Middle St. Johns - Florida Department of Environmental Protection

34 Water Quality Assessment Report: Middle St. Johns
Benthic
Occurring at the bottom of a
body of water.
Ecoregions
In general, ecoregions are delineated by patterns of homogeneity in a
combination of factors such as climate, physiography, geology, soils, and
vegetation. They were refined in Florida for application to aquatic ecosystems
for use as an assessment and management tool. The Middle St. Johns
Basin lies in the Southern Coastal Plain Ecoregion, also referred to as
Ecoregion 75 (Griffith et al., August 11, 1994). Ecoregions are further
delineated into smaller subecoregions, with specific delineation schemes for
both lakes and streams. Stream and lake subecoregions are not intended
to characterize the water quality of a specific lake, but rather define the
expected biological potential of benthic macroinvertebrate communities
for a given set of environmental characteristics.
Stream Subecoregions
Streams in the Middle St. Johns Basin occupy 2 of the 13 subecoregions
delineated for Florida based on physical, chemical, and biological
characteristics (Griffith et al., 1994). The basin lies within the Eastern
Florida Flatwoods Subregion and the Central Florida Ridges and Uplands.
The Eastern Florida Flatwoods are flat plains with 10 to 50 percent coverage
by standing water. The expected natural vegetation is pine flatwoods
and grassland and freshwater marsh and swamp associations. The Central
Florida Ridges and Uplands are generally characterized by typically flat
plains with sandy highlands and ridges and are commonly vegetated by
longleaf pine and xerophytic oaks. Acidic and well-drained soil types
underlie this subregion.
Lake Regions
Florida’s lakes are divided into 47 lake regions according to differences
in land cover, physiography or land surface form, soils, geology, natural
aquatic vegetation, and water quality. A lake region exhibits homogeneity
as a grouping of lakes based on location and common chemical, biological,
and landscape characteristics (Griffith et al., 1997). The Middle St. Johns
Basin contains portions of 8 of the 47 lake regions (Griffith et al., 1997):
Ocala Scrub, Eastern Flatlands, Crescent City/DeLand Ridges, Mt. Dora
Ridge, Apopka Upland, Doctor Phillips Ridge, Orlando Ridge, and
Osceola Slope. Table B.13 in Appendix B provides descriptions of lake
ecoregions in the basin.
The composition of benthic macroinvertebrate species in lakes is most
strongly affected by water color and somewhat less by pH and geographic
ecoregion (Gerritsen et al., 2000). Using this information, five distinct
lake types were identified statewide that help to distinguish further the
expected biological condition of a lake. Four of these types are found in
the Middle St. Johns Basin: acid/colored, alkaline/colored, alkaline/clear,
and acid/clear in Ecoregion 75. Acid/colored lakes are generally low in
nutrients and biological productivity. By comparison, alkaline/colored
lakes have higher nutrient levels and biological productivity. The lakes
with the highest levels of nutrients and biological productivity are alkaline/
clear. Lakes with the lowest levels of nutrients and lowest biological