Establishing a physical and biological basis for salt marsh restoration
ESTABLISHING A PHYSICAL
AND BIOLOGICAL BASIS FOR
SALT MARSH
RESTORATION AND
MANAGEMENT IN THE AVONHEATHCOTE ESTUARY,
CHRISTCHURCH.
KIMBERLY JUPP
University of Canterbury
2007
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
Abstract
In New Zealand salt marsh now only covers approximately 10% of the area it did
prior to European settlement. This loss can been attributed to development of the
margins, reclamation, and dredging. To prevent further loss and regain some areas of
salt marsh, restoration is tool that can be used.
Although sound in theory for
restoration work to be successful, scientific knowledge relating to the environmental
conditions the vegetation types grow in is required. This research uses Geographical
Positioning Systems (GPS) to create ArcGIS maps to give a spatial focus to the study.
Using nine vegetation types, relationships between the sediment size, elevation
and nitrate were explored. This research used GPS to create ArcGIS maps to give a
spatial focus to the study. Oioi rushland and sea rush rushland were found to be the
most abundant vegetation types in the Avon-Heathcote Estuary. With clear links
between vegetation types distribution and sediment size and elevation.
The
abundance of species was most significantly seen when comparing the physical
makeup of the margins surrounding the salt marsh. The areas containing the majority
of the salt marsh in the Avon-Heathcote Estuary were locations surrounded by natural
margins, in the Avon and Heathcote River outlets. This emphasises the importance of
these areas, and that they should be maintained, to prevent future salt marsh loss. The
studies concludes with the need for an Avon-Heathcote Estuary management plan,
which encompasses both the physical processes of the estuary and salt marsh, as well
as regulating development around the margins. To ensure future salt marsh existence,
it is vital that the natural margins of the Avon-Heathcote Estuary are protected, to
ensure future restoration work, and current salt marsh is not destroyed.
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Establishing a physical and biological basis for salt marsh restoration
Table of contents
Chapter One: Introduction
1.0 Background
1.2 Aims of study
1.3 Estuarine Environments
1.4 Salt Marsh
1.5 Restoration
1.6 Thesis Structure
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Chapter Two: Methdology
2.1 Field Site: Avon-Heathcote Estuary
2.1.1 Values
2.2 Previous studies of the Avon-Heathcote Estuary
2.2.1 Ecology
2.2.2 Sediment
2.2.3 Restoration
2.3 Methods
2.3.1 Sediment Sampling
2.3.2 Data Capture
2.4 Data Analysis
2.4.1 Clustyer Analysis
2.4.2 Nitrate, Nitrite, Phosphate
2.4.3 Salinity
2.4.4 Sediment Size
2.5 Spatial Analysis
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Chapter Three: Results
3.1 Vegetation Types
3.1.1 Vegetation Spatial Distribution
3.2 Vegetation Types vs. Sediment Size
3.3 Vegetation Types vs. Elevation
3.4 Vegetation Types vs. Nitrate, Nitrite and Phosphate
3.5 Vegetation Types vs. Salinity
3.6 Restoration Criteria
3.7 Limitations of the study
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Chapter Four: Discusion 2.2.3 Restoration
4.1 Vegetation Types and spatial distribution
4.2 Vegetation Types vs. Sediment Size
4.3 Vegetation Types vs. Elevation
4.4 Vegetation Types vs. Nitrate, Nitrite and Phosphate
64.5 Restoration 2.2.3 Restoration
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Establishing a physical and biological basis for salt marsh restoration
4.6 Management Issues
4.7 Recommendations
4.8 Future Research
Chapter Five: Conclusions
Acknowledgements
Literature Cited
Appendix One: Determining usefulness of restoration
Appendix Two: Avon-Heathcote Estuary zone descriptions and purposes
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List of Figures
Figure 1.1 Location of the Avon-Heathcote Estuary study area in Canterbury, New Zealand
7
Figure 1.2 Map showing the study areas surveyed in Jupp et al. (2007)
9
Figure 1.3 Cross sections depicting the natural stages of salt marsh vegetation, A. High
elevation tidal flat, B. Salt marsh vegetation colonising on higher points of tidal flat, C.
High marsh becomes fully vegetated, apart from creeks (Long and Mason 1983, p13)
13
Figure 1.4 Two-dimensional model depicting ecosystem development (Developed by
Bradshaw 1988, p56)
15
Figure 1.5 Stages in restoration. (Modified from Holl and Cairns 2002)
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Figure 2.1 Energy distribution of a tide-dominated estuary (Masselink & Hughes 2005,
p168)
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Figure 2.2 Model depicting current literature topics relating to the Avon-Heathcote Estuary,
the star indicates where this research fits
22
Figure 2.3 Kimberly capturing the margins of the Avon-Heathcote Estuary using a Trimble
Geo-XM unit
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Figure 2.4 Base station
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Figure 2.5 GNSS rover and external antenna
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Figure 3.1 Oioi (Apodasmia similis)
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Figure 3.2 Sea rush (Juncus krausii)
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Figure 3.3 Suaeda (Suaeda novae-zelandiae)
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Figure 3.4 Coastal ribbonwood (Plagianthus divaricatus)
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Figure 3.5 New Zealand musk (Mimulus repens)
Figure 3.6 Map showing spatial distribution of the major salt marsh community types in the
Avon-Heathcote Estuary, as well as the area of artificial and natural margins.
37
Figure 3.7 Map showing the materials which make up the margins of the Avon-Heathcote
Estuary and the locations of the salt marshes
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Figure 3.8 Sediment size distribution surrounding areas of salt marsh in the Avon-Heathcote
Estuary
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Figure 3.9 Percentage of sediment size in each sample for each vegetation type
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Figure 3.10 Elevation around the margins of the Avon-Heathcote Estuary, obtained using a
Trimble R8 GNSS rover
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Figure 3.11 Elevation range of vegetation types present in the Avon-Heathcote Estuary
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Figure 3.12 Distribution of soil nitrate levels, in areas of salt marsh growth in the AvonHeathcote Estuary
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Figure 3.13 Elevation range of vegetation types present in the Avon-Heathcote Estuary
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Establishing a physical and biological basis for salt marsh restoration
Chapter One
Introduction
1.0 Background
Around the world, increased human activity in the coastal environment has
had a detrimental impact on salt marsh ecosystems. With 22 out of the world’s 32
largest cities bordering estuaries, including New York and London, much of the
world’s salt marsh vegetation is under threat and declining at a rapid rate (Hutchison
1972). This trend is also evident in New Zealand, with 90% of the country’s salt
marsh vegetation having disappeared since European settlement (Dugan 1993). In
Canterbury, the Avon-Heathcote Estuary has undergone the same decline as a results
of increased human activities around the margins and catchment. Located in eastern
Christchurch (Figure 1.1), the Avon-Heathcote Estuary contains one of the largest
areas of salt water creek in the province (Rodrigo 1985). As salt marsh decline is
beginning to be documented and acknowledged by governments, salt marsh
restoration has taken a pivotal role in ensuring that it is present for future generations.
For restoration to be successful, scientific knowledge of the environmental variables
operating in healthy salt marsh systems is required.
This research combines
ecological and sediment understanding and relates these to zonation of salt marsh
vegetation.
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Establishing a physical and biological basis for salt marsh restoration
Figure1.1 Location of the Avon-Heathcote Estuary study area in Canterbury, New Zealand
1.2 Aims of study
Recent salt marsh restoration work around the Avon-Heathcote Estuary has
had very limited success. This has produced static, artificial-looking marsh areas in
which species dynamics do not resemble those of adjacent natural ecosystems and,
therefore, in which species have had a low survival rate (Jason Roberts, Coastal Parks
Ranger, Christchurch City Council, pers. comm. 2007). For salt marsh restoration to
be effective a greater level of emphasis needs to be placed on the concepts and
scientific understanding of New Zealand’s salt marsh systems. This research fits into
the conceptual idea that estuaries are dynamic environments with interrelating
biological and physical relationships.
It aims to create a framework that draws
together ecological knowledge and understanding to ensure restoration work is
effective and cost efficient. The biological component of this framework relates to
information regarding the salt marsh vegetation. The study conducted by Jupp et al.
(2007) found 10 vegetation types in existence in the Avon-Heathcote Estuary. These
were obtained through 495 vegetation surveys around the estuary; cluster analysis was
then used to form vegetation types. These groups will be used in this study and will
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be statistically analysed using ArcGIS and box and whisker graphs to test the
relationship between the vegetation types and the sediment conditions they grow in.
Surface sediment samples were taken at 50 sites across the range of salt marsh
vegetation types and tested for nitrate, phosphate, and salinity, along with sediment
size and elevation; the latter obtained using a Trimble GNSS R8 Rover. A framework
will then be created using the results obtained, to form criteria relating to the sediment
conditions each vegetation type grows best in and thus where it should be planted.
With continual activity and change occurring around and in the Avon-Heathcote
Estuary, monitoring the diversity and extent of salt marsh species has become
extremely important to ensure sustainable management. Throughout this report, ‘the
estuary’ will refer to the Avon-Heathcote Estuary. Figure 1.2 shows the locations of
the main areas of salt marsh in the estuary.
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Establishing a physical and biological basis for salt marsh restoration
Figure 1.2 Map showing the study areas surveyed in Jupp et al. (2007)
1.3 Estuarine Environments
Estuaries are highly complex environments, with of interactions between the
ocean, fresh water, land, atmosphere and humans activity (Day et al. 1989). These
sensitive landforms provide a habitat for a large variety of salt marsh flora as well as
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Establishing a physical and biological basis for salt marsh restoration
supplying productive feeding grounds for fauna. They are also popular roosting areas
for migrating birds. Estuaries can be described as an ‘urban sponge’ in terms of the
way the salt marsh traps sediment and pollution from runoff around the catchment
(Kennish 1991).
Definition
As every estuarine environment is slightly different, this has made defining the
term ‘estuary’ very difficult.
The most commonly used and widely accepted
definition (Day et al. 1989; Macpherson 1978; Rodrigo 1985) states that an estuary is
a “semi-enclosed coastal body of water which has a free connection with the open sea
and within which sea water is measurably diluted with fresh water derived from land
drainage” (Pritchard 1967, p3).
This definition will be used throughout this
dissertation, in reference to the Avon-Heathcote Estuary.
Estuaries can be classified based on the physical processes which created them and
Pritchard devised four possible sub-classifications.
1) Drowned Rivers (Chesapeake Bay Estuary and Southampton Water Estuary):
2) Fjord-type (Milford Sound and Loch Etive):
3) Bar-built (Avon-Heathcote Estuary and Vellar Estuary):
4) Tectonic (San Francisco Bay)
(Pritchard 1952)
Temporary landforms
Created during the Holocene, estuaries are geologically young, being less than
5000 years old.
They are regarded as being temporary waterbodies, as over
geological time infilling and other changes relating to the flood (inward) and ebb
(outward) flows of the tide can affect the estuaries’ existence. A change in this
delicate balance between these two flows usually results in the infilling of an estuary.
Infilling can be caused if the flood tide is faster than the ebb resulting in more
nearshore sediment being transported into the estuary. In addition, if the ebb flow
velocity is slower than the flood, the tide will not be strong enough to move the
sediments back out into the sea, causing infilling to occur. The ebb flows must also
be strong enough to remove the catchment sediment brought into the estuary via the
river systems present.
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Other factors, including the bathymetry, tidal range and
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Establishing a physical and biological basis for salt marsh restoration
currents, sediment size and supply and human activities around the margins of the
estuary, all affect the life of the estuary.
