darwin harbour mangrove monitoring methodologydarwin harbour are regarded as pristine and largely...

DARWIN HARBOURMANGROVE MONITORING

METHODOLOGY

LAND MONITORING SERIES NO. 3 SErrEMBER 2002

Report No. 25/2002 Moritz-Zimmermann, A., Comely, B. and Lewis, D.

DARWIN HARBOUR

MANGROVE MONITORING METHODOLOGY

Technical Manual

September 2002

Land Monitoring Series No. 3

Report No. 25/2002

Department of Infrastructure, Planning and EnvironmentConservation and Natural Resources GroupNatural Resource Management DivisionLand MonitoringPO Box 30Palmerston NT 0831

This report may be cited as:

Moritz-Zimmermann, A., Comley, B. and Lewis, D. (2002). Darwin HarbourMangrove Monitoring Methodology Technical Manual. Land Monitoring Series No.3,Report No. 25/2002. Department of Infrastructure Planning and Environment,Darwin, Northern Territory.

Darwin Harbour Mangrove Monitoring MethodologySeptember 2002

i

EXECUTIVE SUMMARY

Mangroves in Darwin Harbour are floristically diverse, comprising one of largesttracts of mangrove forest throughout the Northern Territory and Australia. Themajority of mangrove communities in Darwin Harbour are largely intact and inpristine condition. The coastline around Darwin Harbour is characterised by longnarrow river arms and experiences a macro-tidal flooding regime and monsoonalclimate. These specific environmental conditions make the mangroves of DarwinHarbour unique and necessitate local mangrove studies.

Approximately 2% of mangroves have been cleared in Darwin Harbour for residentialestates and commercial and industrial developments. Future development mayincrease pressure on the mangrove ecosystem therefore the Northern TerritoryGovernment has initiated the Mangrove Monitoring Program (MMP), a scientificunderstanding of mangroves that is important for the ongoing management of coastalecosystems. The MMP contributes information to the future planning of DarwinHarbour and the sustainable management of its mangroves.

The MMP site network covers the harbour from Sadgroves Creek, Charles DarwinNational Park, East Arm, Middle Arm to West Arm. A total of 38 monitoring sitesalong eight transects have been established in representative mangrove communitiesclassified by Brocklehurst and Edmeades (1995). Attributes monitored are primaryproductivity, vegetation stand structure, species composition, phenology,regeneration, debris, soil chemistry and fauna. The integration of these attributesassists in the interpretation of data anomalies and significant differences between andamongst mangrove communities.

This manual provides a background to monitoring and research in mangrovecommunities. It describes in detail the methods developed and implemented by theDepartment of Infrastructure, Planning and Environment to assess mangrove primaryproductivity, changes in stand structure and species composition to determine long-term mangrove health and condition. The methods described here may be subject tomodifications as the monitoring program evolves and results over time are analysedwith respect to mangrove health and development impact.


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ACKNOWLEDGEMENTS

This work was made possible through the efforts of many staff members of theConservation and Natural Resources Group, especially through the support of RodApplegate.

We gratefully acknowledge the assistance of our colleagues in the field, often underarduous conditions: Patrick Gray, Ivan Bulmer, George Dakis, Carly Steen, JackyStanger, Jo Sedman, Kristen McAllister, Christine Bach, Chandra Salgado, MariaKraatz, Northern Territory University students and many other volunteers. RodMetcalfe, Ian Lancaster, Gary Willis, Jack Burr and Paul Jonauskas provided valuablesupport with the boat-based fieldwork.

Special thanks to the staff members involved in the reviewing of this report. Theirinput was much appreciated.


iii

CONTENTS

EXECUTIVE SUMMARY ..................................................................................i

ACKNOWLEDGEMENTS................................................................................ ii

LIST OF FIGURES ..........................................................................................v

LIST OF TABLES ...........................................................................................vi

ACRONYMS .................................................................................................. vii

1. INTRODUCTION ................................................................................................................... 1

1.1 Mangrove Survey of Darwin Harbour .............................................................................. 2

1.2 Mangrove Research........................................................................................................... 3

1.3 Mangrove Monitoring Reports.......................................................................................... 5

2. BACKGROUND..................................................................................................................... 5

2.1 Darwin Harbour Mangroves.............................................................................................. 5

2.2 Geomorphology ................................................................................................................. 6

2.3 Climate ................................................................................................................................ 9

2.4 Salinity and Tidal Regime ................................................................................................. 9

2.5 Importance of the Mangrove Ecosystem....................................................................... 10

2.6 Pressures on the Mangrove Ecosystem........................................................................ 10

3. MANGROVE MONITORING PROGRAM ........................................................................... 12

3.1 Objectives......................................................................................................................... 12

3.2 Monitoring Attributes ...................................................................................................... 13

3.3 Monitoring Sites............................................................................................................... 14


iv

4. FIELD METHODOLOGY..................................................................................................... 15

4.1 Site Selection Criteria...................................................................................................... 15

4.2 Design and Establishment of Monitoring Sites ............................................................ 15

4.3 Site Information and Description ................................................................................... 17

4.4 Vegetation......................................................................................................................... 214.4.1 Stand Structure and Composition............................................................................... 21

4.4.2 Regeneration .............................................................................................................. 31

4.4.3 Debris ......................................................................................................................... 32

4.4.4 Phenology................................................................................................................... 32

4.4.5 Productivity ................................................................................................................. 33

4.4.6 Allometric Relationships ............................................................................................. 37

4.5 Fauna................................................................................................................................. 384.5.1 Crab Density and Soil Aeration .................................................................................. 38

4.6 Soil..................................................................................................................................... 394.6.1 Sampling Regime ....................................................................................................... 40

4.6.2 Salinity ........................................................................................................................ 43

4.6.3 Water Content............................................................................................................. 44

4.6.4 pH ............................................................................................................................... 45

4.6.5 Temperature ............................................................................................................... 46

4.6.6 Sulphuric Acid Potential.............................................................................................. 46

4.6.7 Soil Field Description and Classification .................................................................... 48

5. ECOLOGICAL RESEARCH ON MANGROVES................................................................. 48

5.1 Links Between Mangroves and Fish.............................................................................. 49

5.2 Sesarmid Crab Project .................................................................................................... 50

5.3 Links Between Mangroves and Insects......................................................................... 51

5.4 Biological Diversity/Recovery from Disturbance/Rehabilitation ................................ 51

6. COMMUNITY-BASED MANGROVE MONITORING PROGRAM ...................................... 53

7. REFERENCES..................................................................................................................... 54


v

APPENDIX 1. Mapping Units of Darwin Harbour…………………………………………………60

APPENDIX 2. Darwin Harbour Mangrove Communities…………………………………………61

APPENDIX 3. Site Information Attribute Codes and Descriptions………………………………62

APPENDIX 4. Site Information Field Recording Sheet…………………………………………..65

APPENDIX 5. Basal/Crown Density/Phenology/Crab Burrow Field Recording Sheet………..66

APPENDIX 6. DBH Field Recording Sheet………………………………………………………..67

APPENDIX 7. Regeneration and Debris Field Recording Sheet………………………………..69

APPENDIX 8. Soil pH/Eh/Temperature/Conductivity Field Recording Sheet………………….70

APPENDIX 9. Soil Water Content and Munsell Field Recording Sheet………………………..71

APPENDIX 10. Leaf Litter Field Recording Sheet………………………………………………..72

LIST OF FIGURES

Figure 1. Projects associated with MMP……………………………………………………………3

Figure 2. MMP transect locations and design……………………………………………………...4

Figure 3. Reports associated with MMP…………………………………………………………….5

Figure 4. Geomorphology of Darwin Harbour………………………………………………………6

Figure 5. Three major mangrove regions of Port Darwin…………………………………………7

Figure 6. Darwin Harbour mangrove zonation……………………………………...……………...8

Figure 7. Average monthly rainfall and air temperature………………………….……………….9

Figure 8. Mangroves cleared for Tiger Brennan Drive extension………………………………11

Figure 9. Overview of MMP attributes……………………………………………………………..13

Figure 10. Mangrove monitoring site design……………………………………………………...15

Figure 11. Monitoring site photo point……………………………………………………………..18

Figure 12. Overview of vegetation attributes……………………………………………………...21


vi

Figure 13. Overview of stand structure attributes……………………………………………...…21

Figure 14. Basal wedge……………………………………………………………………………..23

Figure 15. Use of the basal wedge………………………………………………………………...23

Figure 16. Measuring tree height…………………………………………………………………..25

Figure 17. Procedures for measuring DBH……………………………………………………….26

Figure 18. Tree tag…………………………………………………………………………………..27

Figure 19. Forestry densiometer…………………………………………………………………...30

Figure 20. Overview of primary productivity studies……………………………………………..34

Figure 21. Leaf litter monitoring trap……………………………………………………………….35

Figure 22. Overview of soil attributes……………………………………………………………...39

LIST OF TABLES

Table 1. Distribution and monitoring site (M) replicates……….………………………………...14

Table 2. General site information: site specifics…………………………………………………..19

Table 3. General site information: soil……………………………………………………………..20

Table 4. General site information: vegetation.…………………………………………………….20

Table 5. Mangrove monitoring (M) and leaf litter (L) sites……………………………………….35

Table 6. Overview of soil and soil sampling methods……………………………………………41

Table 7. Soil sampling regime………………………………………………………………………42

Table 8. Soil water sampling regime……………………………………………………………….42

Table 9. Test trials of soil pH………………………………………………………………………..45

Table 10. pH indices and acid sulfate soil potential………………………………………………47


vii

ACRONYMS

ACC Angle Count Cruising

BAF Basal Area Factor

CCS Coasts and Clean Seas

CMMP Community Mangrove Monitoring Program

DBH Diameter at Breast Height

DBIRD Department of Business, Industry and Resource Development (formerDepartment of Primary Industries and Fisheries – DPIF)

DIPE Department of Infrastructure, Planning and Environment (former Departmentof Lands, Planning and Environment – DLPE)

EC Electrical Conductivity

FC Foliage Cover

FPC Foliage Projective Cover

LASD Log and Stump Densities

MMP Mangrove Monitoring Program

NFI National Forest Inventory

NHT Natural Heritage Trust

NT Northern Territory

NTU Northern Territory University

SASD Seedling and Sapling Densities


1

1. INTRODUCTION

As the Darwin urban area expands in response to an increasing population base andrise in commercial development, there are potential consequences for mangrovecommunities within the city’s natural harbour. The most obvious effect of urbandevelopment would be the removal of mangroves necessary for new residential andcommercial sites. Population growth in the Darwin urban area has recentlyexperienced rapid increase, for example, the satellite city of Palmerston grew at anunprecedented rate of 8% from 1999 to 2000 (Elliott, 2001). Further, majorindustrial developments contributing to the economic benefit of the NorthernTerritory have been positioned within the harbour, eg. the new port facility and theproposed LNG Plant. However despite these developments, mangrove communities inDarwin Harbour are regarded as pristine and largely intact (Brocklehurst &Edmeades, 1996). Estimates of the loss of mangrove habitat over 20,000 hectaresfringing the harbour, indicate that about 2% or 400 hectares have been cleared forvarious urban and industrial developments (DLPE, 2000).

In the late 1980s concern over the pressure on coastal mangroves in Darwin Harbourfrom urban and industrial developments led to a study instigated by the NorthernTerritory Government. Dames and Moore (1988) developed a Draft MangroveManagement Plan for the then Conservation Commission of the Northern Territorywhere the maintenance of 80% of the productivity of Darwin Harbour mangroves wasrecommended. The 80% productivity recommendation was taken from theInternational Union of the Conservation of Nature recognising that the removal ofmore than 20% of mangrove productivity from any discrete system would bedetrimental to its functionality (Hamilton & Snedaker, 1984). It is acknowledged thatby retaining a percentage of mangrove productivity within each vegetationcommunity does not equate to retaining the equivalent proportion in terms of area(Dames & Moore, 1988).

Recognising the pressure on mangroves from urbanisation, the NT Government madea commitment to conserve 80% of the mangrove productivity in Darwin Harbour byincorporating the recommendations of the Dames and Moore study in the DarwinRegional Land Use Structure Plan (NTDLH, 1990). As a result, the Department ofInfrastructure Planning and Environment (DIPE) established a monitoring program toobtain baseline data on mangrove productivity to assess the condition of mangrovecommunities in Darwin Harbour.

The coastline around Darwin Harbour is characterised by long narrow river arms, andthe region experiences a macro-tidal flooding regime and a monsoonal climate. Thesespecific environmental conditions make the mangroves of Darwin Harbour uniqueand necessitate local mangrove studies. Until recently, only few studies had beenundertaken in NT mangroves. Consequently, relatively little scientific data isavailable to base sound management decisions. Data from other parts of Australia andoverseas have a limited relevance to the mangroves of Darwin Harbour, since theecology of mangroves is strongly determined by factors such as tidal regime, climate,freshwater inputs, substrate and topography.


2

The mangrove communities of Darwin Harbour were formally mapped andcharacterised by DIPE in 1995 (Brocklehurst & Edmeades, 1995). In 1997, DIPEestablished 38 leaf litter sites to assess litter fall as a measure of primary productivityin the harbour’s mangrove communities. In conjunction, DIPE established 27permanent monitoring sites consistent with the leaf litter sites in 1999. These siteswere the first systematic attempt at monitoring long-term changes of mangrovecommunities in the harbour in terms of stand structure and species composition.Parallel to this government monitoring program, a number of scientific studies wereundertaken to enhance overall knowledge of mangrove ecosystems (eg. Metcalfe,1999; Metcalfe, in prep; Salgado-Kent, 2002; Martin, in prep; Coupland, in prep;Comely, 2002) (see Fig. 1). Recently DIPE released a report ‘Mangrove Managementin the Northern Territory’ (DIPE, 2002) to provide direction for research andmanagement of mangrove ecosystems. This report provides input for the developmentof a plan of management for Darwin Harbour due for release in 2003.

The sole focus on mangrove productivity as a measure of mangrove health andcondition has now shifted towards an understanding of ecological processes andbiodiversity based on sound scientific data. This scientific understanding will providea more comprehensive base to objectively assess the impacts of development inDarwin Harbour. The NT Government is also moving to provide conservationprotection to over 90% of the mangroves in the harbour through zoning under thePlanning Scheme.

This report describes in detail the methods implemented for the DIPE’s MangroveMonitoring Program (MMP). Its purpose is to provide a reference for officersengaged in field data collection for the MMP. It is by no means an exhaustive orconclusive document but rather an evolving document subject to refinement as dataanalysis and experience in mangrove monitoring dictate future monitoring direction.

