A method to Assess Wetland Condition in Victoria ...

Development of a Wetland Catchment Disturbance Index P. Papas, S. Lyon, C. Jin and J. Holmes

Development of a Wetland Catchment Disturbance Index

Phil Papas1, Shanaugh Lyon1, Changhao Jin1 and Janet Holmes2

1

Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, 123 Brown Street, Heidelberg, Victoria 3072

2

Freshwater Sustainable Ecosystems, Department of Sustainability and Environment, 8 Nicholson Street, East Melbourne, Victoria, 3002

Report produced by:

Arthur Rylah Institute for Environmental Research Department of Sustainability and Environment PO Box 137 Heidelberg, Victoria 3084 Phone (03) 9450 8600 Website: www.dse.vic.gov.au/ari

© State of Victoria, Department of Sustainability and Environment 2008 This publication is copyright. Apart from fair dealing for the purposes of private study, research, criticism or review as permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any means (electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department of Sustainability and Environment. All requests and enquires should be directed to the Customer Service Centre, 136 186 or email [email protected] Citation: Papas, P., Lyon, S., Jin, C. and Holmes, J. (2008) Development of a Wetland Catchment Disturbance Index. Arthur Rylah Institute for Environmental Research. Department of Sustainability and Environment, Heidelberg, Victoria ISBN 978-1-74208-706-1 (print) ISBN 978-1-74208-707-8 (PDF) Disclaimer: This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Authorised by: Victorian Government, Melbourne

Contents LIST OF TABLES AND FIGURES......................................................................................................................... II ACKNOWLEDGEMENTS..................................................................................................................................... III ACRONYMS .............................................................................................................................................................IV SUMMARY ................................................................................................................................................................ V 1

INTRODUCTION............................................................................................................................................... 1 1.1 1.2 1.3 1.4 1.5

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WETLANDS AND WETLAND CONDITION ................................................................................................ 7 2.1 2.2

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WETLAND CATCHMENTS ............................................................................................................................... 9 WETLAND CATCHMENT DISTURBANCE ......................................................................................................... 9 RELATIONSHIPS BETWEEN CATCHMENT DISTURBANCE AND WETLAND CONDITION .................................... 10

DEVELOPMENT OF THE WCDI MODEL ................................................................................................. 17 4.1

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WETLAND DRIVERS ....................................................................................................................................... 7 WETLAND CONDITION ................................................................................................................................... 8

WETLAND CATCHMENT DISTURBANCE FRAMEWORK .................................................................... 9 3.1 3.2 3.3

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PURPOSE AND OBJECTIVES ............................................................................................................................ 1 BACKGROUND............................................................................................................................................... 1 INDICES ......................................................................................................................................................... 3 STAKEHOLDERS AND USE OF THE CDI .......................................................................................................... 5 APPROACH .................................................................................................................................................... 6

THE LDI AS A SURROGATE FOR WETLAND CATCHMENT DISTURBANCE ....................................................... 17

TRIALLING AND TESTING THE WCDI.................................................................................................... 20 5.1 5.2 5.3

DATASETS ................................................................................................................................................... 20 IDENTIFYING WETLAND CATCHMENTS ........................................................................................................ 22 PRELIMINARY RESULTS USING THE WCDI IN THE WIMMERA REGION OF VICTORIA ................................... 23

6

GUIDELINES FOR THE USE OF THE WCDI AND CONCLUSIONS .................................................... 25

7

REFERENCES.................................................................................................................................................. 26

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GLOSSARY....................................................................................................................................................... 28 APPENDIX 1 NATIONAL INDICATORS FOR WETLAND ECOSYSTEM CONDITION ........................................................ 30 APPENDIX 2 INDEX OF WETLAND CONDITION MEASURES. ..................................................................................... 31


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List of tables and figures List of tables Table 1. IWC wetland catchment subindex measures ............................................................................... .2 Table 2. Examples of wetland condition assessment methods and their indicators in Australia and New Zealand.......................................................................................................................................... 3 Table 3. Relationship between potentially threatening activities in the catchment and impacts in the wetland as follows....................................................................................................................... 12 Table 4. The potential impacts of catchment disturbances on the components of wetland physical form 14 Table 5. The potential impacts of catchment disturbances on the components of wetland hydrology..... 14 Table 6. The potential impacts of catchment disturbances on the components of wetland water properties .................................................................................................................................................... 15 Table 7. The potential impacts of catchment disturbances on the components of wetland soils .............. 16 Table 8. Potential impacts of land use and infrastructure on wetland condition ...................................... 17 Table 9. Land use categories and impacts associated with them used in the LDI/WCDI......................... 18 Table 10. Condition categories and linguistic descriptors for the LDI/WCDI adapted from the CDI ....... 19 Table 11. Sources of data used in developing the WCDI ........................................................................... 21 Table 12. Preliminary Landscape Disturbance Index (LDI) scores for 27 wetland sites in the Wimmera region of Victoria........................................................................................................................ 24

List of figures Figure 1. Conceptual diagram showing the key characteristics of all wetlands (hydrology, physicochemical environment and biota), key wetland drivers, geomorphology and climate and the relationships between them........................................................................................................... 8 Figure 2. Conceptual diagram showing a wetland in the Wimmera region of Victoria ............................. 11 Figure 3. Location of wetlands where the LDI was applied....................................................................... 20 Figure 4. Example of mapped wetland catchment boundaries and surrogate ‘catchment’ boundary assigned to 250m for selected wetlands in the Wimmera region ............................................... 23


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Acknowledgements Funding for the project was obtained from the National Land and Water Resources Audit. The following people are thanked for providing comments on the Draft Conceptual Framework Paper which has been used in this report: Dr. Jane Roberts (Consultant, Australian Capital Territory), Associate Professor Jenny Davis (Murdoch University, Western Australia) and Glen Scholtz (Department of Water Land and Biodiversity Conservation, South Australia).


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Acronyms DSE

Department of Sustainability and Environment, Victoria

IWC

Index of Wetland Condition

LDI

Landscape Disturbance Index

NAP

National Action Plan for Salinity and Water Quality

NLWRA

National Land and Water Resources Audit

NHT

Natural Heritage Trust

NRM

Natural Resource Management

NWC

National Water Commission

Qld DNRW

Queensland Department of Natural Resources and Water

WCDI

Wetland Catchment Disturbance Index

WWTF

Wetlands and Waterbirds Taskforce


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Summary A Wetland Catchment Disturbance Index (WCDI) based on wetland catchment land use data has been developed in Victoria. The WCDI forms one of six themes that will together report on wetland condition at a National level through the framework for comparable assessment of the ecological condition of Australian rivers and wetlands, which is being implemented by the National Water Commission. The WCDI is applicable to naturally-occurring wetlands without a marine or riverine hydrological influence. Future iterations of the WCDI will investigate including riverine (floodplain) wetlands. Wetlands, wetland condition and wetlands drivers are explained in the context of a general wetland conceptual model adapted from the Victorian Index of Wetland Condition (IWC). Wetland catchments and wetland catchment disturbance are also detailed in a conceptual framework, which explores the relationship between wetland catchment disturbance and wetland condition. Due to the absence of quantitative wetland catchment disturbance data, quantitative wetland catchment disturbance models could not be constructed at this stage. In the absence of this data, a Landscape Disturbance Index (LDI), that was developed to assist with the testing of the IWC, has been used to provide a measure of catchment disturbance. LDI/WCDI scores were calculated for 27 wetland catchments and surrogate wetlands catchments in the Wimmera region of Victoria. Future work on the WCDI, should include an assessment of available datasets in jurisdictions outside Victoria, testing of the reliability and accuracy of the expert opinion approach used in the development of the LDI and WCDI, testing the currency and accuracy of the land use data used in the development of the LDI and WCDI and experimental validation methods as a means of validating the LDI and WCDI.


