Flow variability and the ecology of large rivers
TL;DR: This paper identifies 11 relatively independent measures of hydrological variability that help categorize river types and are each associated with aspects of fish biology that enhance the value of the Flood Pulse Concept for river conservation, management and restoration.
Abstract: Ecological processes in large rivers are controlled by their flow variability. However, it is difficult to find measures of hydrological variability that characterize groups of rivers and can also be used to generate hypotheses about their ecology. Multivariate analyses of the hydrographs of 52 rivers worldwide revealed distinctive patterns of flow variability that were often correlated with climate. For example, there were groups of rivers that corresponded broadly with ‘tropical’ and ‘dryland’ climates. However, some rivers from continental climates occupy both extremes of this range, illustrating the limitations of simple classification. Individual rivers and groups of rivers may also have different hydrographic ‘signatures’, and attempts to combine measures of hydrological variability into indices mask biologically significant information. This paper identifies 11 relatively independent measures of hydrological variability that help categorize river types and are each associated with aspects of fish biology. Ways are suggested by which the Flood Pulse Concept can be expanded to encompass hydrological variability and accommodate differences among groups of rivers from different climatic regions. Such recognition of the complex role of hydrological variability enhances the value of the concept for river conservation, management and restoration.
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TL;DR: This literature review has focused this literature review around four key principles to highlight the important mechanisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes.
Abstract: The flow regime is regarded by many aquatic ecologists to be the key driver of river and floodplain wet- land ecosystems. We have focused this literature review around four key principles to highlight the important mech- anisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes: Firstly, flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic com- position; Secondly, aquatic species have evolved life history strategies primarily in direct response to the natural flow regimes; Thirdly, maintenance of natural patterns of longitu- dinal and lateral connectivity is essential to the viability of populations of many riverine species; Finally, the invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. The impacts of flow change are manifest across broad taxonomic groups including riverine plants, invertebrates, and fish. Despite growing recognition of these relationships, ecologists still struggle to predict and quantify biotic responses to altered flow regimes. One obvious difficulty is the ability to distin- guish the direct effects of modified flow regimes from im- pacts associated with land-use change that often accom- panies water resource development. Currently, evidence about how rivers function in relation to flow regime and the flows that aquatic organisms need exists largely as a series of untested hypotheses. To overcome these problems, aquatic science needs to move quickly into a manipulative or experimental phase, preferably with the aims of restora- tion and measuring ecosystem response.
3,018 citations
Colorado State University1, The Nature Conservancy2, Cooperative Research Centre3, University of Washington4, Patuxent Wildlife Research Center5, United States Geological Survey6, United States Forest Service7, UNESCO-IHE Institute for Water Education8, University of the Witwatersrand9, International Water Management Institute10
TL;DR: The ecological limits of hydrologic alteration (ELOHA) as mentioned in this paper is a framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale.
Abstract: SUMMARY 1. The flow regime is a primary determinant of the structure and function of aquatic and riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine ecosystems on a global scale, and the pace and intensity of human development greatly exceeds the ability of scientists to assess the effects on a river-by-river basis. Current scientific understanding of hydrologic controls on riverine ecosystems and experience gained from individual river studies support development of environmental flow standards at the regional scale. 2. This paper presents a consensus view from a group of international scientists on a new framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale. This framework, the ecological limits of hydrologic alteration (ELOHA), is a synthesis of a number of existing hydrologic techniques and environmental flow methods that are currently being used to various degrees and that can support comprehensive regional flow management. The flexible approach allows
1,408 citations
Cites background from "Flow variability and the ecology of..."
...…of hundreds of ecologically relevant flow metrics and techniques for quantifying human-caused flow and ecological alteration (Richter et al., 1996; Puckridge et al., 1998; Olden & Poff, 2003; Arthington et al., 2004, 2007; Kennen, Henriksen & Nieswand, 2007; Mathews & Richter, 2007), provide a…...
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...Keywords: environmental flows, hydroecology, hydrologic modelling, river management, streamflow classification...
