The aim of this report is to see how rising sea level will affect
wildlife and plants in Dublin’s saltmarshes particularly Portmarnock where our data was
collected. The first objective will be to look at the rate of change. Is the saltmarsh under
immediate threat, is this change slowly happening or is it going to be a sudden change. Here
the I.P.C.C climate models will be looked at to see how accurate they are and should we trust
them. We will also use the Permanent service for mean sea level, this will look at the sea
level in Dublin from 1938. The next objective in this report will be the problem of coastal
squeezing. Most of Dublin’s coastline have built up areas, where are these plants to retreat to.
Can these structures be moved to allow these habitats to survive? The final objective will be
to look at future engineering projects, have the Dublin county councils planned anything for
3. 2
the future and should we be looking to other countries for inspiration to try and save these
rare and important habitats.
Literature Review
Sea level change and the area of shallow-marine habitat: Implications for marine
diversity.
This journal looks at sea level databases from around the globe and uses it to look at shallow
marine habitat. It looks at the diversity of species within these habitats and how they will be
affected. It has also used the fossil record as a proxy to measure past sea level change and the
diversity of species within these habitats
Recent variations in sea-level on the north and east coasts of Ireland and associated
shoreline response.
This paper has been looking at the data from from gauges at Dublin, Belfast and Malin head
over a 65 year period. It has identified rising and falling from all the different sets of data. It
has identified the rising in Dublin before 1961 and seen it being to fall thereafter. It has
looked at the Isostatic uplift in the north of the country and has concluded that the Isostatic
rebound in the south has reached its peak.
Coastal Vulnerability and implications of sea-level rise for Ireland.
This journal looks at Ireland’s coastal vulnerability. It has identified that Ireland has a low
population density along its coast and concluded that Ireland has a low vulnerability factor. It
has also concluded that 30% of its wetlands will be lost if there is a 1 metre rise in sea level
and that the Department of marine and natural resources have set up sub departments to plan
to try and save these wetlands.
4. 3
Perched salt marshes on a high energy coast: Implications for sea level
reconstructions.
This journal looks at the conditions for perched saltmarshes and the species that dwell in
them. It has identified how conditions on a high energy coast like the north of Ireland must be
just right. It has identified halophytes (plants that thrive in saltwater) and how they have
outcompeted the plants that grow in fresh water due to coastal spray.
Intergovernmental Panel on Climate Change: Data Distribution centre.
Every time the I.P.C.C release a report they release their predictions on climate change and
their predictions on sea level rise. They also offer computer models which give a number of
different scenarios for future sea level rise. This is a quality database which should be utilised
for this project.
Co-ordination communication and adaptation for climate change in Ireland: an
Integrated approach (c.o.c.o.a.d.a.p.t)
This paper released by the E.P.A and ICARUS looked at the implications of climate change
in Ireland. They did touch on coastal habitats but focused mainly on the west of Ireland and
Mayo. They also looked at the commercial aspect of the changes. The coastal habitats they
looked at where dunes and vegetated sea cliffs but why not saltmarshes?
Tidal Marsh plant community response to sea level rise: a mesocasm study. Aquatic
Botany
In this paper Sharpe has looked at the intrusion of saltwater into freshwater tidal coastal
vegetation and has concluded that saltwater will not immediately kill the diversity of species
it is not until a constant brackish water arrives that the less salt tolerant species start to die
5. 4
off. This all depends on the rate of change, like in Portmarnock a slow rate will allow these
species to retreat but if its fast they will be inundated and die off quickly.
Towards successful adaptation to sea-level rise along Europe’s coasts. Journal of coastal
research
In this journal Klien and Nicholls have looked the vulnerability of each European coastal
country and have gave them a high vulnerability and low vulnerability. In Ireland’s case the
vulnerability is low. They have also stated that Ireland’s awareness to sea level rise is low
with no real plan of adaptation. They have made recommendations in that countries should be
sharing ideas and looking at each others problems.
Climate change adaptation in Ireland: a blueprint without a builder.
This report has looked at Ireland’s framework adaptation towards climate change and sea
level rise and has concluded that Ireland has no real concrete plans when it comes to
implementing change. It has concluded that Ireland has not followed any of the E.U
directives.
Remote sensing tools to quantify ecological impacts of sea level rise on barrier estuaries.
