81
involved using a highly destructive instrument known as a crowfoot—a horizontal
bar hung with hooks—that was dragged along the river bottom (Blodgett et al.
1998). Massive removal of mussels reduced abundance and diversity of aquatic
habitat for other organisms and reduced organic matter processing in the stream
bed. Because organic matter lowers the dissolved oxygen content of river water as
it decays, removal of mussels indirectly altered water quality.
Buffalo fish are bottom-feeders that eat insect larvae, zooplankton, attached
algae, shellfish, and organic detritus. These fish can grow to be more than a meter
long and 37 kg in weight (Forbes 1988; Greenberg 2002). Buffalo fish supported the
primary commercial fishery on the Illinois River, a tributary of the Mississippi, with
up to ten million tons of the fish sent to commercial markets each year until they
were fished to commercial extinction during the 1890s (Forbes and Richardson
1920; Greenberg 2002). Removal of these bottom-feeders from the river system
likely altered water quality and aquatic food webs, although scientific studies documenting these effects were not conducted at the time of the population crash in these
fish (Wohl 2013).
Floodplain deforestation is typically undertaken with floodplain drainage, levee
construction, and other activities designed to facilitate human use of the floodplain.
Removal of floodplain forests reduces the stability of the floodplain and the attenuation of downstream fluxes of water, solutes, sediment, and organic matter.
Floodplain deforestation also reduces sources of large wood to the river corridor and
thus habitat abundance and diversity in both the channel and floodplain. Reductions
in habitat can lower biomass and biodiversity (Sedell and Froggatt 1984). Loss of
shading and organic matter inputs also change nutrient availability and biogeochemical cycling.
Because the floodplain includes the riparian zone, floodplain deforestation
results in loss of riparian buffers. Riparian buffers are vegetated bands along the
active channel that filter fluxes of material from adjacent uplands and retain both
nutrients and contaminants, thus improving water quality (Gregory et al. 1991;
Naiman et al. 2005). Riparian buffers increase the resistance of the channel banks to
erosion, thus limiting lateral channel movement and introduction of sediment from
bank erosion (Griffin et al. 2005; Gurnell 2014). Riparian vegetation shades the
channel, ameliorating diurnal and seasonal fluctuations in water temperature.
Riparian vegetation also sheds organic matter into the channel, providing an important nutrient source for primary production (Naiman et al. 2005). Finally, riparian
vegetation provides critical habitat for diverse organisms from invertebrates to
mammals (Sabo et al. 2005). Floodplain deforestation and loss of riparian buffers
thus create a cascade of secondary effects in river ecosystems.
Riparian grazing also reduces or eliminates riparian vegetation. Riparian grazing
typically involves domestic animals, particularly cows. Wild ungulates that have
reached unnaturally high population densities as a result of removal of predators can
also severely overgraze riparian areas (Ripple and Beschta 2004).
Sustained, high-intensity riparian grazing can create a variety of effects (Trimble
and Mendel 1995; Myers and Swanson 1996). These include reducing or eliminating favored plant species. Continued high numbers of grazing animals compact
3.2 Direct Alterations of River Networks and River Corridors
involved using a highly destructive instrument known as a crowfoot—a horizontal
bar hung with hooks—that was dragged along the river bottom (Blodgett et al.
1998). Massive removal of mussels reduced abundance and diversity of aquatic
habitat for other organisms and reduced organic matter processing in the stream
bed. Because organic matter lowers the dissolved oxygen content of river water as
it decays, removal of mussels indirectly altered water quality.
Buffalo fish are bottom-feeders that eat insect larvae, zooplankton, attached
algae, shellfish, and organic detritus. These fish can grow to be more than a meter
long and 37 kg in weight (Forbes 1988; Greenberg 2002). Buffalo fish supported the
primary commercial fishery on the Illinois River, a tributary of the Mississippi, with
up to ten million tons of the fish sent to commercial markets each year until they
were fished to commercial extinction during the 1890s (Forbes and Richardson
1920; Greenberg 2002). Removal of these bottom-feeders from the river system
likely altered water quality and aquatic food webs, although scientific studies documenting these effects were not conducted at the time of the population crash in these
fish (Wohl 2013).
Floodplain deforestation is typically undertaken with floodplain drainage, levee
construction, and other activities designed to facilitate human use of the floodplain.
Removal of floodplain forests reduces the stability of the floodplain and the attenuation of downstream fluxes of water, solutes, sediment, and organic matter.
Floodplain deforestation also reduces sources of large wood to the river corridor and
thus habitat abundance and diversity in both the channel and floodplain. Reductions
in habitat can lower biomass and biodiversity (Sedell and Froggatt 1984). Loss of
shading and organic matter inputs also change nutrient availability and biogeochemical cycling.
Because the floodplain includes the riparian zone, floodplain deforestation
results in loss of riparian buffers. Riparian buffers are vegetated bands along the
active channel that filter fluxes of material from adjacent uplands and retain both
nutrients and contaminants, thus improving water quality (Gregory et al. 1991;
Naiman et al. 2005). Riparian buffers increase the resistance of the channel banks to
erosion, thus limiting lateral channel movement and introduction of sediment from
bank erosion (Griffin et al. 2005; Gurnell 2014). Riparian vegetation shades the
channel, ameliorating diurnal and seasonal fluctuations in water temperature.
Riparian vegetation also sheds organic matter into the channel, providing an important nutrient source for primary production (Naiman et al. 2005). Finally, riparian
vegetation provides critical habitat for diverse organisms from invertebrates to
mammals (Sabo et al. 2005). Floodplain deforestation and loss of riparian buffers
thus create a cascade of secondary effects in river ecosystems.
Riparian grazing also reduces or eliminates riparian vegetation. Riparian grazing
typically involves domestic animals, particularly cows. Wild ungulates that have
reached unnaturally high population densities as a result of removal of predators can
also severely overgraze riparian areas (Ripple and Beschta 2004).
Sustained, high-intensity riparian grazing can create a variety of effects (Trimble
and Mendel 1995; Myers and Swanson 1996). These include reducing or eliminating favored plant species. Continued high numbers of grazing animals compact
3.2 Direct Alterations of River Networks and River Corridors