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Cited by 991Hydrology and Sediment Transport ProcessesEcology and biodiversity studiesFish Ecology and Management Studies

Alterations of Riparian Ecosystems Caused by River Regulation

NILSSON, CHRISTER, BERGGREN, KAJSA·2000·BioScience
DOI 10.1641/0006-3568(2000)050[0783:aorecb]2.0.co;2
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Abstract

An estimated two-thirds of the fresh water flowing to the oceans is obstructed by approximately 40,000 large dams (defined as more than 15 m in height) and more than 800,000 smaller ones (Petts 1984, McCully 1996). Many additional rivers are constrained by artificial levees or dikes. These hydrological alterations—to ensure water for agricultural, industrial, and domestic purposes; for hydroelectricity; or for flood protection—have changed ecosystem structures and processes in running waters and associated environments the world over. In this article, we discuss the global-scale ecological changes in riparian ecosystems resulting from dam operations. Comparative studies of free-flowing and regulated rivers have increased our understanding of the environmental effects of dams (Rosenberg et al. 1995). The first studies concentrated on large reservoirs; reaches downstream from dams were of subsequent concern. Early work also focused on aquatic systems. By the 1980s rivers were viewed in a larger perspective, as central elements in entire catchment areas (Ward 1997). In this process, the importance of riparian ecosystems successively attracted more attention (Naiman and Décamps 1997). Riparian ecosystems occupy the ecotone between upland and aquatic realms (Figure 1). More precisely, the riparian ecosystem can be defined as the stream channel between the low- and high-water marks plus the terrestrial landscape above the high-water mark (where vegetation may be influenced by elevated water tables or extreme flooding and by the ability of the soils to hold water; Naiman et al. 1993). Natural riparian ecosystems include a variety of community types, including strips of spruce forest on periodically frozen ground with dense moss carpets, floodplain landscapes with deciduous trees and shrubs on heterogeneous substrates, and deltas with distinct plant zonation and well-developed forests having diverse animal communities. Some floodplain landscapes, such as those in South America, Europe, Africa, and Asia, cover tens of thousands of km2 of land (Welcomme 1979, Petts 1984). Riparian areas are particularly sensitive to variation in the hydrological cycle and serve as good indicators of the environmental change that is caused by dam operations. Moreover, riparian processes have a central ecological role in most landscapes. Riparian ecosystems offer habitats for many species, function as filters between land and water, and serve as pathways for dispersing and migrating organisms (Naiman and Décamps 1997). Riparian ecosystems also have many economic and recreational values. Dams are affecting riparian ecosystems all over the world. Consider the 139 regulated and free-flowing rivers in the United States, Canada, Europe, and former USSR that exceed 350 m3/s in mean annual discharge. Eighty-five of them, representing 77% of the total water discharge, were strongly or moderately regulated and fragmented by dams (Dynesius and Nilsson 1994). Many environmental effects of dams are immediate and obvious. For example, dams obstruct migration pathways for fish, and reservoirs trap waterborne sediment. Other environmental effects are gradual and subtle, making them difficult to predict. If a river is regulated, for example, the flood extent and the nutrient loads will certainly change but the exact nature of these changes and their magnitudes and time periods often remain unforeseeable. Every river is unique in terms of its flow patterns, the landscapes it flows through, and the species it supports, implying that the design and operating pattern of every dam is also unique. So are the effects of the dam on the river and its associated ecosystems (Johnson 1998). In most cases, dams are built to ensure less variable flows in the rivers downstream, which is attained by increasing fluctuations of water levels in the reservoir behind the dam. Welcomme (1979) described this as a change from “flood-rivers” to “reservoir-rivers.” In other cases, dams are built to facilitate diversions of water, which can leave the channels permanently or intermittently dry or at least strongly reduce flows. Conversely, dams are often built in arid areas with pronounced periods of rain and drought to ensure water availability during the dry season. In addition to modifying the environment at the dam site proper, a dam affects riparian communities upstream by raising water levels and modifying water-level fluctuations and downstream by altering flow regimes. Many rivers have been turned into chains of storage reservoirs and run-of-river impoundments without any rapids left. This includes the Volga, Mississippi, Paraná, and most hydroelectric rivers in northern Sweden. One dam controls the water up to the next dam so that the upstream and downstream effects of dams overlap (Figure 2). The dams on Earth keep back approximately 10,000 km3 of water. This is equivalent to five times the volume of water in all the rivers in the world (Chao 1995) or to a 10 cm deep l

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  • Disconnection of floodplains from the river channel alters aquatic and terrestrial biodiversity and ecosystem services such as natural flood retention, nutrient removal, and flood-recession agriculture.

    “their disconnection from the river channel alters aquatic and terrestrial biodiversity and ecosystem services such as natural flood retention, nutrient removal, and flood-recession agriculture ( 11 ).”

    From Mapping the world’s free-flowing rivers (2019) · cites this paper as [11]

  • Floodplains are among the most productive and diverse riverine ecosystems globally.

    “Indeed, floodplains are among the most productive and diverse riverine ecosystems globally”

    From Mapping the world’s free-flowing rivers (2019) · cites this paper as [11]

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Research works printed but not linked: 3

  1. Dogra B. 1986. The Indian experience with large dams. Pages 201-218 in
  2. Hight SD, Drea JJ Jr. 1991. Prospects for a classical biological control pro- ject against purple loosestrife (Lythrum salicaria L.). Natural Areas Journal 11: 151-157.
  3. Petts GE. 1984. Impounded Rivers. Chichester (UK): John Wiley & Sons. Pielou EC. 1998. Fresh Water. Chicago: University of Chicago Press.

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Authors
NILSSON, C., & BERGGREN, K.
Affiliations
Mid Sweden University (SE)
Corresponding author
BERGGREN, KAJSA
ORCID
NILSSON, CHRISTER
Venue
BioScience
Publisher
Oxford University Press (OUP)
Published
2000
Volume
50
Issue
9
Pages
783
ISSN
0006-3568 (ISSN-L)
DOI
10.1641/0006-3568(2000)050[0783:aorecb]2.0.co;2
OpenAlex
W2267292643
Cited by
991
References
53
Citations by year
2026: 34 · 2025: 49 · 2024: 35 · 2023: 60 · 2022: 50 · 2021: 58 · 2020: 45 · 2019: 70 · 2018: 107 · 2017: 54 · 2016: 50 · 2015: 48 · 2014: 37 · 2013: 39 · 2012: 39
FWCI
14.13
Type
journal article
Language
en
Open access
closed
Locations
  • BioScience (publishedVersion)
  • BioOne Complete (BioOne) (submittedVersion)
Funders
Skogs- och Jordbrukets Forskningsråd
Topics
  • Physical Sciences › Environmental Science › Ecology › Hydrology and Sediment Transport Processes
  • Physical Sciences › Environmental Science › Ecology › Ecology and biodiversity studies
  • Physical Sciences › Environmental Science › Nature and Landscape Conservation › Fish Ecology and Management Studies
Keywords
riparian zones, river regulation, dams, hydrological change, floodplain landscapes, levees, floodplain forests, floodplain wetlands, floodplain grasslands, floodplain management

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