In this report they have used remote sensing as a tool to look at the impact of sea level rise on
estuarine eco-systems. This was a technique that I wanted to use in this report but with
limited time and resources I was not able to accomplish this. They looked at archival data and
compared it with modern images of estuarine eco-systems. There results were not conclusive,
they did notice small changes but not significant ones which would suggest that this
technique is not ready to be used.
Sea level rise: the impacts and economic costs of sea level rise on coastal zones in the E.U
and the costs and benefits of adaptation
6. 5
This report was written by habitats directive which is an E.U controlled institution tasked
with protecting habitats throughout Europe. In this report they looked at all the possible high
risk areas and calculated the cost. They gave possible solutions but mainly from a
commercial point of view. While they did touch on coastal habitats and a few mentions of
coastal squeezing. They gave no real solutions to saving these habitats from sea level rise.
METHODOLOGY
1.) Collection of Data at Portmarnock Saltmarsh county Dublin, Sunday 15th February
2015.
Plate 1: Erecting quadrats in Portmarnock.
Source: Justin Donaghy, 2015.
1.1) Established a transect line that will cross most zones of interest.
1.2) Used a 0.5 squared quadrat to identify the plant species present
1.3) Identified plants using an identification key.
1.4) Estimated percentage cover of vegetation
7. 6
1.5) Recorded grid reference.
1.6) Recorded distance between each sample.
1.7) Identify the plant zonation’s
Plate 2: 0.5 quadrat.
Source: Justin Donaghy, 2015.
2.) Analysis of data from the Dublin Tidal station using the Permanent service for mean
sea level.
1.1) In this data manipulation we used excel 2013.
1.2) Up loaded Dublin data from Permanent service for mean sea level.
1.3) Allocate correct data to x-axis and y-axis.
1.4) Produce scatter box.
8. 7
1.5) Add trend line.
1.6) Add R2 value and equation.
3.) Analysis of future adaptation projects or hard engineering projects to save these
habitats.
1.1) Analysed data from E.U Habitat directives.
1.2) Analysed future suggestions of government report.
1.3) Analysed future proposals of I.C.A.R.U.S report on climate change
adaptation.
Results
Quadrat results
Sample 1 Co-ordinates : 5325 113/ 006 08 106
Cord Grass 50%
Mud flats no vegetation 50%
Sample 2 Co-ordinates 5325116 / 006 08 103
Cord Grass 70%
Mud Flats no vegetation 30%
10. 9
Mud Rush ( Juncus Maritimus) 40 %
Sample 8
5325186/ 006 08 105
Sea Couch Grass (Elymus Pycnanthus) 90%Coverage
Sea Purslane ( Halimione portulacoides) 10% Coverage
Sample 9
5325192/ 006 08 109
Sea Couch Grass (Elymus Pycnanthus) 95% Coverage
Sea Rush (Juncus Maritmus) 5 % Coverage
Sample 10
5325198/ 006 08 109
Sea Couch Grass ( Elymus Pycnanthus) 90% Coverage
Shrubby Sea Blite ( Suaeda fruticosa) 10 coverage
These samples were taken on the 15th of February 2015. The tools we used were a G.P.S
device, magnifier, Plant identifier log, 0.5 squared quadrat and a log book. A transect line
was established and we identified the three different zonation’s (see figure 1). We decided to
take about three different samples per zonation’s. This we hoped would eliminate bias and we
would get a varied and balanced samples.
11. 10
Figure 1: Diagram of Grid reference samples and different zonation of
Portmarnock saltmarsh.
Source: Justin Donaghy and Deirdre O’crowley (2015).
12. 11
The grid reference points were taken on February 15th 2015. They mark out our transect line
which crosses the three different zonation’s. As you can see we tried to have three different
samples in each zonation.
Figure 2: Representative concentration pathway. (R.C.P)
Source: Intergovernmental panel on climate change (2014).
13. 12
These models were released by I.P.C.C, as you can see they all have different scenarios. The
reason for this is they all have different inputs. The problem here is that future climate is
unpredictable. The I.P.C.C do not know how much more CO2 will be pumped into the
atmosphere, they do not know how quickly the world’s major ice sheets will melt. These
models makes it hard for the worlds governments to prepare (Intergovernmental panel on
climate change, 2014).
Figure 3: Dublin Tide station 1938-1980.
Source: Permanent service for mean sea level Dublin, 2015.
y = -0.0222x + 6993.8
R² = 8E-05
6880
6900
6920
6940
6960
6980
7000
7020
7040
1930 1940 1950 1960 1970 1980 1990
Sealevel(mm)
Year
Dublin Tide Station 1938-1980
14. 13
Figure 4: Dublin Tide station 1938-2009.