Sections one and two of this report discuss the background and physicalcharacteristics of Darwin Harbour in a regional context. Section three describes indetail the MMP: its objectives, monitoring site locations and monitoring attributes.This is followed by detailed descriptions of field methodology for assessingproductivity, vegetation stand structure and composition, regeneration, debris,phenology, allometric relationships, several soil attributes and crab hole density inSection four. Sections five and six outline previous and current mangrove studiesconducted in the harbour.

1.1 Mangrove Survey of Darwin Harbour

The basis of the MMP is the Mangrove Survey of Darwin Harbour, as part of a largerNational Forest Inventory (NFI) Project, (Brocklehurst & Edmeades, 1995). The aimof this survey was to:♦ Provide a map and inventory of the Darwin Harbour mangrove communities and

relevant data on density, stand, structure, standing basal area, condition and wherepossible standing biomass. This provides the area and structure of individualmangrove communities and their spatial relationships to the harbour as a whole.

♦ Determine cost-effective methods for mangrove survey including the effectivenessof remote sensing image classification to define mangrove communities.

♦ Serve as a pilot survey to refine techniques for a possible future survey of all NTmangrove forests.


3

Figure 1. Projects associated with the Mangrove Monitoring Program (MMP).

1.2 Mangrove Research

The MMP consists of a network of monitoring sites in the mangrove communities ofDarwin Harbour (Fig. 2) and serves as a framework for mangrove research. Thisframework facilitates communication and effective use of research data through thedevelopment of standardised methods; the establishment of research sites (monitoringsites) and the provision and exchange of data and relevant information.

Studies undertaken by DIPE measure the productivity and natural condition ofmangroves in Darwin Harbour. In addition, postgraduate students from the NorthernTerritory University (NTU) have undertaken five research projects. DIPE and theDepartment of Business, Industry and Resource Development (DBIRD) havesupported the projects both financially and operationally (see Section 5). The NTUresearch projects provide important information that will feed into the MMP todetermine appropriate modifications to the current methodologies. Results of theseprojects will also help to identify key indicators of health to determine the impacts ofcoastal development on mangrove communities/systems in Darwin Harbour.

MANGROVE MONITORING PROGRAM (MMP)

LinksBetween

Mangroves& Fish

SesarmidCrab Project

LinksBetween

Mangroves& Insects

BiologicalDiversity ofMangroves

MangroveRehabilitation

Mangrove Survey of DarwinHarbour (Brocklehurst &

Edmeades 1995)CommunityMangroveMonitoringProgram(CMMP)

Recoveryfrom

Disturbance

MangroveProductivity

&Management


4

Figure 2. Satellite image of Darwin Harbour showing MMP transect locations, and diagramof a typical transect illustrating site and leaf litter trap set up. Note: not to scale.

Seaward edge

Landward edge

Transect line

0km

6km

Sites

Leaf litter traps

Woods Inlet

WEST ARM

EAST ARM

MIDDLEARM

BlackmoreRiver

ElizabethRiver

WestArmCreek

JonesCreek

SadgrovesCreek Reichardt

Creek

PioneerCreek


5

1.3 Mangrove Monitoring Reports

There are several reports stemming from the MMP that have been initiated overrecent years (Fig. 3). The Mangrove Management in the Northern Territory (DIPE,2002) report provides direction for research and management of mangroveecosystems. The MMP is a central component of mangrove research and monitoringin Darwin Harbour. The bottom three reports illustrated in Figure 3 arecomplementary rather than stand-alone documents. The Community MangroveMonitoring Program (CMMP) (see Section 6) is a derivative of the MMP, whereas theInterim Mangrove Data Assessment report is an exploration of data from both theMMP and CMMP datasets (Potter, in prep).

Figure 3. Diagram of reports assocaited with the MMP.

2. BACKGROUND

2.1 Darwin Harbour Mangroves

The mangroves of Darwin Harbour constitute one of the most significant mangroveareas in Australia (Wightman, 1989). They occupy an area of approximately 20,400ha, representing about 5% of mangrove communities in the NT (Brocklehurst &Edmeades, 1995) and 2% of Australia’s mangroves. On a global scale, DarwinHarbour mangroves contribute 0.1% of the remaining world mangrove area(Brocklehurst & Edmeades, 1995).

MangroveMonitoring in Darwin

Harbour

DARWIN HARBOURMANGROVEMONITORINGMETHODOLOGY

Technical Manual

September 2002

COMMUNITY MANGROVEMONITORINGPROGRAMImpact Assessment…...

Technical Manual andFinal ReportIn Preparation

INTERIM MANGROVEDATA ASSESSMENT

In Preparation

MANGROVEMANAGEMENT IN THENORTHERN TERRITORY

Northern TerritoryGovernment

2002


6

Mangrove species diversity in Darwin Harbour is high when compared with the restof the NT coastline (Wightman, 1989). Approximately 48 species of plants arerecognised as being regular inhabitants of mangrove communities found in the NT, ofwhich approximately 36 species have been identified in Darwin Harbour(Brocklehurst & Edmeades, 1995). For comparison, a total of about 80 species aretypical of mangrove environments found worldwide (Saenger et al., 1983). Althoughno rare mangrove species occur in Darwin Harbour, their extent and diversity makethem locally, nationally and globally important.

2.2 Geomorphology

Darwin Harbour is a drowned river valley system of about 380 ha and is located onthe north-western coast of the NT. The harbour’s catchment is about 1,720 ha(Padovan, 1997) and includes three major rivers, Elizabeth, Darwin and BlackmoreRivers, as well as numerous creeks (Fig. 4). Post-glacial marine flooding of the lowerparts of these rivers and creeks has developed East Arm, Middle Arm, West Arm andWoods Inlet. The hinterland of Darwin Harbour is a dissected plateau underlain byPrecambrian rocks with a variable cover of Cainozoic laterite and weatheredsediments (Semeniuk, 1984).

Figure 4. Geomorphology of Darwin Harbour.

WESTARM

MIDDLEARM

EASTARM

BlackmoreRiver

ElizabethRiver

WestArmCreek Pioneer

Creek

WoodsInlet


7

Overall, the morphology of Port Darwin can be broadly categorised into three mainenvironments: riverine channels, the Darwin Harbour embayment and open oceaniccoastline (Fig. 5) (Semeniuk, 1984). Within the Darwin Harbour embayment, erosionand sedimentation processes have created about seven medium-scale geomorphicunits: hinterland margin, alluvial fans, tidal flats, tidal creeks, spits/cheniers, rockyshores, sub-tidal channels and bays (Semeniuk, 1984). Apart from sub-tidal channels,all of these units provide suitable habitats for mangroves. Within these habitats,differences in tidal level, inundation frequency, tidal erosion, tidal sedimentation,wave action and freshwater recharge create a variety of environmental conditions (eg.gradients in salinity and different substrates). The distribution of mangrove speciesreflects these conditions, creating an assembly of distinct communities, which formzones along the coastline (Fig. 6).

Figure 5. The three major mangrove regions of Port Darwin. The embayment zonerepresents Darwin Harbour (adapted from Semeniuk, 1984).

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2.3 Climate

Darwin Harbour experiences a monsoonal climate, characterised by a highly seasonalrainfall regime and an annual period of aridity. North-westerly winds bring 90% ofannual rainfall during the wet season (October to April), whereas in the dry season(May to September) south-easterly winds are predominant and rainfall is extremelylow (Fig. 7). Temperatures and solar radiation are high throughout the year and annualevaporation exceeds rainfall by some 600 mm (Wightman, 1989).

Figure 7. Average monthly rainfall, maximum and minimum air temperature at DarwinAirport for the period 1941 to 1986 (data drawn from Love et al., 1987).

2.4 Salinity and Tidal Regime

A highly seasonal rainfall regime has a significant effect on water quality of theharbour. A survey by Padovan (1997) recorded a maximum salinity of 36.9 ppt at theend of the 1990 dry season, and a minimum of 28.2 ppt during the following wetseason. A distinct increase in salinity values with distance from river mouths wasfound in the wet season. This is due to the large quantities of freshwater input fromrivers, hinterland sheet flows and subterranean seepage entering Darwin Harbour.Even after rains have stopped, the subterranean freshwater seepage from the terrestrialhinterland continues well into the dry season (Semeniuk, 1985).

Another dominant feature of Darwin Harbour is its large tidal range. The maximumtidal range is 7.8m, with a mean spring range of 5.5m and a mean neap range of1.9m (Padovan, 1997).

050

100150200250300350400450

Jan

Feb Mar Apr May Jun Ju

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Nov Dec

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m]

10

15

20

25

30

35

Tem

pera

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[Deg

rees

Cel

cius

]

Rainfall Temp (C0)


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2.5 Importance of the Mangrove Ecosystem

Mangroves play a vital part in the marine ecosystem and protect the coastline fromerosion and storm surge (Hutchings & Saenger, 1987). Mangrove forests formeffective, self-repairing barriers against severe storms, storm surge and tropicalcyclones. Trees act as windbreaks, and their extensive root systems trap and stabilisesediments. The mangroves are also important sediment sinks, reducing the siltation ofwaterways and estuaries, improving water quality and protecting coral reefs fromupstream sediment loads, particularly after heavy rain (Saenger et al., 1983).

The diverse mangrove ecosystem provides habitat for a wide array of animals. Manyfish and prawn species, including species significant to recreational and commercialfisheries, utilise the mangroves as nursery and spawning grounds (Robertson & Duke,1987; Hamilton & Snedaker, 1984).

Mangrove fauna, such as crustaceans and fish, migrate out of the mangrove ecosystemand contribute significantly to the marine food chain. Estuarine and near-shorefisheries harvest the products of this complex food chain. Their yields are stronglylinked to mangrove productivity (Saenger et al., 1983). They produce large amountsof organic matter (Woodroffe et al., 1988) and nutrients (Metcalfe, 1999), whichsupport not only the fauna and flora of the mangrove ecosystem itself, but alsoadjacent habitats.

Since mangroves are an integral part of the coastal zone, their sustainablemanagement and conservation is vital. Increasing pressure from coastal development,land clearing and pollution may significantly effect the ecology of mangrove systemsand consequently alter the ecological balance of the entire marine ecosystem(Hutchings & Saenger, 1987).

2.6 Pressures on the Mangrove Ecosystem

There are a number of direct and indirect threats to the mangrove ecosystem. Themost obvious includes clearing and land filling for infrastructure and development(Fig. 8). The world’s rapidly expanding aquaculture industry poses a detrimentalthreat to mangroves (Odum & Johannes, 1975; Boto, 1992) where, aside fromremoving mangroves, large-scale mortality has been reported often with littlesubsequent recovery in areas adjacent to intensively developed sites (Odum &Johannes, 1975).


11

Forms of pollution include heavy metal, herbicide and pesticide accumulation inmangrove sediments, result in chronic effects on both mangrove fauna and flora(Hogarth, 1999). Mangrove environments have also been reported to show signs ofstress from nutrient enrichment, although published information concerning thereaction of mangroves to elevated nutrient levels is scarce (Odum & Johannes, 1975).Oil and petroleum by-products have often killed mangroves by coating aerial rootsand pneumatophores, clogging lenticels and killing roots by asphyxiation (Hogarth,1999; Odum & Johannes, 1975). High levels of sedimentation can have a similareffect on mangroves. Plants have been reported to die within a few weeks afterdeposition of 20-30cm of sediment (Odum & Johannes, 1975; Hong & San, 1993).

When mangroves die their roots decay, large scaled erosion may occur so thatrecovery many be postponed indefinitely. Where recovery does occur it appears totake about 20 years or more where the full height of trees may not be reached for afurther 50 years (Odum & Johannes, 1975).

Figure 8. Clearing of mangrove vegetation for infrastructure development in Darwin.


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3. MANGROVE MONITORING PROGRAM

The MMP consists of a network of monitoring sites and a framework for mangroveresearch in Darwin Harbour. It was established to increase the knowledge andunderstanding of mangrove ecology and to provide resource managers and scientistswith baseline data. There are four primary objectives.

3.1 Objectives

� Objective 1

To help determine the natural status and condition of the mangroves in DarwinHarbour.The detailed assessment at each monitoring site includes measurements of vegetationstand structure, regeneration, primary productivity and environmental attributes. Thedata forms an important baseline in the determination of productivity rates anddetecting species and structural changes over time.

� Objective 2

To monitor seasonal and annual changes in productivity of mangrovecommunities in Darwin Harbour.Repeated monitoring over time help provide indications of the natural variability inmangrove productivity and regeneration as well as provide information onenvironmental changes within each mangrove community.

� Objective 3

To determine the impact of coastal development on Darwin Harbour Mangroves.The set up of the MMP aims to determine the underlying causes of shifts in speciescomposition and structural formation as related to development.

Data collected by the MMP will reveal natural variability and fluctuations underrelatively pristine conditions. These conditions may change as Darwin’s populationincreases and impacts associated with this growth, such as pollution and clearing,effect the mangrove ecosystem.


13

� Objective 4

To establish a monitoring framework and standard methodology for present andfuture research.The MMP aims to provide a framework for mangrove research in Darwin Harbour.Part of the framework was the establishment of permanent monitoring sites sharedacross a number of research projects.

The MMP plays a key role in the provision and exchange of data. Since relativelylittle was known about the overall ecology of Darwin Harbour mangroves, a numberof studies have been undertaken with a focus on productivity of mangrovecommunities (see Section 5).

3.2 Monitoring Attributes

Shown in Figure 9 are the attributes measured in the MMP, ranging from soil studiesto the estimation of primary productivity. For example, studies elsewhere demonstratethat primary productivity is strongly related to soil conditions, which in turn areaffected by the presence of crabs (Smith et al., 1991). The mangrove ecosystem alsointeracts significantly with the surrounding marine and terrestrial ecosystems. Theseinfluences are assessed and/or measured, where possible (see Sections 4.3, 4.6 &Appendices 4 & 5).

MangroveMonitoring

VegetationStand

Structure

PhotoDocumentation

Crab Holes

Soil

SiteInformation/Description

Regeneration

PrimaryProductivity

Phenology

Figure 9. Overview of the MMP attributes.


14

3.3 Monitoring Sites

Permanent sites were established in representative mangrove communities. Theidentification of representative sites was based on the Mangrove Survey of DarwinHarbour (Brocklehurst & Edmeades, 1995). In this survey mangroves were classedinto 10 communities according to their floristics and structural characteristics (seeAppendix 1). A map illustrating the distribution and extent of these communities isprovided in the Appendices (Appendix 2).

