Middle St. Johns - Florida Department of Environmental Protection

222 Water Quality Assessment Report: Middle St. Johns
Table B.13: Characteristics of Lake Ecoregions in the Middle St. Johns Basin
Ecoregion
Description
This region contains ancient sand dunes with excessively drained, deep, sandy soils
and sand pine scrub forest. Common soil series are Candler and Astatula. The Ocala
Ocala Scrub
Scrub contains acid, mostly clear lakes with low nutrient levels. Clear lakes are found
on higher sandy ridges.
The Eastern Flatlands is a diverse lake region because of the variability of landforms
and its latitudinal extent. Most landforms parallel the coast and reflect the marine
forces that controlled their shape and formation. Ancient barrier islands, lagoons,
dune ridges, spits, and sandbars have left the current region ribbed by low sand ridges
and intervening valleys and swampy lowlands. The lake chains of the St. Johns River
are the dominant features. North of Lake Harney, river vegetation changes from wet
grassland prairies to hardwood swamp forests.
Eastern Flatlands
Crescent
City/DeLand
Ridges
Mt. Dora Ridge
Apopka Upland
Doctor Phillips
Ridge
Orlando Ridge
Osceola Slope
The ecoregion contains a mix of different lake types. The lakes that make up the St.
Johns River—which include Harney, Jesup, Monroe, and George—are generally
alkaline, hardwater, eutrophic, and colored. Inputs of mineralized water from salt
springs and marine sediments influence the chemistry of these lakes. Other flatwoods
lakes are acid to slightly acid, colored softwater lakes of moderate mineral content with
variable trophic states.
The ecoregion contains several sandy upland ridges. The thick sand soil that makes
up the parent material for these ridges is deeply weathered Plio-Pleistocene coastal
sand deposits. Candler and Astatula are the typical soil series. Most natural
vegetation consists of longleaf pine/xerophytic oak forests and some areas of pine
scrub forests. Lakes that have formed on lowland type soils may be more
characteristic of the smaller darkwater lakes of the Eastern Flatwoods. Many other
lakes are clear, acid, and oligotrophic with low mineral content and derive most of their
flow from rainfall and subsurface inflows.
The ridge extends from near the Lake/Marion County border near Altoona south to the
towns of Eustis and Mount Dora. It contains high sand hills, 75 to 180 feet in
elevation, with excessively drained to well-drained sandy soils. Many small,
circumneutral, clear lakes with low color, low nutrients, low chlorophyll, and moderate
to high alkalinity dot the landscape. Steeply sloping sandhills and old orange groves
surround the lakes.
This is a region of residual sandhills modified by karst processes, with many small
lakes and scattered sinkholes. Elevations range from 70 to 150 feet. Longleaf pine
and xerophytic oaks would have been the natural vegetation, although most have
been replaced with citrus, pasture, and urban/residential development. The physical
and chemical characteristics of the lakes are varied. Some lakes are acid, clear,
softwater lakes of low mineral content; some clear lakes have moderate nutrient
levels; and there are also darker colored lakes with circumneutral pH values.
The ridge, which comprises thick sands, ranges in elevation from 100 to 170 feet and
contains many solution depression lakes. Soils on the ridges are primarily sands, but
some wetter, lowland type soils are also present. These soils are underlain by clayey
sands and fine sands and silt of the Hawthorn Group or other unidentified formations.
There are over thirty lakes in this region. Most are clear, with circumneutral pH, and
are low in nutrients. As a group, these are some of the clearest lakes in Central
Florida. The clearest of the group tend to be also the deepest.
Consisting of an urbanized karst area of low relief with elevations from 75 to 120 feet,
the ridge comprises poorly sorted quartz sand and pebbles embedded in kaolinitic clay
(Scott et al., 1980). The natural vegetation consists of longleaf pine and xerophytic
oaks. Lakes are generally characterized as clear, alkaline, hardwater lakes of
moderate mineral content. They are mesotrophic to eutrophic, but it is difficult to
distinguish between natural conditions and the impacts of urbanization. Lakes tend to
be more phosphatic and green than those in the Crescent City/DeLand lake region.
This lake region is composed of Pleistocene lagoonal deposits with a top layer of
medium to fine sands and silts. Elevations are generally 60 to 90 feet. Vegetation is
primarily pine flatwoods, but some low, dry ridges contain turkey oak and scrub.
Lakes are acidic, relatively low nutrient, and colored.