Human Influence
Estuaries are naturally fluctuating environments, with their form and extent
constantly being altered due to erosion and sediment deposits (Dyer 1973). In many
countries around the world, including New Zealand, human activity around the
margins and catchment has increased the level of infilling of many estuaries. This has
been caused by accelerated catchment erosion due to land use changes, and
modification of river flow regimes due to water abstractions and dam building
(Wassilieff 2006). Reclamation of adjacent land near the estuarine environment has
slowly reduced the area of estuaries and their salt marsh vegetation. The above
activities can all be linked to intensified development occurring in the coastal
environment. This raises the question relating to how these waterbodies can be
managed in a sustainable manner. Currently in Christchurch the only legislation that
exists relating to the management of the Avon-Heathcote Estuary is the Resource
Management Act 1991 (RMA) and the Regional Coastal Environment Plan (RCEP)
2005.
However, leniencies towards penalties relating to resource consents have
resulted in unregulated construction and activities occurring in the margins and
catchment of the Avon-Heathcote Estuary.
1.4 Salt Marsh
Salt marshes are found in the mid to high latitudes in temperate regions around
the world (Mitseh and Jørgensen 2004). This research focuses on coastal estuarine
salt marsh, which grows between the upper limit of high water spring tides and the
upper limit of the high water neap tides (Jefferies 1972, Chapman 1960).
Salt
marshes contain resilient and adaptable plants in terms of the environment they grow
in. These halophytes are by definition able to grow in both saline and fresh water
conditions, as well as with tidal fluxes, which results in the vegetation being
inundated and exposed twice daily. Salt marsh plants have very strong distribution
patterns and can be divided into three zones relating to how close they grow to the
waters, edge. The first zone, lower marsh, consists of rushland vegetation, sea rush
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Establishing a physical and biological basis for salt marsh restoration
(Juncus krausii) and oioi (Apodasmia similis), or herbaceous plants, such as glasswort
(Sarcocornia quinqueflora) and suaeda (Suaeda novae-zelandiae). The mid-marsh
zone is made up of herbaceous species, including buck’s horn plantain (Plantago
coronopus) and bachelors button (Cotula coronopifolia), which often grow in
brackish water found in this zone of marsh. Lastly, zone 3, the upper marsh, consists
of larger more stable plants: oioi (Apodasmia similis), tall fescue (Schedonorus
phoenix) and coastal ribbonwood (Plagianthus divaricatus) (Jones & Marsden 2005).
Their vertical range is restricted by tidal energy as well as the current, and
horizontally they are restricted by the surrounding topography and bathymetry.
Seaward growth is determined by inundation and the level of salt tolerance of the
species growing there (Zeller and Adam 2002). Elevation affects zonation patterns
such that species diversity increases with elevation.
Formation
The natural formation process of salt marshes has been outlined by Long and
Mason (1983) (Figure 1.3).
They state that salt marsh vegetation will grow on
sheltered shores with elevations above Mean High Water Neap (MHWN) tide. As
vascular plants become established, they aid in the trapping of sediment, which in turn
reduces the tidal or wave energy, and slowly continues the accretion process. As the
elevation increases, a more diverse selection of species is established until the shore
becomes fully vegetated.
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Figure 1.3 Cross sections depicting the natural stages of salt marsh vegetation, A. High elevation
tidal flat, B. Salt marsh vegetation colonising on higher points of tidal flat, C. High marsh
becomes fully vegetated, apart from creeks (Long and Mason 1983, p13)
Importance
Salt marshes are highly productive environments in terms of nutrient
processing and hold extreme importance in the estuarine environment. Migrating
birds rely heavily on these environments, as they provide essential roosting and
feeding grounds. Salt marshes also act as sediment traps, collecting excess sediment
runoff from the surrounding catchment.
As development increases around the
margins, so does the level of the sedimentation in the salt marshes. Contaminants
either from urban runoff or sewage can be naturally treated through the salt marsh
processes, which is an example of ecological engineering (Mitseh and Jørgensen
2004). Salt marsh plants are able to filter out the pollutants and store them in the
sediments beneath in their rhizomes. This results in the plants cleansing the estuaries.
This natural sewage treatment process has resulted in the salt marsh being solely used
for this purpose in some areas (Kennish 1991). Salt marshes also act as a natural
flood protection, by decreasing wave and surge energy.
Although extremely
important environments, they are under threat due to increased human activities
occurring around the margins and catchments of estuaries. In New Zealand salt marsh
only covers approximately 10% of the land it did prior to European settlement (Harris
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Establishing a physical and biological basis for salt marsh restoration
1992). In the early 1960s, estuaries and salt marshes were unappreciated and regarded
as waste, barren land, with no beneficial use except for reclamation purposes to
extend urban areas (Williams 1990). As time passed and populations increased,
towns and cities were built around these waterways because of the great uses they
offered the people. This then created more pressure on the coastal environment,
which resulted in negative outcomes on the environment. However, over the last 40
years an increase in estuarine related literature has caused a change in perceptions.
Salt marshes are now thought of as wetlands, rather than swamps. The late twentieth
century change in the name of Travis Swamp to Travis Wetland is one such example
in the study area. With a change in attitude, local governments now need to enforce
restriction on the types of activities that are conducted around estuaries to prevent
further destruction occurring to salt marsh vegetation.
1.5 Restoration
As the awareness of salt marsh depletion grows, so is the realisation that
management frameworks and controls need to be implemented to ensure salt marsh
vegetation is present for future generations. Restoration is one of the possible tools
that is being used to ensure this is the case. Much of the restoration work that is
conducted around the world and in New Zealand is not backed up by any prior
scientific knowledge or in some cases, no knowledge exists at all (Andel and Aronson
2006).
For restoration to take place, the concepts behind it, and how other
environment practices fit around it, must be understood (Figure 1.4). During natural
ecosystem development there is a growth in biomass and nutrient content as well as
species diversity but when destruction occurs both variables are reduced. After this
degradation occurs the first option is to take no action, where the environment may
slowly return to its original state or it may reduce in health even more. The second
option is to recreate the environment if successful restoration has taken place; if it
falls short, this is referred to as rehabilitation. Lastly, replacement is an alternative
option. This is where the ecosystem is changed deliberately and differs from the
original environment, for example, a new community may be introduced.
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Establishing a physical and biological basis for salt marsh restoration
Figure 1.4 Two-dimensional model depicting ecosystem development (Developed by Bradshaw
1988, p56)
Definition
Ecological restoration has been described as “the process of assisting the
recovery of an ecosystem that has been degraded, damaged, or destroyed” (Society for
Ecological Restoration International (SER) 2004, p4).
Restoration must also
encompass “technical, historical, political, social, cultural and aesthetic components to
result in sustainable success” (Higgs 1997, p1).
Determining Targets
It is extremely important to set restoration goals at the beginning of the project
so appropriate monitoring methods can be formed as well to obtain the appropriate
scientific knowledge relating to the environment and ecosystems present (Holl and
Cairns 2002; Bakker et al. 2000; Hobbs and Harris 2001).
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Establishing a physical and biological basis for salt marsh restoration
Figure 1.5 Stages in restoration. (Modified from Holl and Cairns 2002)
Planning in restoration work is extremely important (Figure 1.5); above is a
simplified restoration process. The original did not include research to gain scientific
knowledge, so this has been added in the planning section as it is an extremely
important component. This research project aims to collect and process scientific
knowledge relating to the salt marsh vegetation in the Avon-Heathcote Estuary.
Ecological restoration can aim to restore entire communities of just one species in the
ecosystem either by rescuing species from extinction or reintroducing native species
to the environment. As both strategies have differing project targets, it is important to
state what the aims are for each individual project. Ehrenfeld (2000) devised three
approaches that vary in the level of analysis that should be used to determine the
targets for a restoration project:
1) Species
This focuses on key species, for example, the main aim being to
prevent the extinction of native species. The surrounding ecosystem
and landscape level interactions may be disregarded.
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Establishing a physical and biological basis for salt marsh restoration
2) Ecosystem function
This target focuses on the processes of the ecosystem concerned, for
example nutrient processing, tidal cycles and zonation processes.
Emphasis is placed on diverse groups of interests but relationships
between, for example, biodiversity and functional stability are not
clear.
Problems exist of how to determine the boundaries of the
ecosystem concerned.
3) Ecosystem Services
This combines the above two targets, but includes public perception as
well as the aspects outlined by Higgs (1997, p1). The purpose of the
restoration is considered and should incorporate management plans.
(Harris and Diggelen 2006)
Which of these three types of restoration project is chosen must relate to the
scale and expectation of the undertaking.
Measurement of Success
One of the important components of restoration work is to determine whether
or not it is successful in accomplishing the targets set at the beginning. The Society
for Ecological Restoration International (SER) (2002) devised nine factors that should
be used to determine successful restoration (Appendix 1).
The list focuses on
ecosystems and recognizes that the biota is the most important component of
restoration work. However, it does recognise that human indicators are also important
in terms of employing personnel to implement management strategies. Restoration
should be perceived as being an ongoing process and continues even when the success
limit has been met. It is not a static activity, as the environment and ecosystems are
forever changing. Therefore, restoration must be considered in the same regard. To
successfully carry out a restoration project there must be a level of understanding of
how the ecosystem works. Harper (1987) suggests that relationships between the
species present and soil conditions should generate this knowledge. This approach is
used to determine scientific understanding relating to the salt marsh zonation patterns
in the Avon-Heathcote Estuary in this project. To ensure future restoration work that
is conducted on the Avon-Heathcote Estuary is successful, an increased level of
scientific knowledge is to be collected and analysed as the main part of this study.
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1.6 Thesis Structure
The methodology, which follows, consists of the information relating to the
field site, as well as the data collection methods. Sediment analysis techniques are
also included. The results section is divided into four sections relating to each of the
variables used to test for relationships against the vegetation types. These results are
discussed in relation to the literature and, finally, the conclusion states the main
findings, as well as recommendations for future research.
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Chapter Two
Methodology
2.1 Field Site: Avon-Heathcote Estuary
Located in eastern Christchurch, the Avon-Heathcote Estuary is one of the
four major estuaries in the South Island. It is fed by the Avon and Heathcote Rivers
which enter the estuary via the north and southwest corners respectively, into an 8
km2 waterbody. Saline influences stretch 8 km upstream to Wainoni Street Bridge on
the Avon River, and 11 km up the Heathcote River to the Radley Street Bridge
(Christchurch City Council 1980). The estuary has been described as a bar-built
(Griffin & Thomson 1992), well-mixed (Knox et al. 1973) estuary with strong tidal
influences. The estuary was created through the formation of New Brighton Spit from
longshore currents transporting sediment from the Waimakariri River (Harris 1992).
Bar-built estuaries are often shallow and sheltered from wave actions (Pritchard
1967).
Well-mixed estuaries are characterised by small or no vertical salinity
gradients due to the high level of water mixing. The estuary can also be described in
terms of the main processes which occur. The Avon-Heathcote Estuary is greatly
influenced by tidal processes and tidal energy. In tide-dominated estuaries both of
these factors often increase towards the landward end of the outer zone as a result of
tidal shoaling (Masselink & Hughes 2005, Figure 2.1). Due to this tidal influence, the
estuary is drained, except for the main channels from the Heathcote and Avon Rivers,
during low tide.
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Figure 2.1 Energy distribution of a tide-dominated estuary (Masselink & Hughes 2005, p168)
2.1.1 Values
Historic
The Avon-Heathcote Estuary is an important natural feature in the Canterbury
region due to its high productivity and diversity of biota (Christchurch City Council
2001). Throughout history the estuary has held great importance to both Maori and
European settlers to the Canterbury region. Many estuaries throughout New Zealand,
including the Avon-Heathcote Estuary, were used as settling grounds. Their rich
biodiversity and production made them ideal for food and material gathering. Native
plants, such as oioi (Apodasmia similis), were used by Maori as thatching for the
outsides of their houses.