Source: Permanent service for mean sea level Dublin, 2015.
Figure 5: Dublin Tide station1980-2010.
Source: Permanent service for mean sea level Dublin, 2015.
y = 1.5817x + 3851.2
R² = 0.2645
6800
6850
6900
6950
7000
7050
7100
7150
7200
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Sealevel(mm)
Year
Dublin Tide Station 1938-2009
y = 7.2543x - 7465.3
R² = 0.5851
6800
6850
6900
6950
7000
7050
7100
7150
7200
1975 1980 1985 1990 1995 2000 2005 2010 2015
Sealevel(mm)
Year
Dublin Tide Station 1980-2010
15. 14
Figure 6: Sea level change of Aberdeen, Southend and Holyhead.
Source: Permanent service for mean sea level, 2015.
These scatter boxes were produced using excel and data from the permanent service for mean
sea level database. We were looking to find a correlation value, a relationship between the
sea level height and the years. This is called the R2 value. The higher the R2 value the greater
the relationship which means there is a correlation. The lower the R2, means there is no
correlation.
y = 0.5803x + 5850.7
R² = 0.2593
Aberdeen
y = 1.22x + 4647.8
R² = 0.3811
Southend
y = 2.7669x + 1501.4
R² = 0.6663
Holyhead
6800
6850
6900
6950
7000
7050
7100
7150
7200
1850 1900 1950 2000
Sea-Levelheightabovereference(mm)
Year
British data
aberdeen
southend
Holyhead
Linear (aberdeen)
Linear (southend)
Linear (Holyhead)
16. 15
Discussion
The Permanent service for mean sea-level was established in 1933 basically for the collection
of sea level data. They have stored data from collection points from all around the world. The
data we will look at is the data collected at Dublin port. It is the only recording station in the
Republic of Ireland, the west coast has no recording stations.
We will look at the data at three different time brackets and compare the data, looking at the
correlation value to see if there is a relationship between time and sea-level. We will look at
all the data from 1938 (the year it started recording) – 2009 (Figure 4). Then look at specific
time brackets like 1980-2010(Figure 3) then from 1938-1980 (Figure 3) to see if there is any
significant change.
As you can see from figure 3(1938-1980) the trend line is straight suggesting that there is a
weak relationship between time and sea level as the points in the scatter box are high some
years and low in others. This would suggest just a natural variations and no real climb in sea
level. Figure 5(1980-2010) shows a different story, the R2 value is much higher and the trend
line is more of an angle. This suggests a significant rise over a 30 year period. Figure 4 shows
show’s all of the data collected from it started until present day, it has a lower R2 value than
figure 5 and less of an angle in its trend line but this is over a longer period and it is
significant as it shows the same trend as figure 5.
Also added are results from three other measuring stations in Britain. Aberdeen, Southend
and Holyhead. As we can see from figure 6 the trend lines have the same pattern as the
Dublin data.
17. 16
This evidence suggests that there is a gradual rise in sea-level. Studies have shown that sea-
level has been rising at a rate of 0.04- 0.1 inches per year since 1900 (N.O.A.A: National
Oceanic and atmospheric Administration, 2015). From our evidence from our scatter boxes
this rate seems to be on the rise. What does this mean for the plants and wildlife in
Portmarnock and the Dublin area?
As I have said in my introduction Dublin has a lot of built up areas along its coast. As we can
see from Plate 1 the salt marsh is surrounded by a road and the town itself is just a stone’s
throw from the marsh itself. This is a classic example of coastal squeeze. In Ireland the
transfer of coastal sediment has almost ceased (Devoy, 2008). Along most of Ireland’s coast
there have been barriers built to combat erosion and you will find that along Ireland’s coasts
especially Dublin you will find roads. Even in Dublin’s east coast you will find the east coast
railway to Greystones (Devoy, 2008).
Plate 3: Image of Portmarnock Beach
Source: Google maps, 2015.
Road which
surrounds
Saltmarsh
18. 17
In 2009 the European Union set guidelines for climate change adaptation. These guidelines
were to show member states strategies on combating climate change including adaptation for
rising sea level. In response the Irish government did its own risk assessment and produced
guidelines to combat it. It was called the National climate change adaptation framework. The
framework failed to address any real issues and had no real plan to combat the problem of the
loss of the saltmarshes (Irish Environment, 2015). A report was released by I.C.A.R.U.S
(Irish climate analysis and research units) a department of geography at Maynooth
University. It was called C.O.C.O.A.D.A.P.T (Co-ordination, communication and adaptation
for climate change in Ireland). In their report they looked at all aspects of Irish society and
how would impact. They also looked at biodiversity and concluded that there is a high risk to
their habitats but gave no definitive result on what should be done. While this report did look
at coastal habitats, saltmarshes did not feature in their report. This would suggest that more
research needs to be done.