The MMP to date has focused on eight of the 10 dominant mangrove communities.A total of seven transects were positioned across the tidal range extending from theseaward edge to the landward edge of the mangroves, crossing all major mangrovecommunities. Sites were established by using a transect-line plot method.Selection criteria for these transects include:♦ representative mangrove habitats of (harbour, tidal creek).♦ representative spatial coverage of Darwin Harbour (East Arm, Middle Arm,

West Arm).♦ accessibility by land or boat.

Within each of the seven transects a series of sites were set up to represent thedominate mangrove communities in Darwin Harbour (Fig. 2).Selection criteria for the sites include:♦ homogeneity in terms of vegetation composition; and♦ representative of the mapped community description identified by Brocklehurst

and Edmeades (1995).

A total of 27 monitoring sites were established. Each of the eight communities wererepresented with a minimum of three sites, however community seven had less as aresult of its patchy occurrence in the harbour. Table 1 provides a summary of themonitoring sites and their location.

Sites were labelled according to their general location in the Harbour (East Arm,Middle Arm & West Arm), transect number (one-eight) and mangrove communityaccording to Brocklehurst and Edmeades (1995). For example, site E1.8: East Arm(E), transect number (one), in a Sonneratia alba woodland (eight).

Table 1. Distribution and replicates of monitoring sites (M) with respect to Darwin HarbourArms, transects and mangrove zones.

East Arm Middle Arm West ArmMangrove E1 E2 M1 M2 M3 W1 W2 ReplCommunity Harbour Creek Harbour Creek Creek Harbour Creek No.1 M M M 32 M M M M M 53 M M 24 M M M M 45 M M M 36 M M M M M 57 M 18 M M M M 4Totals 6 2 4 4 4 5 2 27


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4. FIELD METHODOLOGY

Methods are described for the establishment of sites, and the collection andmeasurement of mangrove productivity, vegetation stand structure and composition,debris, regeneration, phenology and allometric relationships. Also included aremethods to determine crab burrow density and methods to monitor several soilattributes such as salinity, pH, temperature and water content (Fig. 9).

Most of the methods are based on the Survey Manual for Tropical Marine Resourcesby English et al. (1997), with slight modifications to suit local conditions andobjectives of the MMP.

4.1 Site Selection Criteria

Mangrove forests were investigated using aerial photographs and vegetation maps.Subsequent field trips were undertaken to ground truth photographs, maps andsatellite images to select suitable areas that were homogenous mangrove communities.

4.2 Design and Establishment of Monitoring Sites

Figure 10 illustrates the MMP site layout adapted from Sullivan and Egan (1996):

DownSlope

CornerPicket 1

CornerPicket 4

CornerPicket 2

CornerPicket 3

Centre Point

Photo Point

20m

20m

1m 1m

Transect 1Transect 2

Figure 10. Design of mangrove monitoring sites.


16

Dimensions

A plot size of 20 x 20 m was most suitable for the different mangrove communitystructures and densities in Darwin Harbour. The plot size covered representative areasin all mangrove communities sampled in the harbour.

Site Set up

The plots were set up using a 100 m measuring tape and compass. In order to makethe monitoring sites permanent and easy to locate, corner, centre and photo pointswere marked with PVC pipes. The MMP followed recommendations from othermangrove studies by using 1.5 m long and 50 mm wide PVC pipes that were pushed0.5 m into the ground (English et al., 1997). To allow for tidal and rain water to flowthrough the pipes, small holes were drilled in the sides of each pipe, hencemaximising their resistance against tidal movements.

Identification Procedure

For easier identification of sites the following system was set in place:

♦ Aluminium tags:Permanent aluminium tags were pop-riveted to all PVC pipes at each monitoring siteand engraved with the site number (eg. E1.8), photo point (P), centre post (C) andcorner posts (one, two, three & four).

♦ Corner posts:The corner posts were numbered clockwise with post one located in the upper rightcorner up slope of corner post two, as demonstrated in Figure 10.

♦ Centre post:The aluminium tag at the centre post had a site ID, however a C instead of a numberengraved as with the corner posts.

♦ Photo point:The aluminium tag of the photo post was marked with a site ID only (P). The post wasestablished between corner post one and the centre of the site. The distance and anglebetween photo point and corner post one varied from site to site due to poor visibilitycaused by variations in vegetation structures and densities. In general, most photopoints were set up about 3-5 m from corner post one.


17

4.3 Site Information and Description

Site information is beneficial in the interpretation of the results, particularly in theinterpretation of data anomalies and significant differences between sites of the samemangrove community.

During the establishment of the monitoring sites general information about the site(including a sketch), vegetation and soils were recorded (see Appendix 4 & 5). Someof the recorded environmental attributes and indexes were adopted from Brocklehurstand Edmeades (1995). Attributes marked with (*) in Tables 2, 3 and 4 were recordedat each monitoring visit.

Hand Drawing of Monitoring Site

The drawing illustrated the monitoring site and immediate surroundings. It included:♦ location of corner, centre and photo point posts♦ angle and distance of photo point to corner point one♦ aspect of site (from corner post one to two)♦ location of transect♦ aspect of transect (from land to sea)♦ location of leaf litter traps♦ location of nearby creek lines and other landmarks♦ location of and, if possible, distance to neighbouring mangrove communities

Geographic Position

Geographic positions were gauged with a handheld GPS, accurate to ± 25 m. Inaddition, elevation and geographic position of transects E2, E3, M1, M2 and W1 weremeasured with a Trimble RTK (Real Time Kinematic) GPS by a surveyor. Theaccuracy of the elevation data is ± 10-20 mm and of the geographic position ± 1m.Descriptions of general site areas and geographic positions are useful in relocatingmonitoring sites.

Slope

The slope of the monitoring site was measured with a clinometer from the centre post.

Environmental Conditions

Several environmental conditions of each monitoring site were recorded. Attributesincluded factors such as tidal zone, hinterland relief (m), amount of water run-off andseepage (refer to Appendix 3). These features recognise the degree of exposure eachmonitoring site experiences relative to tidal waters and freshwater input. Informationrelative to leaf litter and microrelief (bioturbation) is also included and providesindications of soil aeration status. This information is beneficial in interpreting othermonitoring attributes.


18

Disturbance

Adjacent land use, potential future land use and types of disturbance were recorded toidentify potential impacts to mangrove communities. Although all sites of the MMPare in undisturbed mangrove habitats, adjacent land use may change in the future.

Photo Point

Permanent photo points were installed to illustrate the monitoring sites and possiblechanges in vegetation structure over time (Fig. 11). Photos were taken of the photopost from corner post one facing towards the centre of the site.

Figure 11. Photo Point, E1.1, Charles Darwin National Park. A board on top of thephoto point identifies the site and monitoring date.

Dar

win

Har

bour

Man

grov

e M

onito

ring

Met

hodo

logy

Sept

embe

r 200

2

19

Tab

le 2

. Gen

eral

site

info

rmat

ion:

site

spe

cific

s.(*

) attr

ibut

es re

cord

ed a

t eac

h vi

sit.

Site

Info

rmat

ion

Des

crip

tion

App

licat

ion

Site

IDEa

ch si

te h

as a

uni

que

ID: H

arbo

ur A

rm/T

rans

ect N

o/M

ap U

nit

♦

Site

Des

crip

tion

Loca

tion

Nam

e of

gre

ater

are

a, c

reek

or c

lose

st la

ndm

ark

and

Geo

-Cla

ss (m

arin

e, e

stua

rine,

rive

rine)

♦

Site

Des

crip

tion

East

ing/

Nor

thin

gM

easu

rem

ent o

f the

geo

grap

hic

posi

tion

of th

e si

te♦

Si

te D

escr

iptio

nM

ap U

nit

Iden

tific

atio

n of

map

uni

t/pla

nt c

omm

unity

num

ber

♦

Site

Des

crip

tion

Spec

ies*

Iden

tific

atio

n of

all

spec

ies f

ound

with

in th

e si

te♦

Si

te D

escr

iptio

nA

cces

sH

ow th

e si

te c

an b

e ac

cess

ed♦

Si

te D

escr

iptio

nPl

ot P

ositi

onId

entif

icat

ion

of th

e po

sitio

n of

the

site

with

in th

e m

angr

oves

(sea

war

d-m

id-la

ndw

ard)

♦

Site

Des

crip

tion

Asp

ect

Iden

tific

atio

n of

the

aspe

ct o

f the

tran

sect

(lan

d to

see)

and

site

(cor

ner p

ost 1

to 2

)♦

Si

te D

escr

iptio

n

Tida

l Zon

eEs

timat

e of

the

freq

uenc

y of

tida

l flo

odin

g♦

Si

te D

escr

iptio

n♦

En

viro

nmen

tal C

ondi

tions

Slop

e*M

easu

rem

ent o

f the

slop

e of

the

site

in d

egre

es (c

linom

eter

)♦

Si

te D

escr

iptio

n♦

En

viro

nmen

tal C

ondi

tions

Hin

terla

nd R

elie

f*Es

timat

e of

the

relie

f of t

he a

rea

adja

cent

to m

angr

oves

(ter

rest

rial)

♦

Site

Des

crip

tion

♦

Envi

ronm

enta

l Con

ditio

nsR

un-O

ff*

Estim

ate

of th

e sp

eed

of ru

n-of

f with

in th

e si

te♦

Si

te D

escr

iptio

n♦

En

viro

nmen

tal C

ondi

tions

Seep

age

Ass

essm

ent o

f the

pre

senc

e an

d ty

pe o

f see

page

(fre

sh/s

alt)

♦

Site

Des

crip

tion

♦

Envi

ronm

enta

l Con

ditio

nsA

djac

ent a

ndFu

ture

Lan

d U

se*

Iden

tific

atio

n of

pre

sent

and

futu

re la

nd u

ses a

djac

ent t

o th

e m

angr

oves

♦

Site

Des

crip

tion

Hea

lth a

nd C

ondi

tion

A

sses

smen

t

Dar

win

Har

bour

Man

grov

e M

onito

ring

Met

hodo

logy

Sept

embe

r 200

2

20

Deg

ree

of E

xpos

ure*

Estim

ate

of th

e %

of s

ite m

argi

ns e

xpos

ed♦

Si

te D

escr

iptio

n♦

H

ealth

and

Con

ditio

n♦

A

sses

smen

tD

istu

rban

ce*

Iden

tific

atio

n of

the

type

and

freq

uenc

y of

dis

turb

ance

Not

e: A

lthou

gh th

e si

tes w

ere

gene

rally

und

istu

rbed

and

in p

ristin

e co

nditi

ons,

biot

urba

tion

by c

rabs

was

reco

rded

as a

bio

tic d

istu

rban

ce.

♦

Site

Des

crip

tion

♦

Hea

lth a

nd C

ondi

tion

Ass

essm

ent

Tab

le 3

. Gen

eral

site

info

rmat

ion:

soi

l.(*

) attr

ibut

es re

cord

ed a

t eac

h vi

sit.

Soil

Info

rmat

ion

Des

crip

tion

App

licat

ion

Subs

trate

Cla

ssC

lass

ifica

tion

of th

e su

bstra

te♦

Si

te D

escr

iptio

nSu

bstra

te T

ype*

Iden

tific

atio

n of

the

mai

n su

rfac

e su

bstra

te ty

pe o

f the

site

♦

Site

Des

crip

tion

Mic

rore

lief*

Iden

tific

atio

n of

the

subs

trate

mic

rore

lief o

f the

site

♦

Site

Des

crip

tion

♦

Envi

ronm

enta

l Con

ditio

ns

Tab

le 4

. Gen

eral

site

info

rmat

ion:

veg

etat

ion.

(*) a

ttrib

utes

reco

rded

at e

ach

visi

t.

Veg

etat

ion

Info

rmat

ion

Des

crip

tion

App

licat

ion

Stat

us a

nd C

ondi

tion*

Ass

essm

ent o

f the

gen

eral

hea

lth st

atus

and

con

ditio

n of

veg

etat

ion

with

in th

esi

te♦

H

ealth

and

Con

ditio

nA

sses

smen

tLi

tter*

Estim

atio

n of

the

pre

senc

e, ty

pe, d

epth

and

% c

over

of l

eaf l

itter

and

det

ritus

♦

Ecos

yste

m p

roce

sses

Alg

al H

eigh

t*M

easu

rem

ent o

f mea

n he

ight

of a

lgal

gro

wth

on

trees

with

in th

e si

te♦

Si

te D

escr

iptio

nA

ge T

ypes

*Id

entif

icat

ion

of th

e do

min

ant a

ge ty

pes o

f tre

es in

term

s of s

tand

stru

ctur

e♦

Si

te D

escr

iptio

nR

oot T

ypes

*Id

entif

icat

ion

of th

e do

min

ant r

oot t

ypes

of t

rees

with

in th

e si

te♦

Si

te D

escr

iptio

nC

anop

y C

over

*Es

timat

ion

of th

e %

can

opy

cove

r of u

pper

, mid

and

low

er st

rata

. Can

opy

cove

r = c

row

n co

ver o

f opa

que

trees

♦

Site

Des

crip

tion


21

4.4 Vegetation

A wide range of vegetation attributes were assessed ranging from regeneration tophenology (Fig. 12). Each attribute measured different aspects of vegetation, such asstand structure, which recorded the health, and condition of each selected tree. Standstructure also contributed to the overall assessment of natural status and condition ofmangrove communities. Vegetation data provides an important baseline for futureassessments.

Vegetation

Regeneration Stand StructureProductivity PhenologyDebris

Figure 12. Overview of vegetation attributes.

4.4.1 Stand Structure and Composition

Stand structure incorporates a number of vegetation attributes outlined in Figure 13.Two methods can be used to determine stand structure, which forms a baseline for thedetermination of standing biomass, a component of primary productivity (see Section4.4.5). These include ‘full plot’ and ‘Angle Count Cruising’ (ACC) methods.Repeated measurements of basal area and diameter at breast height (DBH) determinestanding biomass productivity for each mangrove community.

Stand Structure

Angle Count Cruising Method:♦ Basal Area♦ Stem Density♦ Relative Stem Density♦ Relative Abundance♦ Mean DBH♦ Mean Height♦ Health and Condition Status

StemDensity

(direct count)

CrownDensity

Figure 13. Overview of stand structure attributes.


22

Repeated measurements of DBH and stem density aid in establishing basal area tocalculate standing biomass productivity of each mangrove community (Objective 2).

Classification of Vegetation StrataThe classification of vegetation strata followed the method suggested by Brocklehurstand Edmeades (1995):

♦ Trees: DBH > 2cm/girth > 6.3cm; height >1m♦ Shrubs/saplings: DBH < 2cm/girth < 6.3cm; height >1m♦ Seedlings: DBH < 2cm/girth < 6.3cm; height <1m

(Diameter at Breast Height: DBH = 1.3 m)

Full Plot MethodAll trees in a specifically defined area (20 x 20 m quadrat) are measured for DBH todetermine stem density, basal area and mean stand diameter by analysis. Trees aremeasured according to standard forestry rules, or 20 cm above the root collar (proproots) for Rhizophora spp. (according to English et al., 1994). Full plots are moreaccurate than ACC plots and are recommended for long term monitoring, althoughACC plots are desirable for rapid assessments (less trees to measure).

Angle Count Cruising MethodThe ACC method was first developed by Bitterlich in 1948 and is widely used toestimate basal area and stem density of mangrove trees per ha. Supplemented withmeasurements of DBH of counted trees, the method can also be used to describe thesize distribution of trees in mangrove forests, and provides a useful method forcomparison of mangrove forests at different locations (English et al., 1997). ACCplots are a sub-sample compared with full plots.

The ACC method was also used to select a certain number of representative treeswithin each site to compare future measurements of individual trees. It is a plotlessmethod, in that it does not sample a specific, known area of forest (English et al.,1997). Instead it uses angular sighting, covering an area of forest in accordance withthe size class of the trees which fall within the scale used referred to as basal areafactor (BAF).

The relatively fast and simple method utilises a Bitterlich gauge also known as arelaskope or a basal wedge. For the MMP a stainless steel basal wedge was used withdimensions of 400 x 400 x 50 mm, and gaps on all four sides (Fig. 14). The widths ofthe gaps are 1, 0.75, 0.5 and 0.25 cm and referred to as BAF.

Basal Wedge Gap Size [cm] = square root (BAF)


23

Figure 14. Design of a basal wedge.

The accuracy of the ACC method using a basal wedge, according to Brocklehurst andEdmeades (1995), is ± 10% for trees less than 40 cm, DBH and has a tendency tounderestimate trees with a DBH greater than 40 cm. Also demonstrated was mangrovetrees have a DBH smaller than 40 cm, therefore the method was deemed suitable forthe MMP.

Method:The observer does a 3600 sweep from a selected point, counting all trees equal orgreater than the selected BAF (Fig. 15).

Figure 15. Use of the Bitterlich gauge/relaskope/basal wedge. (from English et al., 1997).

50 cm

Distance between eye and basal wedge

BAF 1

BAF 0.25BAF 0.5

BAF 0.75


24

The number of trees recorded within a sweep depends on the size of the BAF used. Awider BAF includes more trees in the count.

In the field, the BAF of the basal wedge was determined to obtain a minimum numberof 30-40 trees per sweep. This sample size was recommended by English et al.,(1997) as adequate to be representative of a site. A minimum of 30 trees was alsostatistically sufficient to determine stand structure, productivity and to detect changesover time.

Each ACC sweep distinguished between species and the health status of the trees(dead or alive). This incorporated sweeps at the four corner posts and centre post toobtain a representation of a particular mangrove community, making it possible tocalculate the following:

♦ total basal area per ha♦ basal area per species per ha♦ basal area of dead trees per ha♦ dominance of species and dead trees(see stand structure calculations).

Additional measurements of DBH of each tree selected by the centre ACC sweepallows calculations of stem density including:♦ total stem density per ha♦ stem density per species per ha♦ stem density of dead trees per ha

In order to obtain stand structure information of the general area in the vicinity of themonitoring sites; ACC counts were taken at all four corner posts including the centrepost. However, ACC sweeps of only the four corner posts is sufficient although thefive sweeps is desirable for greater accuracy. The results of these counts were thenaveraged.

Measuring the basal count at the four corner posts also assisted in determining themost suitable BAF to be used for the ACC centre count for selecting trees formeasuring DBH to determine basal area.


25

The ACC centre count, was used to select trees with the basal wedge for furthermeasurements including the following:

♦ DBH♦ height♦ species♦ health status (dead or alive);♦ condition status

Field sheet proformas can be found in the Appendices (Appendix 7 & 4):Tree heights were measured with height poles (Fig. 16), found to be the most suitablemethod in dense mangrove stands.

Figure 16. Measurement of tree height using ‘height poles’.


26

Tree diameters of the selected trees from the centre post sweep are permanentlytagged for long term monitoring and measured at breast height (1.3m) or, in the caseof Rhizophora, 20 cm above the root collar (prop roots). If a tree has unusual growthforms or branches at 1.3m, measurements were followed by the rules outlined byEnglish et al., (1997) (Fig. 17).

Figure 17. Procedure for measuring DBH of trees with unusual or different growth forms(from English et al., 1997).


27

Permanent aluminium tags are attached to the trees with plastic cable ties (Fig. 18).Although nails are commonly used in forestry studies to attach tags to trees, they werefound to be unsuitable in mangroves as diameters of some are too small and the nailmay cause the stem to split. In larger trees, a nail could cause deformations in treegrowth, in turn biasing DBH measurements.

The tags were positioned about 1cm above the diameter measurement points (1.3m) tomark the location for repeated measurements. Therefore, the diameter should beremeasured directly under the cable ties. However, since these ties have the ability tomove, heights should be checked before measuring.

Figure 18. Tree tag.


28

Stand structure calculations from the Angle Count Cruising method (ACC):

The basal area per ha (BA [m2/ha]) is calculated directly from the trees counted bythe ACC sweeps from the four corners posts and centre post. The number of trees ismultiplied with a constant determined by the BAF used for the count:

BA [m2/ha] = count x (gap size [cm])2 ORBA [m2/ha] = count x BAF

By measuring the DBH of all trees selected by the centre ACC count it was possibleto determine the stem density of each monitoring site. The calculation involves twosteps:

1. Stem density (SD (ACC)/ha) was calculated for each individual tree encounteredin the ACC (Cintron & Novelli, 1984):

SD (ACC)/ha = BAF/0.00007854*(DBH)2

2. Total stem density per ha (total SD (ACC)/ha) was calculated as the sum of allstem densities represented by individual trees.

Total SD (ACC)/ha = Σ (SD (ACC)/ha)

Relative dominance and relative stem density describe the contribution of eachspecies in percentage to basal area and stem density respectively. They werecalculated from the ACC data according to English et al., (1997):

Relative Dominance = (BA of species/ BA of all species) x 100

Relative Stem Density = (SD of species/SD of all species) x 100

Other stand structure attributes calculated from the data include:♦ mean DBH♦ mean height♦ proportion of dead/alive trees♦ number of species

All the stand structure attributes above are calculated separately for each species andfor alive and dead trees. The results are summarised for each monitoring site andaveraged for each mangrove community.


29

Stem Density

Stem density of mangrove trees formed part of the stand structure inventory of eachmonitoring site. Two methods can be used to calculate stem density per ha (SD/ha) asoutlined below:

Method:1. Calculation from ACC data (Cintron & Novelli, 1984) (see calculations from

ACC method above); and2. Direct count of all trees within the 20 x 20m site: SD/ha = count x 10000/areaarea = 20m x 20 m = 400m2

the equation can also be written as:SD/ha = count x 50area = 20 x 20m = 400m2

Test trials demonstrated that the direct count method (two) was more accurate than theACC calculations suggested by Cintron and Novelli (1984) (one) and therefore, moresuitable for the objectives of the MMP. In order to compare the two methods, stemdensities for the MMP sites were calculated using the ACC method (centre count) andthe equations adopted from Cintron and Novelli (1984). Both methods were employedand compared in terms of accuracy, for the purpose of biomass productivity. Directcounts (method two) of all trees within the quadrat was considered more appropriate.

Canopy Density

Canopy density indicates the percentage of the site occupied by the vertical projectionof mid and upper vegetation strata. It can be expressed as:1. foliage cover (FC) (leaves and branches); and2. foliage projective cover (FPC)(leaves only).

Canopy density was recorded as part of the stand structure inventory for eachmonitoring site. The data provides a baseline of characteristic canopy densities ofmangrove communities under undisturbed conditions. Correlations with leaf litterproductivity have been demonstrated elsewhere using a similar vegetation attributes,leaf area index (English et al., 1997).

English et al., (1997) also recommend canopy density as a useful indicator forenvironmental stress, since leaf shedding and leaf growth are sensitive to a wide rangeof environmental factors. Changes in canopy density, together with other standstructure data, may provide indications of mangrove health and condition andassociated factors causing these changes.


30

Method:Canopy density (McDonald et al., 1990) was determined with a spherical forestrydensiometer, consisting of a concave mirror with 24 - 6.5mm squares engraved in thesurface (Fig. 19). The design is such that the observer views the same degree of arcoverhead regardless if the user is in a low lying or tall canopy area.

Sites were randomly selected (four to five) within each monitoring site. At eachlocation four readings were taken, facing N, E, S and W, therefore a total of 16 to 20readings were recorded and averaged.

For each reading the densiometer was held at the same position, far enough from theobserver’s body so the head was just outside the grid. In order to take a reading theobserver imagines four dots in the corners of each square and counts the numbers ofdots covered by leaves and branches (recorded separately) for FC and leaves for FPC.To obtain a percentage FC or FPC the counts for each randomly selected site weremultiplied by 1.04. The overall canopy density of the site was calculated as the meanof all readings. Since the methodology distinguished between branch and leaf cover,canopy density could be expressed in FC (branches and leaves) as well as FPC (leavesonly).

Figure 19. Forestry densiometer.


31

4.4.2 Regeneration

In order to understand the natural recruitment and regeneration patterns of mangrovecommunities, the density of seedlings and saplings was recorded at each site.Correlations between seedling densities and productivity rates, phenology patterns,stand structure may provide important information about the factors affectingmangrove regeneration (McKee, 1995).

Method:Regeneration was recorded within 1 m wide belt transects located between cornerposts one - two and three - four. At patchy sites, an additional transect was establishedacross the centre of the plot. All seedlings and saplings (DBH < 2 cm) within thosetransects were identified, counted and categorised into the following size classes:

Seedlings: 0-0.3 m; 0.3-0.5 m; 0.5-1 m

Saplings: 1.0-2.0 m; >2.0 m

Transects were temporarily marked with tapes or ropes. Seedlings and saplings werecounted from outside the transects to avoid disturbance through trampling.

Seedling and sapling densities (SASD) were calculated per species, per size class, perha:

SSD/ha = count x 10000/areaarea = 1 m x 20 m = 20 m2

This equation pertains to one transect and should only be calculated for the onereplicate opposed to lumping the two transects. The results of each transect can thenbe added together and averaged.


32

4.4.3 Debris

Logs and stumps provide habitat and shelter for a variety of animals and theirdecomposition releases nutrients into the mangrove ecosystem. Research in mangroveareas destroyed by cyclones suggested that the movement of debris at high tides mayhave a destructive effect on seedlings (McGuinness, 1992). Monitoring log and stumpdensities (LASD) may provide indications of the role and significance of debris in themangrove ecosystem, particularly their effects on regeneration and the condition andhistory of the site.

Method:The number of logs (diameter > 10 cm) and stumps (diameter > 5 cm) were recordedparallel with regeneration data within the two 1 m wide transects between corner postsone - two and three - four. The LASD were calculated per ha:

LSD/ha = count x 10000/areaarea = 1 m x 20 m = 20 m2

Similarly, as for regeneration, this equation pertains to one transect and should onlybe calculated for the one replicate opposed to lumping the two transects. The resultsof each transect can then be added together and averaged.

4.4.4 Phenology

Reproductive phenology of vegetation describes the seasonal timing and abundance offlowers, fruits and propagules. Flowering and fruiting cycles are species specific inthe mangroves (Metcalfe, 1999). Since seedlings need certain environmentalconditions to be able to successfully establish and survive in harsh mangroveenvironments, the timing of these cycles are correlated with seasons and henceenvironmental conditions (Metcalfe, 1999).

MethodIn order to document annual cycles, reproductive phenology was recorded monthly incollaboration with leaf litter collection from the leaf litter traps (see Leaf LitterProductivity). In addition, the abundance of flowers, fruits and propagules wasestimated during the establishment of each monitoring site.


33

4.4.5 Productivity

Mangroves are considered to be among the most productive ecosystems in the world(Woodroffe & Bardsley, 1987). On an area basis, their net vegetation production rateshave been quoted to exceed temperate forests and in some cases equal those oftropical forests (Hutchings & Saenger, 1987). As tidal forests, a portion of theirorganic matter and nutrient products is exported, feeding into complex estuarine andmarine food chains. The remainder is recycled within the mangrove ecosystem itself.

Prior to the MMP, the only data available on mangrove productivity in DarwinHarbour was based on a single, small-scale study of leaf litter productivity, limited toonly one creek system. No research had been undertaken relative to standing biomassand the biomass productivity of mangroves in Darwin Harbour.

Although research on mangrove productivity was undertaken in other parts ofAustralia (mainly on temperate shores and on the East Coast) (Smith, 1998), theunique regional setting of Darwin Harbour made it difficult to apply their results. Inaddition, the estimates of productivity of these studies did not incorporate below-ground biomass, which, due to a high root to shoot ratio, is an important attribute ofmangrove productivity. Consequently, several studies were designed and undertakento determine mangrove productivity in Darwin Harbour.

Productivity is defined as the accumulation of biomass within a given time period andtraditionally can be divided into primary and secondary productivity. Primaryproductivity is the rate at which primary producers (chiefly green plants) accumulateorganic substances from inorganic substances through photosynthesis orchemosynthesis.

Secondary production is the accumulation of biomass through the consumption of endproducts of primary production (plants), for example the growth rate of a crabpopulation feeding on plants. The term is also used for all other trophic in the foodchain.

Figure 20 exhibits the attributes measured for primary productivity of DarwinHarbour mangrove communities:1. accumulation of standing biomass (including roots) during tree growth2. production of leaves, flowers and fruits


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Primary Productivity

Leaf Litter Productivity♦ Monthly monitoring of organic litter

Biomass Productivity♦ Development of allometric relationships

between DBH and above and belowground biomass

♦ Annual monitoring of changes in DBH

Figure 20. Net primary productivity studies.

The MMP was designed to continue initial studies undertaken by two MSc studentsthrough NTU. These studies were initiated in order to determine the naturalfluctuations in productivity over a longer time period.

Research shows that productivity varies significantly between mangrove communities(Woodroff & Bardsley, 1987). Given that the productivity of mangroves may notequate to area, rates were determined for each mangrove community. This approachproposed to identify areas of high and low productivity.

