7
In addition to the obvious downstream movements of water and sediment, longitudinal connectivity includes upstream movements by organisms. Lateral connectivity is present within the river corridor—between the main channel and secondary
channels and floodplains, and between the river corridor and adjacent uplands.
Vertical connectivity is present within the river corridor over relatively short distances between the channel or floodplain and the hyporheic zone. Vertical connectivity exists over longer distances between the atmosphere and the river corridor and
between ground water and the river corridor. Each of these forms of connectivity is
explored in greater detail in Chap. 2.
The history of economic development and industrialization in most countries is
a history of altering rivers to convert them from ecosystems and spatially heterogeneous corridors to simpler, more spatially uniform channels. People have built
levees and drained floodplains, in the process severing connections between the
channel and floodplain. Communities and industries have dumped waste products
into river corridors, changing water quality, nutrient loads, and the ability of individual organisms and biotic communities to survive within the river. People have
regulated flows to reduce flooding and store water for dry periods or to generate
hydropower, in the process altering natural river flow regimes. People have channelized rivers to reduce their lateral mobility and used rivers to transport goods ranging
from masses of cut logs to immense barges. And, people have relied on rivers for
water supplies and fisheries.
The unintended cumulative effects of the long history of river manipulation are
increasingly apparent (Williams et al. 2014). Irrigated agriculture has expanded
174% globally since the 1950s and now accounts for ~90% of global freshwater
consumption (Scanlon et al. 2007). Widespread nutrient pollution of river corridors
that reflects use of agricultural fertilizers reduces river ecosystem processes
(Woodward et al. 2012). Indeed, disruption of global nitrogen and phosphorus
dynamics has likely exceeded planetary boundaries of a safe operating space for
humanity with respect to global environments (Rockström et al. 2009; Steffen et al.
2015). Other widespread contaminants in river corridors include metals, synthetic
chemicals such as pesticides and PCBs, untreated human and animal wastes, and
pathogens (Meybeck 2003; Wohl 2014). Nearly 80% of the world’s population is
exposed to high levels of water insecurity resulting from lack of potable water
(Vörösmarty et al. 2010).
Decades of intensive river engineering have facilitated greater construction and
settlement within river corridors, resulting in substantial increases in flood damages
and exposure to flood hazards (Jongman et al. 2012). Reservoirs trap an estimated
26% of global sediment flux to the oceans (Syvitski et al. 2005), so that sediment
flux has declined despite accelerated erosion in uplands, causing widespread erosion of river deltas (Syvitski and Kettner 2011). Dams and diversions homogenize
river discharge (Poff et al. 2007) and river engineering homogenizes the configuration of river corridors (Peipoch et al. 2015). Both of these forms of homogenization
reduce the ability of river corridors to support diverse and abundant biota and to
provide ecosystem services (Moyle and Mount 2007). Projected mean future extinction rates of freshwater fauna in North America exceed those of terrestrial fauna by
1.2 Healthy Rivers
In addition to the obvious downstream movements of water and sediment, longitudinal connectivity includes upstream movements by organisms. Lateral connectivity is present within the river corridor—between the main channel and secondary
channels and floodplains, and between the river corridor and adjacent uplands.
Vertical connectivity is present within the river corridor over relatively short distances between the channel or floodplain and the hyporheic zone. Vertical connectivity exists over longer distances between the atmosphere and the river corridor and
between ground water and the river corridor. Each of these forms of connectivity is
explored in greater detail in Chap. 2.
The history of economic development and industrialization in most countries is
a history of altering rivers to convert them from ecosystems and spatially heterogeneous corridors to simpler, more spatially uniform channels. People have built
levees and drained floodplains, in the process severing connections between the
channel and floodplain. Communities and industries have dumped waste products
into river corridors, changing water quality, nutrient loads, and the ability of individual organisms and biotic communities to survive within the river. People have
regulated flows to reduce flooding and store water for dry periods or to generate
hydropower, in the process altering natural river flow regimes. People have channelized rivers to reduce their lateral mobility and used rivers to transport goods ranging
from masses of cut logs to immense barges. And, people have relied on rivers for
water supplies and fisheries.
The unintended cumulative effects of the long history of river manipulation are
increasingly apparent (Williams et al. 2014). Irrigated agriculture has expanded
174% globally since the 1950s and now accounts for ~90% of global freshwater
consumption (Scanlon et al. 2007). Widespread nutrient pollution of river corridors
that reflects use of agricultural fertilizers reduces river ecosystem processes
(Woodward et al. 2012). Indeed, disruption of global nitrogen and phosphorus
dynamics has likely exceeded planetary boundaries of a safe operating space for
humanity with respect to global environments (Rockström et al. 2009; Steffen et al.
2015). Other widespread contaminants in river corridors include metals, synthetic
chemicals such as pesticides and PCBs, untreated human and animal wastes, and
pathogens (Meybeck 2003; Wohl 2014). Nearly 80% of the world’s population is
exposed to high levels of water insecurity resulting from lack of potable water
(Vörösmarty et al. 2010).
Decades of intensive river engineering have facilitated greater construction and
settlement within river corridors, resulting in substantial increases in flood damages
and exposure to flood hazards (Jongman et al. 2012). Reservoirs trap an estimated
26% of global sediment flux to the oceans (Syvitski et al. 2005), so that sediment
flux has declined despite accelerated erosion in uplands, causing widespread erosion of river deltas (Syvitski and Kettner 2011). Dams and diversions homogenize
river discharge (Poff et al. 2007) and river engineering homogenizes the configuration of river corridors (Peipoch et al. 2015). Both of these forms of homogenization
reduce the ability of river corridors to support diverse and abundant biota and to
provide ecosystem services (Moyle and Mount 2007). Projected mean future extinction rates of freshwater fauna in North America exceed those of terrestrial fauna by
1.2 Healthy Rivers