Front Cover
 Title Page
 A listing of Florida Lakewatch...
 List of Figures
 Table of Contents
 Part 1: Oxygen and water
 Part 2: Temperature and water
 Part 3: Biological productivity,...
 Part 4: Methods used for measuring...
 Florida Lakewatch

Title: Beginner's guide to water management: oxygen and temperature
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066274/00001
 Material Information
Title: Beginner's guide to water management: oxygen and temperature
Physical Description: Book
Creator: Florida LAKEWATCH
Publisher: University of Florida Cooperative Extension Servce, Institute of Food and Agricultural Sciences
Publication Date: 2004
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066274
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Front Cover
        Cover 1
        Cover 2
    Title Page
        Title 1
        Title 2
    A listing of Florida Lakewatch information circulars
        Unnumbered ( 5 )
        Unnumbered ( 6 )
        Page i
    List of Figures
        Page ii
    Table of Contents
        Page iii
        Page iv
    Part 1: Oxygen and water
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Part 2: Temperature and water
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
    Part 3: Biological productivity, oxygen and temperature
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Part 4: Methods used for measuring dissolved oxygen in water
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Florida Lakewatch
        Page 28
Full Text

A Beginner's Guide to Water Management -
Oxygen and Temperature

Information Circular 109

Department of Fisheries and Aquatic Sciences
Institute of Food and Agricultural Sciences
University of Florida
Gainesville, Florida
June 2004
1st Edition

Florida LAKEWATCH would like to extend a special thanks
to the Lake County Water Authority for their financial assistance.

This publication was produced by:

Florida LAKEWATCH 2004
University of Florida / Institute of Food and Agricultural Sciences
Department of Fisheries and Aquatic Sciences
7922 NW 71st Street
Gainesville, FL 32653-3071
Phone: (352) 392-4817
Toll-Free Citizen Hotline: 1-800-LAKEWATch (1-800-525-3928)

E-mail: lakewat@ufl.edu
Web Address: http://lakewatch.ifas.ufl.edu/

Copies of this document and other information circulars are available for
download from the Florida LAKEWATCH Web site:


As always, we welcome your questions and comments.

A Beginner's Guide to Water Management -

Oxygen and Temperature

Information Circular 109

Department of Fisheries and Aquatic Sciences
Institute of Food and Agricultural Sciences
University of Florida
Gainesville, Florida
June 2004
1st Edition


Florida LAKEWATCH would like to extend a special thanks
to the Lake County Water Authority for their financial assistance.

This publication was produced by:

Florida LAKEWATCH 2004
University of Florida / Institute of Food and Agricultural Sciences
Department of Fisheries and Aquatic Sciences
7922 NW 71st Street
Gainesville, FL 32653-3071
Phone: (352) 392-4817
Toll-Free Citizen Hotline: 1-800-LAKEWATch (1-800-525-3928)

E-mail: lakewat@ufl.edu
Web Address: http://lakewatch.ifas.ufl.edu/

Copies of this document and other information circulars are available for
download from the Florida LAKEWATCH Web site:


As always, we welcome your questions and comments.

Beginner's Guide to Water Management The ABCs (Circular 101)
An introduction to the terminology/concepts used in today's water management arena, in a glossary format. 44 pp.

A Beginner's Guide to Water Management Nutrients (Circular 102)
A basic introduction to the presence of phosphorus and nitrogen in lakes two nutrients commonly associated
with algal growth and other forms of biological productivity. Limiting nutrients are discussed, along with
conceptual and mathematical tools that can be used to achieve a variety of water management goals. 36 pp.

A Beginner's Guide to Water Management Water Clarity (Circular 103)
Anyone interested in the subject of water clarity can benefit from reading this circular. Topics include factors
that can affect water clarity in Florida lakes; techniques for measuring water clarity; and methods used for
managing water clarity. 36 pp.

A Beginner's Guide to Water Management Lake Morphometry (Circular 104)
The size and shape of a lake basin (i.e., lake morphometry) can tell us a great deal about how a lake system
functions. In some instances, it can help explain why one lake has more algae or aquatic plants than another. It
can also be helpful in anticipating changes that may occur due to management practices or prevailing weather
patterns. This booklet covers many of these concepts as well as techniques used to evaluate lakes. 36 pp.

A Beginner's Guide to Water Management Symbols, Abbreviations and Conversion Factors (Circular 105)
This booklet provides the symbols, abbreviations and conversion factors necessary to communicate with water
management professionals in the U.S. and internationally. Explanations for expressing, interpreting and/or
translating chemical compounds and various units of measure are included. 44 pp.

A Beginner's Guide to Water Management Bacteria (Circular 106)
This circular begins with a brief tutorial on the presence of naturally occurring bacteria in Florida lakes followed
by a discussion of bacterial contamination and how one might test for it. Also included: wastewater treatment plants
versus septic tank systems; indicators used for detecting bacteria; and laboratory methods commonly used for
analysis. Lastly, an easy 4-step process is provided for tracking down bacterial contamination in a waterbody. 38 pp.

A Beginner's Guide to Water Management Fish Kills (Circular 107)
A discussion of the five most common natural causes of fish kills including low dissolved oxygen; spawning
fatalities; mortality due to cold temperatures; diseases and parasites; and toxic algae blooms. Human-induced
events are also covered, along with a section on fish stress a component of virtually every fish kill situation.
The last section provides instructions on how to collect fish and/or water samples for analysis. 16 pp.

A Beginner's Guide to Water Management Color (Circular 108)
Aside from water clarity, the color of water in a lake is one of the main attributes that captures people's attention
- particularly if the color begins to change. While most of these changes are the result of natural processes, it's
important to know that changes in color can affect the biological productivity of a waterbody, including the
abundance of aquatic plants and/or algae. Topics include apparent color, true color, suspended substances,
dissolved substances, and a brief discussion about light refraction. The last section provides two empirical
models that can be used to determine if color is the result of algae or suspended solids (i.e., in a specific lake). 32 pp.

Copies of these publications can be obtained by contacting the Florida LAKEWATCH office at 1-800-LAKEWATch
(1-800-525-3928). They can also be downloaded forfree from the Florida LAKEWATCH Web site:
or from the
UF/IFAS Electronic Data Information Source (EDIS): http://edis.ifas.ufl.edu


t -... r' e.":- z---- "
cm: --


West Crystal Lake in Seminole County.

n 1957, G. Evelyn Hutchinson, a world of these characteristics. In Part 3, we will tie it all
famous limnologist (lake scientist), had this together with information on how these dynamics
to say about the importance of oxygen in affect the ability of plants and animals to live in
aquatic systems: water (a.k.a. biological
productivity). Part 4 includes
"A skillful limnologist can prob- more technical information
ably learn more about the nature ; on the methods used to
of a lake from a series of o i obtain oxygen and tempera-
determinations than from any ". ture measurements.
other kind of chemical data. If Because this publication
these ci i,.,, determinations are .is intended for a varied
audience, we've tried to
accompanied by observations on psent te mteria
i -. ....present the material in
Secchi disk tirili rii lake ii reader-friendly portions
color, and some morphometric' and placed the technical
data, a great deal is known about information into sidebars.
the lake." ..Be sure to take a minute to
S review the outline on the
Many would agree that .- ~.-
Many would agre tt following page to familiarize
this statement is as valid
yourself with the chapter
today as it was in 1957. heain cote
headings and content.
However, he did forget to Lastly, we'd like to
mention one thing: in addition explain why LAKE WATCH
explain why LAKEWATCH
to oxygen, the temperature doesn't include oxygen
of water is an equally monitoring in its normal
important component of lake ecosystems. In fact, utine. Even though its obviously
sampling routine. Even though it is obviously
oxygen and temperature are so closely linked thatant, this type of sampling is not logistically
important, this type of sampling is not logistically
it's nearly impossible to discuss one without the feasible on a regular basis. As described in Part 4,
other. Sometimes it's difficult to know which
the equipment is expensive and the process can
should be considered first. be difficult to do. However, arrangements can be
For the purposes of this circular, we'll start made if you suspect that oxygen problems are
with oxygen as it is key to the survival of all occurring your lake. For more information,
occurring your lake. For more information,
aquatic organisms not to mention us landlubbers! please call us at 1-800-LAKEWATCH (525-3928).
Part 1 begins with a brief tutorial about
oxygen in water, including how it enters and Editor s Note: While many of the concepts described in this
exits a waterbody and how it is measured. In circular are similar in the saltwater environment, we will
be limiting our discussion to freshwater systems.
Part 2, we will delve into the physical properties of be limiting our discussion to freshwater systems.
water (e.g., forms of water, density of water, etc.)
and the influences that temperature has on each The term morphometric refers to the size and shape of an object.