Spiritually they are important as water holds extreme
significance within the Maori society. Maori believe, it represents the lifeblood of
existence and that discharging into water bodies is culturally insensitive (Te Taumutu
Runanga 2004).
Recreation
Being close to the central city, the Avon-Heathcote Estuary, offers many
recreational activities to tourists and the public (Williams 2005).
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location for wind surfing, kite surfing, sailing, kayaking, canoeing, swimming, fishing
and bird watching, as it is sheltered from the open-coast wave environment of Pegasus
Bay (Christchurch City Council 2006).
Research
The estuary holds great significance in terms of educational value. Local
primary and secondary schools, and the University of Canterbury use the estuary as a
natural laboratory to explore the complex relationships between the flora, fauna and
environmental conditions of the area (Morgans 1969).
For over 40 years, the
University of Canterbury has produced honours dissertations, Masters and PhD theses
on estuarine topics creating a wealth of knowledge in this subject.
The above differing values have resulted in many management issues for the
Avon-Heathcote Estuary. An example of how this has affected the estuary is the
removal of the treated sewage from the Avon-Heathcote Estuary to Pegasus Bay. For
many decades now, the Wastewater Treatment Plant discharged treated sewage into
the estuary from the oxidation ponds (Christchurch City Council 2006). The Ocean
Outfall Project, now underway, is using micro tunnelling to lay pipes in the estuary
bed to re-direct these discharges into the open ocean environment 3 km off Jellico
Street. This method is designed to have minimal impact on the flora and fauna of the
estuary, compared to the dredging methods first proposed for pipeline construction
(Moore 2006).
2.2 Previous studies of the Avon-Heathcote Estuary
The Avon-Heathcote Estuary has been a popular subject for past research as well as
technical reports.
This literature can been grouped into three distinct categories
relating to (i) sediment and (ii) ecology, which make up the majority, and a small
proportion relating to (iii) restoration (Table 2.1). This research aims to draw together
these three subjects, to create a scientifically sound salt marsh restoration framework
for the Avon-Heathcote Estuary (Figure 2.2).
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Establishing a physical and biological basis for salt marsh restoration
Figure 2.2 Model depicting current literature topics relating to the Avon-Heathcote Estuary, the
star indicates where this research fits
Area
Ecology
Table 2.1 Key studies on the Avon-Heathcote Estuary in areas of ecology, sediment and
restoration
Focus
Source
Main finding in relation to present study
Salt marsh
vegetation and
literature
review
Knox et al.
1973
•
•
•
•
•
Tidal mudflat
snail
Griffin and
Thomson
1992
Salt marsh
McCombs
and
Partridge
1992
Marine
invertebrates
Dowling
2002
•
•
•
•
•
•
•
Macroalgae
Salt Marsh
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Murphy
2006
Jupp et al.
2007
•
•
•
•
One of the first significant studies focusing on the ecology of the
Avon-Heathcote Estuary
Detailed synthesis of previous research giving an overall view of the
physical characteristics and status of the flora and fauna
Found that high levels of nutrients exist in the rivers, with the levels
decreasing toward the estuary mouth as dilution from seawater occurs
Dominate salt marsh species found to be sea rush (Juncus krausii), oioi
(Apodasmia similis) and coastal ribbonwood (Plagianthus divaricatus)
Salt marsh surrounding Bridge Street Bridge is the most significant
area due to the diversity of species present
Researched the distribution and numbers of the tidal mudflat snail
(Amphibola crenata)
Presence of the snail has increased indicating that the environmental
conditions have improved, with change linked to improvements in the
Sewage Treatment Plant, resulting in a higher quality of sediment for
the habitat of the snail.
Focused on the distribution of salt marsh vegetation in 470 sites around
the Avon-Heathcote Estuary
Presence/absence vegetation surveys were conducted then analysed
using cluster techniques to form 12 distinct vegetation types.
Main purpose of the study was to give an indication of the species
present and to be used a baseline study.
The ecology of the talitrid amphipod’s (Transorchestia chiliensis) was
researched to determine its life history patterns and its potential
suitability to be used as a biomonitor of trace metal contamination in
the Avon-Heathcote Estuary
Found that the health and growth of the species was a useful indicator
of environmental stress
Ecological effects of sea lettuce (Ulva lactuca L) and its mechanical
removal on benthic invertebrates was explored in relation to sediment
The Saturn DigiSizer 5200 was used. This is one of the only previous
studies relating to the Avon-Heathcote Estuary that has used this
method
Comparative vegetation study to McCombs and Partridge
Found significant change in salt marsh from rushland vegetation to
smaller herbaceous plants. Ten vegetation types were found,
emphasising the change that had occurred over the 14 years
23
Establishing a physical and biological basis for salt marsh restoration
•
Sediment
Macrofauna
and sediment
Voller 1973
Morphology
Millward
1975
•
•
•
•
•
Geology
Macpherson
1978
•
•
Heavy metals in
sediment
Rodrigo
1985
•
•
•
Restoration
Heavy metals in
sediment
Deely 1991
Restoration in
the Linwood
Paddocks
Thomsen
1999
•
•
•
•
•
Kimberly Jupp
GPS was used to accurately record survey locations. A detailed map
of the Avon-Heathcote Estuary’s margins and salt marsh extent was
also captured
Spatial patterns of invertebrate macrofauna were explored in relation to
salinity and sediment. Found a strong relationship exists
Found sediment size decreases from the mouth to the river entrances,
changing from sandy sediments to mud and silts
Morphology of an estuarine environment was researched, with special
reference to the Avon-Heathcote Estuary’s origin and evolution,
including the changing morphology and channel patterns
Grain size linkage to their source was analysed, and the effects of the
urban surroundings on the sediment budget was also examined
States that sediment sources are changing due to increased
development around the margins, causing an increase in finer
Explores the geology of the Avon-Heathcote Estuary stating that the
muddiest sediments occur close the Avon and Heathcote River
entrances. This deposition is influenced by sediment supply rates and
wave energy
States that the change in geology is due to physical alterations caused
by the growth and development of the surrounding catchment and
margins
Relationships between sediment and the presence of heavy metals and
how this affects the locality of the mudflat snail, are explored
Found that this species is weakly influenced by the geomorphology of
the estuary
Clear links found between heavy metal presence in the sediment and
increased urbanisation around the catchment of the estuary.
Explored relationships between sediment size and heavy metal
distributions and linked this to increased industrial activity
Sediment samples, taken to a depth of 10 cm, found sediment size
changed from sandy, poorly mixed sediment at the estuary mouth, to
well mixed sediment containing a higher amount of silts further in the
estuary
Focuses on restoration, looking at the distribution of salt marsh
vegetation in relation to elevation, pH, salinity and sediment type
The salt marsh tolerance to heavy metals and nutrient levels is also
explored
Created goals and management criteria to allow for sustainable salt
marsh restorations to occur in the Linwood Paddocks
24
Establishing a physical and biological basis for salt marsh restoration
2.2.1 Ecology
The majority of literature written relating to the ecology of the Avon-
Heathcote Estuary has focused on macroalgal and the fauna of the estuary (Table 2.1).
There has been very little attention given to the salt marsh vegetation.
This is
interesting as it is this vegetation that is one of the reasons the macroalgal and fauna
exist.
The previous literature, relating to the salt marsh in the Avon-Heathcote
Estuary, has merely quantified the data with no analysis of zonation patterns being
conducted. The comparative study conducted by Jupp et al. (2007) found significant
difference in the occurrence of salt marsh species in the Avon-Heathcote Estuary. A
change from rushland vegetation to smaller herbaceous plants was found.
This
research aims to build on this quantitative study by exploring the spatial patterns of
the salt marsh. Relationships between sediment variables and the different vegetation
types found in Jupp et al. (2007) are used to generate environmental characteristics
that each vegetation type is found in.
2.2.2 Sediment
A considerable amount of sediment related literature focusing on the Avon-
Heathcote Estuary exists.
It has, however, concentrated on the distribution of
sediment size around the estuary and how it influences the distribution of fauna.
There has been no research which solely links sediment variables to the zonation
patterns of the salt marsh vegetation. This research will explore the relationship
between salt marsh vegetation types and sediment size, elevation of salt marsh,
salinity of the sediment, and nutrient levels, to explore whether or not any such
relationship exists.
2.2.3 Restoration
As wetlands around the world, and in New Zealand, are continuing to
decrease, the awareness of their importance and benefit to ecology is increasing. This
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
newfound importance is resulting in enhanced restoration work being conducted. For
restoration work to be successful, a level of scientific understanding is required
relating to the ecosystem concerned.
Unfortunately, there is a lack of literature
relating to salt marsh restoration work in the Avon-Heathcote Estuary. This has
resulted in unsuccessful attempts to restore sections of the estuary to its original state.
Thomsen (1999) is the only research focusing on salt marsh restoration in the Avon-
Heathcote Estuary. This current research differs from her study; although the same
sediment variables are to be tested for, they are to be related to vegetation types rather
than individual species, as Thomsen does. To explore the relationships between
vegetation types is far more beneficial as some species fall into more than one
vegetation type. Therefore, by studying the vegetation types rather than individual
species, more natural and realistic assumptions can be made about the relationships
between vegetation types and different sediment variables and environmental
conditions.
2.3 Methods
Building on the quantitative salt marsh surveys conducted by Jupp et al.
(2007), this research explores the spatial distribution of the vegetation in relation to
both the physical and environmental characteristics of the Avon-Heathcote Estuary.
2.3.1 Sediment Sampling
During the summer of 2006/07, 290 surface sediment samples were collected
at various locations around the Avon-Heathcote Estuary. Due to time constraints only
a portion were analysed in each test. Surface samples, taken to a depth of 10 cm,
were chosen as they contain information relating to the estuary’s depositional
environment, rather than historic changes, which are not explored in this research.
Sample locations were taken at the same place as the vegetation surveys were
conducted (Jupp et al. 2007), which were chosen in terms of their proximity to the
shore. Each sample position was captured using a Trimble Geo-XT unit in carrier
phase. Using the carrier frequency significantly improves the precision of GPS to a
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
horizontal accuracy of 0.1-0.5 m (Justin Harrison, Laboratory, Field and Equipment
Technician, Department of Geography, University of Canterbury, pers. comm. 2007).
To work in carrier phase, the GPS needs to be locked with at least four satellites for a
period of time. If the lock is lost, it can add valuable time out in the field waiting for
carrier phase to be established again. This study used 10 min as the minimum time
for the position to be calculated. A high degree of accuracy was required for this task
to allow for accurate comparisons for future research looking at the salt marsh in the
Avon-Heathcote Estuary. Once collected, the samples were refrigerated between 3 - 5
°C for eight months until they were analysed.
2.3.2 Data Capture
Shoreline mapping
To further explore the spatial distribution of the salt marsh vegetation, a
detailed map of the Avon-Heathcote Estuary margins was created using GPS (Figure
2.3) irst to be created in such detail of the Avon-Heathcote Estuary. A Trimble GEO-
XM GPS unit was used in code phase to map the margins of the Avon-Heathcote
Estuary. This has a horizontal accuracy of 1-3 m (Justin Harrison, Laboratory, Field
and Equipment Technician, Department of Geography, University of Canterbury,
pers. comm. 2007). It shows where hard edges have been built and the areas of
natural shoreline that remain. The area of salt marsh coverage was also captured, as
polygons, and mapped to provide a clear visual of where the salt marsh is located.
