Multiple Stressors in River Ecosystems

Status, Impacts and Prospects for the Future

Sergi Sabater, Arturo Elosegi, Ralf Ludwig

• Publisher: Elsevier
• Year: 2018
• ISBN:
  9780128118009
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

Multiple Stressors in River Ecosystems: Status, Impacts and Prospects for the Future provides a comprehensive and current overview on the topic as written by leading river scientists who discuss the relevance of co-occurring stressors for river ecosystems. River ecosystems are subject to multiple stressors that threaten their ecological status and the ecosystem services they provide. This book updates the reader's knowledge on the response and management of river ecosystems to multi-stress situations occurring under global change. Detailing the risk for biodiversity and functioning in a case-study approach, it provides insight into methodological issues, also including the socioeconomic implications.

• Presents a case study approach and geographic description on the relevance of multiple stressors on river ecosystems in different biomes
• Gives a uniquely integrated perspective on different stressors, including their interactions and joint effects, as opposed to the traditional one-by-one approach
• Compiles state-of-the-art methods and technologies in monitoring, modeling and analyzing river ecosystems under multiple stress conditions

Chapter 1

Defining Multiple Stressor Implications

Sergi Sabater⁎^,†; Arturo Elosegi^‡; Ralf Ludwig^{§ ⁎} IEA (UdG), Girona, Spain
^† Catalan Institute for Water Research (ICRA), Girona, Spain
^‡ University of the Basque Country (UPV/EHU), Bilbao, Spain
^§ Ludwig Maximilians Universitaet Muenchen (LMU), Munich, Germany

Abstract

Stressors rarely occur alone in the environment. Particularly in river ecosystems, many stressors often act jointly and produce complex responses. A realistic appraisal positions us in the necessary joint analysis of natural and human-driven stressors. In this chapter, we aim to define what a stressor is, how it affects the receptors, and the multiple ways in which stressors interact. We emphasize the existing literature analyses of the effects of multiple stressors, as well as the outcomes most commonly found. Multiple stressors can affect biodiversity and the functioning of river ecosystems, but also the goods and services that societies derive from rivers. Stressors differ in nature and need to be considered hierarchically, as they may differ in their associated energy as well as in their frequency of occurrence. Direct and indirect feedback between stressor effects result in interactions that range from synergistic to antagonistic and may produce ecological surprises. Ecosystems differ in their resistance and resilience to stressors, and they can show thresholds beyond which critical shifts occur between ecosystem states.

Keywords

Stressor; Stress; Receptor; Effect

Acknowledgments

This work has been supported by the European Community 7th Framework Programme Funding under Grant agreement no. 603629-ENV-2013-6.2.1-GLOBAQUA.

1.1 Global Environmental Change: A Source of Stress

The term Anthropocene was coined by Crutzen (2006) to name the current epoch in the Earth's history, in which a global environmental change caused by humans is affecting the sedimentary records on a planetary scale. This term responds to the modern manner of understanding humanity's position within the ecosystems, instead of considering them as strange and disruptive elements to nature. As a matter of fact the present state of the biosphere cannot be understood without human fingerprints; pristine ecosystems, if they still exist, are increasingly rare, and the actions of humans reach the most remote places on Earth. Global environmental change is general and affects both ecosystems and people.

As stated by Margalef (1997), humankind produces an “acceleration in the use of power and the aggravation of many ecological problems to the global scale” by using exosomatic energy derived from fossil sources. Effects include land use transformations and climate change. The melting of ice caps and the drowning of Pacific atolls as the sea level rises are among the vast evidence of shifting climate regimes throughout the planet. The transformation of land from forest to agricultural fields and to urban dwellings is also a relevant aspect of global environmental change. Satellite images have shown than in the last 30 years, over 170.000 km² have been converted from aquatic to terrestrial areas as wetlands were drained, whereas an additional 115.000 km² have followed the reverse path as land was drowned by reservoirs (Donchyts et al., 2016). Approximately 40% of the Earth's surface is currently occupied by croplands and pastures (Foley et al., 2005). The use of phosphorus and nitrogen fertilizers has increased worldwide two- and sevenfold, respectively, while the area of irrigated cropland has doubled during the last 40 years (Tilman et al., 2001). The steady rise in human population, the development of global economies, and the migration of people from rural to urban areas is increasing the demand for food and transportation, as well as the intensity of alterations of urban ecosystems (Grimm et al., 2008). These global demands exert strong pressure on water resources, with nearly 15% (40,000 km³ year^{− 1}) of the world's total runoff is currently derived for hydropower, flood control, and water supply (Oki and Kanae, 2006). Thus global environmental change is deeply transforming biogeochemical cycles, such as that of carbon, nitrogen, or water.