Figure 1
The Three Forms of Water and the Energy Required to Move From One Form to Another 9

Figure 2
Water Density and Temperature in Water 10

Figure 3
Lake Stratification and Temperature Profiles 11

Figure 4
Diel (Daily)l Oxygen Curve 18

Figure 5
Dissolved Oxygen Percent Saturation 25

Table 1
Correction Factors for Lake Altitude 26


Table of Contents

Introduction i

List of Figures ii

Table of Contents iii

Part 1 Oxygen and Water
Oxygen, Temperature and Altitude 1
Dissolved Oxygen 1
Measuring Dissolved Oxygen (DO) in Water 3
Oxygen Saturation 3
Sidebar: The Difference Between Dissolved Oxygen and Oxygen Saturation 3
Part 1 Section Summary 5

Part 2 Temperature and Water
Factors Influencing Water Temperature 7
Sidebar: The Relationship Between Air Temperature and Water Temperature is Two-Sided 7
Forms of Water 8
Water Density 8
Sidebar: Lake Stratification and Temperature Profiles 11
Sidebar: Technically Speaking: Definitions for the Physical Properties of Water 10
Thermal Stratification in Lakes 11
Sidebar: Plants and Their Effect on Stratification 12
Lake Turnovers 13
Sidebar: Saltwater Stratification 14
Sidebar: Turnover Terminology 15
Part 2 Section Summary 15

Part 3 Biological Productivity, Oxygen and Temperature
Oxygen and Biological Productivity 17
Algae, Aquatic Plants and Oxygen 18
Other Factors That Can Decrease Oxygen in Water 19
Temperature and Its Affect on Fish Populations in Florida Lakes 19
Sidebar: Analyzing Fish Kills 20
Sidebar: Cold-water Vs. Warm-water Fish 21
Part 3 Section Summary 21

Part 4 Methods Used for Measuring Dissolved Oxygen in Water
Electronic Measuring Methods 23
Chemical Analysis 24
Sidebar: Technically Speaking: The Mechanics of a DO Meter 24
Sidebar: What Does LAKEWATCH Do? 26
Part 4 Section Summary 26

Selected Scientific References 27

Florida LAKEWATCH (General Information) 28


14, 0


Water's ability to hold and release not really a factor. However, in areas of higher
oxygen is perhaps its most valuable elevation, even in neighboring Georgia, altitude
attribute, as oxygen is critical to the can play a role in the amount of oxygen available
survival of all aquatic life. Because of this unique in water. The rule here: as altitude increases, the
trait, many organisms including algae, bacteria, amount of oxygen in a lake decreases. This can be
aquatic plants, amphibians, insects, and fish are explained by simple physics. At higher altitudes,
able to breathe or "respire" underwater. The there is less pressure being exerted on the surface
downside of this arrangement is that oxygen of a waterbody and, as a result, there is less oxygen
concentrations tend to fluctuate considerably being "pushed" into the water from the atmosphere.
within the aquatic environment. Sometimes there
can be a surplus and, at other times, oxygen Dissolved Oxygen
levels can drop so low that fish and other animalsis a si e m e
Water HO is a simple molecule made
can become stressed or even die. When this
up of two atoms of hydrogen (H,) and one atom
happens, people become alarmed and frequently, of oxygen (0). However, the oxygen that fish and
the first assumption is that the fish kill resulted
other organisms use underwater does not come
from pollution. However, what many people don't from the actual water molecules themselves. That's
realize is that the vast majority of these events i
because the single atoms of oxygen found in water
are the result of naturally occurring processes. molecules are bound to the two hydrogen atoms
molecules are bound to the two hydrogen atoms
To have a better understanding of these
Sand are not available. Instead, all aquatic organisms
processes and the effects they can have on the
use dissolved oxygen gas (O,) that is constantly
biological community of a lake or waterbody entering water from two main sources: the
entering water from two main sources: the
we will begin with a look at the relationship atmosphere and from photosynthesis.
between oxygen and water.
between oxygen and water. Oxygen from the atmosphere continuously
enters the surface of a waterbody through a
Oxygen, Temperature process known as diffusion. Molecule by molecule,
and Altitude oxygen gas (02) is pushed into the water by
The first thing you need to know about pressure from the air above. Wind and wave
oxygen and water is that there are two main action can accelerate the diffusion process because
factors that set the limits on how much oxygen waves create more surface area for oxygen to
can be "held" by a freshwater lake: temperature enter the water. Artificial wave action, via aerators,
and altitude. can also increase oxygen concentrations in water.
In the southeastern portion of the United
States, water temperature plays the largest role in 2 There are times when cooler water may not necessarily hold
influencing the amount of oxygen in a waterbody. more dissolved oxygen than warm water See Lake Turnover
The rule of thumb: warm water holds less oxygen section described on page 13.
than cool water.2 3 The term "dissolved oxygen is a bit of a misnomer as the
Because most lakes in Florida are situated at oxygen gas (0) that enters water doesn't dissolve, but instead,
So j a s l l ai is moves around through the water column amongst the water
sea level or just above sea level, lake altitude is moecues (H20).


The amount of
oxygen in a lake or The amount
waterbody is constantly of oxygen
changing. This is due to in a lake or
the fact that, even as
oxygen is entering the waterbody
aquatic environment, it is constantly
is also being removed changing.
by biological activity
within the water.
Biological activity includes the regular day-to-day
functions of virtually all the inhabitants of a
waterbody, including algae, bacteria, fish, insects,
plants, etc. As these organisms carry on about
their normal activities, they are constantly re-
moving oxygen from the water and releasing
carbon dioxide as a by-product. This process is
known as respiration.
Respiration is essentially the opposite of
photosynthesis. Much of the time, the respiration
that occurs within a waterbody is offset by
photosynthesis so there is a surplus of oxygen
available in the water. But not always. As mentioned
earlier, photosynthetic activity is reduced under
low light conditions (e.g., cloudy weather). This
means that once the sun goes down, algae and
aquatic plants are no longer producing oxygen
but they are continuing to consume oxygen. As a
result, the lake's oxygen supply takes a double
"hit." If a lake experiences several days of low
oxygen production due to cloudy weather or
other low light conditions, it could encounter low
oxygen concentrations that can be detrimental to
fish and other organisms in the water.
2 For more on the subject, see LAKEWATCH
SInformation Circular 107 A Beginner's Guide to
0 Water Management Fish Kills (Understanding Fish
Kills in Florida Freshwater Systems).
Photosynthesis is perhaps the most critical
source of oxygen, especially in waterbodies Additionally, in lakes where a large amount of
where algae or aquatic plants are abundant. As aquatic vegetation or algae have died all at once,
we learned in grade school, photosynthesis is a increased activity within the bacterial community
process whereby plants and algae use carbon alone can pull oxygen from the water faster than
dioxide, water, and sunlight to make their own it can be replaced (i.e., as the bacteria work to
food. Oxygen is a by-product of this activity. As decompose the plant or algal material). If there is
long as photosynthesis is taking place, oxygen is enough dead plant or algal material involved,
continuously being released into the water. In the oxygen problems can occur even during daylight
early morning hours, or in the evening, or during hours.
low light conditions, photosynthetic activity is See Part 3for more about the effects that low c, II '
reduced. At night, it stops all together. can have on the biological productivity of a waterbody.


Oxygen Saturation
Many people will be surprised to learn that
there are times when a waterbody can actually
become supersaturated with oxygen. In other
words, the water is holding so much oxygen that
; it isn't able to hold anymore. Under these condi-
S : rtions, water can be described as having a dissolved
S oxygen saturation of greater than 100 percent.
At times, this percentage can be as high as 140,
150 or even 300 percent!
When water is supersaturated, oxygen
molecules will begin to move around within the
Measuring Dissolved Oxygen (DO) water column, looking for a little elbowroom. If
In Water there is none available, the oxygen gas will
Dissolved oxygen concentrations can be return to the atmosphere or attach itself, in the
determined by conducting a series of complex form of bubbles, to submersed plants or along the
chemical reactions or they can be measured bottom. In the summer, when daylight hours are
electronically with an oxygen meter. The disadvan- at a maximum, this happens with some regularity.
tage to chemical analysis is that it involves
substances that are potentially dangerous and it
The Difference Between Dissolved
is time consuming. Today, most scientists rely on
electronic meters even though there are complica- Oxygen and Oxygen Saturation
tions related to their use, as well. For one thing,
they must be calibrated properly for accurate It is important to note that oxygen saturation
readings. Otherwise, the measurements are is NOT the same as dissolved oxygen:
meaningless, or worse, inaccurate readings can
lead to the wrong conclusions when monitoring a Dissolved oxygen is the amount of oxygen
lake. Secondly, a good meter costs about $1,000; measured in water, in milligrams per liter
for many individuals or monitoring programs, (mg/L).
this can be prohibitive.
See Part 4 on page 23for detailed information on how to Oxygen saturation is the potential that a
measure DO using chemicals and/or with a DO meter. waterbody has for holding oxygen, based
primarily on water temperature and altitude.
What is the "normal" dissolved oxygen
concentration in freshwater systems? Percent oxygen saturation is the ratio
In most freshwater environments, DO between actual dissolved oxygen measure-
measurements usually range somewhere between ments and the water's potential for holding
six and ten milligrams per liter (mg/L). When oxygen. Knowing the percent oxygen
measurements drop down to three or four milli- saturation of a waterbody can help determine
grams per liter, fish and other aquatic life will whether there is an oxygen surplus or a
begin to experience stress, especially if the drop deficit. If there is a deficit, it means that the
in oxygen occurs suddenly. Few organisms are amount of respiration occurring in the
able to survive in water when dissolved oxygen water, from aquatic life, is exceeding photo-
levels are below 2 milligrams per liter. synthesis and/or diffusion. Under such
circumstances, the potential for a fish kill or
Note: In water management circles you may also see
other oxygen related problems is high
measurements that are represented as parts per million ygen related problems is high
(ppm). This is the same as "milligrams per liter." (i.e., illness, fish stress, etc.).

