Girt by dirt: The ecology of spring ecosystems in north-eastern Australia

Abstract

Freshwater springs have been the focus of human civilisation for thousands of years as they provide a consistent and easily accessible source of water. Similarly, springs are important to flora and fauna and are known biological hotspots. Yet, despite their importance as a water resource, research into spring ecosystems is a relatively recent activity with increased interest in Australia only since the late 1980s. This interest was triggered by the many new species being identified, the high levels of biodiversity that Great Artesian Basin (GAB) spring wetlands contain and the realisation that many springs had already become extinct due to water extraction. Therefore, a better understanding of spring ecology and the threatening processes that are likely to affect their functioning is essential to their sustainable management.Grouping (or classifying) large areas of the landscape is a common first step in biogeographical studies. Classification can identify similarities in the types of ecosystems (e.g. types of wetlands) and therefore becomes helpful to research and management as it can be used to infer ecosystem processes and attributes when detailed knowledge is incomplete. Broad-scale classifications that are potentially relevant to Australian spring wetlands include those based on landscape and climatic characteristics (e.g. the Interim Biogeographic Regionalisation of Australia - IBRA), the natural spatial clumping of spring wetlands and the separation of GAB discharge springs from other GAB and non-GAB springs based on their hydroperiod (e.g. permanent and non-permanent). Comparisons of spring aquatic invertebrates from groups based on these classifications have to some extent validated the use of these classifications for investigating spring wetlands.Spring research in Australia has also focused on those situated in arid to semi-arid landscapes (especially those of the GAB) where there is little to no opportunity for obligate aquatic fauna to disperse. This focus combined with the many genetic studies used in species identifications have supported dispersal as a dominant role in limiting the structure of spring biological communities. Ecological theory suggests that while dispersal provides opportunities for colonisation; habitat quality and quantity are important in determining the establishment of biological populations and communities. Water is the dominant habitat variable characterising any wetland and groundwater is the prevailing source of water constraining the biological structure and function of spring wetlands, but many other habitat characteristics can affect biota (i.e. habitat templets). Multiple case studies have been provided, that support the influence of habitat characteristics, including relationships between biological communities and water temperature, water quality characteristics and wetland size.Some springs are considered evolutionary refugia which is the basis for their recognition as biological hotspots with high levels of endemic species. This has assumed that springs provide wetted habitats that have persisted for thousands of years with little available information in support. The geochemistry and microfossils of sediment profiles from two spring wetlands presented in the thesis reinforce that distinct changes occur in the landscape and climates over the long-term timescales in which each spring has existed. While ecosystem change in all springs is inevitable some spring complexes, such as GAB discharge springs have potentially persisted as a wetland for many thousands of years. However, the addition of anthropogenic pressures has in the last few hundred years generated changes that have caused catastrophic consequences for spring ecosystems and the information from the sediment profiles supports this.Under future climate change, environmental stressors such as higher temperatures and lower rainfall are likely to be highly damaging to surface water ecosystems. Groundwater ecosystems such as springs are relatively immune to these changes and some may continue to provide stable hydrologic refugia as they have done in the past. However, anthropogenic threats will continue to ultimately result in consequences to the spring biota that are not easily reversible. It is shown here that the capability to resist anthropogenic change and maintain spring biological and functioning will rely on successful management of the threats caused by changing stressors.This thesis contributes to the ecological understanding of spring ecosystems in north-eastern Australia, in particular the relationships between habitat characteristics and the aquatic biota. The outcomes of the thesis are to highlight that the anthropogenic influences (pressures) can change these natural stressors and threaten significant consequences to spring biota. Importantly it provides a method for framing a ‘cause and effect’ conceptual understanding of spring ecosystems (pressure – stressor – ecological response) that is beneficial to all scientific monitoring and research. A risk assessment using this PSR framework has been developed for identifying relevant threats to wetlands that can guide monitoring, assessment and controls for successful adaptive monitoring and management.