Nonpredatory Interspecific Interactions among Plants and Animals in Freshwater Communities - Freshwater Ecology: Concepts and Environmental Applications - page 419

large-scale example of managing disturbance in wetland restoration is the
Kissimmee River project in Florida (Middleton, 1999). This project at-
tempted to reverse the effects of channelization and flood control structures
put in place between 1964 and 1971 by returning the system to natural hy-
drology (Toth, 1996). Disruption of the natural floods led to more dryland
plant species in the floodplains around the river, more lentic species of
macrophytes (including the invading water hyacinth), and more animals in
the pools adjacent to and within the river adapted to lentic habitats (Toth,
1996; Harris et al., 1995). Several species of wading birds and waterfowl
declined with channelization (Weller, 1995). Restoration to reintroduce
flooding and reverse channelization started in 1984 and will ultimately in-
volve 70 km of river channel. These efforts have already increased flood-
ing, increased the numbers of wetland plants and waterfowl, and restored
lotic species to the river. The newly restored habitats are being colonized
rapidly by invertebrate communities (Merritt et al., 1999). Efforts are un-
der way to evaluate the success of this project at the ecosystem level (Dahm
et al., 1995).
Disruption of flooding can cause major changes in a river ecosystem,
from geomorphological to biotic. Such is the case with the Glen Canyon
Dam on the Colorado River. Lack of flooding and continuous release of
clear, cold water has drastically changed the communities in the river, lead-
ing to a depauperate river dominated by a few algal and invertebrate species
(Stevens et al., 1997). The cold-water releases have allowed establishment of
introduced trout and have had a negative impact on native warm-water
fishes. However, the lack of flooding has also led to increases in fluvial
marshes bordering the Colorado River (Stevens, 1995). These marshes in-
crease wildlife habitat and lead to an increased diversity of terrestrial and
wetland species. In March 1996, a limited artificial flood was instigated. The
scouring reestablished sandbars but did not completely remove harmful in-
vading species, such as carp, catfish, and tamarisk (Middleton, 1999). The
cost of the release was $1.8 million of power-generating capacity to the dam.
Disturbance of terrestrial habitats can cascade to aquatic habitats. For
example, riparian disturbance can increase sediment input, lower input of
detritus, decrease the amount of pebble and cobble substrate, and influence
invertebrate and algal communities (Stevens and Cummins, 1999). Many
pollutants enter aquatic habitats from terrestrial sources and disturb the
communities. Watershed disturbance is a prime source of nutrients that of-
ten cause eutrophication.
Succession
Succession has long been hypothesized to drive the seasonal cycle of
planktonic organisms in lakes. Long-lived fishes and macrophytes respond
less strongly to seasonal cycles than organisms with shorter life spans.
However, most lake species exhibit predictable seasonal cycles in their life
histories.
The Phytoplankton Ecology Group created the most complete model
of seasonal succession of plankton for temperate lakes with summer strat-
ification. This group of 30 limnologists created a model consisting of 24
steps (Sommer, 1989). I present a simplified version here: