EUTROPHICATION EXPLAINED FROM THE DESK
Due to the growing interest in the quality sustain a flourishing fish population. Again O F THE
of Florida's lakes by those who live beside the term is qualified by "early" and "late".
them and those who enjoy them for An early mesotrophic lake provides good CH I F
recreation, we are presenting a two part swimming. A late mesotrophic lake nor-
series explaining what eutrophication is and mally provides excellent fishing. D I
a possible answer to the problem.This first 3. Eutrophic H L I S
story defines eutrophication and the stages The use of this term is so broad as to be
through which a lake passes as it "ages" in almost useless because it describes a set of
geologic time. The series was written by conditions from a good fishing, swimmable Our District claims one of the fastest
staff biologist Howard M. Rose. lake to a mud filled rotting organic morass growing populations in the country, and this
Eutrophication deals with changes in well on its way to becoming a swamp. (This will require, as a basic for effective
biological productivity. It is a natural latter condition would be classified late management, a knowledge of HOW MUCH
process that ultimately results in extinction eutrophic.) OF WHAT KIND OF WATER IS WHERE
of a lake, pond, or swampy area. The A fourth classification needs to follow in AND HOW IT VARIES IN PLACE AND
eutrophic process tends to conserve soil and that the inevitable result of complete TIME. We need to practice means of in-
minerals that would otherwise be "lost" to eutrophication is extinction.Thus, the loss of creasing and extending our usable water
the sea. Man does not cause a lake to valuable materials to the sea has been crop. Nature supplies us with just so much
become eutrophic but he can hasten the forestalled and rich new forest or farmland water and by water-budget methods we can
natural eutrophication by dozens or hun- has been gained, determine what these limits are.
dreds of years. Most of us would prefer that a lake stay The Floridan Aquifer provides an enor-
Basically, the term eutrophic has various mesotrophic and find it hard to understand mous storage potential of vast economic
stages: how a lake can become eutrophic so quickly, worth. Most of the time and over most of the
1. Oligotrophic Nutrient input from citrus processing, area this great, natural, underground
Applied to a lake this term implies a body sewage, muck farming, phosphate mining, storage reservoir is filled to overflowing. It
of water that is relatively barren of biologic septic tanks and other sources can cause supplies the enormous discharge of all the
life. The term is often qualified in the rapid eutrophication, particularly when great springs of the District, such as Silver,
maximum and minimum sense by using coupled with the flood prevention techniques Rainbow, Crystal River, Homosassa,
"early" oligotrophic (barren) and "late" of channelization and lake level Chassahowitzka, Weeki Wachee and a host
oligotrophic (becoming productive), stabilization, of smaller ones such as Crystal Springs,
Oligotrophic lakes in general do not support Once a lake has become highly eutrophic which is about 20 miles northeast of Tampa
a significant fish population, but are ex- it is very difficult to reverse the process. and is the principal source of flow in the
cellent for swimming. Biologic time can be made to reverse and a Hillsborough River during drought ti
2. Mesotrophic lake to rejuvenate but only at the cost of As another example, Gourd Neck Spring. .,
As materials build up on a lake bottom labor and capital. Lake Apopka discharges into the lake at a
and decomposers act upon them, the lake Next month the HYDROSCOPE will study rate of about 18 millions of gallons a day.
water begins to hold nutrients in solution one method of lake rejuvenation that today The Floridan Aquifer is the chief source of
and phyto and zoo plankton increase. Rooted is considered to be the most feasible in all waters withdrawn for human needs in
plants begin to comprise a significant part terms of existing technology and cost-lake our District-more than 90 per cent of all our
of the flora. The increased food materials level fluctuation. supplies are developed from artesian wells,
both flowing and pumped, from this
tremendous underground reservoir. With
an average annual recharge to the aquifer of
XECU TIVE DR TOR 700,000 gallons per day per square mile, a
UT IVE DI B well pumping 1,000 gpm would require 2.05
square miles, or 1,232 acres, to produce this
much water without taking any water out of
R GES SC N storage. Likewise a well producing 5,000
gpm would require 10.1 square miles of
recharge area, or 6,160 acres. It's obvious
this kind of well spacing would be im-
Dale H. Twachtmann, who has held the Mr. T, as District personnel know him, practical.
