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PART I
Processes in Aquatic Ecosystems
Ecologists study the interactions of living organisms with their physical, chemical and biological environments. These interactions are complex, dynamic and occur across multiple scales of space and time. To help describe, understand and predict these complex interactions, ecologists use various ways to classify ecological systems. For example, areas can be classified into different habitats according to the species or assemblages that live there. In turn, the interacting assemblages of organisms in these different habitats are defined as ecological communities. The species in these communities and their habitats, along with crucial ecological processes such as the transfer of energy and nutrients, are interwoven to form ecosystems. Although we talk of aquatic and terrestrial ecosystems, in reality these are tightly linked as well. Processes occurring at interfaces, such as the land-water edge, are vital to sustaining the ecosystems on either side, and these interfaces or ecotones are often âhot-spotsâ of chemical and biological activity.
Humans depend entirely on the natural ecosystems around them. The ecological processes that integrate energy, nutrients and water flowing through freshÂwater, marine and terrestrial ecosystems provide humans with essential ecosystem goods and services. Goods include oxygen, fresh water and food. Services include assimilation of nutrients and carbon dioxide, provision of recreational opportunities and aesthetic pleasure (e.g. the beauty of a lake) and protection from extremes of weather. Underpinning the sustained provision of these goods and services are multiple, interacting ecological processes. Ecological processes also govern the important characteristics of all habitats, communities and ecosystems. Consequently, they provide a useful framework to organize chapters in this first part of the book.
Physical processes provide and sustain the structure of aquatic habitats and influence how light and solar energy enter aquatic environments, affecting factors such as water density and photosynthesis. In turn, physical processes govern many chemical processes such as the cycling of dissolved gases and nutrients in the water column. Together, both types of processes provide the habitats and other requirements of the organisms that mediate biological processes such as energy transfer between producers, consumers and decomposers.
Part I of this book begins by reviewing the diversity of inland waters in Australia, emphasizing the importance of variability in water regime and the significance of linkages across multiple scales, from molecules to the global hydrological cycle (Chapter 1). As the flow of water has a major effect on physical, chemical and biological processes in aquatic ecosystems, we have split our treatment of processes into standing (lentic) waters (Chapters 2â4) and running (lotic) waters (Chapters 5â7) to illustrate ecological parallels and contrasts. The section concludes with an integrative chapter about the main physical, chemical and biological processes in groundwaters as well as aspects of their management (Chapter 8). In Part II, we explore how human activities have affected ecological processes in Australian aquatic ecosystems and how we can best use our understanding of ecological processes to manage, conserve and, where necessary, restore them.
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CHAPTER 1
Australian Waters: Diverse, Variable and Valuable
1.1 The Challenge for Aquatic Ecologists
Aquatic ecologists study how organisms in inland waters interact with their environment and each other. Such studies often explore how human activities modify aquatic ecological processes and the quality and quantity of fresh water. Not only do the findings of these studies help water managers, they also add to our basic knowledge of ecology and environmental science. This book is about that basic knowledge and how we can use it to better manage and protect our fresh waters.
Fresh water is essential for all life. Therefore, we must protect and manage aquatic ecosystems that supply fresh water. Aquatic ecosystems provide essential ecosystem services (Daily 1997) for humans, ranging from flood control and water purification through to cultural values and recreational benefits (Millennium Ecosystem Assessment 2005). These services are often overlooked because many of them are subtle (e.g. the role of groundwater in supporting many terrestrial plant communities, Section 8.7) but, without them, humans and other dependent organisms could not survive. Most ecosystem services are mediated by ecological processes. Aquatic ecologists investigate how these processes work and how we can sustain them in inland surface waters and groundwaters.
Every day, the media report concerns about the quantity and quality of the country's water resources. Growing anxiety about the effects of climate change and increasing human population densities on finite water resources is not restricted to Australia; worldwide, scientists and managers grapple with unprecedented environmental pressures, burgeoning urbanization, agricultural problems and intensifying threats to biodiversity. Technological advances have helped resolve some of these issues but, ironically, have also exacerbated many of the multiple stressors on aquatic ecosystems such as salinization, eutrophication, sedimentation, acidification and other forms of pollution.
To address these problems, aquatic ecologists need an integrated knowledge of a wide variety of different disciplines such as physics, chemistry, microbiology, hydrology and geomorphology as well as ecology, biology and genetics, along with hybrid fields such as ecohydrology and ecohydraulics (Rice et al. 2010). This broader discipline, encompassing the physical, chemical and biological sciences of aquatic ecosystems, is called limnology. Our book synthesizes threads of these diverse sciences, focusing on interactions among physical, chemical and biological processes in surface and groundwater ecology. We then outline ways in which this scientific information can be used to tackle problems such as erosion, salinization, eutrophication and urbanization in Australian inland waters. These problems challenge aquatic ecologists worldwide, but across most of Australia their solutions are complicated by the continent's great natural variability in water regimes and the shortage of long-term empirical data for nearly all our aquatic ecosystems.
This is an exciting time to be an aquatic ecologist. Much fundamental science remains to be done, important and complex management issues abound and Australian inland waters are, for the most part, beautiful places to work. We have plenty to learn and do.
1.2 Defining Some Common Terms
Before going further, let's define a few terms used repeatedly in this book. In the previous section, we referred to aquatic ecologists. Although âaquaticâ means âassociated with waterâ, this book excludes estuarine and marine ecosystems and focuses on the ecology of fresh and saline inland waters, both temporary and permanent as well as groundwaters. Throughout the text, we use âfreshâ to specifically mean non-saline water, and âaquaticâ as a general adjective for all inland waters. All inland waters (encompassing everything from the deepest permanent fresh lake to the most fleeting saline pool) are collectively referred to as âinland watersâ, âwaterbodiesâ, âwatersâ or âaquatic ecosystemsâ, and we use the terms interchangeably.
Although there are numerous definitions that seek to capture the diversity of inland waterbody types, we prefer this one that also explicitly recognizes the implications of water regime (Section 1.4) for the biota and ecological processes:
This functional definition, modified from the widely used one in the Ramsar Convention on Wetlands (Section 12.3), encompasses physical featu...