See Part 3 on page 17for more about the effects of low
c, !, on aquatic life.



Fanning Springs, Florida


Measuring percent oxygen saturation and activities within the aquatic environment,
Scientists have developed a technique for respiration can sometimes create an oxygen
calculating the percent oxygen saturation of a deficit, causing problems for a lake's inhabitants.
waterbody. Using a nomogram,4 one can use both
the temperature of the water and dissolved Measuring Dissolved Oxygen (DO) In Water -
oxygen measurements to determine what the Dissolved oxygen concentrations can be determined
percent oxygen saturation should be at any by conducting a series of complex chemical
given time. reactions or measured electronically with an oxygen
meter (a.k.a. a DO meter).
See page 25for a detailed explanation on how to use a Chemical analysis involves substances that
nomogram. are potentially dangerous and the process is time
consuming. Today most scientists use electronic
Part 1 Section Summary meters. When using a DO meter, one should
always be sure it is calibrated properly.
Oxygen, Temperature and Altitude See page 24 for instructions on how to use a DO meter.
Temperature and altitude are the two main factors
In most freshwater environments, DO
that set the limits on just how much oxygen can be
,,i measurements typically range between six and
"held" by water. In the southeastern portion of the masrem s tpilly rage between ix
United States, the temperature of the water plays ten milligrams per liter (mg/L). At three or four
United States, the temperature of the water plays
milligrams per liter, fish and other aquatic life
the largest role. The rule of thumb is that warm ill gi periene s
will begin to experience stress.
water holds less oxygen than cool water.5 In areas
of higher elevation (i.e., outside of Florida), lake Oxygen Saturation Oxygen saturation is NOT
Oxygen Saturation Oxygen saturation is NOT
altitude can play a role; as altitude increases, the i
S n n a l d the same as dissolved oxygen. Dissolved oxygen is
amount of oxygen in a lake decreases.
Sthe amount of oxygen measured in water, in
Dissolved Oxygen In the aquatic environment, milligrams per liter (mg/L). Oxygen saturation is
virtually all aquatic organisms use dissolved oxygen the potential that a waterbody has for holding
gas (02) for respiration. This gas is constantly enter- oxygen, based primarily on water temperature and
ing water from two main sources: the atmosphere altitude. Percent oxygen saturation is the ratio
and from photosynthesis. between actual dissolved oxygen measurements
The atmosphere continuously provides and the waterbody's potential for holding oxygen.
oxygen gas through a process known as diffusion Knowing the percent oxygen saturation of a
(i.e., tiny oxygen molecules are pushed into the waterbody can help determine whether there is
water by pressure from the atmosphere above). an oxygen surplus or a deficit.
Photosynthesis is thought to be the predomi- If there is a deficit, it means that the amount
nant source of oxygen in many lakes, especially of respiration occurring in the water (i.e., from
in waterbodies where algae or aquatic plants are aquatic life) is exceeding photosynthesis and/or
abundant. (Algae and plants use sunlight and diffusion. Under such circumstances, the potential
carbon dioxide for growth and release oxygen for a fish kill or other oxygen related problems is
into the water as a by-product.) high (i.e., illness, fish stress, etc.).
Furthermore, the amount of oxygen in a
Furthermore, the amount of oxygen in a 4 A nomogram is a graphic representation that
waterbody is constantly changing due to biological onsiss o s ra ines are o to sae
consists of several lines marked off to scale and
activity within the water. Aquatic organisms arranged in such a way that a straight-edge can be
remove oxygen from the water in a process used to connect known values on two separate parallel
known as respiration, which is essentially the lines (a line above and a line below), where an un-
opposite of photosynthesis. Much of the time, known value can be read at the point of intersection
respiration that occurs within a waterbody is along a middle line. See Figure 5 on page 25.
offset by photosynthesis, so there is a surplus of
oxygen in the water; but not always. Depending 5 There are times when cooler water may not
oxygen necessarily hold more dissolved cie i r i. See Lake
on the water temperature, the amount of sunlight, ed o p .
Turnover section described on page 5.



Lake Alice on the University ofFlorida campus in Gainesville, Florida.


Now that we have a better understanding
of the relationship between oxygen and The relationship between air temperature
water, we can begin to look at the role and water temperature is two-sided.
that temperature plays in all of this. We will start While it's true that air temperature is a major
off with a quick review of how lake water cools influence on water temperature, the reverse is
and/or heats and then continue with more detailed also true. Lakes, ponds, and coastal areas
information on the influence that temperature (bays, marshes, etc.) act as thermal reservoirs
has on the physical properties of water, including for the surrounding countryside. In other
the forms of water and their related densities. words, a large lake or waterbody can help
After that, we will discuss thermal stratification keep the surrounding landmass cooler in the
and lake turnovers two phenomena that are summer and warmer in the winter. This
closely linked with water temperature. phenomenon is known as the thermal inertia
of the hydrosphere.
Factors Influencing Water Temperature At times, a nearby lake or waterbody can
even offer protection from freezes during
Energy from the sun and air temperature periods of cold weather by transferring heat
are the two main factors that influence water from water back into the air. Thus, lakes serve
temperature. But there are other influences, as as natural climate modifiers in agricultural
well. Inflows and outflows (creeks, streams, areas, protecting crops from frost and freeze
wastewater discharge, groundwater seepage, damage by warming the air. In Florida, many
etc.); the shape and depth of the lake basin (i.e., orange groves, nurseries and farms are
lake morphometry); wind and waves; even the located near lakes to take advantage of this
color of the water can influence temperature. protection.
The size of a waterbody and the volume of Such an arrangement may seem ideal but
water generally determines just how much it can also result in contention between lake
management and the agricultural community.
influence air temperature will have on a lake. maaeme a agruura o u
For example, some years ago a group of lake
For instance, in the summer months, water in a
managers proposed lowering the water levels
small shallow lake will heat up faster than a large in Lake Apopka, to solidify the lake bottom and
deep lake. The same is true during the winter in improve the lake's fishery. Ultimately, this
northern climates; a small shallow lake may strategy was not selected partly because
freeze while large deep lakes may only experience the loss of water would have greatly reduced
ice formations along the shoreline, or not at all. the freeze protection for orange groves near
Thanks to the ever-present energy from the the lake. Community leaders judged the risk of
sun, water temperatures are slower to change freeze damage to the region's agriculture to be
than air temperature. Of course, in the wintertime, unacceptable.
the sun has a more difficult time doing its job. Professionals who manage freshwater
Because water temperatures are slow to systems should remember that there are often
change, the aquatic environment is a fairly stable many factors that have to be considered when
place to live for many organismsdeveloping a lake management plan.
place to live or many organisms.


