Table of Contents
List of figures
List of Tables
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Acknowledgements
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There are many people that need to be thanked for their support and help over the last year. Firstly I would like to thank Dr Melissa Neave and Dr Eleanor Bruce, my two supervisors, for all of the support and guidance they provided.
I would like to thank Lake Macquarie City Council for providing the grant money that was used to cover research costs. I would also like to thank in particular Mark for the assistance and information he provided.
Graham Lloyd was also a great help to me in assisting me in conducting the fieldwork.
There were many other people that helped me along the way by supporting me, providing me with knowledge and assisting me in the research process. Thanks to everyone who assisted me, I greatly appreciated it.
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Abstract
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Abstract
HHuman impact through development in coastal areas has lead to changes to estuaries and the life they support. Changes in water quality and the trends that occur and in seagrass communities are influenced by activities in the catchment and are related to one another.
This project involves three main objectives to study variability in water quality with time, variability in seagrass and the relationship between them. Lake Macquarie was chosen as the study site as it was believed to have a seagrass population and water quality characteristics of many estuaries in NSW and is facing pressure form further development in the catchment.
In order to manage seagrass communities effectively knowledge of their functioning and relationship with the water they live in is necessary. The information gained from this project can be used for assessing if changes in water quality (resulting from activities in the catchment) will have an influence seagrass growth and thus whether management of seagrass communities should be based on catchment management.
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Chapter 1: Introduction
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Chapter 1
Introduction
This sThis study aims to improve the success of seagrass management programs by expanding knowledge on the relationship between certain water quality parameters and seagrass growth and development. This aim is achieved through an investigation of water quality trends and associated changes in seagrass distributions in Lake Macquarie, NSW.
1.1 Background
As populations expand in coastal environments seagrass communities are increasingly threatened by anthropogenic impacts (Hauxwell et al. 2003, Short and Wyllie-Echeverria 1996, Walker and McComb 1992). In Australia, for example, numerous seagrass beds have been either deliberately cleared or inadvertently destroyed over the last century (Larkum et al. 1989). Despite the acknowledged importance of seagrass communities to the marine environment, however, there are still numerous aspects of seagrass decline that are not well understood.
In the coastal estuary of Lake Macquarie, NSW, seagrasses have been identified as being important for the healthy functioning of the ecosystem. Significant developments in the catchment of Lake Macquarie over the last century have negatively impacted on the quality of the water body and the distribution of its seagrass populations (AWACS 1995). To date, however, the impact of human activities on the lake, and the spatial and temporal patterns in water quality and seagrass populations have not been extensively or reliably investigated. Thus, the
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Chapter 1: Introduction
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purpose of this study is to examine water quality and seagrass trends in Lake Macquarie and with a view to identifying whether there are any relationships between the two.
1.2 Project Objectives
The three objectives of this study are:
- to investigate temporal variations in water quality in Lake Macquarie for the period 1983 to 2001;
- to identify changes in seagrass distributions in Lake Macquarie for the period 1983 to 2001; and
- to evaluate the relationship between seagrass and water quality variations in Lake Macquarie for the period 1983 to 2001.
1.3 Water Quality and Seagrass
Seagrasses are aquatic angiosperms which predominate in nutrient-poor coastal waters (McMahon and Walker 1998). There are four species of seagrass present in Lake Macquarie; Zostera capricorni, Halophila ovalis, Posidonia australis and Rupia sp (King 1986). However, within this study only sites growing Zostera were investigated.
Several factors in Lake Macquarie contribute to the health of local seagrass populations including; water quality, boat mooring, removal by residents, and invasions by pest species (AWACS 1995). Within this study, however, the focus is on the link between water quality and seagrass distributions.
The quality of water in Lake Macquarie is important both in terms of supporting a healthy ecosystem and for providing recreational and aesthetic benefits for human users (LMCC 2000). In terms of seagrass growth, the most significant water quality parameters are those that influence light penetration and aquatic nutrient levels. Nutrient levels are important because they are directly required for seagrass growth and because they affect the growth of algae in the water which has a subsequent influence on light penetration. As estuarine water quality is known to vary spatially, temporally and seasonally, this study will examine water quality in Lake Macquarie over these scales.