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TL;DR: Long-term streamflow records are used on intermediate-sized rivers across the continental United States to show that dams have homogenized the flow regimes on third- through seventh-order rivers in 16 historically distinctive hydrologic regions over the course of the 20th century.
Abstract: Global biodiversity in river and riparian ecosystems is generated and maintained by geographic variation in stream processes and fluvial disturbance regimes, which largely reflect regional differences in climate and geology. Extensive construction of dams by humans has greatly dampened the seasonal and interannual streamflow variability of rivers, thereby altering natural dynamics in ecologically important flows on continental to global scales. The cumulative effects of modification to regional-scale environmental templates caused by dams is largely unexplored but of critical conservation importance. Here, we use 186 long-term streamflow records on intermediate-sized rivers across the continental United States to show that dams have homogenized the flow regimes on third- through seventh-order rivers in 16 historically distinctive hydrologic regions over the course of the 20th century. This regional homogenization occurs chiefly through modification of the magnitude and timing of ecologically critical high and low flows. For 317 undammed reference rivers, no evidence for homogenization was found, despite documented changes in regional precipitation over this period. With an estimated average density of one dam every 48 km of third- through seventh-order river channel in the United States, dams arguably have a continental scale effect of homogenizing regionally distinct environmental templates, thereby creating conditions that favor the spread of cosmopolitan, nonindigenous species at the expense of locally adapted native biota. Quantitative analyses such as ours provide the basis for conservation and management actions aimed at restoring and maintaining native biodiversity and ecosystem function and resilience for regionally distinct ecosystems at continental to global scales.
1,210 citations
TL;DR: A generic approach is proposed that incorporates essential aspects of natural flow variability shared across particular classes of rivers that can be validated with empirical biological data and other information in a calibration process and can bridge the gap between simple hydrological "rules of thumb" and more comprehensive environmental flow assessments and experimental flow restoration projects.
Abstract: Accounting for natural differences in flow variability among rivers, and understanding the importance of this for the protection of freshwater biodiversity and maintenance of goods and services that rivers provide, is a great challenge for water managers and scientists. Nevertheless, despite considerable progress in understanding how flow variability sustains river ecosystems, there is a growing temptation to ignore natural system complexity in favor of simplistic, static, environmental flow ''rules'' to resolve pressing river management issues. We argue that such approaches are misguided and will ultimately contribute to further degradation of river ecosystems. In the absence of detailed empirical information of environmental flow requirements for rivers, we propose a generic approach that incorporates essential aspects of natural flow variability shared across particular classes of rivers that can be validated with empirical biological data and other information in a calibration process. We argue that this approach can bridge the gap between simple hydrological ''rules of thumb'' and more comprehensive environmental flow assessments and experimental flow restoration projects.
1,134 citations
Cites background from "Flow variability and the ecology of..."
...Key words: benchmarking; classification; flow-ecological relationships; flow variability; natural flow regime paradigm; river ecosystem condition....
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...…and droughts), rate of change from one flow condition to another (e.g., rate of rise and fall of flood hydrographs), and the temporal sequencing of flow conditions should be included as they influence many aspects of river ecosystems (Poff et al. 1997, Puckridge et al. 1998, Lytle and Poff 2004)....
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TL;DR: A predicted increase in the severity and frequency of disturbances with global climate change requires a comprehensive understanding of the disturbance ecology of running waters.
Abstract: Perturbations in ecosystems consist of a sequence of 2 events: the disturbance, marked by the application of the disturbing forces, and the response shown by the biota to the damage inflicted by the disturbance. The disturbance must be effectively characterized, without confounding it with the response, for progress to be made in the study of the disturbance ecology of streams. A disturbance may take the form of a pulse, a press, or a ramp, and the consequent trajectory of the response may be a pulse, a press, or a ramp.Floods and droughts are the major forms of natural disturbance in flowing waters and, although the effects of floods have been relatively well studied, those of droughts have been largely neglected. Floods accentuate downstream and lateral transport links, often with damaging consequences, whereas droughts fragment the continuity of streams. Both floods and droughts destroy and generate habitat patchiness and patchiness of the biota. During recovery, there are changes in the biotic...
1,126 citations