Forms of Water Water Density
Depending on its temperature, water exists Water density changes with water temperature.
in three distinct forms a solid, a liquid, and a gas: Anyone who is interested in studying the aquatic
d o b z d C iu i.., sciences will need to be familiar with the following
Solid At or below zero degrees Celsius (i.e., 32 h
temperature-related dynamics, as they can have
degrees Fahrenheit), water becomes solid in the t d
form of ice. a major influence on the biology and chemistry
form of ice.
of lakes.
Liquid At zero to 100 degrees Celsius (33 212 F) See F
See Figure 2 on page 10.
water exists as a liquid.
As water cools from 35 degrees Celsius (95 F),
Gas At 100 degrees Celsius (212 F), water changes s em 35 trees lsius (5 F),
it becomes more dense until it reaches its maximum
from a liquid to a gas, through boiling. However,
Sa l o a density at 4 degrees Celsius (39.2 F). After that,
it can also change from a liquid to a gas, at any
an interesting phenomenon occurs: as water
temperature above freezing, through evaporation. an interesting phenomenon occurs: as water
becomes colder than 4 degrees Celsius, the density
See Figure 1 on page 9for a diagram of the three begins to decrease. Finally at zero degrees Celsius,
forms of water and the i',,i,1 required to move from water becomes ice and is less dense (i.e., lighter)
one form to another, than its liquid counterpart. At this point, ice
floats to the surface even though it is a solid.
While Floridians are less familiar with This is a good thing. Otherwise, ice would
water's solid form (i.e., ice, snow, and sleet), we form on the bottom of the lake, increasing in
are quite familiar with the liquid version as it is volume and eventually displacing all the liquid
abundant throughout the state in thousands of water.
lakes and ponds, dozens of rivers, springs, and If this were to happen, there would be no
along 1,200 miles of coastline, habitat left for fish and other organisms. Moreover,
The third form of water the gas or "vapor" floating layers of ice on the surface of a lake also
phase is not as visible as the other two, but its act as a thermal barrier, helping to prevent
presence is definitely felt in the form of humidity, further loss of heat from the waterbody.
especially on a hot summer day. Or it can also
take the form of fog on a cold morning. Needless There is another interesting aspect to the
to say, the liquid form is the most popular, as relationship between water density and water
residents and tourists spend billions of dollars on temperature that causes significant changes in
water-related activities every year. lakes:


The difference in water density, for every during the summer in Florida, it is common to
one degree of change (Celsius), increases dramati- have water temperatures of 30 degrees Celsius at
cally at higher water temperatures, whereas the the top of a lake and 29 C at the bottom. So,
smallest density difference for one degree of although the lake may only have a one degree
change occurs at 4 degrees Celsius (39.2 F). difference in water temperature between the top
In other words: the difference in water and bottom, the density difference between the
density between 29 and 30 degrees Celsius (84.2 two layers may be great enough to prevent the
86 F) is significantly greater than the difference in water from physically mixing (i.e., from wind/
water density between 4 and 5 degrees Celsius wave action).
(39.2 41 F) about 40 times greater! If these conditions were to last long enough,
it could result in a loss of oxygen within the
See Figure 2 on page 10 for an illustration of the relation- bottom l d ultimately have a detrimental
bottom layer and ultimately have a detrimental
ship between water density and temperature in water, affect on aquatic organisms, including mussels

Accordingly, as the difference in density and other invertebrates.
increases, so does the amount of energy required See the next section of this chapter for more about
to mix the two layers of water. For example, thermal stratification.

Figure 1
The Three Forms of Water and the Energy Required to Move
From One Form to Another

Temperature (-10 aC 0 c) (0C) (20 bC) (20 C)
(-23.3 F} 132 El (32 F) 68 'F) (6p oF)

Sgram I gram ga
Phase Solid solid rm 1 rami gram
ice"e wat water

t t t +
5 calories 80 calories 20.2 calories 540 calories
Energy Specific Het c Heat of Fusion cSpei Heat of Wter Heat of Evporalon
O.5 calories PC 80 calories/g mPC t1.01 clre gm / C 540 calories / gmn C

The figure above describes the three different forms of water and the amount of energy
required for a "phase change" to occur from one to another. Notice that it takes a lot
more energy for water to change from a liquid to a gas (i.e., about 540 calories per gram
[gm] of water) compared to the energy it takes to change from a solid to a liquid, which is
about 80 calories.


Figure 2 Water Density and Temperature in Water



30 -

Sship between zero and 10 degrees Celsius,

Indicating that the maximum density is at 4 C.
S 15-
0-Density (gm/cm)

sionals describe the p p ti Figure 2 illustrates the relationship between
5-9voc68 (gm. m3)A water density and temperature in water. The
I smaller graph shows the expanded relation-
Sship between zero and 10 degrees Celsius,
r 4 4o indicating that the maximum density is at 4 C.
Density (gmncm3)

Professionals describe the physical properties of water using a somewhat specialized
vocabulary. Anyone wanting to learn about oxygen and temperature in water should be
familiar with the following terms and definitions:

Calorie A calorie is a measure of energy. The scientific community defines a calorie as the amount of
energy required to raise the temperature of 1 gram of water by one degree Celsius.
Note: T is not the same as food calorie (a.k.a. kilo calorie or big calorie) which equals 1,000 "energy"
calories. In other words: a 165-calorie bagel should be,. to as a 165-kilo calorie bagel.

Heat refers to the motion of the particles of matter.

Heat of fusion is the heat that is required to convert one gram of a material from its solid form to a
liquid state at the melting temperature (i.e., measured in calories). The mathematical equation for the
heat of fusion is L = Q/m, where Q is the total heat absorbed and m is the mass of the substance.

Heat of evaporation is the heat of water at the point of evaporation (i.e., boiling water). Additionally,
there is a relationship between the amount of evaporated water and the heat energy used to make it
evaporate. This quantity can be measured in units of calories. The heat of evaporation is also determined
based on the temperature dependence of the vapor pressure and air pressure.

Phase change refers to the process by which water changes from one form to another (e.g., from a
liquid to a solid). During a phase change, the physical properties of water may change, but its chemical
properties remain the same.

Specific heat is the amount of energy (i.e., measured in calories) required to raise the temperature of
one gram of water, by one degree Celsius.

Temperature A measure of the average kinetic energy of molecules.


Thermal Stratification in Lakes Lake Stratification and
If you swim in a lake during the summer, Temperature Profiles
you may notice that the water near your feet (i.e.,
the deeper water) is cooler than the water at the
Figure 3 (below) compares the relationship
surface. This is because the surface water has
S, between lake depth and temperature for a lake
been warmed by the sun and, as a result, has
in Iowa and Florida. Both temperature profiles
become less dense or "lighter" than the cooler
S shown in the graph were taken in August.
water below it. This warm/cool layering effect is
known as thermal stratification. As illustrated in the figure, the uppermost layer
Most of the time, such density differences of warmer water is called the epilimnion. The
are caused by differences in water temperature. deeper, relatively undisturbed layer of cooler water
Even a difference as slight as one degree can is the hypolimnion and the layer of water
result in stratification. Furthermore, as the between these zones is the metalimnion. This
difference in temperature increases (i.e., between is the zone where water temperature changes
the surface water and the bottom of the lake), so most rapidly in a vertical direction (a.k.a. the
will the stability of the stratified layers; the thermocline).
"stronger" the stratification, the more difficult it
is for the water to mix. Notice that in the Florida lake, there is a much
A textbook example of thermal stratification smaller temperature difference between the
can be found in many of the deeper lakes up surface and bottom; temperatures range from
north. In fact, much of the terminology used to about 30 degrees Celsius (C) down to 24 C, a
describe this concept was originally developed difference of only 6 degrees. In the Iowa lake,
from research conducted on northern lakes. In a the temperature span is considerably larger,
"typical" northern lake, it has been found that ranging from 25 C down to about 10 C (i.e., a
differences in water density will cause the water 15-degree difference). This tells us that the
column to split into three distinct temperate stratification in the Florida lake is not as strong
regions. These regions are defined as follows: or stable as the stratification in the Iowa lake.

* The uppermost, well-mixed layer of warmer Note: While "strong" stratification happens less
water is called the epilimnion. frequently in Florida's shallow lakes, it does
occur in the deeper spring-fed or sink hole lakes
* The deeper, relatively undisturbed layer of found throughout the state.
cooler water is the hypolimnion.
Figure 3
* The layer of water between these zones is the Figure0- -
metalimnion, the zone where water temperature Epiimnion
Epilimnion -5 o
changes most rapidly in a vertical direction.
Metalimnion -10- thermocline
Within the metalimnion, there is an area ------------ c
scientists refer to as a thermocline. Technically- 0
speaking, a thermocline is defined as a layer of Hypolimnion -20
water where the temperature decline exceeds one
degree Celsius (1 C) per meter. In other words: -25-
the area acts as a barrier, or a transitional zone, -30
separating the upper warmer layer from the o Iowa
deeper cooler layer. The upper warmer part of Florida
the metalimnion mixes with the epilimnion, -40-
while the bottom cooler part of the metalimnion 10 15 20 25 30 35
mixes with the hypolimnion. Temperature (
11Temperature (


As a general rule, warmer water above the In the fall, when the water begins to cool,
thermocline does not mix significantly with the the thermocline will migrate upward until density
cooler water below the thermocline. Consequently, differences are so weak that mixing occurs once
the location of the thermocline in northern lakes is again, between the surface and the bottom. This
relatively stable over a period of weeks. However, mixing is commonly referred to as a lake turnover.
during spring and summer months, it is constantly
See page 13 for more about lake turnovers.
being pushed deeper into the water column as the
upper layer of water warms up along with the air
per n Florida, the stratification dynamic is a little
different. Because most lakes in the state are
L relatively shallow, there is usually only a small
difference between water temperature measured
at the surface and at the bottom. As you can see
from Figure 3, even in August, there is a much
smaller temperature difference between the surface
and bottom of the Florida lake versus the Iowa
lake: the surface/bottom temperatures shown for
the Florida lake range from about 30 degrees
Celsius down to 24 C a difference of only six
degrees. In the Iowa lake, the temperature span is
considerably larger, ranging from 25 C down to
about 10 C (i.e., a 15-degree difference). This tells
us that stratification in the Florida lake is not as
"strong" or stable as stratification in the Iowa lake.
Of course, there are always exceptions. Florida's
deeper sinkhole lakes sometimes experience
g- substantial stratification, particularly during calm
sunny days when there is plenty of solar energy
Available to warm undisturbed surface waters.
This temporary condition can last a few hours or
~ days, depending on weather conditions.