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Establishing a physical and biological basis for salt marsh restoration
Figure 2.3 Kimberly capturing the margins of the Avon-Heathcote Estuary using a Trimble GeoXM unit
Elevation
Elevation was measured at the same locations as the vegetation surveys and
sediment samples were taken. To ensure a high level of vertical accuracy, a Trimble
R8 GNSS (Global Navigation Satellite System) was used. This is a multi-channel,
multi-frequency GNSS receiver, antenna, and data-link radio combined in one
compact unit (Trimble 2007). An accuracy of approximately 1.5 - 3 cm can be gained
using the GNSS this is because both the American GPS
and Russian GLObal
NAvigation Satellite System (GLONASS) systems are used resulting in the
availability of more satellites. This system allows for the use of a portable base
station set at a location with known coordinates. A benchmark located at 5742412.19
(northing), 2487650.86 (easting), in the New Zealand Map Grid (NZMG), was chosen
for the base station (Figure 2.4). As the signal range of this is approximately 4 km, a
booster was set up to allow for GNSS capture around the entire estuary. This simply
boosts the satellites’ signal from the base station to the booster, then to the GNSS
rover (Figure 2.5).
After capture, the data were then transferred using Trimble
Geomatics Office and added as a shapefile to ArcGIS.
Figure 2.4 Base station
Figure 2.5 GNSS rover and
external antenna
2.4 Data Analysis
2.4.1 Cluster Analysis
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Establishing a physical and biological basis for salt marsh restoration
The software package SPSS was used for the analysis of the vegetation survey
data collected by Jupp et al. (2007). A single dataset was used including the species
presence/absence data for each plot surveyed.
Sites where the salt marsh had
disappeared between 1992 and 2007 due to sediment infilling were removed, as SPSS
does not recognise variables containing no value. Direct comparisons were made
between communities of changes in the vegetation. Cluster analysis was used to
compare the plot/species data. The Jaccard (Williams et al. 1973) sorting strategy was
employed, this uses between-group linkages and similarities. Nine vegetation types
were eventually specified after outlier removal. The initial analyses separated out a
number of data outliers, most representing odd sites around the margin. These are
listed as ‘outlier’ in further tables and no further interpretation of their composition is
included. Sites were progressively removed from the analysis until the minimum site
group size was three.
2.4.2 Nitrate, Nitrite, Phosphate
The levels of nitrate, nitrite and phosphate nutrients were measured using
Quantofix test strips. The nitrate and nitrite testing was conducted using the same test
strips. A ratio of 1:5 of soil and deionised water was used. Samples were stirred for 1
min every 3 hr for 6 hr. The test strips were dipped into the sample for 1 s and
nutrient levels were recorded after 1 min using the scale provided in the pack. This
method has a testing range of 0-500 mg/l NO3- for nitrate levels and for nitrite, 0-80
mg/l NO2-. Phosphate levels were determined by taking 5 ml of sample and adding 5
drops of phosphate -1 (nitric acid) and then shaken. Secondly, 6 drops of phosphate 2 were placed in a test tube. The test stick was placed in the 5 ml of sample then the
test tube, both for 15 s, the measurement being taken 1 min after.
2.4.3 Salinity
The level of soil salinity was determined using the Rhoades and Miyamoto
(1990) method. A volume of 1:5 soil and distilled water was used; each sample was
stirred for 1 min every half an hour for 4 hours. This was to ensure the diffusion
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
process takes place. Samples were covered with foil to prevent evaporation and then
refrigerated for 24 hours at 4°C. Using an ATAGO refractometer the relative salinity
was measured.
2.4.4 Sediment Size
Samples were firstly wet sieved to 1ø with distilled water, which removed the
large organic material. Each sample was divided in two; larger particles of 1 ø were
grouped together and weighed. The sediment less than 1 ø was dried at a low
temperature of 50 °C to prevent the sediment baking. As this research focuses on
particle sizes smaller than 1 ø, it was not essential to place as much focus on the larger
sediments. A Saturn DigiSizer 5200 was used to measure the particle size 0.1 to 1000
µm. This limit is shown in relation to the Wentworth Size Class, which has been used
in all previous literature relating to sediment (Table 2.2).
Table 2.2 Wentworth size class and grade limits, and grade limits measured by the DigiSizer
(Based on Murphy 2006, p25)
Wentworth
Class
Size
Phi ø
Grade Limits
DigiSizer Grade Limits
Boulder
-8
>256 mm
Cobble
-6
256 - 64 mm
Pebble
-2
64 – 4 mm
Gravel
-1
4 – 2 mm
Very coarse sand
0
2 – 1 mm
2 – 1 mm
Coarse sand
1
1 – 0.5 mm
0.945 – 0.501 mm
Medium sand
2
500 – 250 µm
473.87 – 251.57 µm
Fine sand
3
250 – 125 µm
237.49 – 126.08 µm
Very fine sand
4
125 – 63 µm
119.03 – 63.19 µm
Coarse silt
5
63 – 31 µm
59.65 – 31.67 µm
Medium silt
6
31 – 15.6 µm
29.89 – 15.87 µm
Fine silt
7
15.6 – 7.8 µm
14.98 – 7.95 µm
Very fine silt
8
7.8 – 3.9 µm
7.51 – 3.98 µm
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
Clay
9
<3.9 µm
<3.76 µm
The application of laser particle sizing consists of using a laser beam to
measure the size of particles through diffraction and diffusion (Jenifer Jackson,
Equipment Technician, Department of Geology, University of Canterbury, pers.
comm. 2007). In preparation of the sample, the organic material was removed, to
prevent skewness in the results, using 12 ml of hydrogen peroxide (30%) and 15 ml of
distilled water in evaporating dishes and placed in a fume hood. Left for a week, the
sediments were disaggregated using a rubber cork. Each sample was analysed three
times through the Saturn DigiSizer 5200 to account for particles that may have been
obscured from the laser. The DigiSizer has been previously used only on a few
occasions, on research relating to the Avon-Heathcote Estuary (Pyrtle et al. 2006).
This is due to the recent advancement in the technological capabilities for measuring
sediment size of fine particles. It was chosen over pipette analysis due to time
constraints and as the majority of the samples were made up of muds and clays.
2.5 Spatial Analysis
ArcGIS was used to create maps displaying the results spatially to make
interrelationships clear. Statistical analysis was conducted using Statistica to make
direct comparisons between the results. The maps were created for each variable
(nitrate, elevation, sediment size) by coding each salt marsh polygon with the
characteristic (e.g. for elevation: the elevation class) that dominated the area in the
field.
Previous salt marsh related research has merely quantified the abundance of
each species. Although helpful in determining the level of change, this gives no
information relating the environmental and physical conditions each species lives in.
This research uses the above methods to form spatial understandings of salt marsh
distribution in relation to elevation, sediment size and nitrate. The physical nature of
the margins has also been explored through the creation of the map. Relationships
can be then be explored using the map to relate to the location and distribution of the
salt marsh.
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Establishing a physical and biological basis for salt marsh restoration
Chapter Three
Results
3.1 Vegetation Types
A description of the nine main vegetation types found from the vegetation
surveys of the salt marsh around the Avon-Heathcote Estuary by Jupp et al. (2007) is
made in this chapter. In the title of each of the following vegetation type sections, the
number in the brackets indicates the number of sample sites which fall into each
category.
Type 1. Oioi rushland (174 sites)
This is a simple vegetation type comprising oioi (Apodasmia similis) (Figure
3.1), often in association with sea rush (Juncus krausii) and/or coastal ribbonwood
(Plagianthus divaricatus).
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.1 Oioi (Apodasmia similis)
Type 2. Sea rush rushland (131 sites)
This vegetation type mainly consists of one species, this being sea rush
(Juncus krausii) (Figure 3.2) however, coastal ribbonwood (Plagianthus divaricatus)
is also present in some sites closer to the banks.
Figure 3.2 Sea rush (Juncus krausii)
Type 3. Salt marsh herbfield (89 sites)
This comprises a diversity of salt marsh herbs along with some larger plants.
Glasswort (Sarcocornia quinqueflora) is the most common, along with buck’s horn
plantain (Plantago coronopus), orache (Atriplex prostrata), suaeda (Suaeda novae-
zelandiae) (Figure 3.3), native primrose (Samolus repens), salt grass (Puccinellia
stricta) and selliera (Selliera radicans).
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.3 Suaeda (Suaeda novae-zelandiae)
Type 4. Couch grassland (7 sites)
This vegetation type occurs in the upper marsh zone and comprises thick
swards of couch (Elytrigia repens). Remnant sea rush (Juncus krausii) is found in
places and creeping bent (Agrostis stolonifera) is also common in areas that back onto
pasture.
Type 5. Tall fescue and coastal ribbonwood (19 sites)
The dominant upper marsh vegetation comprises a mix of exotic tall fescue
(Schedonorus phoenix) and native coastal ribbonwood (Plagianthus divaricatus),
along with flax (Phormium tenax), couch (Elytrigia repens) and taupata (Coprosma
repens).
Type 6. Three square sedgeland (21 sites)
Three square (Schoenoplectus pungens) dominates this vegetation type.
Raupo (Typha orientalis) and tall fescue (Schedonorus phoenix) also occur around the
location of the freshwater spring in Raupo Bay. Otherwise, associated species are
typically few where this vegetation occurs on mudflats.
Type 7. Coastal ribbonwood shrubland (6 sites)
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Establishing a physical and biological basis for salt marsh restoration
Coastal ribbonwood (Plagianthus divaricatus) (Figure 3.4) occurs with few
associated salt marsh species. However, this tall shrub has allowed the aggressive reed
canary grass (Phalaris arundinacea) to colonise. This vegetation type was not
recorded in the original sampling (McCombs and Partridge 1992), and has appeared
as a novel type.
Figure 3.4 Coastal ribbonwood (Plagianthus divaricatus)
Type 8. Native musk herbfield (2 sites)
This vegetation type is somewhat similar to the salt marsh herbfield (Type 3)
but with the addition of native musk (Mimulus repens) (Figure 3.5) instead of
glasswort (Sarcocornia quinqueflora), and other more salt-tolerant herbs such as
suaeda (Suaeda novae-zelandiae) and bachelors button (Cotula coronopifolia), which
do not exist here. Native musk is indicative of brackish conditions.
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.5 New Zealand musk (Mimulus repens)
Type 9. Native primrose herbfield (1 site)
This rather depauperate and rare vegetation type is characterised by the
presence of native primrose (Spergularia media), without its normal salt marsh
associates.
3.1.2 Vegetation Type Spatial Distribution
The salt marsh vegetation types in the Avon-Heathcote Estuary have clear
patterns of distribution (Figure 3.6).
The majority of salt marsh vegetation is
clustered around the Avon and Heathcote River entrances. These areas are diverse,
with three community types found in both locations. The most common vegetation
type, oioi rushland, is only found at the Avon River entrance in the northern reaches
of the estuary. The other common rushland vegetation type, sea rush rushland, is
however, dispersed around the entire estuary. It is located in both river entrances as
well as along the margins in the estuary itself. Salt marsh herbfield, which is the most
common of the herbaceous vegetation types, is also spread around the estuary, but is
mostly located near the banks away from the water’s edge. Calders Green is the only
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Establishing a physical and biological basis for salt marsh restoration
location where couch grassland is located; it is an isolated area containing only seven
sites. Vegetation type 7 is only found up the Avon River on the eastern bank between
vegetation types 1 and 6. This vegetation type is average in size with 19 sites.