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1

Introduction

1.1

Purpose and objectives

The purpose of this project is to develop and trial a Wetland Catchment Disturbance Index (WCDI) for wetlands in Victoria. The project is part of a series of projects coordinated by the National Land and Water Resources Audit (NLWRA) and Wetlands and Waterbirds Taskforce (WWTF) in Australia to develop national indicators for wetland extent, distribution and condition. It also complements work in Victoria to develop and implement an Index of Wetland Condition (IWC). The specific objectives of the project are: 1. to develop and trial an approach for assessing catchment disturbance using knowledge gained from the development of a Landscape Disturbance Index (LDI) for wetlands in Victoria; and 2. to develop a model and guidelines for the general application of a WCDI.

1.2 1.2.1

Background National program for assessing wetland extent, distribution and condition

The National Action Plan for Salinity and Water Quality (NAP) and the Natural Heritage Trust (NHT) provided the framework for integrated natural resource management in Australia from 1997 to 30 June 2008. The goal of NAP was to prevent, stabilise and reverse trends in salinity and improve water quality (Australian Government NAP website). The goal of NHT was to achieve the conservation, sustainable use and repair of Australia’s natural environment (Australian Government NHT website). Under NAP and NHT national outcomes, resource condition and indicator headings were established for a range of natural resource assets, including inland wetlands. The NLWRA coordinated work to identify suitable indicators for each asset. The WWTF advised the NLWRA on the development of indicators for inland wetlands. In 2007, the Queensland Department of Natural Resources and Water undertook a national project ‘Development of National Indicators for Wetland Ecosystem Extent, Distribution and Condition’ for the NLWRA. The project was informed by a National Water Commission (NWC) sponsored project to provide methods for comparing and integrating existing river and wetland health outputs to facilitate national reporting from comparable state, territory, and regional NRM assessments (National Water Commission 2007). The project identified a national framework and indicators to assess wetland extent, distribution and condition (Queensland Department of Natural Resources and Water unpublished), (Appendix 1). The indicators are arranged under the themes identified by the National Water Commission (2007) that represent the major elements of river and wetland condition or health. They are a mixture of biotic and abiotic elements and were selected to represent those components that are the most important and responsive parts of the wetland ecosystem (Queensland Department of Natural Resources and Water unpublished). The framework and indicators were agreed to by the WWTF. It was agreed by the NLWRA and the WWTF to take the national indicators for inland wetlands forward for further development and trialling, including the indicator ‘disturbance in the wetland catchment’ (Appendix 1). The catchment disturbance theme is one of six that will together report on wetland condition at a National level through the Framework of Assessment of River and Wetland Health (FARWH). This project aims to develop and trial a suitable method to measure catchment disturbance.


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1.2.2

Victoria’s Index of Wetland Condition

In 2005, the Victorian Department of Sustainability and Environment (DSE) developed the IWC ‘to provide a standard, relatively simple and rapid statewide method for determining wetland condition in Victoria’ (Department of Sustainability and Environment 2005). The IWC is a hierarchical index with six sub-indices based on the characteristics that define wetlands: wetland catchment, physical form, hydrology, soils, water properties and biota (Department of Sustainability and Environment 2005). The components within each characteristic and the policy, practical and ecological requirements of the project guided the selection of measures that make up the IWC (Department of Sustainability and Environment 2005). The measures selected were either direct measures of the components themselves, or surrogate measures of the impacts on the component or threats to the component (Appendix 2). The wetland catchment measures selected for the IWC (Table 1) relate to land use within 250 m of the wetland boundary as well as to properties of the wetland buffer (Department of Sustainability and Environment unpublished). The IWC definition of the wetland buffer is the native vegetation adjacent to the wetland (from the maximum inundation level outwards). For the purposes of the IWC measure, native vegetation is defined as vegetation where native species make up more than 25% of the total understorey cover. The buffer only includes native vegetation contiguous with the wetland, that is, where there is no break between the native vegetation and the wetland boundary. It may extend any distance away from the wetland but the maximum buffer width class measured in the IWC is greater than 50 metres (Department of Sustainability and Environment unpublished). Table 1. IWC wetland catchment subindex measures (Department of Sustainability and Environment unpublished). IWC sub-index Wetland catchment

Key ecological component Wetland catchment Wetland buffer

Measure % of adjacent land (within 250 metres of the wetland) in each land use intensity class (as defined for the IWC) Average buffer width % of wetland perimeter with a buffer

In 2007 and 2008, the IWC has been used provisionally by a number of catchment management authorities in Victoria to identify and address implementation issues. It has also been tested by DSE to validate the accuracy of the method and refine the IWC scoring. One of the objectives of validation was to test that the IWC measured wetland condition consistently across a condition gradient. Victoria developed an LDI as a rapid and approximate means of selecting wetlands across the spectrum of condition for testing the IWC. The use of the LDI for this purpose was based on the assumption that disturbance in the landscape surrounding the wetland is an important factor in determining wetland condition. Therefore, selecting wetlands with a range of LDI scores would provide a selection of wetlands across the spectrum of wetland condition. However, it is recognised that other factors, including activities within the wetland, can also cause changes in wetland condition. The methods and results of the IWC testing and validation are currently being prepared for publication (Phil Papas, Department of Sustainability and Environment pers. comm.). The LDI used surrogate wetland catchments derived by delineating a zone outside the boundary of wetlands and remote-sensed data on land use in this zone. The weighting of each land use in relation to its likely effect on wetland characteristics and the proportion of each land used in the surrogate wetland catchment provided the basis for calculating the LDI for individual wetlands. This project aims to build on this work to develop a CDI to provide a model for measuring the nationally-agreed catchment disturbance indicator (Appendix 1).


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1.3

Indices

An index can be defined as a number derived from a formula, used to characterise a set of data, or a number that represents the change in value or other measurable quantity in comparison with a reference number for a previous period of time. The catchment disturbance index will produce a value derived from a mathematical model based on catchment disturbance impacts on wetland condition. The value will be compared to a reference state, which is that of a wetland catchment unmodified by Europeans. Indices that determine the condition of environmental assets such as rivers and wetlands are commonly used in Australia (Table 2). Examples of indices specific to catchments include the Catchment Disturbance Index for stream catchments in Australia (National Water Commission 2007), and an index that assesses land use impacts on biological and chemical properties of river catchments in the United States (Johnson et al. 2005). Additionally, numerous methods of quantifying a human disturbance gradient have been used in parallel with biotic indices as corroborative confirmation of measured biological integrity or to test the precision (consistency and bias) of the assessment method (e.g., Reiss 2006, Miller et al. 2006, Lopez and Fennessy 2002). Reiss (2006) used an independent human disturbance gradient derived from the Landscape Development Intensity (LDI) index developed by Brown and Vivas (2005), to test the Florida-based Wetland Condition Index. The LDI is based on the amount of non-renewable energy used within a 100 m buffer around a wetland. Miller et al. (2006) used land use, buffer characteristics, and an assessment of potential site stressors to assess the ability of the plant-based Index of Biological Integrity (IBI) to distinguish between categories of condition that could be used in a regulatory framework. Lopez and Fennessy (2002) used a disturbance gradient generated from surrounding land cover characteristics, vegetated buffer characteristics, and the extent of human-induced hydrologic alteration to test a plant community based wetland assessment tool (floristic index) on 20 depressional wetlands in Ohio. Landscape indicators for pressure measures on New Zealand wetlands are being used to develop a rapid method for broad-scale mapping and prioritising palustrine and estuarine wetlands for conservation in New Zealand (Ausseil et al. 2007). A range of GIS indicators are used to account for anthropogenic pressure on wetlands which will be used to rank wetlands into priority order (A-G. Ausseil, Landcare Research, New Zealand, pers comm.). The rapid methodology means that consistent wetland rankings can be produced efficiently without having to wait for the collection of detailed biologic information and conservation resources better targeted (Ausseil et al. 2007). Table 2. Examples of wetland condition indices and their indicators in Australia and New Zealand. Adapted from Department of Sustainability and Environment (2007). Location/ Purpose Victorian Index of Wetland Condition Purpose: Surveillance of wetland condition in naturally-occurring wetlands without a marine influence (Department of Sustainability and Environment 2005).

Indicators used • Wetland catchment: average width of the buffer, percentage of wetland perimeter with a buffer • Physical form: percentage reduction in wetland area, percentage of wetland where activities have resulted in a change in bathymetry • Hydrology: severity of activities that change the water regime • Water properties: activities leading to an input of nutrients to the wetland, factors likely to lead to wetland salinisation, input of saline water to the wetland, wetland occurs in a salinity risk area • Soils: physical soil disturbance • Biota (wetland plants): critical lifeforms, presence of weeds, indicators of altered processes, vegetation structure and health


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Table 2. Continued. Location/ Purpose New Zealand Purpose: Monitoring of condition in palustrine and lacustrine wetlands (Clarkson et al. 2003)

Victorian Index of Stream Condition Purpose: Assessing the condition of homogenous river reaches to assist with the delivery of stream management programs in Victoria. In particular, for use in priority setting, resource allocation, assessing management effectiveness and setting benchmarks.

Murray-Darling Basin Purpose: Monitoring condition of floodplain wetlands in the MurrayDarling Basin (Spencer et al. 1998). Rapid assessment method. Gippsland Lakes, Victoria Purpose: Assess wetland condition in wetlands of the Gippsland Lakes.

Wimmera Wetlands Purpose: To inform Wimmera CMA and aid decision-making. Rapid assessment method. Broad rating of condition applied which considers risk Agency: Wimmera CMA (Butcher unpublished b) Swan Coastal Plain, Western Australia Swan Wetlands Aquatic Macroinvertebrate Pollution Score (SWAMPS). Purpose: Method to assist in the assessment of wetland condition of wetlands on the Swan Coastal Plain, Western Australia. Chessman et al. (2002).

Indicators used • Change in hydrological integrity: impact of manmade structures, water table depth, dryland plant invasion, change in physicochemical parameters, fire damage, degree of sedimentation/erosion, nutrient levels, von Post index • Change in ecosystem intactness: loss in area of original wetland, connectivity barriers • Change in browsing, predation and harvesting regimes: damage by domestic or feral animals, introduced predator impacts on wildlife, harvesting levels • Change in dominance of native plants: introduced plant canopy cover, introduced plant understorey cover Sub-indices relating to five stream components. Indicators for each subindex: • Hydrology (hydrologic deviation, percentage of catchment urbanised, presence of hydropower stations that cause water surges) • Physical form (bank stability, bed aggradation and degradation, presence and influence of artificial barriers, density and origin of coarse woody debris) • Streamside zone (width of vegetation, longitudinal continuity of vegetation, proportion of vegetation cover that is indigenous, presence of regeneration of indigenous species, condition of wetlands and billabongs) • Water Quality (Total phosphorus concentration, turbidity, electrical conductivity, pH) • Aquatic Life (presence of macroinvertebrate families using the SIGNAL index) • Soils: bank stability, pugging by livestock, soil organic content • Fringing vegetation: width, continuity, height diversity • Aquatic vegetation: cover, spatial heterogeneity, attached algae • Water quality: turbidity, conductivity, colour, algal bloom frequency Sub-indices relating to wetland complex and sub-categories: • Landscape sub-index (man made structures, loss of original extent, connectivity, grazing impact, adjacent and upstream land use, exotic species) • Vegetation sub-index (vegetation zone shift, species richness, significant species, significant class, weed species) • Bird sub-index (diversity of feeding groups, species diversity within feeding groups, listed migratory species, threatened species, introduced species) Total Condition Score = Landscape sub-index + Vegetation sub-index + Bird sub-index • Measures of condition were developed and trialed for hydrological integrity, geomorphological integrity, land use, riparian vegetation, wetland vegetation, water quality. • Based on key system drivers of wetland ecology and includes biological, physical and chemical components • • •

Biotic index based on macroinvertebrate data. Macroinvertebrate taxa assigned numerical grades to reflect sensitivity to anthropogenic disturbance (primarily nutrient enrichment). Family and species level grades and scores developed.


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Table 2. Continued. Location/ Purpose South Australian River Murray Wetlands Purpose: Assess wetland condition. Agency: River Murray Water Catchment Management Board. River Murray Catchment Water Management Board (unpublished). North Coast Wetland Assessment Technique, New South Wales Purpose: Assess wetland condition in fresh water wetlands and farm dams. Bolton (2003). Rapid assessment method.

Indicators used • Indicators comprised of habitats essential to the specific wetland type character and function. • Indicators comprised of characteristic species and processes and species and processes indicative of low disturbance and exceptional diversity. • • • • • • • •

1.4

Connectivity: proximity to natural ecosystems, corridors, area of wetland, adjacent land use Human disturbance Bank condition: erosion, pugging, bank gradient Habitat Fringing vegetation: width, diversity, species number, weeds Aquatic vegetation: diversity, species number, cover, weeds Water quality: pH, EC, nitrate, ammonium, phosphate, turbidity, attached biofilm, blue-green algae, water odour Macroinvertebrates

Stakeholders and use of the CDI

At the national, State and regional level natural resource management (NRM) agencies set targets, monitor, evaluate and report on wetland extent, distribution and condition. The key stakeholders for this project are state and territory natural resource management (NRM) agencies. They will have the responsibility of guiding wetland condition assessment within their jurisdictions, coordinating the activities of regional NRM bodies and reporting at a national level. The WWTF and Aquatic Ecosystems Task Group are also important stakeholders as these national coordinating bodies have a role in endorsing the application of the national framework for assessing wetland extent, distribution and condition. The NWC also has an interest in the project in its role of reporting nationally on wetland health under the National Water Initiative under the framework for comparable assessment of the ecological condition of Australian rivers and wetlands (National Water Commission 2007). The WCDI will provide a method to measure the catchment disturbance indicator for wetlands, as outlined in Section 1.2. In Victoria, the catchment disturbance index will be incorporated into the wetland catchment sub-index of the IWC. It is designed to have the potential to be adapted for use in wetland condition assessment frameworks in other jurisdictions. There are a number of practical considerations in developing a catchment disturbance index. These are addressed in this project for Victoria. They include the availability of datasets and analysis tools to support the model outlined in this report. Specific issues in development of a catchment disturbance index include: •

knowledge of relationships between catchment activities and wetland condition;

•

accounting for wetland spatial variability;

•

identifying wetland catchments;

•

modelling the relationship between catchment activities and wetland condition; and

•

validation of the index using an independent measure of wetland catchment condition.


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1.5

Approach

The development of the WCDI included the following tasks: 1. development of a conceptual framework to explore/explain the relationship between catchment disturbance/condition and wetland condition; 2. scoping of information required to apply the framework (including wetlands and other datasets); 3. selecting areas for trials of the development of the WCDI ensuring data and rich and data poor areas are selected and different wetland types are covered; 4. identifying datasets to use in assessing catchment activities for WCDI development in each trial area; 5. developing a method for identifying wetland catchments (actual or arbitrary/surrogate catchments); 6. developing mathematical model(s) to reflect relationships between catchment attributes and wetland condition; and 7. testing the model using wetland condition data.


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2

Wetlands and wetland condition

The Ramsar Convention defines wetlands as ‘areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres’ (Ramsar Convention, n.d.). For the WCDI, we focus on naturally occurring wetlands without a marine or riverine hydrological influence. Water can enter these wetlands from three principal sources: precipitation, local runoff and groundwater. Wetlands generally occur where there are closed depressions in the landscape where water can collect (Paijmans et al. 1985). Geomorphology and climate are considered key wetland drivers that determine the location of wetlands across the landscape. They play an important role in determining characteristics of the wetland catchment and the characteristics of the wetland, such as its physical form, hydrology, water properties, biota and soils (Johnson and Gage 1997, Mitsch and Gosselink 2000). Wetlands themselves are distinguished by three characteristics: the presence of water for all or part of the hydrologic cycle, unique soil conditions (hydric soils) and vegetation adapted to wet conditions (hydrophytes) (Mitch and Gosselink 2000) (Figure 1). Hydrology is considered a key variable of wetland ecosystems, driving the development of wetland soils and leading to the development of the biotic communities (Mitsch and Gosselink 2000). Other features that all wetlands have in common include a physical form (area and shape) and their water properties (i.e. physical and chemical properties).

2.1

Wetland drivers

The key determinants or drivers for wetlands are climate and geomorphology (Department of Sustainability and Environment 2005). Climate has an overriding influence on the distribution and abundance of wetlands globally. Climate also has a major influence on wetland hydrology (flooding duration, seasonality and frequency). Hydrological variability in wetlands is closely associated with rainfall patterns. Over the year these patterns influence the seasonal cycle of filling and drying. Over several years there may be periods that are wetter or drier than average which lead to longer-term changes in wetland filling frequency and duration of inundation. Diurnal and seasonal temperature fluctuations cause variations in daily and seasonal wetland water temperature. Temperature also affects hydrology through evaporation and transpiration. Geomorphic setting is a key factor that determines the water source of wetlands, the size and shape of wetlands, their location, their hydrology, physico-chemical properties of the water and soils (Figure 1) (Semeniuk and Semeniuk 1995, National Research Council 1995, Mitsch and Gosselink 2000). A number of wetland classification schemes are based on geomorphic setting. Examples of such categories are as follows (modified from Brinson 1993, Semeniuk and Semeniuk 1995): • • • • •

depressional wetlands/basins that occur in topogrpahic depressions and are maintained predominantly by overland flow, groundwater and precipitation; riparian (also known as riverine) wetlands that are adjacent to rivers and maintained predominantly by periodic pulses of water from overbank flows; flats that occur in many settings but are principally maintained by precipitation and contain organic soils; slope wetlands that are usually located on a slope where groundwater reaches the surface and is relatively constant; and highlands or hill wetlands that principally occur in wet areas, maintained by precipitation (e.g. alpine bogs).


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Geomorphology

climate

Hydrology (flooding frequency, seasonality and duration)

Physicochemical environment

Biota (vegetation, animals and microbes)

(soil, chemistry, etc.)

Wetland

Figure 1. Conceptual diagram showing the key characteristics of all wetlands (hydrology, physico-chemical environment and biota), key wetland drivers, geomorphology and climate and the relationships between them. Reprinted and adapted with permission from National Research Council (1995) by the National Academy of Sciences, courtesy of the National Academies Press, Washington, D.C.

2.2

Wetland condition

The definition used by the Victorian IWC has been adopted for the purposes of the development of the WCDI. Wetland condition is the state of the biological, physical, and chemical components of the wetland ecosystem and their interactions (Department of Sustainability and Environment (2005). There are other definitions of wetland condition, which include that used by the Queensland Department of Natural Resources and Water: the relative integrity of the wetland ecosystem compared to a reference state. It includes being able to maintain key ecological and physical processes, ecosystem services, and communities of organisms.


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3 3.1

Wetland catchment disturbance framework Wetland catchments

The catchment of a wetland comprises specific landscape features that transmit water to the wetland via surface and ground water movements (e.g., contributing surface drainage areas, groundwater recharge areas, river basins). Wetland catchments are characterised by climate, geomorphologic setting, hydrologic connectivity, geology, soil types and vegetation cover (Figure 2). These structural and climate features set the major layout on which the catchment processes such as hydrologic and geomorphologic processes, dispersal of animals and plants, and nutrient, salinity and pollutant flows take place. The hydrological processes can involve overland flow, through flow along restrictive soil layers; vertical leaching (including preferential flow); rising groundwater tables (Reuter 1998). In turn, these processes can lead to the transport and redistribution of sediment, nutrient, salinity and pollutants. The landscape influences its water bodies through multiple pathways and mechanisms which operate at different spatial scales (Allan and Johnson, 1997). Because wetlands are often located at the topographic low point in the landscape, they act as sinks for materials washed in from the catchment or transported by groundwater (Boulton and Brock 1999). A wetland and its catchment are linked via several pathways such as water, air and biological agents. Broad-scale wetland catchment influences a wetland through large-scale controls on energy, chemistry, hydrology, sediment delivery, and organisms.