There are many reasons to study thermal
< stratification in a lake:
Plants and Their Effect Temperature differences within a stratified
on Stratification waterbody can help us predict the amount of
oxygen that should be available to fish and other
Although plants generally increase oxygen organisms. For example, lakes that experience
levels in lakes, via photosynthesis, an greater differences in water temperature from top
abundance of aquatic plants can also to bottom generally tend to have less oxygen
increase a lake's stratification and, as a near the bottom, even though the water is cooler.
result, restrict the potential for oxygen in (Note: While cooler water has the potential to
hold more oxygen, there are times when dissolved
the water. Too many plants can block out
oxygen concentrations are lower in cool water,
sunlight, creating substantial temperature especially at greater depths where there is no
differences between water on the surface
access to atmospheric oxygen and photosynthetic
and the bottom. Additionally, dense activity is limited due to lack of sunlight.)
aquatic plants can reduce wind and wave
action, limiting the ability of lake water to See Part 3for more about the effects ;lat ',,i aJIL
mix and become further oxygenated. can have on the biological activity within a lake.


Lake Turnovers of the lakes here in Florida, turn over on a regular
When a lake is stratified, water within the basis. Because they are shallow, even the slightest
various layers does not mix unless something wind and wave action can mix the water column,
forces it to such as boat traffic, wind or storm from top to bottom throughout the year.
events, etc. This is because water of differing If a Florida lake does happen to maintain
densities is naturally resistant to mixing. stratification, a lake turnover will generally occur
In some strongly stratified lakes, water may in the fall, but it can also occur during the summer
completely mix only once or twice a year, which given the correct environmental conditions. For
is the only time when water temperatures are example, heavy winds and/or cold rain can break
uniform throughout the water column from the the stratification by physically mixing surface
surface to bottom. This phenomenon usually and bottom waters. This mixes higher oxygen
only occurs in the spring and fall and is referred concentrations within the surface water with the
to as a lake turnover because the lake's water relatively low oxygen concentrations in the
completely mixes or "turns over." bottom layer of water.
In the fall, turnovers take place when air If the volume of low oxygen water at the
temperatures begin to drop and the surface bottom of the lake is much greater than the
waters of a lake begin to cool. As surface waters volume of oxygen-rich water near the surface,
cool, they become more dense and begin to sink the mixing action can result in lowering DO levels
to the bottom, breaking through the stratified throughout the entire water column. As we
layers. As a result of this process, the water learned earlier, if oxygen concentrations should
within the lake is allowed to mix. This scenario is fall below 2 or 3 mg/L, there is a distinct chance
common in deepwater lakes up north, that fish and other aquatic organisms will begin to
In contrast, shallow waterbodies, like many have trouble.

Heavy winds and/or cold rain can break up the stratification by physically mixing surface and bottom waters.


Saltwater Stratification

In addition to thermal stratification, lake water can stratify due to differences in salinity.
This is because salt water is more dense than freshwater.* In many coastal Florida lakes,
surface waters are relatively fresh and float on top of the denser salt water underneath.
At times, this can result in a lake supporting both freshwater and saltwater fish!
This peculiarity occurs in several lakes in northwestern Florida (i.e., the Panhandle),
and other coastal areas throughout the state.

* Typical lake water, with no salinity, has a density of 1.00000 (gm/cm3) whereas the density of seawater
(at approximately 35 parts per thousand) is 1.02822 (gm/cm3).

Western Lake in Walton County, Florida.


Section Summary Although mixing adds oxygen, extreme situations
Part 2 and rapid mixing can have negative effects.
Storms with strong winds and large amounts of
Factors Influencing Water Temperature -
ators Infuenng ater temperature cold rain during extremely hot weather can rapidly
Energy from the sun and the temperature of the
r t mix a lake. During these warm weather conditions,
air surrounding a lake or waterbody are the main i
there is more oxygen in the surface water and
influencing factors on water temperature. Other
infless in the bottom water. Rapid mixing can lower
influences include inflows and outflows, lake
s ad o the oxygen concentrations throughout the water
morphometry, wind, waves and lake color. The
column enough to stress or kill fish.
size of a water-body and the volume of water e
Deep lakes found up north and even some
generally determine the influence that air tem-
S e of Florida's deeper lakes naturally experience lake
perature will have on a lake. Also, due to the
perature will ae o a lae lso ue to turnovers each fall as surface waters cool and
sun's energy, water temperature is slower to
begin to sink to the bottom.
change than air temperature.

Forms of water Depending on its temperature, Turnover Terminology
water exists in three forms: solid, liquid and gas.
In lake science circles, there are several
terms that are used to describe the
Water Density In its liquid form, water density frequency of lake turnovers:
changes with temperature. The difference in
density, for every single degree of change (Celsius), Lakes that mix only once a year are often
density, referred to as monomictic. Accordingly, lakes
increases dramatically at higher water tempera- that mix once a year, during the coldest part of
tures, whereas the smallest density difference for the year, are referred to as cold monomictic
one degree of change occurs at 4 degrees Celsius lakes. Some deeper Florida lakes are consid-
(39.2 F). Accordingly, as the difference in density ered to be cold monomictic waterbodies
increases, so does the amount of energy required because they mix in the wintertime (i.e., once
to mix the two layers of water. the water cools down enough to "de-stratify").
Warm monomictic lakes tend to mix only
Thermal Stratification Because deeper water is once, during the warmest part of the year.
cooler and denser than surface water, a layering Many Canadian lakes fit this category as they
effect often develops in lakes; cooler water stays mix during the summer, just after the spring
thaw and before freezing again in the fall.
deep and warmer water (i.e., which is less dense)
is found near the surface. This condition is called Most northern lakes in the U.S. are considered
thermal stratification; the differences in water to be dimictic because they mix twice a year
(i.e., in the fall and the spring).
densities are the result of differing temperatures. (i.e., in the fall and the spring).
Thermal stratification is often considered Shallow lakes, like many of the waterbodies
the most important aspect of temperature's found in Florida, are considered to be polymictic
influence on lakes. Shallow Florida lakes are not because they can turn over many times each
as well stratified as the deep-water lakes in north- year.
ern states, but there are differences in temperature
between the surface layer and water near the
bottom, often times by several degrees. Stratifica-
tion makes it more difficult for mixing to occur
between the layers. This lack of "mixing" can
keep oxygen from reaching the deeper, stratified
water and, under certain conditions, and can
result in low oxygen problems within a waterbody.

Lake Turnovers Layers of water can "turn
over" when wind and wave action effectively
mixes the water, despite density differences.




C Brown studies a sampling of aquatic plants during a water quality workshop on Hall Lake in Leon County, Florida.


A after reviewing the relationship between Hypereutrophic (hi-per-you-TROH-fic) lakes
oxygen, temperature, and water, we can have the highest level of biological productivity.
now discuss how these factors affect the A typical hypereutrophic waterbody will have
biological productivity of a lake (i.e., the ability very limited water clarity (i.e., due to an abun-
of plants and animals to survive in the aquatic dance of algae) and the potential for lots of fish
environment). We'll start by introducing a few and wildlife. It may also have an abundance of
key terms that scientists commonly use to describe aquatic plants.
biological productivity. Using these definitions,
which are part of the Trophic State Classification
System, lakes are grouped into one of four Oxygen and Biological Productivity
categories called trophic states:6 Over the years, there has been extensive
research conducted to document the relationship
Oligotrophic (oh-lig-oh-TROH-fic) lakes have the between the biological productivity of a lake and
lowest level of biological productivity. the amount of oxygen in the water. As a result of
A typical oligotrophic waterbody will have clear this work, there are a few generalizations that
water, few aquatic plants, few fish, not much can be made. For example, oligotrophic lakes
wildlife, and a sandy or rock/gravel bottom. seem to experience relatively small changes in
oxygen concentrations over a 24-hour period.
Mesotrophic (mees-oh-TROH-fic) lakes have a This can be attributed to the fact that lakes with
moderate level of biological productivity. A typical low productivity experience less photosynthetic
mesotrophic waterbody will have moderately activity and also less respiration (i.e., due to the
clear water and a moderate amount of aquatic smaller number of aquatic organisms within the
plants, fish and wildlife. waterbody).
On the other end of the spectrum, more
Eutrophic (you-TROH-fic) lakes have a high level productive waterbodies, such as eutrophic and
of biological productivity. A typical eutrophic hypereutrophic lakes, have been found to experi-
waterbody will either have lots of aquatic plants ence large fluctuations in oxygen concentrations
and clear water or it will have few aquatic plants over a 24-hour period. This is attributed to the fact
and less clear water (i.e., dominated by algae). that lakes with lots of aquatic plants and animals
In either case, it has the potential to support lots tend to experience high levels of photosynthetic
of fish and wildlife. activity and respiration; there's simply a lot more
going on within the system. These waterbodies
also happen to have the greatest potential for
6 The Trophic State Classification System was developed in
oxygen-related problems.
1980 by two Swedish scientists, Forsberg and Ryding. oxygen-related problems.
It is based on four main criteria: total chlorophyll, total
phosphorus, total nitrogen and water clarity (Secchi See Figure 4 on page 18for an example of the fluctua-
depth). There are times when LAKEWATCH includes tions that occur in dissolved c. i,.'., il concentrations
aquatic plants as an additional criteria for assessing within a lake or waterbody, during a 24-hour period.


Algae, Aquatic Plants, and Oxygen emergent plants, submersed plants, floating
In Florida, it has been documented that plants or floating-leaved plants.7 During day-
hypereutrophic lakes, with chlorophyll concen- light hours, all of these plants add oxygen to the
trations of 100 milligrams per liter (mg/L) or water (and air) via photosynthesis. But they also
greater, have an increased risk for catastrophic use oxygen 24-hours a day. Accordingly, an over-
oxygen loss especially during extended periods abundance of plants can have a variety of negative
of cloudy weather or after a die-off of a dense algal effects on oxygen concentrations in lakes:
bloom. Some of the most problematic situations i i
When there are too many aquatic plants dying
exist when there are several consecutive days of
st when there are seerl consecutive ds of (e.g., from natural causes or weed control) oxygen
hot cloudy weather, with little or no wind. Such levels can drop dramatically due to activity
levels can drop dramatically due to activity
conditions represent a double jeopardy for
conditions represent a double jeopardy for within the bacterial community as it works to
aquatic life. It works like this:
aquatic life. It works like this: decompose the dead plants. When this happens,
As the layer of warm surface water increases bacteria consume even more oxygen.
bacteria consume even more oxygen.
in volume (i.e., from solar heating), there is less
potential for water to hold oxygen in the top When floating and floating-leaved plants are
portion of the lake. If there is no wind, there is too thick, they can prevent oxygen from diffusing
even less oxygen diffusing into the water from into the water. They can also reduce mixing within
the atmosphere. Likewise, cloudy weather the water column by preventing wave action.
reduces the amount of photosynthetic activity Shade created by an abundance of floating
Shade created by an abundance of floating
within the aquatic community. Under such hot
within the aquatic community. Under such hot plants and floating-leaved plants can prevent
conditions, algae and aquatic organisms continue lit fom racing s eed plans ad a e,
light from reaching submersed plants and algae,
to respire, using oxygen faster than it is being li x
limiting their ability to produce oxygen.
produced or diffused into the lake. If the oxygen r
deficit becomes large enough, it can have a
detrimental effect. 7 Emergentplants aquatic plants that emerge or protrude out
Even more dramatic reductions can occur of the water
following a massive algal bloom. As algae begin Submersed plants aquatic plants that grow below the surface.
to die, oxygen levels can drop due to bacteria
SFloating plants aquatic plants that float on the surface; roots
working overtime to decompose the dead algal are not attached to the bottom (e.g., water hyacinth).
material and consuming more oxygen as a result.
Floating-leaved plants aquatic plants that are primarily
A similar dynamic can occur with larger rooted to bottom sediments but also have leaves thatfloat on the
aquatic plants (aquatic macrophytes), including water surface (e.g., water lilies.)

Figure 4 Diel (Daily) Oxygen Curve At "normal" summer temperatures (i.e., in a
I waterbody), dissolved oxygen concentrations
S o- will generally be high if algae and aquatic plant
"! o populations are actively photosynthesizing and
E -
producing more oxygen than is being consumed.
8- This usually occurs in the mid to late afternoon.
o 7_ Conversely, DO concentrations will fall below
Saturation if there is not enough wind to mix
0 6- the water or if plant and animal populations are
Q consuming more oxygen than is being produced.
5 That's why the lowest DO levels often occur during
12am 6am 12pm 6pm 12am
(midnight) (midnight) pre-dawn hours. Also, on cloudy days, when there
is less photosynthetic activity, DO concentrations
Time of Day can potentially drop to lethally low levels.


Other Factors That Can Decrease Oxygen Growth rate Following that same line of
In Water thought, it also means that northern fish grow
For the most part, we have been focusing on more slowly than a similar species in warmer
the effects that aquatic plants and algae have on southern waters. In essence, cooler water translates
oxygen concentrations in a waterbody. However, into a shorter growing season for fish. This has
it's important to note that other substances, from been documented over and over again. For
outside the lake, can also play a role in the oxygen example, largemouth bass in a northern lake
"equation." For example, if a lake is receiving may take up to 15 years to reach a weight of ten
heavy inputs of natural organic matter (i.e., pounds while the southern warm-water variety
dissolved substances from leaves, twigs, grasses, may reach the same weight in only five years.
etc.), oxygen concentrations in the water can dip
to levels that are below saturation. Reproduction Water temperature is also
to levels that are below saturation. extremely important to fish reproduction.
This situation generally occurs in Florida's C e i mpratre are on o t i
Changes in temperature are one of the main
highly colored lakes due to inputs from the .
triggers for fish spawning activity. Rapid
watershed (i.e., during periods of heavy rain) trigges r i panin act Ra
changes in temperature in a lake can cause
and the dynamic is similar to that of a large algal a es in temperate in e cn
fatalities for most fish species during their
bloom die-off. Once the material is introduced to titie or ots during their
.reproductive period; eggs or newly hatched fry
the waterbody, organisms within the bacterial reprodctie perid e or e a d fr
l n t k h t d can die from a dramatic temperature drop.
community will begin to work harder to decompose
community i i r rSometimes dramatic temperature variables
the material and, as a result, may deplete oxygen c e s aba the nest
cause adults to abandon the nest.
faster than it is being produced.
Of course, each of these processes are affected
e ad Is E t O F in a slightly different way, depending on the
individual species. (Details are beyond the scope
Populations in Florida Lakes of this publication. For more information, refer to
As described in the thermal stratification the sources provided in the back of this booklet.)
section (Part 2), water temperature is rarely Since there are several variables that can affect
uniform throughout an entire lake. In fact, it can the ideal temperature for individual species, only
vary by one or two degrees, even within a range general statements can be made.
of a few feet. Because of this, the distribution of In the book, Principles of Fisheries Science
many fish species also varies throughout a (W. Harry Everhart, Alfred W. Eipper and William
waterbody. Different species thrive at different D. Young, 1975), the authors state that 21 degrees
temperatures and as a result, they tend to stay in Celsius represents a general division between
a particular area within a lake, where the tempera- cold-water and warm-water fish populations.
ture is best for them. This means that cold-water species, including
But that's not all. Ambient water temperature trout, do not live at temperatures above 21 C (69 F),
"drives" several important life processes for fish whereas warm-water species, such as channel
including their metabolic rate, growth rate and catfish, do best when water temperatures are well
reproduction. above 21 degrees. In fact, a channel "cat" can
even survive for a while when water temperatures
Metabolic rate Because fish are cold-blooded climb into the 30-degree range (90 F)!
animals, their rate of activity is based on the Fish populations in Florida are considered
temperature of the water. For example, if we to be "warm-water" species because they can
were to compare a fish living in a northern lake tolerate warm water temperatures year-round.
with a similar species in a southern lake, we More than 100 native warm-water species thrive
would find that the northern fish has a slower in the various freshwater habitats around the
metabolism than its southern counterpart; the state, though most people only come into contact
cooler water in the northern lake basically lowers with about a third of them. Out of all of these
a fish's energy requirements and as a result, they fish, it is safe to say that the largemouth bass is
need less food. the single most popular species.