Directorship of the Southwest Florida was appointed acting director in 1962 There are several ways to combat this but
Water Management District for a decade, when Joe Fuller, the preceding director, all either require the use of recharge wells
has stepped down in order to accept a resigned to become the chairman of the or of land-spreading to replenish the shallow
position as coordinator of the soon to be Florida Democratic party.Since then he water-table uquifer in areas where, by
formed water and sewer department of has guided the District to a position of leakage to the underlying Floridan Aquifer,
the City of Tampa. high esteem and professional competence the water would eventually be stored. The
i ghe management field, techniques of getting water to the wells will
Mr. Twachtmann made the an- Derrill McAteer, Chairman of the vary, depending upon the sites available for
nouncement at a staff meeting October District's Board of Governors, indicated temporary surface storage of floodeas in waters
second saying that he expected to leave that an acting Director will be discussed nector recharge well fields could be until .
the District by October 30. at the Board's next meeting.
SEE HYDRO p. 3
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FROM THE DESK OF THE CHIEF HYDROLOGIST
Are we about to run out of water? If so when? What can be done about it?
These and other related questions are foremost in the minds of many thought-
ful citizens and, because of the apparent widespread lack of understanding of
the nature and seriousness of our water-supply problems, I shall try to clarify
the situation as we now understand it.
But to be real blunt about it, we are not about to run out of water. I have never
said, either in oral or written discussions, that we are about to use it all up.
- What I have said is hat, on a long-term average, we estimate that we are now
Using about one-half the available, annual water-crop. Further, that we can
expect, by about 1985, to be using essentially all of the recoverable part of the
annual, average, natural replenishment of our water resource. Then, I have
gone on to say that, if and when this full development occurs, we will begin
the "mining" of water taking out of storage some of the vast quantities of
.water that are available in our immense aquifer systems.
Saying this another way: Even if, by about 1985, we use all of the available
annual water crop, we still will not be running out of water. There will remain
an aquifer storage of many billions of gallons of water.
But the unfortunate part of this rosy-appearing situation is that we cannot -
dare not use up so much of this stored water that we draw the regional water
level down below sea level. Except for short-term periods we can only use
up that part of the aquifer storage that exists above sea level. And, roughly,
this is only a very small fraction of the total volume stored.
The reason is that if we deplete the top storage (the part above sea level
in our aquifers) the bottom storage (The part below sea level) will shrink in
direct proportion to the top-storage depletion, and salt water will move in-
land from the Gulf and upward from below. Once this happens it would be
practically impossible to get the salt water pushed back out, and hydrologically
speaking, we'd be in serious trouble.
Thus, it behooves us to develop our water resources with great care and to
manage our uses of the water in such a manner that we do not permit over-
development. Such thorough management requires a degree of detailed
knowledge not now wholly available to us. If we were concerned with only
managing a surface-water source, one that would be separate from the
aquifers, our task would be fairly simple. Water in streams, lakes and
reservoirs would be where it could be seen, easily measured, and thus well
But we're dealing with ground water as our chief source of supply. Even for
the water that flows in our streams by far most of the streamflow is derived as
.-ground-water seepage through the sides and bottoms of the streams, or as it
becomes instant surface water from the flow of springs. And ground water,
occurring as it does below the surface of the ground, must be measured and
evaluated chiefly by indirect methods. Test-well drilling, test-well pumping,
the measurement of water levels in wells, the development of water-accounting
methods (including water budgets), the examination of rock outcrops, the con-
struction of hydrogeologic models of the underground structures including
aquifers, aquicludes and aquitards, and other similar or related methods in-
clusing geophysical techniques, are needed to evaluate ground-water supplies
of our region. It is a difficult, lengthy and costly process and will take years
before, over our entire District, the detailed information needed for thorough
understanding of our water resources, is available.
Our information at present is sometimes too skimpy for the kind of water
resources management that is needed. We do the best we can with what is
available and gather additional needed information as rapidly as we can.
Through the cooperation of the well drillers large amounts of detailed infor-
maition are accumulating from well-completion reports, and the data these
reports give us are being stored on IBM cards and on maps and charts to
help define the water-resources picture better than ever before.
Additionally through our cooperation with other governmental agencies, partic-
ularly with the U. S. Geological Survey, the U. S. Army Corps of Engineers,
and the Florida Department of Naturla Resources we are engaged in large-
scale cooperative studies--of the geology and water resources of particular
areas and of special projects, such as artificial recharge.