3.2

Wetland catchment disturbance

Catchment disturbance as defined in this study refers to the direct disruption of natural catchment structure and processes by human activities. Land or water use is a specific kind of catchment disturbance. The most important catchment disturbances affecting wetlands include urbanisation, industry, infrastructure, land clearance, agriculture, forestry, fire, and recreation. Fire is included in the catchment disturbances, but we acknowledge that it is not always anthropogenic. Catchment disturbances vary along different spatial and temporal scales. There are several aspects of the whole disturbance regime: extent, intensity, duration, timing, frequency and variability of an individual disturbance, and distribution, co-occurrence or sequence of multiple disturbances. In this study, we develop a conceptual model to depict the relationship between catchment disturbance and wetland condition at a specified point in time. Wetland condition is defined as the state of the biological, physical, and chemical components of the wetland ecosystem and their interactions (Department of Sustainability and Environment 2005). To assess wetland condition in this project, we take into account five fundamental characteristics that define wetland ecosystems used for the development of the Victorian Index of Wetland Condition. They are physical form, hydrology, water properties, soils, and biota (Department of Sustainability and Environment 2005). A wetland as an embedded part of a larger landscape is profoundly influenced by catchment disturbances. Catchment disturbances alter wetland condition and may set the wetland onto a new trajectory. Catchment disturbances affect wetlands in complex ways. A particular disturbance can result in multiple effects on a wetland. Different disturbances will interact and exert their influence at different spatial and temporal scales and by different pathways and mechanisms. Human activities on the catchment are likely to set off a complex cascade of changes that are ultimately manifest in altered and possibly degraded wetland. For example, reduction of vegetation and increases in impervious surfaces that are associated with urbanisation lead to an increase in the volume and rate of runoff entering a wetland. With this overland flow come increased sediment, nutrient and pollutant loads (Lee et al. 2006).


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3.3 3.3.1

Relationships between catchment disturbance and wetland condition Wetland catchment modifiers

The effects of catchment disturbances on wetland condition vary according to (1) wetland catchment characteristics, (2) wetland water source, (3) wetland type, (4) the nature of disturbance, (5) the disturbance interactions, and (6) the whole disturbance regime. The relationship between wetland catchment disturbances and wetland condition will be modified by the characteristics of the wetland catchment, i.e. its topography and geology/soils, the water source of the wetland, the climate and features of the wetland itself, including size and depth (Figure 2). For example, wetlands in catchments with highly erodible soils, steep topographic relief and high rainfall will be more likely to receive sediment derived from disturbance in the catchment than wetlands in catchments with stable soils, low topographic relief and low rainfall. The native vegetation surrounding a wetland (also termed the fringing vegetation or buffer zone) has an important role in regulating the catchment-wetland movement of matter and energy. The vegetation functions as a filter or a mitigator of catchment disturbance processes (Semlitsch and Bodie 2003) (Figure 2). The linkages between a wetland and its catchment are modified by this vegetation. The vegetation captures sediment, nutrient and pollutant, promotes bank stabilisation, and detains storm water. By increasing the residence time of surface runoff, buffer zone vegetation increases the amount of time for chemical, physical and biological processes to occur before runoff enters wetlands. For example, biological degradation by plants and soil decomposers are responsible for the detoxification of herbicide (Mehmannavaz et al. 2001). Consequently, the impacts of catchment disturbances on wetland condition may be modified depending on buffer characteristics and the nature of the linkage. The zone of vegetation may also act to minimise the invasion of exotic species into the wetland (Castelle et al. 1994, Davies and Lane 1995, Boyd 2001). Because hydrology is considered the single most important driver of wetland ecosystems (Mitsch and Gosselink 2007), the sources of water for a wetland are crucial in determining how catchment disturbance alters its condition. A wetland receiving water from local runoff may respond to catchment disturbance differently than a wetland fed by groundwater. If both surface flow and groundwater play a role in maintaining the water budget in an individual wetland, then groundwater–surface water interactions will affect the relationship between catchment disturbance and wetland condition. Riverine wetlands are not in included in the scope of the WCDI at this stage but should be included in future iterations.


10

Native vegetation surrounding the wetland (buffer) ameliorates the effect of disturbance on wetland condition

The wetland catchment boundary is delineated by the surface water catchment of the wetland

Factors that will influence the degree to which the wetland catchment activities impact on wetland condition (modifiers): • climate • wetland catchment topography • wetland catchment geology • wetland catchment soil types

Impacts associated with catchment activities and disturbance including nutrients, pesticides and sediment are transported to the wetland via surface water flow (local runoff and streamflow) and wind

Figure 2. Conceptual diagram showing a wetland in the Wimmera region of Victoria. The wetland catchment is shown as the dotted boundary, native vegetation as green shading and the native vegetation buffer zone within the dotted green boundary. Arrows represent vectors of disturbance, blue arrows indicate disturbance through streamflow and local runoff and orange arrows indicate disturbance through wind. Hydrological processes can be disturbed through changes in surface runoff characteristics (changes in vegetation, soil permeability or presence of farm dams), groundwater levels.

3.3.2

Types of disturbance

Disturbances in wetland catchments are numerous and include but are not limited to clearance of native vegetation, cultivation of catchment soils, application of chemicals to the catchment and introduction of weeds. Resultant impacts from these disturbances affect many wetland components (Table 3).


11

Table 3. Relationship between potentially threatening activities in the catchment and impacts in the wetland. Potentially threatening activities Fire

Catchment disturbance effects

Potential impacts in the wetland

Increase in the amount of sediments, nutrients or pollution in catchment runoff

Increased availability of nitrogen and phosphorus in the wetland soil and water Increased turbidity

Modified physical form of the wetland due to sedimentation Clearing of natural vegetation

Cultivation of soil

Application of chemicals (e.g. herbicides, insecticides and fertilisers)

Extraction of groundwater

Irrigation

Construction of farm dams Urbanisation

Change in the amount and/or pattern of flow of water that feeds the wetland

Modified wetland hydrology

Increase in the amount of sediments, nutrients or pollution in catchment runoff

Increased availability of nitrogen and phosphorus in the wetland soil and water

Introduction of weeds in the wetland catchment Increase in the amount of sediments, nutrients or pollution in catchment runoff

