Geoscience Reference
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contributed to the great flood damage in 1995,
1996 and 1998.
So while there is mounting evidence of species
acting as ecosystem engineers in both positive and
negative ways and in many different situations,
there is little about how ecosystems themselves
in turn may act as
landscape
engineers. Naiman
et al.
(1993) noted that; 'Riparian corridors
possess an unusually diverse array of species and
environmental processes. This 'ecological' diversity
is related to variable flood regimes, geomorphic
channel processes, altitudinal climate shifts, and
upland influences on the fluvial corridor. This
dynamic environment results in a variety of life
history strategies, and a diversity of biogeochemical
cycles and rates, as organisms adapt to disturbance
regimes over broad spatio-temporal scales.'
Miller
et al.
(1995) observed that 'throughout
western North America, flood regimes have
been altered as a result of large-scale water
impoundments and diversions, yet the effects
on riparian landscape structure have not been
quantified.' They found a decline in flooded area
of 75% between 1937 and 1990 for the Rawhide
Wildlife Management Area, and this decline was
reflected in a change in age structure of cottonwood
(
Populus
spp.) stands, indicating a shift from young,
dense stands to older, more open stands. Critical
in their observations was that 'some traditional
measures of landscape structure (i.e. richness,
diversity, dominance, average patch perimeter
length, average patch shape) appeared insensitive
to these changes, although the proportion of the
landscape that changed land types declined with
increasing distance from the river'.
It is clear, thus, that rivers and riparian systems
can affect, modify and manipulate landscapes (or
ecosystems) with attenuation increasing in distance
from the river. However, the nature of rivers
as landscape engineers in the past may become
increasingly constrained as the effects of hard
engineering are manifest, resulting in changes
both in temporal and spatial landscape engineering
effects of river ecosystems.
Naiman
et al.
(1993) proposed that effective
riparian
environmental quality. They argued that riparian
corridors should play an essential role in water and
landscape planning, in the restoration of aquatic
systems, and in catalyzing institutional and societal
cooperation for these efforts. Seventeen years on
it is not clear whether their arguments have
been widely accepted or taken up by society. It
is perhaps time to re-evaluate not only the role
of river organisms as ecosystem engineers within
river ecosystems, but also the wider role of rivers
as landscape engineers, not just for human well-
being, but for the support and maintenance of
other ecosystems along the river as it journeys from
the mountains to the sea.
Rivers as a key support for
future life on earth
While ecosystem services had been developed
as a concept in the 1990s (Daily, 1997) it
was the
Millennium Ecosystem Assessment
(MA)
(2005a) through its conceptual framework
(MA, 2003) which brought the concept to
the fore of environmental policy making, and
started to influence biodiversity conservation
and management discussions. In its conceptual
framework, the MA set out to establish ecosystem
services in a range of categories: provisioning,
regulating, cultural or supporting - all of which it
linked to human well-being. Supporting services
go beyond simply assisting human well-being
directly and show how ecosystems provide services
to support other ecosystems, or other elements of
biodiversity.
For wetlands (including rivers) a specific
synthesis report was prepared for the Ramsar
Convention (MA, 2005b). That report contained
some
key
messages,
among
which
the
most
relevant (rewritten for rivers) are:
The primary indirect drivers of degradation for
rivers have been population growth and increasing
economic development.
Excessive nutrient loading is expected to become
a growing threat to rivers.
The projected degradation of rivers will reduce
their capacity to mitigate impacts and result in
management
could
ameliorate
many
ecological
problems
related
to
land
use
and
