GEOLOGICAL SURVEY 

CIRCULAR 601-K 

An Introduction to the 

Processes, Problems, and 

Management of Urban Lakes 

An Introduction to the 

Processes, Problems, and 

Management of Urban Lakes 

By L. J. Britton, R. C. Averett, and R. F. Ferreira 

WATER IN THE URBAN ENVIRONMENT 

G E 0 l 0 G I C A l S U R V E Y C I R C U l A R 601-K 

1975 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

First printing 1975 

Second printing 19 77 

Free on application to U.S. Geological Survey, National Center, Reston, Va 22092 
Glossary of selected terms ....................... . 

Conversion factors ............................. . 

Abstract ..................................... . 

Man and his lakes .............................. . 

What this report is all about ...................... . 

Physics, chemistry, and biology of lakes ............ . 

Physical characteristics ..................... . 

Light penetration ...................... . 

Temperature ......................... . 

Suspended sediment ................... . 

Morphology .......................... . 

Chemical characteristics ..................... . 

Major chemical constituents ............. . 

Minor chemical constituents ............. . 

Major plant nutrients ................... . 

Dissolved gases ........................ . 

Biological characteristics .................... . 

Plankton ............................ . 

Benthos ............................. . 

Nekton ............................. . 

Processes in lakes .............................. . 

Photosynthesis and respiration ............... . 

Eutrophication ........................... . 

The biogeochemical cycle ................... . 

Sedimentation ........................ . 

Nutrient cycling ....................... . 

Planning and management of watersheds and lakes 

for water quality control ...................... . 

Lake basin planning ........................ . 

CONTENTS 

Page 

IV 

VI 

1 

1 

2 

2 

2 

2 

3 

5 

5 

5 

5 

5 

6 

6 

6 

6 

6 

6 

9 

9 

10 

10 

11 

11 

12 

12 

Page 

Planning and management of watersheds and lakes 

for water quality control--Continued 

Watershed management . . . . . . . . . . . . . . . . . . . . . . 13 

Lake management . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Water quality control . . . . . . . . . . . . . . . . . . . . . . . . 13 

Algal blooms . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Anaerobic conditions . . . . . . . . . . . . . . . . . . . . 14 

Fish kills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Sediment deposition . . . . . . . . . . . . . . . . . . . . 15 

Summary of management options . . . . . . . . . . . . . . 15 

Conducting lake studies . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Measuring the properties of lakes . . . . . . . . . . . . . . . 16 

Physical measurements . . . . . . . . . . . . . . . . . . 16 

Mapping.......................... 16 

Temperature . . . . . . . . . . . . . . . . . . . . . . 16 

Light penetration . . . . . . . . . . . . . . . . . . . 17 

Chemical measurements . . . . . . . . . . . . . . . . . . 17 

Dissolved oxygen . . . . . . . . . . . . . . . . . . . 17 

Alkalinity and pH . . . . . . . . . . . . . . . . . . 17 

Major chemical constituents and 

specific conductance . . . . . . . . . . . . . . 17 

Minor chemical constituents . . . . . . . . . . 18 

Major plant nutrients . . . . . . . . . . . . . . . . 18 

Biological measurements . . . . . . . . . . . . . . . . . 19 

Phytoplankton and periphyton . . . . . . . . 19 

Zooplankton . . . . . . . . . . . . . . . . . . . . . . 20 

Benthic invertebrates . . . . . . . . . . . . . . . . 20 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

ILLUSTRATIONS 

Page 

Figure 1. The major life zones of a lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

2. Seasonal thermal profiles of a warm monomictic lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

3. Representative lake organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

4. Effect of man upon the eutrophication of lakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

5. Sources and cycling of elements in a lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

6. Typical growth pattern of blooming unicellular algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

TABLE 

Table 1. Common forms, minimum requirements, and some sources of elements essential for the growth of algae 

III 

Page 

7 
GLOSSARY OF SELECTED TERMS 

[Many of the definitions in this glossary were obtained or modified from Slack and others (1973).] 

Absorption (n). To take up and incorporate within the 

body. 

Adsorption (n). To take up and hold by adhesion to the 

surface. 

Aerate (v), aerator (n). To charge or treat with air or 

other gases, usually with oxygen. 

Aerobic (adj). Having oxygen. 