Increase in the amount of nutrients or pollution in catchment runoff Exacerbation of soil acidification in the catchment resulting in lowered pH of soil and water Exacerbation of soil acidification in the catchment resulting in lowered pH of soil and water Change in the amount and/or pattern of flow of the water that feeds the wetland Introduction of weeds in the wetland catchment Change in the amount and/or pattern of flow of the water that feeds the wetland Change in the amount and/or pattern of flow of the water that feeds the wetland Increase in the amount of sediments, nutrients or pollution in catchment runoff


Increased turbidity Modified physical form of the wetland due to sedimentation Modified wetland vegetation and fauna habitat Increased availability of nitrogen and phosphorus in the wetland soil and water Increased turbidity Modified physical form of the wetland from sedimentation Increased availability of nitrogen and phosphorus in the wetland soil and water Modified wetland biota abundance, diversity and richness Modified wetland biota abundance, diversity and richness

Modified wetland hydrology Modified wetland vegetation and fauna habitat Modified wetland hydrology

Modified wetland hydrology Increased availability of nitrogen and phosphorus in the wetland soil and water Increased turbidity Modified physical form of the wetland from sedimentation

12

3.3.3

Impacts of disturbance on wetland condition

The potential impacts of catchment disturbances on the key wetland characteristics outlined in Section 1.2.2 (wetland physical form, hydrology, water properties and soils) are summarised in Tables 1-4, respectively. All the disturbances to catchments in Tables 1-4 are focused on surface water catchments. The biota of wetlands is strongly influenced by the wetland characteristics above as well as other factors such as population recruitment, migration and predation. Consequently impacts of disturbance on biota are complex and difficult to disentangle from the impacts on other characteristics and are not included in the WCDI model. It is important to note that these simplified relationships between the components of wetland condition and the individual catchment disturbance cannot reflect nonlinear responses and thresholds, legacy effects from prior human activities, and the ecological synergies among anthropogenic disturbances, natural gradients and intricate and interconnected components of complex wetland ecosystems. The impacts of catchment disturbances on wetland condition are complex. Our knowledge is limited to qualitative observations (e.g. Bouton and Brock 1999) (Tables 4-7). There is little scientific knowledge and understanding on the impacts at both catchment scale and wetland ecosystem scale. Uncertainties on the relationship between catchment disturbance and wetland condition result from inherent complexity and limited scientific knowledge and understanding. Impacts caused by one disturbance may be modified by other disturbances within the system, creating complex interactions between them. Extent of disturbance is not by itself sufficient to predict the strength of the response. The influence of catchment disturbances is further complicated when cycles of change occur, such as when agricultural land reverts to forests, or when change is sequential, as when forested land is first converted to agriculture and subsequently to urban land.


13

Table 4. The potential impacts of catchment disturbances on the components of wetland physical form: ↑ indicates an increase, ↓ indicates a decrease, → indicates almost no impact.

Catchment disturbances Urbanisation Manufacturing and industrial Mining Infrastructure Land clearance Intensive animal production Irrigated agriculture Dryland cropping Grazing modified pastures Grazing natural vegetation Plantation forestry Production forestry Fire Recreation

Physical form Sedimentation ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½

Table 5. The potential impacts of catchment disturbances on the components of wetland hydrology: ↑ indicates an increase, ↓ indicates a decrease, → indicates almost no impact. Catchment disturbances Runoff Urbanisation Manufacturing and industrial Mining Infrastructure Land clearance Intensive animal production Irrigated agriculture Dryland cropping Grazing modified pastures Grazing natural vegetation Plantation forestry Production forestry Fire Recreation


½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ¾ ½ ½ ½

Hydrology Water level Groundwater fluctuation recharge ½ ½ ½ ¾ ½ ½ ½ ¾ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ½ ¾ ½ ½ ½ ½ ½ ½ ¾

14

Table 6. The potential impacts of catchment disturbances on the components of wetland water properties: ↑ indicates an increase, ↓ indicates a decrease, → indicates almost no impact.

Catchment disturbances

Water properties Acidification Pollution Turbidity

Eutrophication

Salinisation

Temperature

½

Dissolved oxygen ¾

Urbanisation

½

½

½

½

Manufacturing and industrial

½

½

½

½

½

¾

½

Mining

¼

½

½

½

½

¾

½

Infrastructure

½

½

½

½

½

¾

½

Land clearance

½

½

½

¼

½

¾

¼

Intensive animal production

½

½

½

½

½

¾

¼

Irrigated agriculture

½

½

½

½

½

¾

¼

Dryland cropping

½

½

½

½

½

¾

¼

Grazing modified pastures

½

½

½

½

½

¾

¼

Grazing natural vegetation

½

½

½

½

½

¾

¼

Plantation forestry

½

½

½

½

½

¾

¼

Production forestry

½

½

½

½

½

¾

¼

Fire

½

½

½

¼

½

¾

¼

Recreation

¼

½

¼

½

½

¾

¼

Devlopment of a Wetland Catchment Disturbance Index

½

15

Table 7. The potential impacts of catchment disturbances on the components of wetland soils: ↑ indicates an increase, ↓ indicates a decrease, → indicates almost no impact.

Catchment disturbances Urbanisation

Soils Eutrophication Salinisation ½ ½

Manufacturing and industrial

½

½

Mining Infrastructure

¼ ½

½ ½

Land clearance

½

½

Intensive animal production

½

½

Irrigated agriculture

½

½

Dryland cropping

½

½

Grazing modified pastures

½

½

Grazing natural vegetation

½

½

Plantation forestry

½

½

Production forestry

½

½

Fire

½

½

Recreation

¼

½


16

4 4.1

Development of the WCDI model The LDI as a surrogate for wetland catchment disturbance

Due to the absence of quantitative wetland catchment disturbance data, quantitative wetland catchment disturbance models cannot be constructed at this stage. Data obtained from targeted wetland catchment experiments that measure disturbance from activities in a wetland’s catchment and its impact on wetland condition is needed to fill this gap. In the absence of this data, the LDI (Section 1.2.2) has been used to provide a measure of catchment disturbance. 4.1.1

Development of the LDI

The National Framework for the Assessment of River and Wetland Health (FARWH) proposed the development of a stream Catchment Disturbance Index (CDI) incorporating the effects of land use, change in vegetation cover and infrastructure (e.g. roads, rail lines) on the likely run-off of sediments, nutrients and other contaminants to rivers and wetlands. The index incorporates the effects of large-scale non-point source impacts. The focus of the stream CDI was to provide a measure of changes caused by human activities that ultimately impact on river condition and biota (National Water Commission 2007). In developing the stream based CDI a set of land use categories were identified from the documented literature on a range of land use changes associated with changes to water quality and aquatic biota (National Water Commission 2007). The LDI is also underpinned by the effects of land use and infrastructure on wetland condition. An expert panel reviewed the categories of impacts used by the stream CDI and derived a set of impacts applicable to wetlands (Table 8). Table 8. Potential impacts of land use and infrastructure on wetland condition. Types of impacts Augmentation of the nutrient supply to a wetland Increase in salinity Release of biocides (pesticides, herbicides and fungicides) Change to the hydrological regime Augmentation of the sediment supply to a wetland Loss of native buffer vegetation Acidification of soil/water

Produced by Land Use and/or infrastructure Both Land use only Both Both Both Both Both

Land use and infrastructure categories were derived from land use mapping undertaken in Victorian between 1994-2005. Based on literature and expert panel review (panel of five wetland ecologists), individual land use and infrastructure categories were assigned a score representing their potential to contribute to each impact (Table 9). When scoring the land use impacts the assumption was made that the land use occurs in the whole catchment and that a buffer zone (of native wetland vegetation) around the wetland does not exist. The mean land use/infrastructure scores for each impact type from the wetland experts (n=5) were averaged averaged across the impact types to produce an overall score for each land use category (Table 9). The weights were derived from the average scores by scaling them to a range of 0 to 0.7 (scores were not scaled between 0 and 1 as a value of 1 would imply that the impact cannot get any worse (National Water Commission 2007).