Leaf Litter Productivity

Organic litter comprises of senescent leaves, twigs, branches, stipules, bark andreproductive structures, such as flowers, fruits and propagules. Its composition andabundance displays significant temporal as well as spatial variations, dependingmainly on the mangrove association and the environmental conditions (Semeniuk,1983).

Method:A total of 38 leaf litter monitoring sites were established along seven transects inDarwin Harbour, including all MMP sites (27) plus 11 additional leaf litter sites.


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Table 5 builds on the work completed by a NTU MSc student (Metcalfe, 1999).

Table 5. Mangrove monitoring (M) and leaf litter (L) sites in respect to location, transect andmangrove community.

East Arm Middle Arm West Arm ReplicatesMapping E1 E2 E3 M1 M2 M3 W1 W2Unit Harbour Creek Creek Harbour Creek Creek Harbour Creek M L1 M/L M/L M/L 3 32 M/L L L M/L M/L M/L M/L 5 73 L M/L M/L 2 34 M/L L L M/L M/L M/L L 4 75 M/L M/L M/L L 3 46 M/L L L M/L L M/L M/L M/L 5 87 M/L 1 18 M/L M/L L M/L M/L 4 5Totals 6/6 2/6 4 4/4 4/5 4/4 5/5 2/4 27 38

Two replicate traps were set up about 5-10 m apart at each monitoring site. The trapswere constructed with 15 mm PVC tubing and a 1 m deep shade cloth(Fig. 21), comprising a sample area of 0.5 m2. They were tied to branches and stemsin the canopy of species representative of the mangrove community. The top of thetraps were positioned well above the highest tide levels, in order to avoid loss of litterthrough tidal inundation. The litter content was collected once every month.

Figure 21. Leaf litter monitoring trap in a hinterland community dominated by Ceriops tagal,Darwin Harbour.


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After collection, litter was oven dried for around two days to a constant dry weight ofapproximately 600C in a Laboro drying oven. Dry weight was recorded immediatelyafterwards on a Sartorius beam balance, accurate to two decimal places. Branches andtwigs larger than 15 mm in diameter were not included. The contribution of eachspecies to the leaf litter sample was estimated in percentage. The abundance offlowers, fruits and propagules was estimated according to the following categories:

0 = absent1 = present2 = few3 = moderately abundant4 = abundant5 = very abundant

Calculations:Leaf litter productivity data was calculated according to Metcalfe (1999) andexpressed in g m-2 month-1 and g m-2 year-1. Since the intervals between collectiondates varied and some traps did not sample the full canopy, the following adjustmentswere adopted from Metcalfe (1999):

♦ monthly productivity data was based on mean daily leaf litter productivityrates; and

♦ productivity rates were multiplied by a conversion factor to allow for theproportion of canopy not sampled by the trap.

The conversion factor was calculated from the height of the trap in relation to theheight of the tree and canopy (Metcalfe, 1999). Although it is not clear if other leaflitter productivity research studies accommodated for differences in trapping time andsampled the percentage of canopy.

Steps to calculate leaf litter productivity:1. mean per site: a = (Dry Weight of Trap A [g] + Dry Weight of Trap B [g]) / 2 2. from 0.5 m2 to 1 m2: b = a x 2 [m2] 3. full canopy: c = b x conversion factor 4. daily productivity: d = c/No of trapping days 5. monthly productivity: e = d x days per month 6. yearly productivity: f = sum of all months calculated under (5)


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Biomass Productivity

The rate of biomass accumulation in a plant is used as a measure of biomassproductivity. In order to measure any changes in biomass, standing biomass should bedetermined first. This involves the development of allometric relationships betweenstanding biomass and DBH and the determination of mangrove community standstructures. The rate of biomass accumulation was designed to be calculated fromannual changes in DBH. The results can then be extrapolated to calculate theproductivity of each mangrove community and for the mangroves of Darwin Harbour.

4.4.6 Allometric Relationships

Non-destructive methods, such as allometric relationships between the biomass of atree and its DBH, are widely used in forestry to estimate biomass and stem volume oftrees and forest stands. In mangroves, allometric relationships have only beendeveloped for above-ground biomass (Clough & Scott, 1989). Since the root/shootratio is relatively high in mangrove trees in comparison to terrestrial plants (Clough &Attiwill, 1982), the study, undertaken by a NTU MSc student, developed allometricrelationships for below ground biomass in addition to above-ground biomass.

The study developed allometric relationships between DBH and above-ground andbelow-ground biomass for the five most dominant species, essentially present in allmajor communities in Darwin Harbour:

Avicennia marinaBruguiera exaristataCeriops tagalRhizophora stylosaSonneratia alba


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4.5 Fauna

The mangrove ecosystem provides temporary and permanent habitat for a widediversity of animals. The majority of mangrove animals are invertebrates such ascrustaceans, molluscs, polychaetes and insects (Hanley, 1992).

The MMP monitored the density and size of crab burrows in order to gauge anunderstanding of the links between vegetation and fauna with an emphasis on soilaeration.

4.5.1 Crab Density and Soil Aeration

Crabs play an important role in the ecology of mangroves. Their burrowing andfeeding activities increase the drainage and oxidation of the soil, increase thedecomposition rate of plant debris in the sediment and alter the abundance of othersoil organisms (Warren, 1990; McGuinness, 1986). Smith et al. (1991) studied theimportance of crab burrows for mangrove productivity. After removing all crabs fromthe study areas, they found a significant decrease in forest growth and reproduction.They concluded that the decrease was possibly due to a reduction in soil aeration andnutrients, which are important for mangrove productivity.

Since crabs live in a close relationship with the surrounding sediment, changes inenvironmental conditions may have an impact on crab populations, in turn may affectsoil chemistry and mangrove productivity.

Method:The abundance of crab burrows was estimated by counting open burrows with arandom sampling design of 20 quadrats (0.5 m2). The burrows were classified intosize classes (< 1 cm, 1-2 cm, 2-3 cm, 3-4 cm, > 4 cm). The means of the number ofopen burrows per size class were multiplied by the mean diameter of each size class tocalculate the percentage area covered by crab burrows. The results can be used as anindex for soil aeration.

Crab Burrow Density/ha = size class count x 1000/areaarea = No of Quadrats x 0.5 m2

Area of Crab Burrows [%] = Σ (Crab Burrow Density x size class diameter) = Soil Aeration Index (SAI)

In addition, the count of open burrows may also give indications about theabundances of intertidal estuarine crabs (Warren, 1990).


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4.6 Soil

The distribution of mangrove species are strongly determined by the properties of thesoils they are growing in (English et al., 1997). These soil properties constitute a verydynamic relationship with tides (eg. frequency and duration of inundations,sedimentation and erosion through tidal water flow), waves, drainage, climate (eg.rainfall and evaporation), geomorphology, hinterland sheet flooding and seepage(Clarke & Hannon, 1969; Semeniuk, 1985; Ball, 1988).

Figure 22 outlines soil attributes selected for the MMP in order to ascertain soil andvegetation relationships.

Soil

Salinity Moisture pH Temperature Sulfate AcidPotential

FieldDescription &Classification

Figure 22. Overview of soil attributes.

Soil attributes, particularly salinity, have been identified by many other studies (Ball,1988; Carlton & Yarbro, 1988) as main determinants of the mangrove environment.They describe major chemical properties of mangrove soils and can be easilymeasured without the need of expensive analytical equipment. The time period tomonitor soil attributes should include years with above and below average rainfalls.


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4.6.1 Sampling Regime

Timing

The soil-sampling regime was designed to determine the full range of annual andseasonal fluctuations in soil conditions. In North Australia, these fluctuations aremainly determined by the highly seasonal rainfall patterns. Soil attributes, such assalinity, can be expected to be highest at the end of the dry season, after a long periodof aridity, and to be lowest at the end of the wet season. These environmentalextremes are most likely to set the limits for species distribution and success(Tomlinson, 1986; Ball, 1988). Timing of soil sampling was therefore essential inobtaining minimum and maximum data on soil conditions.

End of Dry Season (September to October):The period May to September is one of very low rainfall, low humidity and highevaporation. By the end of the dry season (September/October) saline tidal water isthe sole water input for most mangrove communities. Consequently, saltconcentrations reach their maximum values, particularly in the high tidal zones, wherethe frequency of spring tide flooding is lower in the dry season, and high evaporationrates lead to an accumulation of salts on the soil surface, most evident during neaptides (Moritz-Zimmermann, 1997).

End of Wet Season (February to March):Monsoonal rains bring freshwater into the mangrove forests directly and via terrestrialrunoff and seepage from the hinterland margin. Soil salinity decreases substantially,particularly during neap tides (Moritz-Zimmermann, 1997).

Previous soil studies by Moritz-Zimmermann (1997) demonstrated that neap tides aremost suitable to measure the full range of soil conditions in Darwin Harbour.Therefore, wet and dry season soil samples were taken at low tides during neap tides.For a better comparison of sites and data, all soil samples should be taken within avery short time period, ideally, within the same neap tide.

Depth

The physical composition of the soil itself is largely determined by sedimentation anderosion processes of tides. Clark and Hannon (1969) and Moritz-Zimmermann (1997)found significant differences in the permeability and consequently chemistry ofsurface and subsurface soils. The cause could be sedimentation of fine soil particles(clay < 0.0039 mm) on the surface layer, where the dispersion of clay by sodium mayprevent the rapid infiltration of rain and seawater. Water may stay on the surface orflow away without penetrating the surface. The findings suggested that holes in thesurface layer, like crab burrows and rotten roots, may therefore play an important rolein the water circulation of clay soils (Smith et al., 1991).


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Significant differences in soil permeability may lead to differences in soil conditionswith depth (Moritz-Zimmermann, 1997). Therefore, soil samples were taken from thesurface (0-5cm) and from the subsurface (50 cm). A subsurface sample depth of 50cm was recommend by English et al. (1997). This sampling depth was found to beappropriate in examining the soil conditions of mangrove roots, since most mangrovespecies in Darwin Harbour have their main root bulk growing within the first 1 m (B.Comley, pers. com.).

Measurements taken from Soil and Soilwater

Table 6 provides an overview of the measurements taken from the soil and, wherepossible, from the soil water draining into corer holes. Most soil measurements weretaken in the field. However, soil analysis in the field was found to be very timeconsuming, and only a limited number of transects could be sampled within a day andwithin the same tidal regime. Since soils are strongly determined by tides sites shouldbe sampled within the shortest timeframe as possible. Therefore on numerousoccasions soil samples were taken to the laboratory for analysis.

Table 6. Overview of soil and soilwater sampling.(�): method suitable for in situ measurements in the field

Soil Field Laboratory Soil Water FieldConductivity (�) � Conductivity �

pH (�) � pH �

Temperature � Temperature �

Water Content �

Sulphuric Acid Potential (�) �

Field Description andClassification

(�) �

Sample Transport and Storage

In order to avoid oxidation and changes in water content and microbial activities, soilsamples were immediately placed in airtight labelled containers, transported in a coldbox and stored in a refrigerator prior to analysis.


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Repeated Monitoring

Soil salinity and water content fluctuate throughout the year and between years,therefore it is desired to sample attributes such as conductivity, pH, and temperatureon a seasonal basis as outlined in Table 7 and 8. Other soil attributes such as pyriteconcentrations and soil profiles are unlikely to experience such short-termfluctuations, unless the sites encounter significant disturbances and/or changes inenvironmental conditions. Therefore, sulphuric acid potential tests and fielddescriptions and classifications were undertaken only once as part of an inventory ateach site.

Table 7. Soil sampling regime.

Soil Initial SiteSet up

AnnuallyWet/Dry

Every3-5 Years

Conductivity � �

pH � �

Temperature � �

Water Content � �

Sulphuric Acid Potential � �

Field Description andClassification

�

Table 8. Soil water sampling regime.

Soil Water Initial SiteSet up

AnnuallyWet/Dry

Every3-5 Years

Conductivity � �

pH � �

Temperature � �


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4.6.2 Salinity

Soil salinity is the amount of soluble salts in a soil, expressed in terms of percentageparts per million or other convenient ratios (Brady, 1974). In soils the term solublesalts refers to major dissolved inorganic solutes (Rhoades, 1982). The salinity ofmangrove soils is mainly affected by tidal waters, which are a characteristic feature ofthe habitat (Clark & Hannon, 1969). The amount of soluble salts depends on thesoil/water ratio at which the measurement is made. In the mangrove environment, soilwater content depends on tidal inundation, rainfall, evaporation and the physicalcomposition of the soil. It can vary from zero (eg. in a hinterland community duringthe dry season) to saturation (seaward community). (Giglioli & Thornton, 1965; Clark& Hannon, 1969; Carlton & Yarbro, 1988; Ukpong, 1991).

High salt concentrations in the soil are one of the major stress factors plants have tocope with in intertidal environments. Mangrove vegetation has adapted in severalways to overcome the high and fluctuating salinities. Some species are capable oftolerating salinities of up to 90 ppt, which is 2.5 times the concentration of seawater(Tomlinson, 1986). Most species, however, prefer low to moderate salinities (up to 25ppt) and are restricted in their distribution and productivity by high salt concentrations(Ukpong, 1991; English et al., 1997).

Several trials with different methods and probes indicated that the soil/water ratioshould be standardised in order to obtain comparable results. Two methods areoutlined below.

Method 1:

The concentration of soluble salts (salinity) was estimated by using electricalconductivity (EC) measurements of 1:5 air dried soil/water extracts (EC1:5). Thismethod has been widely practiced in soil science (Rayment & Higginson, 1992).Using air-dried soils had the advantage of standardised water contents in all samples.The method also had less impact on the chemistry of the soils than oven drying athigher temperatures. When using EC1:5, consideration must be given as the methodmeasures only the amounts of soluble salts in the soil. The actual salinity experiencedby the plant at the time depends on the water content of the soil, which is stronglylinked with soil texture. Therefore, all three attributes, EC1:5, water content and soiltexture, should be determined.

The EC1:5 was found to be the most accurate and repeatable method and suitable tomonitor soil salinity fluctuations in all mangrove communities over time.


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Method

This method was adapted from Rhoades (1982) and Rayment and Higginson (1992).Soil samples were air dried to constant dry weight, crushed and sieved through a 2mm sieve. Five grams of soil and 25g of distilled water were mixed and mechanicallyshaken for one hour. The suspension was left standing until the soil settled and theturbidity in the extract cleared. The conductivity of the extract was measured with aHanna HI8733 Conductivity Meter. Since EC values increase with increasingtemperatures, all readings were temperature compensated. Fine roots floating in theextract also had an influence on conductivity, hence were removed before the readingswere recorded.