Alga, algae (n), algal (adj). A group of simple primitive 

plants that live in wet or damp places, and generally 

are microscopic in size, containing chlorophyll and 

lacking roots, stems, and leaves. 

Algal bloom (n). A high concentration of a particular 

algal species, amounting to ~ million to I million 

cells per litre of water or more. 

Algicide ( n). A chemical that kills algae. 

Anaerobic {adj). Devoid of oxygen. 

Assimilation (n), assimilate (v). To take up or incorporate within the body. Technically, secondary productivity plus respiration and other losses. 

Autumn overturn (n). The mixing of the entire water 

mass of a lake in the autumn. 

Bacterium, bacteria (n), bacterial {adj). Microscopic 

unicellular organisms. Some bacteria cause disease 

while others perform an essential role in the recycling 

of materials. 

Benthos, benthic zone (n). Organisms living in or on the 

bottom of an aquatic environment. The bottom of a 

lake or stream. 

Biochemical oxygen demand (BOD) (n). The quantity of 

dissolved oxygen, in milligrams per litre, used for the 

decomposition of organic material by microorganisms, such as bacteria. 

Biomass (n). The amount of living matter present in a 

unit area or volume, at any given time. 

Biota (n), biotic (adj). All the plants and animals in a 

particular area. 

Blue-green algae (n). A group of algae with a blue 

pigment, in addition to the green chlorophyll. Bluegreen algae group usually causes nuisance conditions 

in water. 

Carbohydrate (n). Chemical compounds containing carbon, hydrogen, and oxygen, such as sugars, starches, 

or celluloses. Most are formed by green plants and 

serve as basic food units for animals. 

Compensation level or depth (n). The depth of water at 

which oxygen production by photosynthesis balances 

oxygen uptake by respiration of plants and animals. 

The depth is usually where light intensity is reduced 

to about 1 percent of the surface light (Odum, 1971, 

p. 301). 

IV 

Consumer (n). An organism that is unable to manufacture its food from nonliving matter and is dependent 

on the energy and materials stored in other living 

things. 

Decomposition, decomposer (n). The breakdown of 

dead plant and animal tissue by bacteria to the 

elemental state. 

Density (n). The quantity or mass of a substance per 

unit volume. Computed as grams per cubic centimetre, in the case of water. 

Detritus (n). Fragmented material of inorganic or 

organic origin. 

Diatom (n). A unicellular or colonial alga having a 

siliceous shell. 

Dinoflagellate (n). A typically yellow-brown unicellular 

alga that swims by means of two laterally attached 

appendages called flagella (fig. 3). 

Dystrophic (adj). Brown-water lakes with a very low 

lime content and a very high humus content, often 

characterized by a severe lack of nutrients (Ruttner, 

1963, p. 254). 

Ecosystem (n). The community of plants and animals 

interacting together with the physical and chemical 

environment. 

Emersed plant (n). A rooted aquatic plant with leaves or 

other structures extending above the water surface 

(sometimes called emergent plant). 

Enrichment (n). Addition or accumulation of plant 

nutrients within a body of water (Greeson, 1971, 

P• 139). 1 

Environment (n). The sum of all the external physical, 

chemical, and biological conditions and influences 

that affect the life and development of an organism. 

Epilimnion (n), epilimnetic (adj). The upper, relatively 

warm, circulating zone of water in a thermally 

stratified lake. 

Erosion (n). The general process or group of processes 

whereby the materials of the Earth's crust are 

loosened, dissolved, or worn away, and removed from 

one place to another by weathering, solution, corrasion, and transportation (Gary and others, 1972). 

Euphotic zone (n). That part of the aquatic environment 

where light penetration is sufficient for photosynthesis. Refers to the combined littoral and limnetic 

zones of lakes. 

Eutrophication (n), euthrophic (adj). The natural 

process of enrichment and aging of a body of water 

that may be accelerated by the activities of man. 

Pertains to water bodies in which primary production 

is high because of a large supply of available 

nutrients. (See also Dystrophic, Mesotrophic, and 

Oligotrophic.) 
Fauna (n), faunal (adj). A collective term for all the 

types of animals in an area. 

Food chain (n). The transfer of food energy and 

materials from plants through other organisms, with 

repeated eating and being eaten. 

Fungus, fungi (n). Plants lacking chlorophyll, including 

molds, yeasts, mildews, rusts, and mushrooms. 

Grab (n). An instrument designed to "bite" into the 

bottom sediment of a lake or stream to sample the 

bottom materials and the benthos. 

Green algae ( n). Algae that have pigments similar in 

color to those of higher green plants. Some forms 

produce algal mats or floating "moss" in lakes. 

Heterotroph (n), heterotrophic (adj). An organism that 

requires organic material as a source of nutrition; 

includes all animals and most bacteria. 

Homothermous ( adj). At the same temperature throughout. 

Hypolimnion (n), hypolimnetic (adj). The lower, relatively cold, non-circulating water zone in a thermally 

stratified lake. 

Interpretative (adj). A type of sampling program or 

study designed to collect information useful in 

describing a system, and cause-and-effect relationships within the system. 

Invertebrate (n). An animal without a backbone. Common aquatic examples include worms, insects, snails, 

and crayfish. 

Ion (n). An electrically charged particle of matter dissolved in water. For example, in water, salt forms 

sodium ions (Na +) with positive charges, and 

chloride ions (Cr) with negative charges. 

Larva, larvae (n), larval (adj). An active immature stage 

of an animal during which its bodily form differs 

from that of the adult. (See also Nymph.) 

Limnetic zone (n). The open-water zone of a water body 

above the compensation level. 

Limnology (n). The science or study of inland waters. 

Littoral zone (n). The shallow zone of a body of water 

where light penetrates to the bottom. 

Mesotrophic (adj). Intermediate stage in lake classification between the oligotrophic and eutrophic stages, 

in which primary production occurs at a greater rate 

than in oligotrophic lakes, but at a lesser rate than in 

eutrophic lakes. This is due to a moderate supply of 

nutrients. (See also Eutrophic and Oligotrophic.) 

Metabolism (n). The sum of the chemical reactions in 

living cells in which energy is provided for vital processes and materials are assimilated for growth and 

tissue repair. 

Metalimnion (n), metalimnetic (adj). The middle layer of 

water in a thermally stratified lake, in which temperature decreases rapidly with depth. 

v 

Monitoring (n). A type of sampling program designed to 

determine time-trend changes. 

Monomictic ( adj). Lakes having only one circulation 

period per year. 

Nekton (n). Actively swimming aquatic organisms, such 

as fish. 

Nutrient (n). Any chemical element, ion, or compound 

that is required by an organism for the continuation 

of growth, reproduction, and other life processes. 

Nymph (n), nymphal (adj). An immature stage of an 

insect in which the body form resembles the adult. 

(See also Larva.) 

Oligotrophic (adj). Pertaining to waters in which primary 

production is low as a consequence of a small supply 

of available nutrients. 

Organic (n). Pertaining or relating to a compound 

containing carbon. 

Oxidation (n). The process in which oxygen chemically 

combines with a substance, or in which an element 

loses electrons. 

Periphyton (n), periphytic (adj). The community of 

microorganisms, such as algae, that are attached to or 

live upon underwater surfaces. 

Photosynthesis (n), photosynthetic (adj). The process 

whereby green plants utilize light as an energy source 

and convert chemical compounds to carbohydrates. 

In the process, carbon dioxide is consumed and 

oxygen is released. 

Phytoplankton (n), phytoplanktonic (adj). The plant 

part of the plankton. 

Plankton (n), planktonic (adj). The community of floating organisms which drift passively with water 

currents. 

Primary production (n). The synthesis of organic compounds by green plants in the presence of elements 

and light energy. 

Producer (n). An organism that can directly utilize raw 

materials to form organic matter. Includes all green 

plants and some bacteria. 

Production (n). The total amount of energy or organic 

matter produced from raw materials in an area per 

unit time, regardless of the fate of the material. 

Profundal zone (n). The deep zone of a water body in 

which plant growth is limited by the absence of light. 

Reconnaissance (n, adj). A type of sampling program or 

study designed to determine the present status of 

something; a preliminary survey. 

Reduction (n). The process in which a substance loses 

oxygen, or in which an element gains electrons. 

Respiration (n). A life process in which carbon compounds are oxidized to carbon dioxide and water. 

The liberated energy is used in the metabolic processes of living organisms. 
Rotifer (n). A group of many-celled, microscopic zooplankton (fig. 3). 

Secondary productivity (n). The rate of growth of the 

heterotrophs of the community. 

Secondary waste treatment (n). A step in waste treatment in which most of the organic matter of sewage 

is removed. 

