24
within the river corridor (e.g., beaver, ouzels, kingfishers) and those that move in
and out of the river corridor (e.g., moose or migratory songbirds).
Although distinctive biotic communities occupy hyporheic, channel, floodplain,
and upland environments, the boundaries between these environments are leaky,
with continual exchanges of matter and energy. Ecologists describe these exchanges
as subsidies between aquatic and terrestrial environments. Examples include organic
litter entering a channel or floodplain lake from the surrounding riparian forest
(Cuffney 1988); aquatic insects emerging from a water body, which are then preyed
upon by riparian spiders or birds (Baxter et al. 2005); terrestrial insects such as
wasps or ants that are eaten by fish (Nakano and Murakami 2001); deer that move
into riparian zones to graze; and salmon that migrate upstream to spawn and die,
providing substantial nitrogen inputs to the river corridor via their decaying bodies
(Gende et al. 2002). Research continues to discover new dimensions of the complicated energy transfers within river ecosystems and between river ecosystems and
the broader environment (Muehlbauer et al. 2014). Clearly, river biotic communities
do not and cannot exist in isolation. Changes in energy transfers will result in
changes to the abundance and diversity of aquatic and riparian communities, as well
as river ecosystem services.
The need to sustain or restore river organisms, including endangered species,
drives a significant portion of river management. Effectively managing river biota
requires understanding how energy is transferred within river ecosystems and how
physical process and form affect energy transfers. Although the basic food webs of
rivers have been recognized for many decades, only within the past 20–30 years
have ecologists quantified energy transfers between rivers and terrestrial or marine
environments. Explicit recognition of these transfers is important to successful river
management because river ecosystems do not exist in isolation from areas physically outside of the river corridor.
2.3.3 Disturbance Regimes
A healthy river is not static. Inputs of water and sediment change through time and
the river ecosystem responds to these changing inputs. Disturbance regimes characterize these changes in inputs and response in a manner that can inform river
management.
Ecologists define a disturbance as any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment (White and Pickett 1985). A flood is
the preeminent example of a disturbance within a river ecosystem, although other
examples include drought; wildfire in the riparian corridor or adjacent uplands that
alters water and sediment inputs to the river corridor; insect infestations or blowdowns in the riparian forest; or debris flows that enter the river corridor from
2 Rivers as Ecosystems
within the river corridor (e.g., beaver, ouzels, kingfishers) and those that move in
and out of the river corridor (e.g., moose or migratory songbirds).
Although distinctive biotic communities occupy hyporheic, channel, floodplain,
and upland environments, the boundaries between these environments are leaky,
with continual exchanges of matter and energy. Ecologists describe these exchanges
as subsidies between aquatic and terrestrial environments. Examples include organic
litter entering a channel or floodplain lake from the surrounding riparian forest
(Cuffney 1988); aquatic insects emerging from a water body, which are then preyed
upon by riparian spiders or birds (Baxter et al. 2005); terrestrial insects such as
wasps or ants that are eaten by fish (Nakano and Murakami 2001); deer that move
into riparian zones to graze; and salmon that migrate upstream to spawn and die,
providing substantial nitrogen inputs to the river corridor via their decaying bodies
(Gende et al. 2002). Research continues to discover new dimensions of the complicated energy transfers within river ecosystems and between river ecosystems and
the broader environment (Muehlbauer et al. 2014). Clearly, river biotic communities
do not and cannot exist in isolation. Changes in energy transfers will result in
changes to the abundance and diversity of aquatic and riparian communities, as well
as river ecosystem services.
The need to sustain or restore river organisms, including endangered species,
drives a significant portion of river management. Effectively managing river biota
requires understanding how energy is transferred within river ecosystems and how
physical process and form affect energy transfers. Although the basic food webs of
rivers have been recognized for many decades, only within the past 20–30 years
have ecologists quantified energy transfers between rivers and terrestrial or marine
environments. Explicit recognition of these transfers is important to successful river
management because river ecosystems do not exist in isolation from areas physically outside of the river corridor.
2.3.3 Disturbance Regimes
A healthy river is not static. Inputs of water and sediment change through time and
the river ecosystem responds to these changing inputs. Disturbance regimes characterize these changes in inputs and response in a manner that can inform river
management.
Ecologists define a disturbance as any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment (White and Pickett 1985). A flood is
the preeminent example of a disturbance within a river ecosystem, although other
examples include drought; wildfire in the riparian corridor or adjacent uplands that
alters water and sediment inputs to the river corridor; insect infestations or blowdowns in the riparian forest; or debris flows that enter the river corridor from
2 Rivers as Ecosystems