This fish was inadvertently introduced into
Florida waterbodies in 1961 and is now success-
fully reproducing in 24 counties. However, those
who worry about the further spread of such fish,
can take some comfort in knowing that their
distribution is often naturally limited by their
sensitivity to low temperatures.
S This very scenario was demonstrated
recently in Lake Alice, a small waterbody on the
University of Florida campus in Gainesville,
Largemouth bass (Micropterus salmoides salmoides) located in north central Florida. For several
years, the lake supported a population of blue
However, many people do not know that
tilapia that was estimated to be around 12,000

are stocked in lakes throughout the south, provid- for several weeks. By January, dead tilapia
there ar e two different subspecies of largemouth began to float to the surface of the lake. By the

ing excellent fishing. They also provide a perfect middle of the month, all but a few of the tilapia
example of the various temperature tolerances that had died, while native species survived the cold
exist in fish, even within a single species. A case temperatures with few problems.
temperatures were considerably colder than the

in point: it is thought that severe freezes in the
late 1970s helped deplete fish populations in a
number of southern states when water tempera- Analyzing Fish Kills
tures dropped low enough to kill many stocked
Florida largemouth bass. However, Northern While cold-water stress often contributes to fish
largemouth bass survived just fine because of its die-offs, it may not be the only factor. For ex-
tolerance for lower water temperatures. am t lo if the d ead fish h f te o plake. l ot
While there was no immediate mass die-off subtropical (exotic) species only, temperature is
of the Florida subspecies (i.e., in Florida), water likely the main reason for the die-off. But if there
temperatures did get low enough to stress the are many different species of fish that have died,
fish in many lakes within the northern portion of i is ess likely that low temperature was the
the state. It was later thrizd tha t e stress, cause.
from the low temperatures, may have made When fisheries biologists examine fish kills,

many of the Florida subspecies susceptible to they also research weather conditions prior to
disease, as sick fish appeared in north Florida the event. I a cold front came through a week
lakes for months following the freeze and many before the dead fish appeared, it is possible that
probably ultimately died. the fish died right away and sank resurfacing
after a few days or even weeks.
For more information on fish stress, refer to UF/IFAS Seeing large numbers of floating dead fish on
LAKEWATCH Information Circular 107, Under- the surface of your lake can be very disconcert-
standing Fish Kills in Florida Freshwater Systems. ing and concern is highly justified. That is why,
when LAKEWATCH volunteers note weather
Florida lakes are also home to many exotic conditions accurately, the information gives
subtropical and tropical fish species. Several researchers a better overall picture of the lake's
consecutive years of mild winters have allowed ecology and can help explain the reasons
populations of these fish to colonize in lakes contributing to a fish kill, should one occur.
disfurther north in the state anred in north Florida the event. If a cold front came through a weekrge

laks f r norths following te e and mprode lar For more on fish kills, see LAKEWATCH Information
Fonumbers of offspring. One example isfish stress, refer theo UF/IFAS Seeing large numbers of floating dead fish on

standing Fish Kls ing F lorda Freswater Sstem. Circular 107 Understanding Fish Kills in Florida
tilapia (Oreochromis area) from Africa's Nile Freshwater Systems.


Part 3 Section Summary Cold-water Vs. Warm-water Fish

Oxygen and Biological Productivity Discussions about cold-water versus warm-water
Years of research have shown that there is a fish can be confusing as some warm-water
relationship between the amount of oxygen found species do live in northern lakes. For example,
in the water and the biological productivity of a lake some people may be surprised to learn that the
(i.e., the amount of algae, aquatic plants, fish and largemouth bass subspecies Micropterus
wildlife). Lakes with low productivity tend to salmoides salmoides can found in lakes as far
experience small changes in oxygen concentrations, north as Maine and Minnesota. While it is difficult
over a 24-hour period, and highly productive lakes to visually distinguish it from the Florida large-
experience much larger fluctuations. mouth bass (Micropterus salmoidesfloridanus),
these fish are genetically distinct.
Algae, Aquatic Plants and Oxygen For a fisheries manager, this is important
Both algae and aquatic plants play a major information as cold water temperatures can
role in the oxygen cycle as suppliers (via photosyn- affect one subspecies much more dramatically
thesis) and consumers (via respiration). If algae than another. An example: in the 1980s, when
and/or plants are extremely abundant in a large numbers of bass began dying in lakes in
waterbody, there are a number of negative upstate New York (i.e., the result of low pH,
(oxygen-related) effects that can occur especially caused by acid rain), biologists considered re-
when combined with changes in weather or stocking the lakes with Florida largemouth bass.
increases in water temperature. They theorized that since the Florida version
seemed to do well in lakes with naturally low
Other Factors That Can Decrease Oxygen In Water
Large inputs of dissolved and particulate alkalinity (pH), they would also do well in the
northern lakes. However, their "good idea"
organic matter can reduce oxygen concentrations northern lakes. However, their "good idea"
would not have worked because the Florida
in lakes.
subspecies cannot tolerate cold-water tempera-
Temperature and Its Effect On Fish Populations tures, and would have died that first winter.
in Florida Lakes For more on temperature related fish
Water temperature "drives" several important kills, refer to LAKEWATCH I Circular
life processes for fish including their metabolic 107, Understanding Fish 1. in Florida Freshwater
rate, growth rate, and reproduction. Because fish Systems.
are cold-blooded animals, their rate of activity is
based on the temperature of the water. This means
that northern fish grow more slowly than a. .
similar species in warmer southern waters. Also,
because their energy requirements are less than
warm-water fishes, cold water fishes tend to
need less food. During reproductive cycles, rapid
changes in water temperature can cause fatalities
for most fish eggs and larvae.
Fish found in Florida lakes are considered to
be "warm-water." There are also many exotic
tropical and subtropical fish species found in
lakes throughout the state which are even less
cold tolerant than our native warm-water species.
Fortunately, further distribution of these exotic
fish is "naturally" controlled by occasional cold
temperatures. LAKEWATCH director Mark Hoyer with a Florida
largemouth bass (Micropterus salmoidesfloridanus).


Electronic dissolved oxygen (DO) meters, like the one shown here in the foreground (on the left), cost about
$1,000. For many individuals and/or monitoring groups, this cost is prohibitive. Also, the underwater probe
that is used along with the meter is expensive (i.e., around $200) and once they break, the entire probe has to
be replaced. This is one reason why Florida LAKEWATCH is not able to offer oxygen monitoring on a regular
basis. Pictured above: One student is about to lower a Secchi disk into the Suwannee River to measure water
clarity while another prepares to record the measurement.


Scientists measure dissolved oxygen will provide you with three containers of water,
concentrations using electronic with temperatures ranging from about 10, 15 and
instrumentation and/or chemical analyses: 20 degrees Celsius. (Room temperature is about 20 C.)

Electronic Measuring Methods 3 Aerate the water within each of the containers
Today, scientists mostly rely on electronic by shaking them and occasionally lifting the
Today, scientists mostly rely on electronic
dissolved oxygen (DO) meters as a convenient lids, allowing air in. This technique generally
dissolved oxygen (DO) meters as a convenient
way to measure dissolved oxygen in the field provides water samples with an oxgen saturation
way to measure dissolved oxygen in the field.
These instruments eliminate the need for trans- approaching 100%.
porting potentially dangerous chemicals and the Now, measure and record both water tempera-
process is less time consuming than laboratory ture and dissolved oxygen concentrations from
chemical analyses. each of the containers, using a electronic DO
A DO meter requires no reagents and most meter. (Most models measure DO and temperature.)
of the substances that would normally interfere
with chemical determinations have little effect on 5 Find the nomogram chart (on page 25), and
sensor determinations. The most reliable read- place it in front of you, along with a ruler or
ings are obtained from waters with DO concen- straight-edge of some kind.
trations that are one milligram per liter (mg/L),
or higher. Readings for samples with lower 6 On the top axis of the nomogram (i.e., the
concentrations are only approximate, upper-most horizontal line) plot the three
riae oy Water temperature values you just collected.
A reliable, oxygen meter can be purchased
for about $1,000. It is essential that the meter be Then plot their corresponding dissolved oxgyen
values on the bottom horizontal axis.
calibrated correctly for accurate readings. Other- values on the bottom horizontal axis
wise, the measurements are meaningless. Worse Using the ruler or straightedge, draw a line
yet, inaccurate readings can lead to the wrong from each of the temperature values down to
conclusions when monitoring a lake. their corresponding dissolved oxygen values on

A Test for Determining if a DO Meter the bottom axis. The lines you draw should
A Test for Determining if a DO Meter
is Measuring Accurately intersect the middle line in the chart (a.k.a. the
diagonal Percent Saturation Line).
There are a few easy procedures that can be done
to test whether a DO meter is calibrated properly 8 Check to see where the lines are crossing
(also known as "setting a standard"): along the Percent Saturation Line. They
should be hitting at or near the 100 percent mark
SCollect three containers, with lids, and partially (i.e., within at least 0.5 points). If they are close,
fill them each with water (i.e., about 2/3 full). you'll know that the DO meter is calibrated and
Now take two of the containers and add working properly. If they are not close, you'll
2 .know that adjustments need to be made to the
varying amounts of ice to each. Leave one of know that adjustments need to be made to the
DO meter.
the water containers at room temperature. This