Sediment {n). Fragmental material, both mineral and 

organic, that is in suspension or is being transported 

by the water mass or has been deposited on the 

bottom of the aquatic environment (Gary and others, 

1972). 

Sedimentation (n). The process of forming, transporting, 

and depositing sediment. 

Sorption (n), sorb (v). To take up and hold by either 

adhesion or incorporation. A collective term for 

absorption and adsorption. 

Species (n, sing. and pl.). The basic or final unit for the 

classification of organisms. 

Stagnation period (n). The period when warming or 

cooling of the surface water in lakes forms a thermaldensity stratification, preventing the mixing of the 

entire water mass. 

Substrate (n). The physical surface upon which an 

organism lives. 

Submersed plant (n). An aquatic plant that lives entirely 

below the surface of the water (sometimes called submerged or submergent). 

Suspended sediment (n). Fragmental material, both 

mineral and organic, that is maintained in suspension 

in water. 

Taxonomy (n). The division of biology concerned with 

the classification and naming of organisms. 

Tertiary waste treatment (n). An advanced step in waste 

treatment, in which excess nutrients, suspended 

matter, color, odor, and most of the organic matter is 

removed. 

Thermal stratification (n). A temperature distribution in 

which the lake water is distinctly layered because of 

thermal-density differences. 

Toxin (n), toxic (adj). A poisonous substance. 

Turbidity (n), turbid (adj). The ability of materials 

suspended in water to disturb or reduce the penetration of light. 

Water pollution (n). Any impairment of the suitability 

of water for any of its beneficial uses, actual or 

potential, by man-caused changes in the quality of 

the water (Warren, 1971, p. 14). 

Water quality (n). That phase of hydrology that deals 

with the kinds and amounts of matter dissolved and 

suspended in natural water, the physical characteristics of the water, and the ecological relationships 

between aquatic organisms and their environment. 

Watershed (n). The area drained by, or contributing to, a 

stream, lake, or other body of water. 

Zooplankton (n), zooplanktonic {adj). The animal part 

of the plankton. 

CONVERSION FACTORS 

Factors for converting English units to the International System of Units (SI) are given below to four significant figures. However, in 

the text the metric equivalents are shown only to the number of significant figures consistent with the values for the English units. 

English 

ft (foot) 

in (inch) 

in2 (square inch) 

Multiply by 

3.048 X 10"'"1 

2.540 

6.452 

VI 

Metric 

m (metre) 

em (centimetre) 

cm2 (square centimetre) 
Water in the Urban Environment 

An Introduction to the Processes, Problems, 

and Management of Urban Lakes 

By L. J. Britton, R. C. Averett, and R. F. Ferreira 

ABSTRACI' 

Lakes are bodies of water formed in depressions on the earth's 

surface, and as such, act as depositories for a variety of chtmlical 

and biological materials. The study of lakes has become 

increasingly prevalent in recent years. Lakes are a valuable 

resource, and their multiple uses have made them susceptible to 

water-quality problems such as algal blooms, sediment deposition and fish kills. These problems are products of the 

eutrophication process (enrichment, aging and extinction of 

lakes), which is often accelerated by man. Therefore, it becomes 

important to understand the properties and processes of lakes 

which govern lake enrichment, and the measures available to 

control enrichment. 

Lakes are described in terms of their physical (light 

penetration, temperature, sediment, and morphology), 

chemical (chemical constituents, plant nutrients:, and 

dissolved gases) and biological (plankton, benthos, and 

nekton) properties. These properties are all interre]ated, 

and are important variables to measure to evaluate water 

quality. In addition, lake processes, such as photosynthesis, respiration, eutrophication, and biogeochemical cycling, are important factors in determining 

the sources and extent of enrichment, and managing a 

lake for maximum benefit. Meeting demands for water 

of high quality requires a general knowledge of lake 

properties and processes, coupled with lake-basin planning, watershed and lake management, and water-quality 

control. There are many lake-management and control 

practices, but the best tools for quality control are 

preventive measures. Once extensive enrichment has 

occurred, there are few management or control options 

available. 

As lake studies become more common, sampling 

techniques for data collection need increased accuracy 

and consistency, in order to make meaningful comparisons between different lakes. Therefore, the report 

discusses the main factors involved in conducting lake 

studies. These factors include the types and frequency of 

measurements useful in lake reconnaissance studies and a 

review of literature on sampling equipment and techniques. A glossary of selected terms begins the report, 

which is intended for guideline use by urban planners 

and managers. 