Located on the eastern bank in the northern reaches, three square sedgeland, found in
the same number of sites in the Avon River, as the above vegetation type, is situated
between oioi rushland. Lastly, coastal ribbonwood shrubland, the least common is
only found in six sites, in the Charlesworth area to the west of the estuary. As it is not
located directly on the margin of the estuary, it is not as affected by tidal influences as
the rest of the vegetation types. It is situated adjacent to where restoration work is
currently being conducted by the Christchurch City Council (CCC). As well as
vegetation type spatial patterns, distributions occur in terms of their location to
physical features. It has been found that salt marsh herbfield grows near the banks of
the estuary, with the rushland species located near the water’s edge. They therefore
are now affected by inundation and tidal influences. The Brighton Spit also has an
influencing factor, in terms of vegetation type distribution. A large amount of salt
marsh herbfield grows here in the coarser sediment supplied from the nearby dune
system. Overall, the diversity and extent of salt marsh vegetation types increases
towards the Avon and Heathcote River extents.
A significant finding of this research is the relationship between the presence
of natural margins and salt marsh. Natural margins consist of areas that have not been
altered (eg. grass banks, natural sandy shoreline), compared to artificial boundaries
which consist of materials or structures that have been built to replace the natural state
of the estuary, (eg. concrete walls, rubble, gabions). The makeup of the margins in
the Avon-Heathcote Estuary has not been mapped before (Figure 3.7). The map gives
a clear picture of the activities that have occurred around the estuary and how these
differing structures have affected salt marsh growth.
The only vegetation types
growing near artificial margins are salt marsh herbfield and sea rush rushland, with
more variety of species surrounding the natural margins. The majority of the salt
marsh vegetation is found adjacent to the natural margins, this suggests that they
provide the ideal habitat to support these sensitive ecosystems.
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.6 Map showing spatial distribution of the major salt marsh community types in the
Avon-Heathcote Estuary, as well as the area of artificial and natural margins.
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.7 Map showing the materials which make up the margins of the Avon-Heathcote
Estuary and the locations of the salt marshes
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
3.2 Vegetation Types vs. Sediment Size
Sediment size below 1 ø was analysed in this study using the Satin DigiSizer
5200. The majority of sediment in salt marsh areas was classified as medium silt and
fine sand (Figure 3.8). The majority of finer sediment was found to be in the Avon
and Heathcote River entrances, with the coarse sediments located near the estuary
mouth. There are, however, a couple of exceptions in both river entrances.
The results obtained clear patterns between the percentages of sediment type
in each sample, when classified into community types (Figure 3.8). Links were found
between three square sedgeland and the presence of fine sand in the Avon River. A
relationship between the two rushland vegetation types and fine sediments is also
evident.
Vegetation types 1 – 3 contain sites where the majority of samples are either
medium silt or fine sand sediment. These two peaks in the graphs are due to the
location of the sediment sample, with the majority of the fine sand being found in the
estuary basin, near Penguin Street and South Brighton Pines (Figure 3.9). The large
proportion of silt percentages is from sites located in the river entrances.
Vegetation types 4 and 5, the grassland dominated types, have a high
proportion of fine sands present; this is due to their location, close to the bank. As
few sites fall into the remaining vegetation types, it is difficult to draw any
conclusions, except to say that they appear to be uniformed with sediment size equally
distributed in each sample.
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.8 Sediment size distribution surrounding areas of salt marsh in the Avon-Heathcote
Estuary
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
Sediment size distribution for Vegetation Type 1
Sediment size distribution for Vegetation Type 2
70
Percentage of sample (%)
Percentage of sample (%)
70
60
50
40
30
20
10
60
50
40
30
20
10
0
0
3.9-7.7
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
Grain Size (μm)
<3.8
1000+
Sediment Size distribution for Vegetation Type 3
70
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
1000+
Sediment size distribution for Vegetation Type 4
70
60
50
40
30
20
10
0
<3.8
3.9-7.7
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
60
50
40
30
20
10
0
1000+
Grain Size (μm)
<3.8
Sediment size distribution for Vegetation Type 5
70
3.9-7.7
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
Grain Size (μm)
1000+
Sediment size distribution for Vegetation Type 6
70
Percentage of sample (%)
Percentage of sample (%)
3.9-7.7
Grain Size (μm)
Percentage of sample (%)
Percentage of sample (%)
<3.8
60
50
40
30
20
10
0
<3.8
3.9-7.7
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
60
50
40
30
20
10
0
1000+
<3.8
3.9-7.7
7.8-14
Grain Size (μm)
15-31
32-62
63-124 125-249 250-499 500-999
1000+
Grain Size (μm)
Sediment size distribution for Vegetation Type 7
Sediment size distribution for Vegetation Type 8
60
Percentage of sample (%)
Percentage of sample (%)
70
50
40
30
20
10
0
<3.8
3.9-7.7
7.8-14
15-31
32-62
63-124
125-249 250-499 500-999
1000+
70
60
50
40
30
20
10
0
<3.8
3.9-7.7
7.8-14
15- 31
32-62
63-124 125-249 250- 499 500-999
1000+
Grain Size (μm)
Grain Size (μm)
Sediment size distribution for Vegetation Type 9
Percentage of sample (%)
70
60
50
40
30
20
10
0
<3.8
3.9-7.7
7.8-14
15-31
32-62
63-124 125-249 250-499 500-999
1000+
Grain Size (µm)
Figure 3.9 Percentage of sediment size in each sample for each vegetation type
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
3.3 Vegetation Types vs. Elevation
In the estuarine environment, salt marsh grows above the Mean High Water
Spring (MHWS) (Long and Mason 1983).
This is seen in the Avon-Heathcote
Estuary, with the MHWS being at 0.94m and the majority of vegetation growing
above this mark (Phleger 1977) (Figure 3.11). Links between vegetation type and
elevation are seen in some locations around the estuary. It is evident where the salt
marsh herbfield is growing near the banks of the estuary (Figure 3.10). This low lying
land around the Heathcote River and Penguin Street is where the majority of salt
marsh herbfield grows. Clear links between sea rush rushland and an elevation of 1 m
to 1.25 m is apparent. Oioi rushland is also associated with low lying land (0.75 m –
1 m) in the extents of the Avon River. Trends between vegetation type and elevation
are seen on a smaller scale in isolated areas of salt marsh: Charlesworth, Calders
Green and South Brighton Pines. Elevation and species abundance are closely related
(Figure 3.11); as elevation increases, the number of sites in each vegetation type
decreases. The most abundant vegetation types are found to grow at low elevations.
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.10 Elevation around the margins of the Avon-Heathcote Estuary, obtained using a
Trimble R8 GNSS rover
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Establishing a physical and biological basis for salt marsh restoration
n = number of samples
in each community type
Figure 3.11 Elevation range of vegetation types present in the Avon-Heathcote Estuary
3.4 Vegetation Types vs. Nitrate, Nitrite and Phosphate
Using Quantofix nitrate testing strips, measures were limited to the following
concentrates 10, 25, 50, 100, 250 mg/1. This study found that generally soil nitrate
levels decrease from the estuary mouth to the river entrances (Figure 3.12). The
average amount of nitrate found in the estuary sediment ranges from 25-99 mg/1.
Links between vegetation type and nitrate exist in various locations around the
estuary, the most prominent being sea rush rushland, which commonly grows in
nitrate levels of 55 – 99 mg/1. This trend is not site specific but occurs around the
entire estuary. Three square shrubland, which is only located in the Avon River
mouth, was found to only grow in nitrate levels of 55 – 99 mg/1. The range of nitrate
also varies between vegetation types (Figure 3.13).
Oioi rushland has a much
narrower range, whereas vegetation types 4 - 6 cover a larger range. When nitrate
levels are related to abundance of species in each community type, a natural bell curve
is formed.
As species abundance increases, as in the first four most common
vegetation types, nitrate levels increase. The reverse is seen in the remaining, less-
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Establishing a physical and biological basis for salt marsh restoration
common vegetation types. Although the analysis of nitrate was successful, nitrite and
phosphate were not. They were also measured using the Quantofix test strips but the
levels of these nutrients were too low to be measured by this method. Also, literature
states (Thomsen 1999) that nitrite must be measured within 2 mouths after collection.
As the sediment was collected in November 2006, eight months had passed before the
sediments were analysed. This may also be why the phosphate levels were not
recordable.
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Establishing a physical and biological basis for salt marsh restoration
Figure 3.12 Distribution of soil nitrate levels, in areas of salt marsh growth in the AvonHeathcote Estuary
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Establishing a physical and biological basis for salt marsh restoration
n = number of samples
in each community type
Figure 3.13 Elevation range of vegetation types present in the Avon-Heathcote Estuary
3.5 Vegetation Types vs. Salinity
Although the method to measure soil salinity had been successfully conducted
in previous studies (Thomsen 1999), it did not generate correct results in this current
study. The main reason is suspected to be due to the long period of time between
sediment sample collection and analysis. The period of eight months would have
been too long for the salt particles to remain in the samples.
3.6 Restoration Criteria
Following is a summary of the significant relationships between the variables
tested for, and the vegetation types present, in the Avon-Heathcote Estuary (Table
3.1). This table can be used in conjunction with future restoration work that is
conducted in the estuary to ensure that an appropriate range of conditions are present,
or are created, for the vegetation types planted. The table is ordered from most
abundant vegetation type to the least. Oioi rushland appears to grow in a small
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Establishing a physical and biological basis for salt marsh restoration
environmental niche, as it is only found in the Avon River between a small range in
elevation and nitrate levels. Vegetation types 2 and 3 however, are more dispersed
and can grow in a wide range of conditions. This table has been designed to be used
to assist restoration planners to guide them when developing restoration programmes
in the Avon-Heathcote Estuary. It should be used in conjunction with hydrological
understanding to ensure future restoration work is successful.
In this chapter, strong spatial relationships were discovered to exist in relation
to species type’s abundance and the physical properties of the margins surrounding
them. Distribution patterns relating to the physical features and vegetation types were
also found. Relationships between elevation and sediment size are also present when
comparing them to vegetation types. The following chapter will discuss the findings.
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Establishing a physical and biological basis for salt marsh restoration
Table 3.3 Summary of physical characteristic in each vegetation type, the sediment size ranges refer to the peaks seen in Figure 3.9
Vegetation
Species
Distribution
Sediment Size Elevation
Type
Oioi and/or coastal ribbonwood, sea rush
Avon River
Fine silt
0.6 – 1.3 m
1
Oioi
Fine sand
rushland
Sea rush and coastal ribbonwood
Over the entire estuary and in
Medium silt to 0.6 – 1.5 m
2
Sea rush
the Avon and Heathcote
Fine sand
rushland
Rivers
Glasswort, buck’s horn plantain, orache, suaeda, Over the entire estuary and in
Very silt to
0.8 - 2.3 m
3
Salt marsh
native primrose, salt grass and selliera
the Avon and Heathcote
coarse silt
herbfield
Rivers, but located near the
Fine sand
banks
Three square, raupo and tall fescue
Located on the eastern banks
Medium silt
0.8 – 1.3 m
6
Three
in the northern reaches also,
square
three square sedgeland, in the
sedgeland
Avon River, is situated
between oioi rushland
Tall fescue and coastal ribbonwood, along with Vegetation type tall fescue and Medium silt
0.9 – 1.6 m
5
Tall fescue
coastal ribbonwood is only
and coastal flax, couch and taupata
found up the Avon River on
ribbonwood
the eastern bank between
vegetation type 1 and 6
Couch, creeping bent
Calders Green
Fine sand
1.0 – 1.9 m
4
Couch
grassland
Coastal ribbonwood and reed canary grass
Charlesworth
Medium silt to 1.3 – 1.4 m
7
Coastal
coarse
ribbonwood
shrubland
native musk, buck’s horn plantain, orache, Not enough samples
Medium silt
0.7 m
8
Native
native primrose, salt grass and selliera
musk
herbfield
native primrose
Not enough samples
Medium silt
0.9 m
9
Native
primrose
herbfield
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Nitrate
10 – 25 mg/1
10 – 100 mg/1
10 – 100 mg/1
10 – 250 mg/1
10 – 250 mg/1
10 – 250 mg/1
100 – 25 mg/1
0 mg/1
100 mg/1
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Establishing a physical and biological basis for salt marsh restoration
3.7 Limitations of the study
The number of sediment samples that were collected in this study were not
significant for some of the vegetation types, a greater amount needed to be taken.
