8
a factor of five (Ricciardi and Rasmussen 1999). Freshwater faunas have become
increasingly homogeneous as a result of extirpation of native species, introduction
of nonnative species, and habitat alterations that facilitate these two processes
(Rahel 2002). Although freshwater fisheries are not as well tracked as marine fisheries, both commercial and recreational fisheries are causing collapse of fish species
in many rivers (Pauly et al. 2002; Post et al. 2002; Carpenter et al. 2011).
I have visited river corridors around the world and I repeatedly hear people—
river scientists, natural resources managers, concerned citizens—asking what they
can do to restore river ecosystems and the services that they provide. Although they
may not use these scientific terms, the concerns are universal: how can we make the
water clean again, or bring back the fish, or make the river stop eroding its banks
without covering the banks in concrete? How can we make the river healthy again?
River health is a nebulous concept. River scientists do not necessarily embrace
the phrase and they differ in how to define and assess it (Boulton 1999; Karr 1999;
Norris and Thoms 1999). River health continues to be used because it is intuitively
appealing and provides a ready analogy for human health. River health can be
defined as the degree to which river corridor energy sources, water quality, flow
regime, habitat, and biota match the natural conditions (Wohl 2012). This can be
very difficult to assess in regions with many centuries of river manipulation by
humans, but comparison to natural or reference conditions remains the most widely
used standard for any form of ecosystem health (Palmer and Febria 2012). In this
context, natural or reference conditions typically refer to the characteristics of the
river ecosystem present prior to intensive human manipulation of the environment
within the watershed and the river corridor (Wohl and Merritts 2007; Wohl 2011).
The historical timeline of intensive human manipulation varies widely among
diverse locations. In many regions of the world, alteration of upland vegetation for
agriculture or timber harvest was one of the earliest human activities to alter water
and sediment yields entering river corridors. This occurred as early as 8000 years
ago in parts of China (Zhuang and Kidder 2014), and is now occurring in countries
such as Uganda (Kasangaki et al. 2008). Direct engineering of channels and regulation of river flows typically occurred more recently, but again over varying timespans. At least some of the rivers in Eurasia have been channelized for more than a
century (Pišút 2002), whereas river channelization in the United States occurred
primarily during the mid to late twentieth century (Goodwin et al. 1997).
Understanding the perceptions that underlie the use of the phrase ‘river health’
and the processes that create and maintain healthy rivers is critical to management
designed to improve the functioning of rivers as ecosystems. The next chapter
focuses on the processes that support healthy rivers.
References
Boulton AJ (1999) An overview of river health assessment: philosophies, practice, problems and
prognosis. Freshw Biol 41:469–479
Carpenter SR, Stanley EH, Vander Zanden MJ (2011) State of the world’s freshwater ecosystems:
physical, chemical, and biological changes. Annu Rev Environ Resour 36:75–99
1 Introduction
a factor of five (Ricciardi and Rasmussen 1999). Freshwater faunas have become
increasingly homogeneous as a result of extirpation of native species, introduction
of nonnative species, and habitat alterations that facilitate these two processes
(Rahel 2002). Although freshwater fisheries are not as well tracked as marine fisheries, both commercial and recreational fisheries are causing collapse of fish species
in many rivers (Pauly et al. 2002; Post et al. 2002; Carpenter et al. 2011).
I have visited river corridors around the world and I repeatedly hear people—
river scientists, natural resources managers, concerned citizens—asking what they
can do to restore river ecosystems and the services that they provide. Although they
may not use these scientific terms, the concerns are universal: how can we make the
water clean again, or bring back the fish, or make the river stop eroding its banks
without covering the banks in concrete? How can we make the river healthy again?
River health is a nebulous concept. River scientists do not necessarily embrace
the phrase and they differ in how to define and assess it (Boulton 1999; Karr 1999;
Norris and Thoms 1999). River health continues to be used because it is intuitively
appealing and provides a ready analogy for human health. River health can be
defined as the degree to which river corridor energy sources, water quality, flow
regime, habitat, and biota match the natural conditions (Wohl 2012). This can be
very difficult to assess in regions with many centuries of river manipulation by
humans, but comparison to natural or reference conditions remains the most widely
used standard for any form of ecosystem health (Palmer and Febria 2012). In this
context, natural or reference conditions typically refer to the characteristics of the
river ecosystem present prior to intensive human manipulation of the environment
within the watershed and the river corridor (Wohl and Merritts 2007; Wohl 2011).
The historical timeline of intensive human manipulation varies widely among
diverse locations. In many regions of the world, alteration of upland vegetation for
agriculture or timber harvest was one of the earliest human activities to alter water
and sediment yields entering river corridors. This occurred as early as 8000 years
ago in parts of China (Zhuang and Kidder 2014), and is now occurring in countries
such as Uganda (Kasangaki et al. 2008). Direct engineering of channels and regulation of river flows typically occurred more recently, but again over varying timespans. At least some of the rivers in Eurasia have been channelized for more than a
century (Pišút 2002), whereas river channelization in the United States occurred
primarily during the mid to late twentieth century (Goodwin et al. 1997).
Understanding the perceptions that underlie the use of the phrase ‘river health’
and the processes that create and maintain healthy rivers is critical to management
designed to improve the functioning of rivers as ecosystems. The next chapter
focuses on the processes that support healthy rivers.
References
Boulton AJ (1999) An overview of river health assessment: philosophies, practice, problems and
prognosis. Freshw Biol 41:469–479
Carpenter SR, Stanley EH, Vander Zanden MJ (2011) State of the world’s freshwater ecosystems:
physical, chemical, and biological changes. Annu Rev Environ Resour 36:75–99
1 Introduction