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Alafia River Minimum Flows and Levels - Southwest Florida Water ...

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Wood provides advantages as habitat, as it is relatively stable as compared to<br />

s<strong>and</strong> substrata. Even bedrock substrates, though the most stable of all, are<br />

susceptible to smothering by shifting s<strong>and</strong> <strong>and</strong> silt. Wood is a complex structural<br />

habitat with microhabitats (such as interstices that increase surface area) that<br />

provide cover for a variety of invertebrates. As an organic substrate, wood is<br />

also a food resource for utilization by microbial food chains, which in turn<br />

supports colonization <strong>and</strong> production of macroinvertebrates. As physical<br />

impediments to flow, woody structures enhance the formation of leaf packs <strong>and</strong><br />

larger debris dams. These resulting habitats provide the same functions as<br />

woody substrata in addition to enhancing habitat diversity instream. Organisms<br />

in higher trophic levels such as fish have been shown to also depend on woody<br />

structures either for cover, as feeding grounds, or as nesting areas.<br />

Since woody habitats are potentially the most important instream habitat for<br />

macroinvertebrate production, inundation of these habitats for sufficient periods<br />

is considered critical to secondary production (including fish <strong>and</strong> other wildlife)<br />

<strong>and</strong> the maintenance of aquatic food webs. Not only is inundation considered<br />

important, but sustained inundation prior to colonization by invertebrates is<br />

necessary to allow for microbial conditioning <strong>and</strong> periphyton development.<br />

Without this preconditioning, the habitat offered by snags <strong>and</strong> wood is essentially<br />

a substrate for attachment without associated food resources. The development<br />

of food resources (microbes) on the substrate is needed by the assemblage of<br />

macroinvertebrates that typically inhabit these surfaces. After the proper<br />

conditioning period, continuous inundation is required for many species to<br />

complete development. The inundated woody substrate (both snags <strong>and</strong><br />

exposed roots) within the stream channel is viewed as an important riverine<br />

habitat <strong>and</strong> it is assumed that withdrawals or diversions of river flow could<br />

significantly decrease the availability of this habitat under medium to high flow<br />

conditions.<br />

3.3.5 Hydrologic Connections Between the <strong>River</strong> Channel <strong>and</strong><br />

Floodplain<br />

Although not historically addressed in most minimum flow determinations,<br />

floodplains have long been recognized as seasonally important riverine habitat.<br />

A goal of the SWFWMD's minimum flows <strong>and</strong> levels approach is to ensure that<br />

the hydrologic requirements of biological communities associated with the river<br />

floodplain are met during seasonally predictable wet periods. Periodic inundation<br />

of riparian floodplains by high flows is closely linked with the overall biological<br />

productivity of river ecosystems (Crance 1988, Junk et al. 1989). Many fish <strong>and</strong><br />

wildlife species associated with rivers utilize both instream <strong>and</strong> floodplain<br />

habitats, <strong>and</strong> inundation of the river floodplains greatly exp<strong>and</strong>s the habitat <strong>and</strong><br />

food resources available to these organisms (Wharton et. al. 1982, Ainsle et al.<br />

1999, Hill <strong>and</strong> Cichra 2002). Inundation during high flows also provides a<br />

3-6

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