Disproportionate quantities were taken. As the vegetation types were not known the
sediment collection was chosen in terms of proximity to the shore, rather than the
vegetation type present. This resulted in some types being under represented. Future
studies will however, be able to select areas where specific vegetation types are located
by using this research. This will provide the opportunity to carry out more in-depth
analysis on selected vegetation types.
The elevation data is limited due to the amount of data collected. The original
survey plots were captured using a Trimble Geo-XT unit, which does not have sufficient
vertical accuracy. A Trimble R8 was used next, which meant returning to the survey
locations to replot the points. Future studies should use the Trimble R8 initially to ensure
a complete dataset is created.
Another limitation relates to the unsuccessful analysis of nitrite, phosphate and
salinity levels. The period between collection and analysis was too long, which in turn
hindered the results. This occurred due to the separation of time between the summer
collection period and subsequent honours project analysis. In addition, the methods used
to calculate nitrite and phosphate should be altered to ensure results are obtained.
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Establishing a physical and biological basis for salt marsh restoration
Chapter Four
Discussion
As human population continues to increase, development around the coastal
environment has resulted in pressure being applied to these areas. Consequently, coastal
salt marsh vegetation, around the world and in New Zealand, is under threat. Issues
surrounding management and prohibited activities have had a detrimental effect on this
ecologically important vegetation in the Avon-Heathcote Estuary. A possible solution to
combat and prevent further loss is restoration.
However, for this to be successful,
scientific understanding of the vegetation is required.
This research aims to provide a
scientific platform to be used in conjunction with other salt marsh understandings, to
ensure restoration work is successful.
4.1 Vegetation Types and spatial distribution
The Avon-Heathcote Estuary is home to nine vegetation types, with clear spatial
distribution patterns. Due to interactions between land, saline and fresh waters as well as
humans activity, estuaries are highly sensitive environments. The vegetation that grows
in these ecosystems is therefore very vulnerable to extreme changes (Day et al. 1989).
The distribution of the salt marsh can help explain how changes in the margins or
activities around the estuary can affect the abundance of the vegetation. The Avon and
Heathcote Rivers contain the largest area of salt marsh vegetation in the estuary. It was
found that the majority of the salt marsh grows in areas of natural margins, which are
mostly located up the river entrances to the estuary. In comparison, the greater part of the
estuary consists of the artificial, altered margins which contain very little salt marsh
vegetation. This relates to Connell’s Intermediate Disturbance Hypothesis, which states
that as the intervals been disturbance events increases, so does the diversity of species
(Begon et al. 1986). This occurs as there is an increase in time available for invasion of
more species to take place. This emphasises the need for riparian zones to ensure these
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Establishing a physical and biological basis for salt marsh restoration
ecologically important ecosystems are in existence and how changes in the makeup of the
margins can influence the salt marsh.
Both Macpherson (1978) and Rodrigo (1985) findings relate to what was found in
this study, they found that changes occurring in the catchment and margins can have an
effect on the makeup and health of the flora and fauna in the estuary. Salt marsh
therefore grows best in natural environments where it has room to spread landward
without being constrained. Residents have created the majority of the artificial margins
on the eastern side, as flood protection measures. These have been unregulated activities,
which have placed restrictions on the salt marsh in terms of restricting retreat. Regulated
changes conducted by the CCC, including a causeway and dredging, were found to cause
significant changes in the Avon River. In this study, Duncan and Hick (2001) found that
erosion events were linked to these alterations. Current alterations and structures in the
estuary have affected where the salt marsh is located. As only sea rush rushland and salt
marsh herbfield grows near the artificial margins, this suggests that these vegetation types
are more adaptable to change and not as sensitive as the other vegetation types only found
in the river margins.
In terms of the breakdown of each vegetation type, oioi rushland is only found in
the Avon River entrance, suggesting low saline influences. This native plant appears to
grow best in these low energy conditions. With the Bexley Wetlands bordering the Avon
River, it shelters the oioi from both large sediment inputs and contaminants by acting as a
natural buffer. The Heathcote River on the other hand is a more open environment, with
a larger catchment. It contains a higher variety of species indicating less consistency
relating to the environmental factors over space and or time. Sea rush rushland and salt
marsh herbfield are distributed around the entire estuary implying they can grow in a
variety of differing environmental conditions, rather than a tight niche, as oioi rushland
does. The two vegetation types vary in terms of their proximity to the shoreline, the
smaller herbaceous plants are found near the estuary banks, with sea rush growing near
the water, trapping the fine sediments.
These differing locations suggest that oioi
rushland is able to withstand flow currents driven by daily tidal cycles (Owen 1992).
Partridge and Wilson (1989) found that this trend exists due to the trapping properties of
the sea rush. The trend is most predominantly seen on New Brighton Spit, as the coarser
sediments near the banks are sourced from the dune system present on the spit. The finer
sediment is trapped by the sea rush from the inputs via the Avon and Heathcote Rivers.
Three square sedgeland is only found in the locations adjacent to fresh water springs.
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Establishing a physical and biological basis for salt marsh restoration
Raupo is one of the other species which makes up the vegetation type; it is a fresh water
plant, making these conditions ideal for its growth.
As the vegetation type coastal
ribbonwood shrubland is only found in the Charlesworth Reserve, this suggests it prefers
to grow in a small niche. Ribbonwood (Plagianthus divaricatus) cannot tolerate high
saline water, and therefore tends to grow further inland of the shore (Owen 1992).
4.2 Vegetation Types vs. Sediment Size
Salt marsh vegetation grows in areas where fine-grained sediment accumulates in
an estuarine environment. This is due to the abundant supply of sediment in suspension
(Phleger 1977). The majority of fine sediment is located in areas of abundant salt marsh,
in the Avon-Heathcote Estuary. Plants such as sea rush and oioi act as sediment traps,
accumulating the finest sediments, due to the low current velocities and shallow water in
the system (Phleger 1977). Their spatial distribution enforces this, with the majority of
these rushland plants growing in the Avon and Heathcote Rives entrances. This
dominance could be contributed to the increasing input of fine sediments into the estuary
from development in the surrounding catchment and margins. Fine sediment enters the
estuary via these river systems, as runoff from the catchments. As development of the
Port Hills and margins continue, this may increase the presence of these rushland species.
Jupp et al. (2007), who found that there had been a change from salt marsh herbfield to
rushland species, reinforcing this prediction. Although it has been found that sea rush
grows in finer sediment conditions, consideration must be given to the fact that salt marsh
can also influence the condition present, as rushland trap finer sediment they can
influence the area the grow in. There is however, limits to how much salt marsh can
improve and change the environment, relating to the conditions at the beginning and
whether the location is suitable for their growth. As the smaller herbaceous plants prefer
coarser sediments and rushland plants grow best in finer sediments (Partridge and Wilson
1989), the increase in finer sediment will continue this shift in species composition. It
was also found that sediment size increases from the Avon and Heathcote Rivers to the
estuary mouth. This finding has been well documented throughout previous literature
(Voller 1973, Millward 1978, Deely 1991). It is predicted that this coarsening trend will
not change in the future despite development of the catchment continuing to occur
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Establishing a physical and biological basis for salt marsh restoration
resulting in fine sediment runoff due to the dominant input of coarse sediment from the
coastal environments of the spit and estuary mouth in this area.
4.3 Vegetation Types vs. Elevation
As salt marsh grows above the MHWS, elevation is extremely important in
relation to vegetation distribution (Phleger 1977). The tidal range in the Avon-Heathcote
Estuary is 1.88 m at spring tide, with MWHS at 0.94m (Goring 1991). The majority of
the salt marsh in the Avon-Heathcote Estuary, grows above 0.94 m. The results also
show that the less abundant vegetation grows at the higher elevation levels. This suggests
that a minority of vegetation types are found closer to the banks, where elevation is
higher. These species are therefore at the greatest risk because of sea level rise combined
with processes of the estuary infilling. Todd (1999) calculated that by 2050 the estuary’s
water levels will have rise by to 0.2 m and 0.5 by 2100. In addition (Hicks 1998)
predicted that by 2050 sedimentation will have increased to 0.05 m and 0.1 m by 2100.
As the sea level is predicted to rise at a greater rate than sediment, the salt marsh
vegetation may drown. This could change if sedimentation rates continue to increase
with development, causing a greater amount of finer sediments to enter the estuary.
Cahoon’s (1997) model states that as sea level rises salt marsh vegetation will retreat
inland to combat this increase. However, as many of the margins surrounding the salt
marsh are artificial, built structures, restrict landward growth. As the majority of the salt
marsh grows near the natural margins, one would expect that these would not be
restricting. This is however not the case, as the natural margins mostly consist of steep
banks, which back onto residential developments, restricting backward growth. As the
salt marsh herbfield is predominantly located on the banks of the estuary, it will be
smothered by the retreating salt marsh, which may accelerate the loss of these species as
the rushland plants retreat inland, continuing the species shifts documented in Jupp et al.
2007.
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Establishing a physical and biological basis for salt marsh restoration
4.4 Vegetation Types vs. Nitrate, Nitrite and Phosphate
Nitrate is a necessary component of salt marshes, due to the essential
nutrients it provides the vegetation (Jefferies 1972). The levels of nitrate were chosen to
be analysed, as it is present in the treated sewage from Christchurch Wastewater
Treatment Plant. As the discharge location is currently being moved from the AvonHeathcote Estuary to Pegasus Bay, this study can be used as a baseline to compare nitrate
levels. Future studies can be used to compare the effect that removing the treated sewage
will have on the salt marsh. It could be predicted that the salt marsh will initially
decrease in health due to the abrupt drop in nutrients levels, but after a period of time they
may naturally regenerate to a more natural state. No precise relationships have been
established relating vegetation types and nitrate levels, however these findings will be an
ideal baseline, to access future changes relating to the nutrient removal.
4.5 Restoration
For restoration work in the Avon-Heathcote Estuary to be successfully conducted,
scientific and spatial understandings, relating to vegetation species and environmental
variables, is required. This was the main aim of this research and was achieved through
analysis of sediment and elevation data in relation to the distribution of salt marsh
community types. The influence the natural and artificial surroundings have on the
distribution of the salt marsh was also highlighted. It is important to have understandings
of the salt marsh (Harper 1987), to ensure that the environmental conditions where they
are planted are ideal for each vegetation type, to ensure that restoration is successful.
Currently, very little new restoration is being conducted in the Avon-Heathcote
Estuary. There have, however, been plans drafted (Christchurch City Council 2001)
relating to possible restoration work but since the plans were made no further significant
work has been conducted. Thomsen (1999) made recommendations to create a wetland
environment in the council-owned Linwood paddocks. Since then no such activity has
taken place. Currently restoration work is being carried out by the CCC in Charlesworth
Reserve. The outcome has been artificial looking salt marsh areas that do not contain, or
resemble any of the other vegetation types in the natural areas to the south.
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The
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Establishing a physical and biological basis for salt marsh restoration
procedure used in other areas to select species is very simple: species chosen are those
already in existence in the selected area for restoration (Jason Roberts, Coastal Parks
Ranger, Christchurch City Council, pers. comm. 2007).
This method assumes the
environmental conditions are appropriate for these species without using scientific
knowledge to make informed decisions with regards to choosing species for planting.
However, when the plants become established they are able to alter the environmental
conditions to some extent, for example rushland is able to trap finer sediments.
Restoration has also been attempted at Sandy Point, which has also been unsuccessful.
The planting of sea rush may not have been successful due to the elevation of the planted
area. The area that was planted in was near the margins. As this research shows salt
marsh herbfield grows best in these conditions, with higher elevations and coarser
sediment. The hydrological regime should also be looked at in this area to give an overall
scientific understanding of the restoration location. Also for restoration to be successful
targets and success measures need to be set in the initial phase of the restoration project.
These were not set up in this small scale project, giving the restoration no goals to meet
and no indicators to use to whether the work had been successful.
The future proposal, planned by the CCC, is to create a management plan for the
western banks of the Avon-Heathcote Estuary. This was first drafted in the Estuary
Green Edge plan (2001). The focus is on conservation through the restoration of the
Linwood Paddocks south of Sandy Point. The CCC aims to use scientific knowledge
obtained by a Masters Thesis focusing on hydrology. Although good in theory, more in
depth knowledge relating to the salt marsh should be used in conjunction with this,
including understandings relating to the importance of natural margins.
4.6 Management Issues
For restoration to be successful, appropriate management plans and regulations
relating to the activities that can and cannot occur, around the margins of the Avon-
Heathcote Estuary are required. The importance of natural margins is enforced in the
Resource management Act 1991 (RMA),
Under the RMA 1991, section 6 Matters of national importance:
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Establishing a physical and biological basis for salt marsh restoration
In achieving the purpose of this Act, all persons exercising functions and
powers under it, in relation to managing the use, development, and
protection of natural and physical resources, shall recognise and provide
for the following matters of national importance:
a) The preservation of the natural character of the coastal
environment (including the coastal marine area), wetlands, and
lakes and rivers and their margins, and the protection of them
from inappropriate subdivision, use, and development.
Under this section, the RMA recognises the importance of preservation of the natural
margins in the coastal environment, and that this responsibility lies with the city and
regional councils.
This research has found that salt marsh in located in areas of natural margins,
rather than surrounded by structures preventing landward retreat. Therefore, regulations
need to be put in place to prevent further development of the Avon-Heathcote Estuary’s
margins, to protect the salt marsh.
Currently the estuary is split up into different
management areas (Appendix 2), with Environment Canterbury managing the coastal
marine Area (CMA). This includes the foreshore, seabed, and coastal water, and the air
space above the water between the outer limits of the territorial sea (12 nautical miles)
and the line of MHWS (Environment Canterbury 2005). The CCC manages the area
landward of the MHWS. With different land use zone, varying regulations and rules
relate to each, resulting in inconsistencies in management. The separation of areas in the
Avon-Heathcote Estuary has resulted in one regulating authority taking responsibility for
this area. Using the findings of this research it is recommended that a statutory plan be
complied incorporating the entire estuary, including restricting activities that can occur
around the margins of the estuary. The salt marsh should be given sensitive area status,
prohibiting development within certain areas of this ecologically important vegetation. A
holistic approach should be employed to incorporate the ecology, recreational activities,
and development.
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Establishing a physical and biological basis for salt marsh restoration
4.7 Recommendations
Although the CCC is taking steps to enhance the quality of the estuary, through
the management plan for the western banks, it needs to consider the estuary in its entirety.
For successful restoration planning, the Avon-Heathcote Estuary should not be divided up
into separate parts, with differing plans relating to each section. It is recommended that
one planning document is created that encompasses all aspects of the estuary, including
what activities can take place relating to development and natural enhancement
regulations. This research has found salt marsh vegetation grows best surrounded by
natural margins. This needs to be considered in terms of restricting residential properties
on the eastern banks from building hard structures when creating management plans.
As the RMA gives the premise for enforcing the preservation of natural margins a
management plan for the Avon-Heathcote Estuary should be created by agencies involved
with regulating and monitoring the estuarine environment, including Environment
Canterbury. Such a plan should be created involving all areas of the estuary as one
initially, with a holistic approach to management. It should place restrictions on the
activities that can occur in and around the estuary and to help protect the vitally important
margins, to ensure salt marsh stay in existence.
This study only looks at one aspect of restoration, providing ecological salt marsh
knowledge. The findings therefore, need to be used in conjunction with hydrological
understandings as well as given a social context as outlined by SER (2002). This is to
ensure the restoration work incorporates all elements from ecological scientific
understanding, covered in this research, to environmental processes, and the management
strategies in place.
4.8 Future Research
This research has had a scientific focus exploring the spatial distribution of
species in relation to the makeup of the surrounding margins, in terms of creating a
restoration framework. The importance of the margins has been found, highlighting the
need for regulating plans.
Kimberly Jupp
It is suggested that future research explores the current
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Establishing a physical and biological basis for salt marsh restoration
management zones with an attempt to create a single overarching plan that encompasses
the entire estuary. The relationship between the makeup of the margins and the potential
effect of sea level rise on salt marsh as a result of these margins should also be explored.
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Establishing a physical and biological basis for salt marsh restoration
Chapter Five
Conclusions
As cities cope with increasing populations, salt marsh around the world is on the
decline; due to negative effects of high levels of development, draining and reclamation
around the margins and surrounding catchments. Restoration is a tool that is being used,
by local governments, to combat this loss.
However, for restoration work to be
successful, scientific understandings relating to the distribution of the salt marsh is
required. This research aimed to explore the relationship between the vegetation types
found in the Avon-Heathcote Estuary, to environmental variables and margins present.
This was successfully carried out using ArcGIS to create maps, which clearly show the
relationships which exist.
The dominant plant vegetation types in the Avon-Heathcote Estuary were found to
be oioi rushland and sea rush rushland, with these vascular plants growing in locations of
low elevation and fine sediments. The Avon and Heathcote Rivers mouth areas exhibit
the most abundant and diverse salt marsh vegetation, compared to the estuary basin itself.
It was discovered that salt marsh grows in abundance in areas surrounded by natural
margins. The GPS map, showing the makeup of the margins in the Avon-Heathcote
Estuary, clearly shows that the Avon and Heathcote River extends contain the largest
areas of natural margins, which is where the majority of the salt marsh is located.
The proximity of vegetation type to the shoreline showed distribution patterns,
especially in the Penguin Street location, surrounded by artificial margins. Salt marsh
herbfield is located near the landward margins in coarser sediment, with sea rush growing
nearer the shoreline in finer silts. The sediment distribution in the Avon-Heathcote
Estuary found the majority of samples were made of either medium silt or fine sand, with
a shift from coarser sediments at the estuary mouth to finer sediments at the river
entrances. The elevation analysis established a relationship between vegetation type
abundance and elevation: that is the higher the elevation the less abundant the vegetation
type is.
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Establishing a physical and biological basis for salt marsh restoration
This research has added scientific knowledge to the understandings of previous
literature and should be used in conjunction with information relating to hydrological
processes and social perspective to form a legislative management plan for the Avon-
Heathcote Estuary. This holistic approach is needed to aid future restoration work, to
ensure any future development of the margins does not destroy any current salt marsh or
future restoration work that occurs. Salt marshes are biologically important ecosystems
that need to be given a higher level of status to ensure for future existence.
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Establishing a physical and biological basis for salt marsh restoration
Acknowledgements
Following are the people I wish to thank who have all contributed and assisted me
during my research process.
Firstly, I wish to thank my wonderful supervisor Deirdre Hart, for all her help,
advise and encouragement. Deidre, you have been amazing, I appreciate all the time you
have put into helping me put together my research, thanks for both your personal and
professional support.
Thanks to the Coastal Grad Group. This group was an excellent opportunity to
share ideas and progress, and receive comments and advise. Special thanks to Wybren de
Vries and John Carter who have offered their time to discuss further problems, and
Wybren for proof reading my report. Many thanks to Derek Todd for providing feedback
on my research, as well as giving me advise regarding my academic and future career, it
has been much appreciated.
I also thank Justin Harrison in assisting me with the use of the GPS and GNSS
equipment.
Thanks to John Thyne and Paul Bealing for aiding in my GIS understanding, and
answering many little questions I had along the way.
I thank Jennifer Jackson for allowing me to use the DigiSizer 5200 and carrying
out sediment size analysis.
Thanks for teaching me the methods involved from
preparation to comprehending the results.
Thanks to Paul Hedley for assisting we with the elevation field work, you time
was invaluable to me. Thank you very much.
Lastly, special thanks to my family, your support over the years has been amazing.
Thanks for always believing in me and encouraging me to give everything a go, thank
you very much.
Kimberly Jupp
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Establishing a physical and biological basis for salt marsh restoration
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Avon-Heathcote Estuary Ihutai Trust. 2005. Avon-Heathcote Estuary Ihutai: our estuary.
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Bakker, J. P, Grootjans, A. P, Hermy, M and Poschlod, P. 2000. How to define targets for
ecological restoration? Applied Vegetation Science, 3. pp1-72.
Begon, M, Harper, J. L, Townsend, C. R. 1986. Ecology: Individuals, population and
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Appendix One
The following appendix is the nine factors that should be used to determine successful
restoration devised by the Society for Ecological Restoration International (SER) (2002).
Ecosystems
• The ecosystem contains a characteristic assemblage of the species that occurs in
the reference ecosystem and that provide appropriate community structure.
• The ecosystem contains indigenous species to the greatest practicable extent.
• All functional groups necessary for the continued development and/or stability of
the ecosystem are represented.
• The physical environment of the ecosystem is capable of sustaining reproducing
populations of the species necessary for its continued stability or development
along the desired trajectory.
• The ecosystem apparently functions normally for its ecological stage of
development, and signs of dysfunction are absent.
• The ecosystem is suitably integrated into a larger ecological matrix or landscape,
with which it interacts through abiotic and biotic flows and exchanges.
• Potential threats to the health and integrity of the ecosystem from the surrounding
landscape have been eliminated or reduced as much as possible.
• The ecosystem is sufficiently resilient to endure the normal periodic stress events
in the local environment that are an integral part of the dynamics of the
ecosystem.
• The ecosystem is self-sustaining. It has the potential to persist indefinitely under
existing environmental conditions. Aspects of its biodiversity, structure and
functioning will change as part of normal ecosystem development, and may
fluctuate in response to normal periodic stress and occasional disturbance events
of greater consequence. As in any intact ecosystem, the species composition and
other attributes of a restored ecosystem may evolve as environmental conditions
change.
Human systems
• Balance exists between ecological processes and human activities such that human
activities reinforce ecological health and vice versa.
• The people who are dependant on the ecosystem have a key role in setting
priorities and in project implementation.
• Restoration activities are underpinned by economic mechanisms that appropriately
assign the costs incurred and equitably distribute the benefits arising at both a
local and national level.
• The ecosystem serves as natural capital that assures a supply of environmental
goods and services that are useful to people.
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Appendix Two
Conservation 1B (Bromley) Zone
Zone description and purpose
This zone comprising the city's sewage treatment facilities covers a very large and
strategically placed area adjacent to the Avon-Heathcote estuary.
The incorporation of the sewage treatment facilities in a conservation zone reflects the
fact that the great majority of the land area comprises oxidation ponds and farmland
having significant wildlife values, the importance of which is enhanced by its size and
strategic position adjacent to the Avon-Heathcote estuary. The oxidation ponds act as an
artificial wetland and extension to the ecological functions of the estuary itself.
Waste water goes through a primary and secondary treatment system before being passed
through the oxidation ponds, and the water is ultimately released on the outgoing tide into
the Avon-Heathcote estuary.