Predictions for climate change are that air temperature and extreme weather events will increase, while spatial patterns in precipitation and runoff will also change (Milly et al., 2005) (Chapter 2). The Intergovernmental Panel on Climate Change (IPCC) predicts continued increases in greenhouse gases and a push of global temperatures by 2–4.5°C in the next 50 years (Stocker, 2014). Annual average river runoff might increase by 10%–40% at higher latitudes and decrease by 10%–30% over some dry regions. This indeed will affect river flow, with many wet systems becoming even wetter, whereas in drier areas permanent rivers may become intermittent as intermittent ones become ephemeral (Greve et al., 2014). Thus climate change will likely increase the frequency of floods and droughts (Chapter 6), which will in turn affect river geomorphology and habitat availability, and increase water temperature, as well as the concentration of sediments and nutrients (Sabater and Tockner, 2010; Chapter 16). River biodiversity will also suffer due to these changes, especially as a consequence of five major processes, namely the exploitation of water resources, pollution, the modification of flow regimes, the degradation of river habitats (Chapter 4), and the spread of invasive species (Dudgeon et al., 2006; Chapter 3), which could all be considered major stressors. These processes will have detrimental consequences for humans as well, who depend on goods and services provided by natural ecosystems (Kundzewicz et al., 2008; Chapters 17 to 19).

1.2 Stress, Stressor, Receptor, and Effect: Context and Evolution of the Terms

Before analyzing the effects of environmental change on ecosystems and on the associated human societies (socioecological systems), some key concepts should be formulated. Although the word stressor has been sometimes used as synonym of disturbance, the latter is a broader term with a long tradition in ecology (Pickett and White, 1985) and is used to define, when referring to river ecosystems, “any relatively discrete event in time that is characterized by a frequency, intensity, and severity outside a predictable range, and that disrupts ecosystem, community, or population structure and changes resources or the physical environment” (Resh et al., 1988). Thus a disturbance is any event, either natural or anthropogenic, that disrupts the population, community, or ecosystem structure; it is most often an event that by eliminating individuals creates void spaces.

The term stressor, on the other hand, focuses exclusively on anthropogenic disturbances (Segner et al., 2014; Crain et al., 2008; Piggott et al., 2016). A landslide, a large flood, or a tsunami are catastrophic disturbances, but they cannot be considered stressors under this conception. These, together with smaller disturbances such as sediment movement during a spate or a snag falling into a river, to name a few, are natural disturbances. The hydrological alteration caused by hydropeaking, or the presence of xenobiotics, are instead anthropogenic disturbances or stressors. Some stressors, under moderate amounts, may also act as a subsidy for particular groups of organisms (Box 1.1).

Box 1.1

Some Key Terms Used in This Book

• Stressor: Any external abiotic or biotic factor derived from human intervention, which moves a receptor out of its normal operating range, causing either subsidy or stress.
• Receptor: Any biological system impacted by a stressor. Although organisms are the entities most directly affected by stressors, the consequences can be detected at a large range of levels of complexity, from molecular entities to communities, and even ecosystems.
• Stress: A reduction in the biological activity of a receptor as consequence of the presence of a stressor.
• Subsidy: An increase in the biological activity of a receptor as a consequence of the moderate presence of a stressor.
• Effect: Any change produced by a stressor on the receptor. It depends on the intensity, timing, and duration of the stressor, as well as on the sensitivity of the receptor to that particular stressor.

1.3 Types of Stressors According to Their Energy and Frequency

As already mentioned, natural disturbances are intrinsic to the structure and function of river ecosystems, and they shape their dynamic nature. River organisms tend to be adapted by natural selection to the disturbance regime historically existing in their habitats, which act as environmental filters (Angermeier and Winston, 1998). The high prevalence of natural disturbances makes it difficult to detect and assess the influence of anthropogenic stressors on river communities and ecosystems. In fact a la...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1: Defining Multiple Stressor Implications
• Chapter 2: Climate Change and Interactions With Multiple Stressors in Rivers
• Chapter 3: Understanding the Nexus Between Hydrological Alteration And Biological Invasions
• Chapter 4: Multiple Stressors and Hydromorphological Degradation
• Chapter 5: Multiple Stressors in Riparian Ecosystems
• Chapter 6: Water Scarcity as a Driver of Multiple Stressor Effects
• Chapter 7: An Introduction to the Geography of Multiple Stressors
• Chapter 8: Water Stressors in Europe: New Threats in the Old World
• Chapter 9: Multiple Stressors in North America: Perspectives for the New World
• Chapter 10: Multiple Stressors in African Freshwater Systems
• Chapter 11: Multiple Stressors in China's Freshwater Ecoregions
• Chapter 12: Multiple Stressors in the Neotropical Region: Environmental Impacts in Biodiversity Hotspots
• Chapter 13: Multiple Stressors in Australia and New Zealand: Key Stressors and Interactions
• Chapter 14: Detecting and Quantifying the Impact of Multiple Stress on River Ecosystems
• Chapter 15: Application of a Multistressor Risk Framework to the Monitoring, Assessment, and Diagnosis of River Health
• Chapter 16: Projecting the Consequences of Climate Change on River Ecosystems
• Chapter 17: Managing Ecosystem Services Under Multiple Stresses
• Chapter 18: Multi-Stressor Effects on Riverine Drinking Water Production and Management
• Chapter 19: Socio-Economic and Policy Implications of Multi-Stressed Rivers: A European Perspective
• Chapter 20: An Integrated Perspective of Multiple Stressors in River Ecosystems From the Catchment to the Continental Scale
• Chapter 21: Summary, Implications and Recommendations for the Occurrence and Effects of Multiple Stressors in River Ecosystems
• Index