1.4 Study Area Description
Lake Macquarie is a natural estuarine lagoon situated in the lower Hunter Valley, approximately 90 km north of Sydney and close to the city of Newcastle (Figure 1). The current population of Lake Macquarie City is around 190,000 but this is expected to increase in the near future with associated developments predicted to occur in sensitive catchment areas (Lifestyle 2020). These developments have the potential to negatively impact on the functioning of aquatic ecosystems within the Lake.
Figure 1: The position of Lake Macquarie on the NSW coast.Lake Macquarie is classified as a barrier estuary, which is typical of much of the south-eastern coastline of Australia (King 1986). Barrier estuaries are characterised by narrow, elongated entrance channels with broad tidal and backbarrier sand flats (King 1986). Behind the entrance, barrier estuarine lakes comprise shallow, low-energy environments with margins that are often densely covered by seagrasses.
With a surface area of 110 km2, Lake Macquarie is the largest coastal lake in eastern Australia. The water body covers a distance of 22 km in a north-south direction with a maximum width of 9 km (King 1986) and a foreshore length of approximately 170 km. The average depth of the numerous bays that surround the lake is 8 m and the approximate volume of the lake is 880,000 ML (AWACS 1995).
In its natural condition, Lake Macquarie is divided into North and South sections by protruding headlands and has its entrance channel situated on the eastern coastline at Swansea. It is estimated that only 1% of lake volume is exchanged on each tidal cycle and that the total volume of the lake is exchanged approximately two to three times a year (WBM 1987). As the lake has an average tidal range of only 6 mm (King 1986) wind-induced currents are more important in producing water level changes than tides.
The 605 km2 catchment of Lake Macquarie falls within the councils of Lake Macquarie City and Wyong Shire (Woodlots and Wetlands 1999). In a typical year, the catchment sheds approximately 256,000 ML of water as runoff, which is approximately equal to 30% of the lakes volume. This water is received from 19 different sub-catchments with varying landuses including, forest, extensive residential settlements and industrial developments. Power stations, a coal smelter, mining, and rapidly expanding light industries all occur within the catchment.
Lake Macquaire provides a valuable ecological resource for the biota of coastal NSW (Woodlots and Wetlands 1999). But the lake also serves a variety of commercial and recreational uses for the community, having approximately 28 boat launching ramps, 16 sailing clubs, more than 1900 registered moorings, seven regional jetties and over 1200 private jetties (AWACS 1995).
1.5 Study sites
To assess the quality of water and seagrass communities in Lake Macquarie, four study sites were selected. These sites were positioned at the northern end of the lake in a highly urbanised and industrialized region where numerous recreational activities are currently undertaken and where several seagrass communities have been observed. The four sites, hereafter known as Fennel Bay, Marmong Point, Cockle Bay and Cockle Creek (Figure 2), were selected based on a number of factors including; their appropriateness for the aims of the research, the availability of water quality and seagrass data, the surrounding landuses of each site, the proximity to other sites, and previous work done in the area. The Fennel Bay site is positioned within an enclosed bay that is surrounded by urban development, Cockle Creek represents a site in the lake adjacent to a major tributary that drains the catchment and is surrounded by urban, agricultural and industrial landuses and to a lesser extent forests, while Marmong Point and Cockle Bay represent two sites in the main body of the lake.
Figure 2: Lake Macquarie and the location of the four study sites.1.6 Thesis Structure
This thesis is organised as follows: Chapter 2 presents a review of previous work undertaken in the fields of water quality analyses and seagrasses. Chapter 3 describes the methods adopted in this study while the results of the field work are presented in Chapter 4. The results are then interpreted and discussed in Chapter 5. Finally, the thesis is concluded with a summary of the major findings of the study in Chapter 6.
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Chapter 2: Water quality and Seagrass Distributions
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Chapter 2
Water Quality and Seagrass Distributions
The basic objective of this study is to investigate spatial and temporal trends in Lake Macquarie’s water quality and seagrass communities. This chapter explores the current literature on this topic, beginning with an introduction to the major water quality parameters investigated in this study, and including an examination of observed spatial and temporal trends in these parameters. The focus then shifts to an examination of the literature on seagrasses and the factors that impact upon them. The chapter then concludes with a survey of the current literature on links between water quality and seagrass health.