As we can see in figure 2 the I.P.C.C has produced computer models of possible sea level
scenarios. If we compare this data with the data from the Dublin and British data we see a
similar trend. The I.P.C.C ran eight different models each with different inputs (I.P.C.C,
2014). They ran models without the input of the of land glaciers. They ran a model without
the input of the Greenland and Antarctica Ice sheets and on one model did not take into
account thermal expansion. All show sea level rising in the 21st century. The problem with
computer models is that they are not a truth and should only be looked at as a guideline. In
one model R.C.P 8.5, it shows a rise of 1 metre by 2100 and on a different model R.C.P 6.0,
it shows a rise of 0.5 of a metre by 2100. Which one should be trusted? There are so many
variables that go into these computer models that there can be so many outcomes. Tweak a
model with a smaller variable and you could have a very different outcome (I.P.C.C, 2015).
19. 18
On our fieldtrip one of our objectives was to take recordings of the different plant species
using the quadrats shown in plate 2. We also recorded the different zonation’s shown in
figure 1.clearly shown is the upper marsh (which is in blue) the middle marsh (orange) and
lower marsh (purple) The different zonation are caused by the spring and neap tides. The
plants in the upper marsh would be less salt tolerant to the plants in the lower marsh like
cordgrass (Spartina anglica). With relative sea level on the rise all the plants on the marsh
would see a constant inundation of sea water and would struggle to survive (Sharpe, 2012).
With Spartina being an invasive species most botanist would be happy but Spartina has a
strong root system and does combat against coastal erosion (Sharpe, 2012).
Hard or even soft engineering projects for rising sea level can be very costly but effective.
There are usually three approaches to rising sea level (Brown et al, 2013). Retreat,
accommodation and protection. Retreat would usually involve pulling back from any
shoreline that was at risk of inundation but this would only be a human risk. If it where the
case in Portmarnock, the marsh would be able to retreat with it and would survive but the
economic cost would be high (Brown et al, 2013). Accommodation is more of a human
aspect and involves making people aware of flooding and setting up warning systems.
Protection involves soft and hard engineering projects like building dunes and sea walls. This
technique does not really help coastal habitats like Portmarnock as these measures would lead
to coastal squeezing which we are trying to avoid.
Conclusion and summary
The results of our study suggest that Portmarnock saltmarsh is in a healthy condition and is in
no immediate threat. Most of Ireland’s wetland are surviving well for now (Devoy, 2008). If
we take into account our scatter boxes of the data from the P.S.M.S.L the evidence really
speaks for itself, sea level is rising and the rate is getting faster. The problem for these
20. 19
wetlands is that they are literally stuck between a rock and a hard place as they have almost
nowhere to retreat to (see plate 3). The Government has slowly addressed the issue of climate
change and the consequences that go with it. There seems to be less interest in these
saltmarshes and more of an issue in commercial issues. This is understandable. The cost to
save peoples homes will always come before a natural habitat which will be costly in itself. If
these habitats were simply left to die off it would have severe implications for the local
wildlife. There needs to be more research on how to save these habitats at a minimal cost.
Can a compromise be achieved? All the hard and soft engineering projects viewed have
mostly involved building massive sea walls and improving existing sand dunes. As
saltmarshes rely on tidal movements these projects are really pointless in saving saltmarshes.
This is going to be a difficult endeavour luckily we do have time to adapt. If we look at the
representative concentration pathways models, R.C.P 2.6 gives a 0.26 to 0.55 metre rise by
2100, this is the best case scenario, the worst case scenario is R.C.P 6.0 which gives a 0.45 to
8.2 metre rise by 2100 (I.P.C.C, 2014). This does give us time to adapt and mitigate the
problem.
Limitations
More than one field trip should be conducted and at different times of the year. As we went in
February most of the vegetation was dead and very hard to identify. A summer fieldtrip
would be the ideal time. Data needs to be taken at different tides for example high, spring and
neap tides. In the case of Portmarnock there should be established a datum line to monitor
these changes. This would not be difficult and very low cost.
21. 20
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