17

Table 9. Land use categories and impacts associated with them used in the LDI/WCDI. Impact scores range from 0-6 where 0= low potential to contribute to impact and 6 = high potential to contribute to impact. Adapted from National Water Commission (2007).

Impacts on wetland condition Land use category Conservation and Natural Environments Grazing natural vegetation Production forestry (e.g. wood production/timber harvesting, oil, wildflowers, firewood) Plantation forestry Grazing modified pastures Cropping Horticulture Irrigated plantation forestry Irrigated modified pastures Irrigated cropping Irrigated horticulture Intensive animal production Manufacturing and industrial Residential/Commercial/Public services land Utilities (electricity & gas generation/storage/transmission) Transport and communication (Airports, roads, railways) Mining Waste treatment and disposal (Stormwater, landfill, sewage)


Sediment 0 1.6

Loss of buffer zone 0 2.2

Soil/water acidification 0 0.4

Mean Score 0.03 1.17

Weight 0.00 0.16

Nutrients 0 2

Salinity 0 0.6

Biocides 0 0.4

Hydrological change 0.2 1

1.6 3.4 4.2 5 5.4 4.4 4 5 5 5.8 4.6 4.2

1.4 0.8 2.8 4.6 3.8 3 4.6 5.8 5 3.8 3.6 3

1.8 4 3.8 5 4.4 3.6 4.4 5.8 5.4 5.4 4 3.2

3.2 3.6 4 4.8 4 4.8 5.2 6 5.6 4.4 5.4 5.6

3.2 3.4 3.2 4.4 3.8 4 3.8 5 4.4 4.8 4.2 4.2

3 3.4 5 5 4.4 4 5.2 5 4.6 4.6 5.6 5.6

1 1.6 1.8 3 2.8 2.8 2.8 3.2 2.6 3 4.6 3.8

2.17 2.89 3.54 4.54 4.09 3.80 4.29 5.11 4.66 4.54 4.57 4.23

0.30 0.40 0.49 0.62 0.56 0.52 0.59 0.70 0.64 0.62 0.63 0.58

1.6

n/a

1.4

3.8

1.8

4.4

2.2

2.53

0.35

2.4 2.8

n/a 3.4

1.8 0.8

4.4 5.6

3.6 5.4

4.4 4.8

2.2 5.2

3.13 4.00

0.43 0.55

6

2.8

2.6

5.8

4

3

4

4.03

0.55

18

The LDI/WCDI is calculated by summing the value of each land use and infrastructure category after the weighting (Table 9) has been applied and can be represented by the following formula:

LDI/WCDI = 1 – ((F1 * w1) + (F2 * w2)…) Where LDI = Landscape Disturbance Index, WCDI = Wetland Catchment Disturbance Index, F1 = fraction of the catchment that is category 1 land use, w1 = weight associated with land use 1, etc.)

Range standardisation and condition bands

The LDI/WCDI scores range is presently 0.3 to 1 with increments of 0.07. The CDI has five condition categories assigned to the CDI scores. The LDI/WCDI uses the same category descriptors (Table 10). Table 10. Condition categories and linguistic descriptors for the LDI/WCDI adapted from the CDI. LDI score range 0.86 - 1 0.72 – 0.86 0.58 – 0.72 0.44 – 0.58 0.3 – 0.44

LDI Descriptor Largely unmodified Slightly modified Moderately modified Substantially modified Severely modified

Improvements to the LDI/WCDI

Currently the LDI/WCDI does not take into account the ameliorating effect of catchment disturbance by the buffer zone nor the wetland catchment modifiers (climate, wetland catchment geology/soils and wetland catchment topography). In the next iteration of the LDI/WCDI, weightings will be applied to the modifiers and a variable will be added for the buffer zone, resulting in a more realistic output. Further research is needed to understand uncertainties—their sources and their potential reducibility, and to incorporate the uncertainties in the LDI/WCDI model.


19

5

Trialling and testing the WCDI

Trial areas for the development of catchment disturbance models were originally proposed for the Wimmera and North Central Catchment Management regions because of the availability of detailed quantitative physico-chemical, environmental and biotic datasets as well as wetland condition data. Due to project time constraints, only data from the Wimmera CMA region was used. IWC assessment data is available for the for the Wimmera region from 27 wetlands. Preliminary trials of the LDI were done for 27 sites in the Wimmera region as part of the selection of testing sites for the Victorian IWC project (Figure 3). The initial purpose of the LDI was to select wetland sites along a condition gradient. The LDI scores can also be used to make comparisons with the IWC scores and other available data for testing and validation purposes.

Figure 3. Location of wetlands where the LDI was applied.

5.1

Datasets

Land use/infrastructure is the principal data used in the LDI/WCDI. The Department of Sustainability and Environment (DSE) maintain remote-sensed land-use data for Victoria. The data for the index was restricted to those that show changes within surface water wetlands. The interactions of groundwater fed wetlands are complex and requires further research. Additional catchment modifiers of climate region, soil type, native vegetation buffer and catchment topography are to be included in future iterations of the model, hence have been scoped. Wetland features are also to be included in the model building process and will include but not be limited to: wetland size and wetland depth. Current knowledge of wetland catchment processes and wetland types indicate that these variables have important influences on how land use activities will affect wetland condition. All of the datasets, with the exception of climate change, are available from the Corporate Geospatial Data Library (CGDL) (Table 11).