Chemical Analysis The glass stopper lid is immediately inserted
Chemical analysis of the oxygen content in a so the bottle becomes air-tight, eliminating the
water sample involves a complex series of chemi- possible introduction of additional oxygen.
cal reactions that occur upon adding various
chemical reagents at timely intervals. The standard The bottle is inverted several times to mix the
Winkler procedure is used to test for dissolved sample and reagents, at which time Manganous
oxygen in relatively pure waters. If oxidizing or ions will react with dissolved oxygen present in
reducing substances are present (e.g., nitrites or the alkaline sample, forming a manganese (IV)
ferrous iron), they often cause interference oxide hydroxide flocculent. The azide suppresses
leading to erroneous results. interference from any nitrites that may be present.
Modified Winkler methods include the
addition of reagents that eliminate interference Laboratory Procedures
(i.e., like those mentioned above) and are suitable
for determining dissolved oxygen in most natural The solution is then acidified using sulfuric acid.
waters. Before the electronic age, the azide
SB The manganese (IV) flocculate is reduced by the
modification of the Winkler method was the a o r r
addition of iodide to produce free iodine in
standard method for dissolved oxygen determina- p
proportion to the oxygen concentration.
tions. The analysis involved the following series
of field and laboratory procedures. As one can The liberated iodine is titrated to the starch-
imagine, such tedious procedures can make it iodide end-point, using sodium thiosulfate or
difficult to analyze samples, especially if a large phenylarsine.
number of samples need to be processed.
A starch indicator is added to enhance end
Field Procedures point determination by producing a color change
from dark blue to colorless.
* A sample of water, collected in special glass
bottle (BOD bottle) with a glass stopper lid, The dissolved oxygen of the sample is
is treated with manganous sulfate and azide. calculated from the quantity of titrant used.

Technically Speaking: The Mechanics of a DO Meter

D dissolved oxygen meters use an electrode equipped with a
temperature compensating thermistor. The electrode consists of
a gold cathode and a silver anode surrounded by a potassium chloride
electrolyte solution.
The sensor is isolated from the environment by a thin Teflon membrane
that allows gases to enter. As oxygen passes through the membrane, it
is consumed at the cathode and an oxygen pressure gradient is formed
across the membrane.
The membrane offers a resistance to the diffusion of oxygen to the
inside, with the amount passing through the membrane proportional to
Sthe oxygen pressure outside. The application of a polarizing potential
between the cathode and anode produces an electrical current that is
proportional to the amount of oxygen being reduced at the cathode. The
meter instrumentation converts the flow of current to a reading that
indicates the DO concentration in milligrams per liter (mg/L).
Note: Before using the DO meter, it is important that the sensor befitted
with a clean membrane and the meter is calibrated for local atmospheric
A digital DO meter used by LAKEWATCH. pressure.


Figure 5 Dissolved Oxygen Percent Saturation

As described in Part 1, the Percent Saturation of Dissolved Oxygen depends on the temperature of the
water and the elevation of the water testing site (i.e., ignoring biological activity). Because most of Florida
is at sea level, lake elevation is not usually included in the formula. However, in the far northern part of the
state or even in neighboring Georgia, some lakes are located at higher elevations so it is necessary to first
use the table on page 26 to find the correction factor for altitude. Once you have this number, you can
multiply it by the dissolved oxygen measurement (i.e., collected from the lake or waterbody in question).
The resulting value is known as the corrected dissolved oxygen concentration.
Once you have the corrected dissolved oxygen concentration you can use the nomogram chart below
to determine the percent saturation for the waterbody:
* Mark the corrected dissolved oxygen value on the bottom horizontal line of the chart.
* Now mark the corresponding water temperature on the upper horizontal line of the chart.
* Using a straight-edged instrument, connect the two marks and draw a straight line.
* Notice where the line crosses the percent saturation axis (i.e., the diagonal line).The numeric value that
you see at this point of contact is known as the percent dissolved oxygen saturation value.

Water Temperature in Degrees Celsius

r I I I 1 | 1 I I j I I I i [ I j I I I !j
o 5 10 15 20 25 30


2 3 4 5 6 7 S A 11 12 13 14 15 tO 11

Oxygen in mg/L
(Measured with a dissolved oxygen test kit or meter)

Example: If the water temperature for "My Lake" is 14 degrees Celsius (14 C) and if the dissolved
oxygen concentration measurement is 10 mg/L, it can be said that the percent dissolved oxygen
saturation of the water in My Lake is 100%.


Part 4 Section Summary How Does LAKEWATCH
Measure Oxygen and Temperature?
Methods Used for Measuring Dissolved
Oxygen in Water Dissolved oxygen concen- Florida LAKEWATCH does not regularly
trations can be determined by conducting a measure dissolved oxygen in lakes as it is
series of complex chemical reactions or measured too expensive and time consuming. However,
electronically with an oxygen meter. Today most DO measurements are taken electronically
scientists use electronic meters because chemical
by our regional biologists when special
analysis involves substances that are potentially irustanes warrpe i
dangerous and it is time consuming. However, circumstances warrant it. Temperature is not
there are complications related to the meters, as regularly monitored for the same reasons.
well. For one thing, it is essential that they be However, it is possible to calculate an
calibrated correctly for accurate readings. accurate correlation between air tempera-
Otherwise the measurements are meaningless, or ture and water temperature by obtaining air
worse, inaccurate readings can lead to the wrong temperature data from regional weather
conclusions when monitoring a lake. Secondly, stations. For more information, contact the
the cost of a good DO meter (i.e., about $1,000) Floria ati -800-5
Florida LAKEWATCH at sl-800-525-3928.
can be prohibitive for many individuals or
monitoring programs.

Table 1

Using the known atmospheric pressure or altitude (i.e., elevation) for a specific lake location, use the
table below to determine the correction factor. Once you have determined the correction factor, you can
multiply that number by the dissolved oxygen measurement (i.e., collected from the lake or waterbody in
question). The resulting value is known as the corrected dissolved oxygen concentration.

Atmospheric Pressure (mmHg*) Equivalent Altitude (ft) Correction factor

760 0 1.00
730 1094 0.96
699 2274 0.92
669 3466 0.88
654 4082 0.86
623 5403 0.82
593 6744 0.73
578 7440 0.76
562 8204 0.74
532 9694 0.70
517 10,472 0.68

mmHg is the abbreviation for a unit of measure known as millimeters of mercury, which is used to
measure the partial pressure of a gas.


Boyd, C. E. 1990. Water quality in ponds for Aquaculture. Auburn University Auburn, Alabama, USA.

Everhart, W. H., A. W. Eipper, and W. D. Young. 1975. Principles of fishery science.
Comstock Publishing Associates, a Division of Cornell University Press. Ithaca, New York. USA.

Hutchinson, G. E. 1957. A Treatise on Limnology. Volume I. Geography, Physics, and Chemistry.
John Wiley & Sons, Inc.. New York, New York. USA.

Wetzel, R. G. 1975. Limnology. W. B. Saunders Company. Philadelphia, Pennsylvania. USA.



Florida LAKEWATCH (FLW) is one of the In return for participation, volunteers
largest citizen-based volunteer monitoring receive:
endeavors in the country with over 1,500 Personalized training in water monitoring
individuals monitoring more than 700 lakes techniques;
and waterbodies, in more than 50 counties. Use of lake sampling materials and water
Staff from the University of Florida's Depart- chemistry analysis;
ment of Fisheries and Aquatic Sciences train Periodic data reports, including an
volunteers throughout the state to conduct annual data packet regarding their
monthly long-term monitoring of both fresh waterbody;
and saline waterbodies. LAKEWATCH uses Invitations to meetings where FLW staff
the long-term data to provide citizens, agencies provide an interpretation of the findings as
and researchers with scientifically-sound water well as general information about aquatic
management information and educational habitats and water management;
outreach. Access to freshwater and coastal marine
To become part of the FLW team, experts;
volunteers are required to have access to a Free newsletter subscription and educa-
boat and complete a two-hour training tional materials regarding lake ecology and
session. During the session, they will learnagement.
water management.
to collect water samples, take water clarity
measurements, and prepare algae samples For more information, contact:
for laboratory analysis. Once a volunteer is
certified by a regional coordinator and Florida LAKEWATCH
sampling sites are established, he or she UF/IFAS
will sample the designated stations once a Department of Fisheries & Aquatic Sciences
month. Samples are frozen immediately 7922 NW 71st Street
upon being collection and are later deliv- PO Box 110600
ered to a collection center, where they are Gainesville, FL 32653-3071
stored until they can be picked up by FLW Phone: (352) 392-4817
staff and delivered to the UF/IFAS water Toll-free: 1-800-LAKEWATch (1-800-525-3928)
chemistry laboratory at the Department of E-mail: lakewat@ufl.edu
Fisheries and Aquatic Sciences. Web-site: http:/ / lakewatch.ifas.ufl.edu/


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