4.6.3 Water Content

The water content of mangrove soils is an important factor for plant growth. It notonly describes the availability of water to plants but also determines soil salinitylargely determined by tidal regimes, climate (rain and temperature), water holdingcapacity and soil fauna (burrows etc.).

Impact of tidal regime on water content:The frequency and duration of tidal flooding varies significantly between mangrovecommunities. Those closer to the sea, such as communities eight (Sonneratia alba)and one (Rhizophora stylosa) are inundated daily. Mangrove communities closer tothe landward edge, such as community four (low Ceriops tagal), are only inundatedevery fortnight by spring tides. Wet season king tides (7-8 m) are the only tides toreach some communities at the very landward edge (eg. community six, tall Ceriopstagal). Communities classified by Brocklehurst and Edmeades, (1995) are listed in theAppendices (Appendix 1).

Impact of water holding capacity on water content:The water holding capacity of mangrove soils depends on the proportions of clay, siltand sand, soil structure (pore volume), soil colloids, organic matter content andgeneral soil chemistry.

Method:

Water content was measured using a direct gravimetric method. The method removesthe water from the soil by evaporation and calculates the actual water content from theloss of weight (Gardner, 1982).

The weight of the empty tray and weight of the soil sample in the tray (10 gminimum) were measured on a Sartorius beam balance, accurate to two decimalplaces. Samples were dried to constant dry weight (minimum of 24 hours) atapproximately 1000C in a fan forced Laboro drying oven, and immediately weightagain to determine dry weight (Gardner, 1982).


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The water content was calculated according to Gardner (1982) on a dry mass basis:

Water Content [g] = (WET –DRY) / (DRY – TRAY)

WET: weight in g of the wet soil before drying, including tray weight.DRY: weight in g of the soil after drying, including tray weight.TRAY: weight in g of tray.

Multiplication by 100 gives the percentage of water content found in the soil sample:

Water Content [%] = Water Content [g] x 100

4.6.4 pH

The pH gives an indication of soil acidity (Rayment & Higginson, 1992). Changes inpH have a major influence on soil conditions and plant growth. Soil acidity has asignificant effect on the chemical reactions of most nutrients, thus influencing theiravailability to plants (English et al., 1997). Changes in soil acidity also affect thesolubility of other soil chemicals, the activity of soil fauna and important biologicalfunctions through direct and indirect processes. The soil pH itself is influenced by soiland environmental parameters, like tidal regime, water logging, oxygenconcentrations, the presence and solubility of soil compounds and the activity ofmicroorganism and macrofauna (McLean, 1982).

Although most mangrove soils have a pH between six and seven and are wellbuffered, most literature recommend measuring mangrove soils in situ (English et al.,1997), due to the soil’s potential to form acids when exposed to air (see SulphuricAcid Potential). Table 9 illustrates test trials demonstrating pH changes very little, ifthe soil samples were immediately stored in airtight containers and refrigerated. Thisprocedure minimised the oxidation of the soil samples. Even soil with high acidsulfate potential did not show differences in pH between field and laboratory samples.

Method:The pH was measured with a Select Systems IQ200 portable pH meter and a siliconISFET sensor probe. The probe is made out of stainless steel and has a slantedelectrode tip suitable for semisolids, soils and piercing applications. All readings areautomatically temperature compensated.

Table 9. Test trials of changes of soil pH with time.

SITE ZONE pH0h pH1h PH2h pH3h pH4hE3.6 landward 4.73 4.65 6.664 4.54 4.7E3.4 mid 6.15 6.54 6.35 6.46 6.40E3.8 seaward 6.90 6.91 7.53 7.58 7.4


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Measuring the pH in the laboratory was the preferred option, hence saving time in thefield. The ISFET sensor probe requires certain soil water content for measurements ofpH. During the dry season some soils, particularly in the landward zones,demonstrated a very low water content and had to be moisturised for pHmeasurements. Test trials showed this procedure does not significantly affect the pH.

4.6.5 Temperature

Soil temperature was measured with the same meter and probe as for pH.Temperature readings were taken immediately after other soil attributes weresampled.

4.6.6 Sulphuric Acid Potential

Potential acid sulfate forming soils are widely distributed around the NorthernAustralian coastline, including Darwin Harbour. They are commonly found inestuarine and mangrove swamp environments (Hicks et al., 1999). Per definition“Potential acid sulfate soils are typically waterlogged soils rich in iron sulfides thathave not been oxidised.” (Ahern et al., 1998). These soils become extremely acidicwhen exposed to air, forming so called acid sulfate soils with pH values below four.Acid sulfate soils may also release high levels of toxic metals, especially aluminiumand iron into the surrounding environment.

The main source of acid is the oxidation of pyrite. The overall chemical reaction canbe described by the following equation (Ahern et al., 1998):

FeS2 + 15/4O2 + 7/2H2O � Fe(OH)3 + 2SO4 2- + 4H+

Method:The potential of a soil to develop sulfate acids was tested, following the methodssuggested by the NSW Acid Sulfate Soils Laboratory Methods Guidelines (Ahern etal., 1998). The test was originally designed to be undertaken in the field, however dueto the explosiveness of hydrogen peroxide in high temperatures experienced inNorthern Australia, it was safer to carry it out in the laboratory.

To avoid oxidation through contact with air, soil samples were immediately placed inairtight containers and stored in the refrigerator. Freezing is not recommended(English et al., 1997).

A fixed amount of soil (eg. one small scoop) was mixed with a fixed volume of 30%hydrogen peroxide (about 10 drops) and left to react for about three minutes. The pHwas determined before (pHF) and after oxidation with 30% hydrogen peroxide(pHFOX). The change in pH and the strength of the peroxide reaction indicated thepresence of pyrites and the potential of the soil to develop sulfate acids. (Note: the testis not a substitute for analytical tests.).


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Interpretation of test results:

The NSW Acid Sulfate Soils Guidelines (Ahern et al., 1998) recommend thefollowing guidelines for the interpretation of results:

♦ If the pHFOX value is at least on a unit below the field pHF, it may indicatepotential acid sulfate soils

♦ The greater the difference between the two measurements, the more indicative thevalue is of potential acid sulfate soils

♦ The lower the final pHFOX value, the better the indication of a positive result

Table 10 indicates the relationship between pH and potential acid sulfate formingsoils.

Table 10. pH indices and acid sulfate soil potential.

pH FOX POTENTIAL ASS COMMENT< 3strongreaction

high level of certainty The more the pHFOX drops below threethe more positive the presence ofsulfides.

3-4 less positive Laboratory analysis needed to confirm ifsulfides are present.Sands may give confusing results

4-5 neither positive nor negative Laboratory analysis needed to confirm ifsulfides are present. Shell/carbonatecould neutralise some acid or organicacids could cause the reaction.

>5little or nodrop in pH

little acid generating ability Laboratory analysis recommended toconfirm absence of oxidisible sulfides.

If the reaction is very strong but the pH drops very little:Some minerals other than pyrite (eg. manganese) react vigorously with peroxide butshow only small changes in pH.

If the pH drops below four but increases with time:The soil is very likely to be high in organic matter. The oxidation of organic mattercan lead to the generation of acids, but in the absence of pyrite, these soils do not staybelow four on extended oxidation.


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4.6.7 Soil Field Description and Classification

The Resource Assessment Branch of DIPE undertook the soil field description andclassification at the 38 leaf litter monitoring sites (inc. 27 monitoring sites).

The field description was based on McDonald et al. (1984) and included:

♦ depth of horizons♦ colour and mottle patterns♦ field texture♦ organic contents♦ course fragments♦ soil structure♦ fabric♦ cutans♦ voids♦ consistence♦ surface soil condition♦ pan♦ segregation♦ soil permeability and drainage

The soils were classified according to Isbell (1996) into suborders, great groups, subgroups and families, on the basis of locality in the marine environment (level of tidalinfluence) and a field description of their sulfur, organic matter, calcareous and soilmaterial (ie. clay, silt and sand) contents.

5. ECOLOGICAL RESEARCH ON MANGROVES

A number of research studies have been initiated to investigate and attempt toquantify the links between mangrove communities and the vast array of fauna theysupport. Postgraduate students from NTU have conducted the majority of thesestudies in collaboration with NT Government Departments. The following is asummary of this research.


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5.1 Links Between Mangroves and Fish

The Use of Mangroves and their Resources by Fish in Darwin Harbour.

The aim of the research is to investigate the relationships between the differentmangrove assemblages and the fish fauna of Darwin Harbour. This was addressed bysampling fish in three different mangrove habitats in three locations in DarwinHarbour over two years. Several different methods were used to obtain fish samplesfrom a wide range of species and sizes. Stomach contents were analysed to examinethe trophic relationships between groups of fish. Research sites were establishedwithin or in close proximity to MMP sites in Charles Darwin National Park (transectE1) and Jones Creek (transect M3).

Preliminary results show that there is a high diversity of fish that use the mangroveforests in the harbour. More than 60 species from 29 families, have been caught in thenet sampling. The most abundant fish are the various species of mullet, clupeiods(sardine/anchovy) and forktailed catfish. The next most commonly caught fish includearcherfish, garfish, threadfin salmon, sharks and juvenile trevally, queenfish andbarramundi.

Of the three locations sampled in Darwin Harbour, Charles Darwin National Park hasbeen the most ‘productive’ in terms of diversity and abundance of fish. The reasonsfor this are unclear, but the result could be related to several factors including theexposed nature of the site in relation to the open harbour, the more open foreststructure on the seaward edge and the many streams and gutters that flow throughoutthe forest.

Initial analysis of stomach contents of some fish show that many had fed on crabs,shrimps and other invertebrates found within the mangrove forest. The informationwill be used to build a trophic model of the Darwin Harbour mangrove ecosystem.

Results from the study will provide information necessary to the management ofDarwin Harbour in relation to coastal development and the increasing intensity ofrecreational fishing.


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5.2 Sesarmid Crab Project

The Significance of Plant-Animal Interactions in Tropical Mangrove Forests:How Crabs Affect Structure and Production.

The objectives of this study were to gain knowledge in the function of grapsid crabs inmangrove forests by identifying some of the important factors affecting theconsumption of mangrove litter. Also identified were feeding preferences, theirsignificance for the consumption of mangrove material and the survival of seedlingswas also identified.

Study objectives were accomplished by sampling crab numbers and litterconsumption in several assemblages including up-stream and down-stream of twoareas in Darwin Harbour. Sampling was carried out over a two-year period. Inaddition, feeding preferences of the two most abundant grapsid crabs in the harbourwere studied in the laboratory.

Mangrove assemblage was the most important factor affecting the distribution andabundance of grapsid crabs. In many cases, crab species occurrence and abundancewere specific to certain assemblages, areas, aspects and times throughout the samplingperiod reflecting the specificity that grapsid crabs have to particular environmentalconditions at certain sites and times.

Grapsid crabs in Darwin Harbour were found to be important in recycling nutrients byconsuming significant amounts of mangrove litter. In situ experiments of litterprocessing showed that at least 20.4% of litter fall was processed by grapsid crabs.Results showed that mangrove litter consumption by crabs as well as mangroveproductivity increased in the wet season compared to the dry season. Interestingly,litter consumption rates were not related to litter fall rates.

The structure of Darwin Harbour mangrove forests did not appear to be significantlyeffected by grapsid crabs. It has been suggested that in some mangrove forests,grapsid crabs may affect the structure of the forest by consuming propagules thatwould otherwise establish and proliferate. However, in Darwin Harbour highconsumptions by grapsid crabs of Avicennia marina and Ceriops tagal propagulesoccurred in assemblages where both these species are high in numbers.

The study is linked to the MMP, by utilising MMP sites at Jones Creek (M2) andElizabeth River (E2) (Fig. 2) and MMP data on leaf litter productivity andenvironmental attributes.


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5.3 Links Between Mangroves and Insects

The project is studying the role of insects in the pollination biology of mangroves, theimpact of insect predation on mangrove seeds/propagules, and herbivory on matureplants. In addition, the study also assesses the chemical and mechanical defencesmangrove species may have developed against herbivory. This project utilises MMPsites at Jones Creek (M2).

The significance of insects to tropical mangrove communities is poorly understood.Recent studies have suggested that most mangrove species have a unique set ofinsects associated with them (Veenakumari et al., 1997). Unfortunately, little isknown about the relationship between insects and mangroves, and the role they playin the mangrove ecosystem. This project attempts to clarify some of theserelationships.

5.4 Biological Diversity/Recovery from Disturbance/Rehabilitation

The Biological Diversity, Recovery from disturbance and Rehabilitation ofMangroves in Darwin Harbour.

The aims of this research project were to assess the biological diversity of mangrovesin relation to the major tidal zones in Darwin Harbour and to examine the impact ofdisturbance to mangroves by comparison of biota in disturbed and undisturbed sites.The research also aimed to determine the role of environmental factors in delayingrecovery of mangroves in previously cleared and cyclone damaged mangroves whilstresearching optimum field techniques and undertaking mangrove rehabilitation trials(Metcalfe, in prep).


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There are a number of research outcomes including the following:

♦ Baseline data on mangrove vertebrate and invertebrate fauna, indicating mangrovezones with highest biodiversity.

♦ Development of rapid biodiversity assessment techniques.

♦ GIS mapping of Darwin Harbour’s biodiversity resources.

♦ Assessment of the impact of disturbance on mangrove biota, examination of thefauna support function of these forests and possible key indicator species.

♦ Identification of the factors (eg. predation, mechanical damage and light intensity)limiting regeneration in disturbed mangroves.

♦ Assessment of the effectiveness of different rehabilitation techniques.

Initial results indicate that mangroves support a remarkable diversity and abundanceof life, with maximum biodiversity found in the seaward zone. A new species hasbeen identified and certain invertebrate groups appear to be useful indicators forenvironmental health. Two years of field trials and propagation of over 2,500seedlings has led to development of rehabilitation strategies with simple, yet highlysuccessful revegetation techniques devised (Metcalfe, in prep).


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6. COMMUNITY-BASED MANGROVE MONITORING PROGRAM

The Community Mangrove Monitoring Program (CMMP), ‘Impact Assessment ofCoastal Development on Estuarine Mangrove Environments in Darwin Harbour’ is atwo-year initiative jointly funded under the Natural Heritage Trust (NHT), CoastalMonitoring Program (Coasts and Clean Seas) and the NT Government. The CMMPhas been developed to continue scientific mangrove monitoring in Darwin Harbour,however, for NHT the focus was on community awareness and participation.