20

Table 11. Sources of data used in developing the WCDI. Note that Land use is currently the only dataset used in the WCDI (Section 4). Other datasets will be used in future iterations of the WCDI. Input data Land use

Climate region Soil type

Native vegetation buffer Catchment relief

Wetland size

Wetland depth

5.1.1

Source Department of Primary Industries (DPI) CGDL Bureau of Meteorology

Coverage Victoria

Data type Polygon Land use categories

Data name Land use of Victoria at 1:25 000

Australia

Polygon Climate classes

Department of Primary Industries (DPI) CGDL Department of Primary Industries (DPI) CGDL Department of Primary Industries (DPI) CGDL Department of Sustainability and Environment (DSE) CGDL Department of Sustainability and Environment (DSE) CGDL

Victoria

Polygon Soil descriptions

Victoria

Satellite photo

Modified Köppen classification scheme LSYS250 Land Systems of Victoria at 1:250 000 Vic map imagery 2001 SPOT

Victoria

Polygon Relative relief classes

Victoria

Polygon Area of wetland in hectares

Victoria

Polygon Corrick & Norman (1980) wetland category classification

LSYS250 Land Systems of Victoria at 1:250 000 WETLAND_1994 1965-1994 1:25 000 WETLAND_1994 1965-1994 1:25 000

Land use data

A detailed spatial land use dataset (1:25,000 scale) of Victoria is divided into eight regions (Gippsland, Lower Goulburn Broken, Upper Goulburn Broken, Lower Murray, North Central, North East, Port Phillip and South West). The data were sourced under different projects from 1970-2005 and are based on four main sources of information: (i) resource data sets of Victoria held in the Corporate Geospatial Data Library, DSE, (ii) satellite imagery, (iii) regional datasets, and (iv) field information. Infrastructure data for the stream based CDI was in the form of an infrastructure layer consisting of seven categories (i.e. main sealed road, other sealed road, railway, unsealed road, vehicle track, utilities, walking track). DSE maintains spatial roads dataset (Road25), which has similar categories to those used for the stream CDI with the exception that the dataset attributes did not allow the area of each infrastructure type (e.g. sealed road, unsealed road, walking track etc.) to be calculated. Hence, the land use classes ‘Utilities’ and ‘Transport and Communication’ were used. 5.1.2

Climate data

Climate data was sourced from the Bureau of Meteorology is a modification of the widely accepted Köppen classification scheme. The modified Köppen classification recognises six principal groups of world climates that correspond with six principal vegetation groups. These six climatic groups are described as equatorial, tropical, subtropical, desert, grassland and temperate (Stern et al. 2000). Each of the climatic groups is further divided into sub-divisions based upon differences in the seasonal distribution of temperature and precipitation (Stern et al. 2000). The classification is derived from 0.025 x 0.025 degree resolution mean rainfall, mean maximum temperature and mean minimum temperature gridded data. All means are based on standard 30-year climatology (1961-1990). Across Victoria there are five sub-divisions, four within the temperate climatic group (no dry season with hot, warm or mild Development of a Wetland Catchment Disturbance Index

21

summer and distinctly dry and warm summer) and one sub-division within the grassland group (warm and persistently dry). 5.1.3

Soil data

Soil data for the model were derived from the Department of Primary Industries (DPI) Land Systems of Victoria spatial dataset. The dataset provides information on soil type (e.g. clays, sands, calcareous earths). 5.1.4

Native vegetation buffer data

Satellite imagery provides information on the vegetation buffer of each wetland including the vegetation type and width and extent of the buffer. 5.1.5

Wetland catchment topography

Catchment topography or slope gives an indication of how incised a catchment is, a characteristic that influences sediment delivery in a wetland catchment. Catchment relief data for the model was sourced from the Land Systems of Victoria spatial dataset. The landform descriptions include the relative relief classes of plain (300m). 5.1.6

Wetland size and depth data

The size of individual mapped wetlands greater than one hectare has been determined in Victoria. Depth has been used to characterize wetland types used in Corrick and Norman (1980) and Corrick (1982). The data is available from the WETLAND_1994 spatial dataset for all mapped wetlands in Victoria. 5.1.7

Data from other jurisdictions

As the WCDI is based on land use categories used in Victoria, it is best suited for use in this state. Land use datasets from other jurisdictions are required to extend the model’s scope. Future development of the WCDI should include an assessment of available datasets in these regions.

5.2

Identifying wetland catchments

Wetland catchment areas for most of Victoria are not mapped. The exception is the Wimmera region. An arbitrary catchment boundary, however, can be applied to each wetland site as a surrogate to catchment area (Figure 4). The Victorian IWC defines the area of adjacent land in which to assess land use for the ‘wetland catchment’ assessment at 250 m. The surrogate ‘catchment’ boundary was assigned as a 250 m boundary for consistency with the IWC method. A shape file of a 250 m ‘catchment boundary’ was generated for the WETLAND_1994 spatial dataset and also for the WETLAND_2004 (Wimmera) dataset. Testing the effect of using a 250 m ‘catchment’ boundary compared to the mapped wetland catchment was undertaken at sites in the Wimmera during the testing phase of the IWC project (Department of Sustainability and Environment unpublished).


22

Figure 4. Example of mapped wetland catchment boundaries and surrogate ‘catchment’ boundary assigned to 250m for selected wetlands in the Wimmera region. The white areas indicate there are no wetlands and wetland catchments.

5.3

Preliminary results using the WCDI in the Wimmera region of Victoria

The LDI/WCDI scores range is presently 0.3 to 1 with increments of 0.07. The stream based CDI has five condition categories assigned to the CDI scores. The LDI/WCDI uses the same linguistic descriptors (Table 10). Preliminary LDI/WCDI scores for 27 wetlands in the Wimmera region were calculated for the mapped wetland catchment and the surrogate ‘catchment’ boundary (Table 12). Overall there are some minor differences in scores when comparing calculations for the mapped catchment and the surrogate 250 m catchment boundaries. Three of the four deep marsh wetland sites scored a higher LDI when using the surrogate catchment boundary compared to the actual wetland catchment (Table 12 – cells coloured yellow). The catchment areas of the three sites are larger than the surrogate catchment boundary but only by 2-20%. The immediate surrounding land use (i.e. within 250 m) at these three deep marsh sites is classified as ‘conservation and natural environments’ which contributes to a high LDI/WCDI score whereas the land use in the larger catchment area consists of cropping and grazing land use at a higher fraction than the conservation land use categories. This highlights the importance of including additional catchment and wetland modifier data into a model to account for these differences when using mapped wetland catchments.


23

Table 12. Preliminary Landscape Disturbance Index (LDI) scores for 27 wetland sites in the Wimmera region of Victoria. Wetland Identifier 7223519043 7223606002 7124144230 7124338136 7123264972 7124313086 7124318058 7124313055 7123238974 7123283008 7123399921 7224710271 7223671945 7224447130 7223673020 7224521111 7223738993 7223742000 7223670999 7123313043 7223662012 7224722135 7123418977 7124432154 7223650020 7123158943 7223663933

Wetland Category Open water Shallow marsh Open water Shallow marsh Perm saline Perm saline Perm saline Perm saline Shallow marsh Open water Deep marsh Semi saline Open water Open water Semi saline Semi saline Meadow Meadow Semi saline Open water Semi saline Semi saline Deep marsh Deep marsh Semi saline Deep marsh Semi saline

Area (ha)

LDI score (250m)

23.68

0.65

3.86

0.57

90.27

0.62

Cane grass Shallow (