310B Disertation

How sea level rise will affect Dublin’s wetlands

Case study: Portmarnock Saltmarsh

MAY 8, 2015Justin Donaghy

11125993

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

the future and should we be looking to other countries for inspiration to try and save these

rare and important habitats.

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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.

Perched salt marshes on a high energy coast: Implications for sea level

reconstructions.

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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

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.

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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

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

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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

1.5) Recorded grid reference.

1.6) Recorded distance between each sample.

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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.

1.5) Add trend line.

1.6) Add R2 value and equation.

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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%

Sample 3 Co ordinates 5325123 / 006 08 103

Cord Grass 90%

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Mud Flats no vegetation 10%

Sample 4 Co ordinates 5325154/ 006 08 103

Cord Grass ( Spartina anglica) 90 %

Mud flats 10 %

Sample 5

5325160/ 006 08 103

Cord Grass ( Spartina Anglica) 60 %

English scurvy grass ( Cochlearia Anglica) 20%

Mud Rush ( Juncus Maritimus) 20 %

Sample 6

5325163/ 006 08 103

Mud Rush ( Juncus Maritimus) Coverage 60 %

English scurvy grass ( Cochlearia Anglica) ) Coverage 40%

Sample 7

5325176/ 006 08 104

Sea Purslane ( Halimione portulacoides) 60% Coverage

Mud Rush ( Juncus Maritimus) 40 %

Sample 8

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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.

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Figure 1: Diagram of Grid reference samples and different zonation of

Portmarnock saltmarsh.

Source: Justin Donaghy and Deirdre O’crowley (2015).

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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).

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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).

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 19856800

6850

6900

6950

7000

7050

f(x) = − 0.0221987315010571 x + 6993.83615221987R² = 7.66088681244392E-05

Dublin Tide Station 1938-1980

Year

Sea

leve

l (m

m)

Figure 3: Dublin Tide station 1938-1980.

Source: Permanent service for mean sea level Dublin, 2015.

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1930 1940 1950 1960 1970 1980 1990 2000 2010 202067006750680068506900695070007050710071507200

f(x) = 1.58172073771146 x + 3851.20158977516R² = 0.26448291691218

Dublin Tide Station 1938-2009

Year

Sea

leve

l (m

m)

Figure 4: Dublin Tide station 1938-2009.

Source: Permanent service for mean sea level Dublin, 2015.

1975 1980 1985 1990 1995 2000 2005 2010 201567006750680068506900695070007050710071507200

f(x) = 7.25426446069001 x − 7465.25455303322R² = 0.58513581213931

Dublin Tide Station 1980-2010

Year

Sea

leve

l (m

m)

Figure 5: Dublin Tide station1980-2010.

Source: Permanent service for mean sea level Dublin, 2015.

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1850 1870 1890 1910 1930 1950 1970 1990 20106800

6850

6900

6950

7000

7050

7100

7150

7200

f(x) = 2.76693511507901 x + 1501.35729188861R² = 0.666259381248864

f(x) = 1.21997294182492 x + 4647.82492358571R² = 0.381063347212453

f(x) = 0.580343954333332 x + 5850.73388722716R² = 0.259333226006994

British data

aberdeenLinear (aberdeen)southendLinear (southend)HolyheadLinear (Holyhead)

Year

Sea-

Leve

l hei

ght a

bove

refe

renc

e (m

m)

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.

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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.

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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.

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Road which surrounds Saltmarsh

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).

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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

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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.

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