Chapter 1 Minimum Flows and Levels - Southwest Florida Water ...

levels such as fish have been shown to also depend on woody structures either
for cover, as feeding grounds, or as nesting areas.
Since woody habitats are potentially the most important instream habitat for
macroinvertebrate production, inundation of these habitats for sufficient periods
is considered critical to secondary production (including fish and other wildlife)
and the maintenance of aquatic food webs. Not only is inundation considered
important, but sustained inundation prior to colonization by invertebrates is
necessary to allow for microbial conditioning and periphyton development.
Without this preconditioning, the habitat offered by snags and wood is essentially
a substrate for attachment without associated food resources. The development
of food resources (microbes) on the substrate is needed by the assemblage of
macroinvertebrates that typically inhabit these surfaces. After the proper
conditioning period, continuous inundation is required for many species to
complete development. The inundated woody substrate (both snags and
exposed roots) within the stream channel is viewed as an important riverine
habitat and it is assumed that withdrawals or diversions of river flow could
significantly decrease the availability of this habitat under medium to high flow
conditions.
3.3.5 Hydrologic Connections Between the River Channel and
Floodplain
A goal of the District's minimum flows and levels approach is to ensure that the
hydrologic requirements of biological communities associated with the river
floodplain are met during seasonally predictable wet periods. Periodic inundation
of riparian floodplains by high flows is closely linked with the overall biological
productivity of river ecosystems (Crance 1988, Junk et al., 1989). Many fish and
wildlife species associated with rivers utilize both instream and floodplain
habitats, and inundation of the river floodplains greatly expands the habitat and
food resources available to these organisms (Wharton et al. 1982, Ainsle et al.
1999, Hill and Cichra 2002). Inundation during high flows also provides a
subsidy of water and nutrients that supports high rates of primary production in
river floodplains (Conner and Day 1979, Brinson et al. 1981). This primary
production yields large amounts of organic detritus, which is critical to food webs
on the floodplain and within the river channel (Vannote et al. 1980, Gregory et al.
1991). Floodplain inundation also contributes to other physical-chemical
processes that can affect biological production, uptake and transformation of
macro-nutrients (Kuensler 1989, Walbridge and Lockaby 1994).
Soils in river floodplains exhibit physical and chemical properties that are
important to the overall function of the river ecosystem (Wharton et al. 1982,
Stanturf and Schenholtz 1998). Anaerobic soil conditions can persist in areas
where river flooding or soil saturation is of sufficient depth and duration. The
decomposition of organic matter is much slower in anaerobic environments, and
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