There are two major components to the CMMP: 1) the collection, collation andanalysis of scientific data, and 2) raise awareness of the wider community of theimportance of mangrove ecosystems. An important objective of the CCMP was toestablish a network of monitoring sites in the Darwin region adjacent to developedareas to ascertain the effects of coastal development on mangrove communities.Consequently, eight sites have been established at the hinterland margin in landwardmangrove communities relatively accessible to allow public participation.

The community awareness and education component of the program has incorporatedof field activities and presentations relative to the importance of Darwin Harbourmangroves. Various community groups have been involved in the CMMP includingprimary and secondary schools, tertiary institutions and non-profit environmentalorganisations such as Landcare groups. Numerous publicity materials have beenproduced as a requirement of the program including articles for various newsletters,factsheets and posters.

Although most of the methods have been derived from the MMP methodology,additional parameters have been collected (and analysed) as part of the CMMP. Forfurther information, please refer to the CMMP final report:

Lewis, D. (in prep) Community Mangrove Monitoring Program - Impact Assessmentof Coastal Development on Estuarine Mangrove Environments in Darwin Harbour -Technical Manual and Final Report. Report No. 26/2002. Dept. of Infrastructure,Planning and Environment, Darwin, Northern Territory.


54

7. REFERENCESAhern, C. R., Blunden, B. and Stone, Y. (1998) Acid Sulfate Soils Laboratory

Methods Guidelines. Acid Sulfate Soil Management Advisory Committee,Wollongbar, NSW, Australia.

Ball, M. C. (1988) Organisation of Mangrove Forests along Natural Salinity Gradientsin the Northern Territory: An Ecophysiological Perspective. In: FloodplainResearch in Northern Australia: Progress & Prospects (D. Wade-Marshall &P. Loveday Eds.), pp. 84-100. Australian National University Press, Canberra.

Boto, K. G. (1992) Nutrients and Mangroves. In: Pollution in Tropical AquaticSystems. CRC Press, Inc., 2000 Corporate Blvd., NW., Boca Raton, Florida33431: 129-145.

Brady, N.C. (1974) The Nature and Property of Soils. MacMillan Publ., New York,USA.

Brocklehurst, P. and Edmeades, B. (1995) Mangrove Survey of Darwin Harbour,Northern Territory. Conservation Commission of the Northern Territory,Palmerston.

Brocklehurst, P. and Edmeades, B. (1996) The Mangrove Communities of DarwinHarbour. Technical Memorandum No 96/9. Department of Lands, Planningand Environment, Palmerston, Northern Territory.

Carlton, P. R. and Yarbro, L. A. (1988) Physical and Biological Control of MangrovePore Water Chemistry. In: The Ecology and Management of Wetlands Vol. I,Ecology of Wetlands. (D.D. Hook Ed.), pp112-132. Timber Press, Portland,USA.

Clarke, L. D. and Hannon, N. J. (1969) The Mangrove Swamp and Salt MarshCommunities of the Sydney District. II. The Holocoenotic Complex withParticular Reference to Physiography. In: Journal of Ecology 57, 213-234.

Clough, B. F.and Attiwil, P. M. (1982) Primary Productivity of Mangroves. In:Proceedings of the Australian National Mangrove Workshop (B.F. CloughEd.) pp. 213-222. Australian Institute of Marine Science, Cape Furguson,Australia.

Clough, B. F. and Scott, K. (1989) Allometric Relationship for Estimating Above-Ground Biomass in Six Mangrove Species. In: Forest Ecology andManagement, 27 (2), 117-128.

Cintron, G. and Novelli, Y. S. (1984) Methods for Studying Mangrove Structure. In:The Mangrove Ecosystem: Research Methods (S.C. Snedaker & J.C.Snedaker Eds.), pp. 91-113. UNESCO, Paris.


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Comley, B. (2002). Coastal Mangrove Wetland Productivity and Management,Darwin Harbour, Northern Territory, Australia. MSc Thesis, NorthernTerritory University, Darwin.

Coupland, G. (in prep) The Significance of Insects to Tropical MangroveCommunities: Insect Importance in Mangrove Reproduction, Recruitment andHealth. PhD Thesis, Northern Territory University, Darwin (under review).

Dames and Moore. (1988) Draft Mangrove Delineation Study Part 3- Mangrove ZoneManagement Plan, Darwin Harbour, NT. For Conservation Commission ofthe Northern Territory on behalf of the Coastal Management Committee. JobNo. 14133-010-073.

DIPE (2002) Mangrove Management in the Northern Territory. Department ofInfrastructure Planning and Environment, Darwin, Northern Territory.

DLPE (2000) Managing Darwin Harbour and its catchment: a summary of NTGovernment Activities, 2000 Update. Department of Lands Planning andEnvironment, Darwin, Northern Territory. Internal Report.

Elliott, R. (2001). Regional Statistics, Northern Territory 2001: ABS Catalogue No.1362.7. Australian Bureau of Statistics, Canberra, ACT 2601.

English, S., Wilkinson, C. and Baker, V. (1997) Survey Manual for Tropical MarineResources. Australian Institute of Marine Science, Townsville.

Gardner, W. H. (1982) Water Content. In: Methods of Soil Analysis, Part 1 -Chemical and Microbiological Properties (A. L. Page, R. H. Miller, & D. R.Keeney Eds.), pp. 199-211. Agronomy No 9, part 2. American Soc.Agronomy.

Giglioli, M. E. C. and Thornton, J. (1965) The Mangrove Swamps of Keneba, LowerGambia River Basin: Descriptive Notes on the Climate, the MangroveSwamps and the Physical Composition of their Soils. In: Journal of AppliedEcolology 2, 81-103.

Hamilton, L. S. and Snedaker, S. C. (1984) Handbook for Mangrove AreaManagement. Commission on Ecology, Gland, Switzerland.

Hanley, J. R. (1992) Current Status and Future Prospects of Mangrove Ecosystems inNorth Australia. In: Conservation and Development Issues in NorthernAustralia (I. Moffat & A. Web Eds.), pp. 45-54. North Australian ResearchUnit, Australian National University, Darwin.

Hicks, W. S., Bowman, G. M. and Fitzpatrick, R. W. (1999) East Trinity Acid SulfateSoils, Part 1: Environmental Hazards. Technical Report 14/99, CSIRO Landand Water, Australia.


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Hogarth, P. J. (1999) The Biology of Mangroves. Oxford University Press, New York.

Hong, P. N. & San, H. T. (1993) Mangroves of Vietnam. The International Union forConservation of Nature and Natural Resources, Gland, Switzerland.

Hutchings, P. A. and Saenger, P. (1987) Ecology of Mangroves. University ofQueensland Press, Australia.

Isbell, R. F. (1996) The Australian Soil Classification. CSIRO, Collingwood.

Lewis, D. (in prep) Community Mangrove Monitoring Program - Impact Assessmentof Coastal Development on Estuarine Mangrove Environments in DarwinHarbour - Technical Manual and Final Report. Report No. 26/2002. Dept. ofInfrastructure, Planning and Environment, Darwin, Northern Territory.

Love, G., Murphy, K. M. and Butterworth, I. J. (1998). The Present and Possible Future Climatology of the Darwin Harbour. In: Darwin Harbour (Larson, K. K., Mitchie, M. G. & Hanley, J. R. Eds.). ANU NARU Mangrove Monograph No. 4.

Martin, J. (in prep) The Use of Mangroves and their Resources by Fish in DarwinHarbour. PhD Thesis, Northern Territory University, Darwin, NorthernTerritory.

McDonald, R. C., Isbell, R. F., Speight, J. G., Walker, J. and Hopkins, M. S. (1990)Australian Soil and Land Survey. Inkata Press, Melbourne, Australia.

McGuinness, K. A. (1992) Disturbance and the Mangrove Forests of Darwin Harbour.In: Conservation and Development Issues in Northern Australia. (I. Moffat &A. Webb Eds.), pp. 55-62. Australian National University Press, Canberra.

McGuinness, K. A. and Underwood, A. J. (1986) Habitat Structure and the Nature ofCommunities on Intertidal Boulders. In: Journal of Experimental MarineBiology and Ecology 104 (1-3), 97-124.

McLean, E. O. (1982) Soil pH and Lime Requirement. In: Methods of Soil Analysis,Part 1 - Chemical and Microbiological Properties. (A. L. Page, R. H. Miller,& D. R. Keeney Eds.), pp.199-211. Agronomy No 9, Part 2. American Soc.Agronomy, Inc., Soil Science Soc. Amerika, Inc., Madison, Wisconsin, USA.

McKee, K. L. (1995) Seedling Recruitment Patterns in a Belizean Mangrove Forest:Effects of Establishment Ability and Physico-Chemical Factors. Oecologia101, pp. 448-460

Metcalfe, K. (1999) Mangrove Litter Production, Darwin Harbour NT - A Study ofLitter Fall as a Measure of Primary Production in the Mangrove Communitiesof Darwin Harbour. Masters Thesis, Northern Territory University, Darwin.


57

Metcalfe, K. (in prep) The Biological Diversity, Recovery from Disturbance andRehabilitation of Mangrove, Darwin, NT. PhD Thesis, Northern TerritoryUniversity, Darwin.

Moritz-Zimmermann, A. (1997) Impact of Urban Stormwater Drainage Channels onthe Mangrove Ceriops tagal in Northern Australia: Effects on Soils,Vegetation and Seedlings. Masters Thesis (unpublished). Technical UniversityDarmstadt, Germany.

NTDLH (NT Department of Lands and Housing). (1990) Darwin Regional Land UseStructure Plan 1990. NT Department of Lands and Housing, Darwin, NorthernTerritory.

Odum, W. E. and Johannes, R. E. (1975) The Response of Mangroves to Man-Induced Environmental Stress. In: Tropical Marine Pollution (E. J.Fergusonwood & R. E. Johannes Eds.). Elsevier Oceanographic Series 12.Elsevier, Amsterdam, pp. 52-62.

Padovan, A. (1997) The Water Quality of Darwin Harbour, October 1990 –November1991. Report No. 34/1997D. Department of Lands, Planning and Environment, Palmerston, Northern Territory.

Potter, J. (in prep) Interim Mangrove Data Assessment. Department of InfrastructurePlanning and Environment, Palmerston, Northern Territory.

Rayment, G. E. and Higginson, F. R. (1992) Australian Laboratory Handbook of Soiland Water Chemical Methods. Inkata Press, Melbourne, Australia.

Rhoades, J. D. (1982) Soluble Salts. In: Methods of Soil Analysis, Part 1 - Chemicaland Microbiological Properties (A. L. Page, R. H. Miller, & D. R. KeeneyEds), pp. 199-211. Agronomy No 9, part 2. American Soc. Agronomy, Inc.,Soil Science Soc. Amerika, Inc., Madison, Wisconsin, USA.

Robertson, A. I. and Duke, N. C. (1987) Insect Herbivory of Mangrove Leaves inNorth Queensland. In: Australian Journal of Ecology 12, 1-7.

Saenger, P., Hegerl, E. J. and Davie, J. D. S. (1983) Global Status of MangroveEcosystems. Commission on Ecology Papers Number 3. International Unionfor Conservation of Nature and Natural Resources, Gland, Switzerland.

Salgado-Kent, C. P. (2002) The Significance of Plant – Animal Interactions inTropical Mangrove Forests: How Crabs Affect Structure and Production. PhDThesis (unpublished). Northern Territory University, Darwin.


58

Semeniuk, V. (1983) Mangrove Distribution in North Western Australia inRelationship to Regional and Local Freshwater Seepage. In: Vegetatio 53,11-31.

Semeniuk, V. (1984) Mangrove Environments of Port Darwin, Northern Territory:The Physical Framework and Habitats. In: Journal of the Royal Society ofWestern Australia 67, 81-97.

Semeniuk, V. (1985) Development of Mangrove Habitats along Ria Shorelines inNorth and Northwestern Tropical Australia. In: Vegetatio 60, 3-23.

Smith III, T. J., Boto, K. G., Frusher, S. D. and Giddins, R. L. (1991) KeystoneSpecies and Mangrove Forest Dynamics: The Influence of Burrowing byCrabs on Soil Nutrient Status and Forest Productivity. In: Estuarine, Coastaland Shelf Science 33, 419-432.

Smith III,T. J. and Duke, N. C. (1987) Physical Determinants of Inter-EstuaryVariation in Mangrove Species Richness around the Tropical Coastline ofAustralia. In: Journal of Biogeography 14, 9-19.

Smith, S. (1998) Coastal Management in NSW : An Update Briefing Paper.Parliamentary Library Research Service, NSW; No. 7/98.

Sullivan, S. A. and Egan, J. L. (1996) Data Collection Methods for Land ResourceMonitoring Northern Territory. Technical Report No. 96/1. Department ofLands, Planning and Environment, Darwin.

Tomlinson, P. B. (1986) The Botany of Mangroves. Cambridge University Press,Cambridge, USA.

Ukpong, I. E. (1991) The Performance and Distribution of Species along Soil SalinityGradients of Mangrove Swamps in Southeastern Nigeria. In: Vegetatio 95, 63-70.

Veenakumari, K., Mohanraj, P. and Bandyopadhyay, A. K. (1997) Insect Herbivoresand their Natural Enemies in the Mangals of the Andaman and NicobarIslands. In: Journal of Natural History 31, 1105-1126.

Warren, J. (1990) The Use of Open Burrows to Estimate Abundances of IntertidalEstuarine Crabs. In: Australian Journal of Ecology 15, 277-280.

Wightman, G. M. (1989) Mangroves of the Northern Territory. Northern TerritoryBotanical Bulletin No.7, Conservation Commission Northern Territory,Palmerston, Northern Territory.


59

Woodroffe, C. D. and Bardsley, K. N. (1987) The Distribution and Productivity ofMangroves in Creek H, Darwin Harbour. In: Proceedings of the Workshop onResearch and Management held in Darwin Harbour (J. R. Larson, Michie &J.R Hanley Eds.) Mangrove Monograph No. 4, North Australian ResearchUnit, Australian National University, Darwin, Northern Territory.

Woodroffe, C. D., Bardsley, K. N., Ward, P. J. and Hanley, J. R. (1988) Production ofMangrove Litter in a Macrotidal Embayment, Darwin Harbour, NT, Australia.In: Estuarine, Coastal and Shelf Science 26, 581-598.


60

APPENDIX 1

Mapping Units of Darwin Harbour Mangroves

Mangrove Closed ForestMap Unit 1 Rhizophora stylosa closed-forest (shoreline forest)Map Unit 2 Rhizophora stylosa/Camptostemon schultzii closed-forest

(tidal creek forest)Map Unit 3 Rhizophora/Bruguiera/Ceriops closed -forest/open forest (transition)Map Unit 4 Ceriops tagal low closed-forest (mid tidal flat)Map Unit 5 Ceriops tagal/ Avicennia marina low closed-forest (high tidal flat)Map Unit 6 Mixed species low closed forest/open-forest (hinterland)

Mangrove Woodlands/Open WoodlandsMap Unit 7 Mixed species low woodlandMap Unit 8 Sonneratia alba woodlandMap Unit 9 Rhizophora stylosa low woodland (islands, rocky shores)Map Unit 10 Low open woodland (low tidal mudflat)

Dar

win

Har

bour

Man

grov

e M

onito

ring

Met

hodo

logy

Sept

embe

r 200

2

61

APPE

ND

IX 2

Map

of D

arw

in H

arbo

ur M

angr

ove

Com

mun

ities


62

APPENDIX 3SITE INFORMATION

LOCATION 1 Name of greater area (eg Darwin Harbour)2 Name of creek or closest landmark (eg Elizabeth River, Channel Island)3 Geo-Class (marine, estuarine, riverine)

MAPUNIT 1 Rs closed forest/low closed forest (shoreline)2 Rs/Cs closed forest (tidal creek)3 Rs/Be/Ct closed forest/open forest (transition)4 Ct low closed forest (mid tidal flat)5 Ct/Am low closed forest (high tidal flat)6 Mixed species low closed forest/open forest (hinterland)7 Mixed species low woodland8 Sa woodland

SPECIES Aa Aegialitis annulataAm Avicennia marinaBe Bruguiera exaristataBp Bruguiera parvifloraCt Ceriops tagal var. australisEo Excoecaria ovalisLr Lumnitzera racemosaRs Rhyzophora stylosaSa Sonneratia alba

ACCESS 1 Road2 Sea3 Air

PLOT POSITION 1 Seaward edge2 Mid mangrove3 Landward edge

TIDAL ZONE ESTUARINE1 Sub tidal-substrate is permanently flooded with oceanic water

INTER TIDAL2 Irregularly exposed: land surface is exposed by oceanic tides less than often

than daily3 Regularly flooded: oceanic tidal water alternatively floods and exposes the

land surface at least once daily4 Irregularly flooded: oceanic tidal water floods the land surface less often

than daily5 Supra tidal6 Unknown

HINTERLAND RELIEF - Area adjacent to mangroves on dry land1 High 90-300m2 Low 30-90m3 Very low 9-30m4 Extremely low <9m

ADJ LANDUSE - Adjacent hinterland use1 None (either bush or large areas of mangrove)2 Residential3 Industrial4 Recreational5 Park reserve6 Other commercial7 Sewage treatment8 Seawater intake/outfall9 Aquaculture10 Harbour/Marina11 Boat ramp


63

APPENDIX 3 cont..

FUT LANDUSE - Future Hinterland Use1 No foreseeable change (either bush or large areas of mangrove)2-11 as for ADJLANDUSE

DEG_EXPOSURE - Degree of Exposure0 100% of patch margins exposed1 > 50 % of margins exposed2 < 50% of margins exposed

RUN_OFF 1 No run-off2 Very slow3 Slow4 Moderately rapid5 Rapid6 Very rapid

SEEPAGE 0 Nil1 Fresh2 Salt

DIST_TYPE - Disturbance type (might be more than one)0 No observable disturbance

ANTROPOGENIC (MAN INDUCED)1 Fire (hinterland)2 Logging3 Grazing/pig rooting (hinterland)

NATURAL4 Cyclone/wind-storm5 Floods6 Underband erosion7 Tree fall8 Die-back (peripheral regions)9 Trunk rot on significant number of trees (caused by teredo worms)10 Lighting11 Excess salinity12 Other

BIOTIC_DIST - Biological agents causing disturbance1 Animal (pig..)2 Antropogenic (man)3 Invertebrate (crab, teredo worm..)4 Vegetation5 Other

DIST_FREQ - Disturbance Frequency1 Little evidence of disturbance over the past 30 years2 Single major disturbance in period 10-30 years3 A few disturbances, all > 10years ago4 Single recent disturbance 1-10 years5 Frequent recent disturbance, 1-10 years6 Current disturbance


64

APPENDIX 3 cont..SOILSUBSTR_CLASSESTUARINE 2 Unconsolidated bottom - with a substrate of cobbles,

gravel, sand, mud or organic material (25% or greater cover of particlessmaller than stones, vegetative cover > 30%)

5 Rocky shore - with the same substrate as rock bottom6 Unconsolidated shore - same substrate as (2)

SUBSTR_TYPE - Main substrate type (greatest percentage cover of plot) Visual appraisal1 Mud (silt and clay) (unconsolidated bottom, unconsolidated shore)2 Sandy mud (predominantly mud with sand particles)3 Shelly mud (predominantly mud with shell particles)4 Shelly sand (predominantly sand with shell particles)5 Shells6 Muddy sand (predominantly sand with mud)

MICRO_RELIEF - Substrate micro relief1 Substrate bioturbated (soil turned over by organisms)2 Substrate root structured3 Both (1) and (2)4 Nil

VEGETATIONCONDITION 1 Healthy

2 Trunk rot3 Crown Damage4 Overmature5 Senescent6 Dead Branches7 Leaning Branches

ROOT_TYPE (can be more than one, in order of dominance)1 Pneumatophores (Avicennia, Xylocarpus, Sonneratia)2 Knee-roots (Bruguiera)3 Buttress roots (Bruguiera, Ceriops)4 Aerial Roots (Rhizophora, Avicennia, Acanthus)5 Stilt roots (Rhizophora)

LITTER_TYPE AGE_TYPE - Dominant age structure in terms ofstand structure

1 Leaf 1 Sapling2 Detritus 2 Pole trees3 Both 3 Mature trees

4 Overmature trees5 Senescent

PHENOLOGYP/A presence/absence of species in the plotSTERILE trees with no buds, flowers, fruit or propagulesFRUIT mature fruitPROPAGULE seedling still attached to parent tree

STERILE, BUD, FLOWER, FRUIT, PROPAGULES, FRUIT_DROP1 <5 some on some of plants2 25-5 a lot on some of plants3 50-25 some on a lot of plants4 75-50 a lot on a lot of plants5 100-75 all plants

VEGETATIVES StaticG GrowthD DeciduousN Senescent


65

APPENDIX 4

SITE ID:______________ DATE :_________________________RECORDERS:______________________________________________EASTING:_______________ NORTHING: ____________________TRANSECT ASPECT:________________________________________LOCATION: _______________________________________________MAP UNIT: ________________________________________________FOREST TYPE: ____________________________________________SPECIES: ______________________________________________________

SITE SOIL ACCESS: SUBSTR_CLASSPLOT POSITION: SUBSTR_TYPETIDAL ZONE: MICR0_RELIEFHINTERLAND RELIEF:

ADJ LANDUSE: VEGETATIONFUT LANDUSE: STATUSHealthy/Unhealthy/Dead

DEG_EXPOSURE: CONDITION:RUN_OFF: LITTER: Yes/No

SEEPAGE: LITTER_DEPTH:DISTURBANCE: Yes/No LITTER_COV [%]:DIST_TYPE: LITTER_TYPE:BIOTIC_DIST: ALGAL_HEIGHT (mean):DIST_FREQ: ROOT_TYPES: PLOT SIZE: AGE_TYPES (dominant):PLOT ASPECT:SLOPE:DIST_WATER:

Site Map and Comments:(incl. aspect, leaf litter traps, creek lines, transect etc)


66

APPENDIX 5SITE ID: _______ DATE :_________ RECORDER: _______________

BASAL WEDGE COUNTS, 4 corner posts & centre, all trees >2cm DBH Factor:

Species Count 1 Count 2 Count 3 Count 4 Centre Total

Total

CROWN DENSITY [%], 4-5 locations, 4 random readings per location facing N,E,S,W

1A 1B 1C 1D 2A 2B 2C

LEAFBRANCHTOTAL

2D 3A 3B 3C 3D 4A 4B

LEAFBRANCHTOTAL

4C 4D 5A 5B 5C 5D

LEAFBRANCHTOTAL

PHENOLOGY

Species Sterile Bud Flower Fruit Propagules Fruit_drop Vegetative

CRAB BURROW DENSITY (15-20 random quadrats)

SizeClasses

< 1cm 1-2 cm 2-3 cm 3-4 cm > 4cm Total

Count

TotalNo of Quadrats/Transects: ___________ Quadrat:Area/Transect Length:____


67

APPENDIX 6SITE ID: _______ DATE :_________ RECORDER: _______________

Basal Area Factor:No Tag No. Species DBH Height Status Condition Comments123456789101112131415161718192021222324252627282930313233343536

Status: 1 Living, 0 DeadCondition: 1 Healthy, 2 Trunk rot, 3 Crown Damage, 4 Overmature, 5Senescent, 6 Dead Branches, 7 Leaning


68

APPENDIX 6 cont..

SITE ID: _______ DATE :_________ RECORDER: _______________Basal Area FactorNo Tag No. Species DBH Height Status Condition Comments373839404142434445464748495051525354555657585960616263646566676869707172

Status: 1 Living, 0 DeadCondition: 1 Healthy, 2 Trunk rot, 3 Crown Damage, 4 Overmature, 5Senescent, 6 Dead Branches, 7 Leaning


69

APPENDIX 7

SITE ID: _______ DATE:____________ RECORDER: _______________

SHRUBS/SAPLINGS/SEEDLINGS (dia<2cm, girth<6.3cm) transect width 1m

Seedlings SaplingsSpecies 0 - 0.3m 0.3 - 0.5m 0.5 - 1.0m 1.0 - 2.0m > 2.0m

No of Transects:_____ Transect Length: ___ Transect Width: ___

DENSITY (1 x 20m transect, 20m2) CountStumps (> 5cm diameter, girth >16 cm)

Logs (dia > 10cm, girth > 31.4cm)

No of Transects: ____ Transect Length:____


70

APPENDIX 8SITE ID: _______DATE:_________RECORDER(S): _____________________________

TIME: _________TIDE: Neap/Spring HIGH TIDE: _________________________

Soil(in situ)

Soil Water(in situ)

Soil (Lab)

Depth 5 cm 50cm

5 cm 50 cm 5 cm 50cm

pH 12

3

4

5

EH [mV] 12

3

4

5

Temp [Co] 12

3

4

5

Conductivity[mS/cm]

1

2

3

3 4

5

5 cm 50 cm pH H2O2 pH pH H2O2 pH CommentsBeforereaction

after Beforereaction

after

1234

H2O2(in situ)

5

Comments:


71

APPENDIX 9

SITE ID: _______DATE :_________RECORDER(S): _____________________________

TIME: _________TIDE: Neap/Spring HIGH TIDE: _____________________________

Water Content 5 cm 50 cmTRAY Wet TRAY Dry TRAY Wet TRAY Dry

(incl. Tray) (incl. Tray) (incl. Tray) (incl. Tray)

1

2

3

4

(Laboratory)

5

Colour Matrix Colour MottlesMoist Dry Abund Size Contrast Colour

Hue Value Chroma Hue Value Chroma [%] [mm]

1

2

3

4

Munsell(Lab)5 cm

5

Colour Matrix Colour MottlesMoist Dry Abund Size Contrast Colour

Hue Value Chroma Hue Value Chroma [%] [mm]

1

2

3

4

Munsell(Lab)50 cm

5


72

APPENDIX 10DATE :____________EAST ARM RECORDER: _______________

Flowers/FruitSite Zone Trap Species DryWt [g ] Flower Fruit Prop

DateCollected

DryingTime [h]

E1 1 A RsE1 1 B RsE1 2 A RsE1 2 B RsE1 4 A CtE1 4 B CtE1 5 A Am

CtE1 5 B Am

CtE1 6 A CtE1 6 B CtE1 8 A SaE1 8 B SaE2 2 A RsE2 2 B Rs

BpE2 3 A BeE2 3 B Be

RsCt

E2 4 A CtE2 4 B CtE2 5 A CtE2 5 B Am

CtE2 6 A Ct

LrMl

E2 6 B CtLr

E2 8 A SaE2 8 B SaE3 2 A Cs

RsE3 2 B Am

RsE3 4 A CtE3 4 B CtE3 6 A Be

CtLr

E3 6 B CtLr

E3 8 A SaE3 8 B Sa


73

APPENDIX 10 cont..DATE :____________MIDDLE ARM RECORDER: _______________

Flowers/FruitSite Zone Trap Species DryWt [g ] Flower Fruit Prop

DateCollected

DryingTime [h]

M1 1 A RsSa

M1 1 B RsM1 5 A Am

CtM1 5 B Am

CtM1 6 A Ct

BeEoAm

M1 6 B CtEoBe

M1 8 A SaM1 8 B SaM2 2 A Rs

BpM2 2 B Am

RsBp

M2 3 A BeCt

M2 3 B BeRsCt

M2 4 A CtM2 4 B CtM2 6 A Ct

EoM2 6 B Ct

EoM2 7 A Ct

LrM2 7 B Am

LrCt

M3 2 A RsM3 2 B RsM3 3 A Rs

CtM3 3 B Rs

CtBe

M3 4 A CtM3 4 B CtM3 6 A CtM3 6 B Ct


74

APPENDIX 10 cont..

DATE :____________WEST ARM RECORDER: _______________

Flowers/FruitSite Zone Trap Species DryWt [g ] Flower Fruit Propr

DateCollected

DryingTime [h]

W1 1 A RsW1 1 B RsW1 2 A Rs

BpW1 2 B RsW1 4 A CtW1 4 B Ct

AmW1 6 A CtW1 6 B CtW1 8 A SaW1 8 B SaW2 2 A RsW2 2 B RsW2 4 A CtW2 4 B CtW2 5 A CtW2 5 B Ct

AmW2 6 A CtW2 6 B Ct

Flowers/FruitFlower: Flowers and budsFruit: incl. fruit with propagule/hypocotyle notdeveloped yet, e.g. Ceriops, RhizophoraProp: Propagule (fruit and hypocotyle)

0 = absent

1 = present

2 = few

3 = moderately abundant

4 = abundant

5 = very abundant

darwin harbour mangrove monitoring methodologydarwin harbour are regarded as pristine and largely...

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