The ponds are of high ecological value, particularly for bird life. Black and pied
cormorants, New Zealand shoveler and pied stilts are just a few of the species which use
the ponds, their islands and surrounds. Many birds also use the adjacent farm land for
feeding and nesting, and this area is of vital importance to the pukeko population. The
water released into the pond and into the Avon-Heathcote estuary is high in nutrients for
invertebrates, which in turn provides food for birds and fish, both in the ponds and in the
Avon-Heathcote estuary.
Environmental results anticipated
(a)
The conservation and enhancement of the wildlife habitat within the oxidation
ponds and on adjacent farmland.
(b) To ensure the release of treated effluent into the Avon-Heathcote estuary and
its margins is at a standard which does not adversely affect the environment,
and in particular plant, land and aquatic life in the estuary.
(c) To minimise any odours being released from sewage treatment operations, and
its effect on living zones in the vicinity.
(d) The retention of the greater part of land in the zone (east of Cuthberts Road) as
an open space area generally free of structures.
Conservation 1 (Natural, ecological and scenic parks) Zone
Zone description and purpose
Areas in the Conservation 1 Zone include habitats for birds, fish and invertebrate species.
These areas also have significant scientific, educational, recreational and landscape
values. In addition, a large number of these sites are important areas for tangata whenua,
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both in the past and present. Covering a large proportion of the zone are sites which have
been specifically identified for their ecological heritage value and which are listed in Part
4, Appendix 2. As vegetation and habitat remnants of pre-human Christchurch, these
areas are important resources which maintain and enhance the city's identity and
character.
The importance of these areas for passive and generally informal recreation is becoming
more appreciated, and management of these sites must take into account the impacts of
human activities on fragile ecological systems. Some sites may contain facilities
associated with education, research, ecotourism, recreation or associated uses.
Environmental results anticipated
(a)
Control of development and impacts of public use in this zone environment,
in a manner which ensures its character remains substantially unchanged.
(b) The conservation and enhancement of ecological, scientific, landscape,
botanical, cultural, heritage, and functional values of land in this zone.
(c) The maintenance and enhancement of the City's identity and character, by
providing representation of important natural and heritage values.
(d) Protection and enhancement of ecological heritage sites identified within the
zone.
Conservation 1A (Coastal margins) Zone
Zone description and purpose
The Conservation 1A (Coastal Margins) Zone extends inland from mean high water
springs (the landward boundary of the coastal marine area) to provide a buffer between
coastal processes and urban development. The zone includes the coastal dune system, part
of the margins around the estuary and Brooklands Lagoon and the coastline from Sumner
to Boulder Bay. The amount of coastal margin available is constrained by existing urban
settlement. The estuary itself is within the coastal marine area and therefore activities
taking place on it are the responsibility of the Canterbury Regional Council.
Much of the land in the zone is ecologically fragile. The zone aims to recognise and
protect areas of significant natural flora and fauna, and prevent these areas being subject
to the adverse effects of inappropriate use or development, particularly disturbance of the
land surface and of vegetation.
Environmental results anticipated
(a)
(b)
Protection of the integrity, functioning and resilience of the coastal
margin.
Conservation and enhancement of significant areas which are unique to the
coastal area and in particular the protection of areas identified for their
ecological heritage value.
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(c)
(d)
(e)
(f)
Management of land resources in the zone to ensure the natural character
of the coastal environment remains substantially unchanged.
Recognition of coastal hazards, particularly sea and wind erosion, and
provision for avoiding or mitigating such effects.
Maintenance and enhancement of public access to the coast, but
minimising vehicle access within the zone.
Recognition of the remaining baches in the Conservation 1A Zone at
Taylors Mistake, Boulder and Hobson Bays as part of the social and
cultural history of Christchurch and as part of the character at Taylors
Mistake.
Open Space 2 (District Recreation and Open Space) Zone
Zone description and purpose
Many parks in the Open Space 2 Zone have substantial physical resources within them
such as clubrooms, changing sheds and toilet facilities. As well as these, recreation
facilities such as tennis courts, goal posts, cycle and walkways, are common in this zone.
Some parks also contain community facilities of value to the local neighbourhood.
These areas may also contain sites with natural, ecological and/or historic values. The
pressure of high public use on any natural, ecological and historic values must therefore
be taken into account in management of areas in the zone. Three sites within the zone
have been identified for their ecological heritage values (refer Part 4, Appendix 2).
Environmental results anticipated
(a)
(b)
(c)
(d)
(e)
(f)
Provision for a high level of public use of open spaces and recreation areas
within the zone.
The provision of buildings and facilities necessary to facilitate both formal
and informal recreation, consistent with overall maintenance of an open
space character which is not dominated by buildings and hard surfacing.
The maintenance of a system of large areas of public open space for
recreation throughout the city, which are well distributed and readily
accessible to people in all parts of the urban area.
Enhancement of city amenities by the presence and further development of
green open space and opportunities for tree planting.
The exclusion or mitigation of activities and buildings which cause adverse
environmental effects in terms of the Environmental results anticipated in
the surrounding living zones.
Maintenance and enhancement of the ecological heritage sites identified
within the zone.
Conservation 3 (Waterway conservation) Zone
Zone description and purpose
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Land in this zone includes the surface of waterways and their margins, except the
Waimakariri River, which is zoned Conservation 3W, and some minor waterways and
areas within other conservation or open space zones. It is not always possible to show
land zoned Conservation 3 on the planning maps because of the narrowness of some
waterways and their margins.
The zone provisions take into account the protection of the natural and cultural values of
the waterways and their margins, the surrounding land activities, the desirability or
otherwise of public access to and along waterways and the varying levels of public use of
the waterways.
Land within the zone has moderate to high ecological and/or cultural values and this
contributes significantly to the identity and character of these areas. One site in particular
has been identified for its ecological heritage value and is listed in Part 4, Appendix 2.
Some areas within the zone may also contain important areas of historical and
contemporary significance for Maori.
Environmental results anticipated
(a)
(b)
(c)
(d)
(e)
(f)
(g)
The conservation and enhancement of the open space and landscape
character of waterways and associated land margins.
The conservation and enhancement of river habitats, improvement of the
quality of river banks and their surrounds, and limiting those activities which
are likely to have adverse effects on the ecological and natural character of
waterways.
The conservation and enhancement of the "garden city" values of the city's
waterways in the central urban area.
The maintenance and enhancement of the recreation and amenity values of
waterways and associated land margins, and access to and along them.
The enhancement and further development of waterway and other linkages
throughout the city, thereby enhancing the city's identity and character.
Activities on the surface of waterways which have a low impact and which
are non-motorised, except on the Lower Styx.
Protection and enhancement of the ecological heritage sites identified within
the zone.
The Coastal Marine Area
The statutory area that a “Regional Coastal Plan” must deal with is the “Coastal Marine
Area”, but for the reasons set out below Environment Canterbury has prepared this
Regional Coastal Environment Plan which covers both the Coastal Marine Area and areas
immediately landward of this. The Coastal Marine Area is the foreshore, seabed, and
coastal water, and the air space above the water between the outer limits of the territorial
sea (12 nautical miles) and the line of Mean High Water Springs (MHWS). Generally,
MHWS is the line of the average of the highest tides (known as spring tides). Where this
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line crosses a river, the Coastal Marine Area boundary has been determined in accordance
with the Act. On all the maps of this plan, MHWS is shown as an indicative line only.
Due to the changing nature of much of our coastline it is very difficult to show this line
accurately. The position of some unauthorised reclamations is an issue yet to be resolved
regarding the placing of the Coastal Marine Area boundary. MHWS has not been
surveyed on the Canterbury coast. Therefore, this indicative line cannot be used as a
legally defined line due to the margin of error involved. In the event of any dispute as to
the precise location of the line of MHWS Environment Canterbury undertakes to establish
the line for that specific area.
Chapter 6: Natural Character and Appropriate Use of the
Coastal Environment
Objective 6.1
To protect, and where appropriate enhance, the following areas, sites and habitats of high
natural, physical, heritage or cultural value:
(a) Areas of Significant Natural Value – 9 (identified in Schedule 1, and shown on
the Planning Maps in Volume 2);
(b) Those Areas listed in Schedules 2 and 3;
(c) Areas within the intertidal or subtidal zone that contain unique, threatened,
rare, distinctive or representative marine life or habitats (including coastal
wetlands) or are significant habitats of marine species generally;
(d) Areas used by marine mammals as breeding, feeding or haul out sites and
breeding, roosting or feeding areas of indigenous bird species;
(e) Areas, including adequate buffer zones, that contain locally, regionally,
nationally or internationally significant: ecosystems, vegetation, individual
species, or habitat types, (for example coastal lakes, wetlands, lagoons,
estuaries);
(f) Historic, archaeological, and geo-preservation sites in the coastal marine area;
(g) Coastal landforms and landscapes, submerged platforms and seascapes that
are regionally, nationally or internationally representative or unique, including
the Kaikoura coast, Banks Peninsula, Kaitorete Spit, and the Timaru reefs;
Objective 6.2
To protect, and where appropriate enhance, natural character and amenity values
of the Banks Peninsula coastal environment including:
• Volcanic and coastal landforms and features;
• Estuarine and coastal vegetation and habitat;
• Coastal processes and ecosystems;
• Areas of high water quality;
• Areas of high visual amenity value, and/or otherwise unmodified by structures or
other activities, in particular the outer bays and open coast.
Policy 8.7
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Activities in the Coastal Marine Area should not take place where they have, or have the
potential to have, a significant or irreversible adverse effect on the natural or cultural
values of an Area of Significant Natural Value, or on the natural or cultural values of
areas of the coastal environment adjacent to an Area of Significant Natural Value; unless:
(a) there are special or extraordinary and unique reasons why the activity should
be sited in the area; and
(b) any adverse effects on areas of significant indigenous vegetation or significant
habitats of indigenous fauna, are avoided, remedied or mitigated.
Chapter 8: Activities and Occupation in the Coastal Marine
Area
Activities controlled by the Act
Section 12 of the Act provides that certain activities in the Coastal Marine Area can not
take place unless they are expressly allowed by a rule in an operative regional coastal
plan and in any relevant proposed regional coastal plan, or where they are expressly
allowed by a resource consent. These activities are:
(a) reclaiming or draining any foreshore or seabed;
(b) erecting, reconstructing, placing, altering, extending, removing or demolishing
any structure or any part of a structure that is fixed in, on, under or over any
foreshore or seabed;
(c) disturbing any foreshore or seabed (including by excavating, drilling, or
tunnelling) in a manner that has or is likely to have an adverse effect on the
foreshore or seabed (other than for the purpose of lawfully harvesting any
plant or animal);
(d) depositing in, on, or under any foreshore or seabed any substance in a manner
that has or is likely to have an adverse effect on the foreshore or seabed;
(e) destroying, damaging or disturbing any foreshore or seabed (other than for the
purpose of lawfully harvesting any plant or animal) in a manner that has or is
likely to have an adverse effect on plants or animals or their habitat;
(f) introducing or planting any exotic or introduced plant in, on, or under the
foreshore or seabed; and
(g) removing any sand, shingle, shell, or other natural material from the land of
the Crown in the Coastal Marine Area.
Rules in this plan are able to authorise the above activities without the need for resource
consents, although such authorisations may be subject to conditions. These activities and
other activities are controlled through the Objectives, Policies and Rules in this plan. No
person may carry out any activity that contravenes a Rule in this plan unless the activity is
expressly allowed by a resource consent, or is an existing lawful activity allowed by
Section 20 of the Act. Activities in the Coastal Marine Area that are not subject to
controls under Sections 12, 14, 15, 15A, 15B, or 15C of the Act, and that are not subject
to the Rules in this plan do not need to be authorised by resource consents.
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