2.1 Water Quality
This study focuses primarily on conditions that are likely to alter seagrass distributions by affecting the availability of light and nutrients in aquatic ecosystems. Patterns and trends that occur in water quality are also discussed. As there are numerous physical, chemical and biological indicators available to assess the health of a water body it is important to select parameters appropriate to the research objective.
The following sections summarise the indicators used in this study to evaluate the quality of water in Lake Macquarie. These parameters will be assessed to determine how they change over the period of investigation.
2.2.1 Nutrients
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Chapter 2: Water quality and Seagrass Distributions
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Nutrients are conveyed to coastal waterways from terrestrial, atmospheric and oceanic sources and are often enhanced by human activities (McClelland and Valiela 1998). Major anthropogenic sources of nutrients often enter coastal waterways from non-point sources and include runoff from agricultural areas (e.g. fertilisers), urban stormwater, urban wastewater, eroded soils and aquaculture (Costanzo et al. 2003). As they can be more readily monitored and regulated, point sources of nutrients are generally less important than diffuse (non-point) sources but can still have significant negative impacts on coastal waterways (Radke et al. 2003).
Excessive nutrient loads can lead to eutrophication in coastal waterways. The general pattern of change in such situations involves a shift from large macrophytes (including seagrasses) towards fast-growing macroalgae and phytoplankton (including harmful species that occur in blooms). High loadings of organic matter also promote oxygen consumption through decomposition and can potentially lead to events of low oxygen concentration that harm benthic invertebrates, fish, and other organisms (Radke et al. 2003).
2.2.2 Oxygen
Reduction in dissolved oxygen concentrations is amongst the most important consequences of eutrophication on aquatic organisms. Dissolved oxygen status influences the uptake or release of nutrients from sediment. When oxygen is depleted, the nitrification pathway is blocked and denitrification efficiencies may be lowered. As a consequence, more nutrients (e.g. nitrogen and phosphorous) are released from the sediment in bio-available forms. These nutrients help to sustain algal blooms and therefore continue to supply organic matter to the sediments (Hauxwell et al. 2003). Low bottom water oxygen concern and ammonia gas, which can be harmful to benthic organisms and fish. Even short-lived anoxic (oxygen deficient) events can cause the mass mortality of fish and benthic organisms.
2.2.3 Chlorophyll a
Chlorophyll a concentrations can be used to indicate phytoplankton abundance and biomass in coastal and estuarine waters. They can be an effective measure of trophic status, are potential indicators of maximum photosynthetic rate and are a commonly used measure of water quality. High levels often indicate poor water quality and low levels often suggest good conditions. However, elevated chlorophyll a concentrations do not automatically indicate a degraded system; rather, it is the persistence of elevated levels that is a problem.
It is natural for chlorophyll a levels to fluctuate over time. Chlorophyll a concentrations are often higher after rainfall, particularly if the rain has flushed nutrients into the water. Higher chlorophyll levels are also common during the summer months when water temperatures and light levels are high because these conditions lead to greater phytoplankton numbers. Elevated concentrations of chlorophyll a can reflect an increase in nutrient loads and increasing trends can indicate eutrophication of aquatic ecosystems (Radke et al. 2003)
2.2.4 Light Parameters
Turbidity is a measure of water clarity. It is an optical property that expresses the degree to which light is scattered and absorbed by molecules and particles (Radke et al. 2003). Turbidity results from soluble coloured organic compounds and suspended particulate matter in the water column. Light qualities of the water can be measured using a Secchi disk, through the calculation of Total Suspended Solids (TSS) or by measuring the percentage light transmission
Increased turbidity and lowered light transmission can significantly change an ecosystem. The most obvious effect of increased turbidity is a reduction in available light for photosynthesis, which limits the depth to which seagrasses can grow (Abal and Dennison 1996). In addition, turbidity caused by suspended sediment can smother benthic organisms and aquatic habitats such as seagrass communities. Suspended sediment may also transport contaminants (particulate nutrients, metals and other potential toxicants), promote the growth of pathogens and waterborne diseases, impede the detection of marine pests and lead to dissolved oxygen depletion in the water column if it is caused by particulate organic matter.