MAN AND HIS LAKES 

Lakes and reservoirs are significant and ever-changing 

features of the landscape. Because they form in depressions on the earth's surface, they are depositories for 

material moved by both air and water. Their ultimate 

fate is to become filled with sediment and support 

terrestrial life. 

Man's attraction to lakes is well marked in his history. 

Yet, in spite of his long use of lakes and reservoirs for 

water supplies, waste disposal, power generation, navigation, and recreation, he understands very little of their 

characteristics. The study of inland waters (limnology) is 

less than 100 years old (Welch, 1952, p. 4) and only in 

the past several decades has a significant literature 

developed. 

Much recent literature on limnology has been concerned with eutrophication, the enrichment and filling 

of lakes with plants and sediment. Today, accelerated 

eutrophication, resulting from man's activities, is a 

serious problem in many lakes. As a result, new 

approaches to lake and reservoir management are being 

sought, and public awareness of the need for lake 

management is increasing. 

Many lakes and reservoirs, which were once far 

removed from significant human impact, are now found 

near the edges and sometimes well within urban areas. 

Thus urban planners are now faced with the task of 

managing lakes for maximum public benefit. 
Urban lakes and reservoirs have a multitude of uses 

and lake management must take these uses into consider~ ation. In many areas, natural lakes are scarce, and 

reservoirs have been formed to provide water for 

agricultural and domestic consumption, as well as for 

recreation. 

While reservoirs differ somewhat from natural lakes 

both have a number of characteristics and problems U:. 

common. Unless otherwise specified, the term "lake" 

will be used in this report to denote both natural and 

manmade standing bodies of water. 

The framework for this circular is based upon 

experience in studying lakes of the San Francisco Bay 

area. While urban lakes in other parts of the country 

may have somewhat different physical, chemical, and 

biological characteristics than those near San Francisco 

all such lakes have one thing in common--intensive u~ of their water and watersheds by the public. The result is 

a need for greater understanding of lake processes, and 

how lakes can be managed to insure the highest possible 

quality of water compatible with optimum use. 

Ownership and management of urban lakes are under 

the jurisdiction of various agencies. Too often each 

agency collects limnological data independently of the 

other agencies, and a comparison of results between 

lakes is difficult to make. Consequently, there is a need 

for consistency and accuracy of sampling and sampling 

techniques if a meaningful comparison is to be made. 

WHAT THIS REPORT IS ALL ABOUT 

This circular was written as a part of a comprehensive 

reconnaissance of the physical resources of the San 

Francisco Bay area begun in 1969 by the U.S. Geological 

Survey, in cooperation with the Department of Housing 

and Urban Development. 

Specifically the circular has three major objectives: 

1. To provide the urban planner with a brief introduction to the properties and processes of lakes 

and how these properties and processes affect 

water quality. 

2. To inform the urban planner of common lake 

problems and possible management solutions to 

these problems. 

3. To provide the urban planner with guidelines for 

making lake reconnaissance surveys. 

Pertinent literature on the various subjects discussed is 

referenced, and the reader is urged to consult the 

literature for a more thorough discourse. Problems and 

management of real-estate lakes, lakes created for 

particular housing or commercial areas or developments, 

have been thoroughly covered in a report by Rickert and 

Spieker (1971). This document should be consulted by 

2 

planners concerned with real-estate lakes. Many of the 

problems of real-estate lakes are common to all lakes 

and some overlap between the circular by Rickert and 

Spieker and the present report is inevitable. 

A glossary of the technical terms used in this report 

follows the contents. 

PHYSICS, CHEMISTRY AND BIOLOGY 

OF LAKES 

The physical, chemical and biological systems of lakes 

are complex and interrelated. Any one influences and is 

influenced by the others. For example, sunlight penetrating the water triggers the growth of phytoplankton (floating one-celled plants). If conditions are favorable, the 

phytoplankton become so numerous that they reduce 

light penetration. Reduced light penetration may not only 

result in the arrest of continued phytoplankton production, but it may also influence the rate of warming of 

the lake water by the sun (Welch, 1952, p. 176). Thus a 

biological process (phytoplankton production) is 

influenced by and influences light penetration, which in 

turn influences the heat balance of the lake. 

PHYSICAL CHARACTERISTICS 

LIGHT PENETRATION 

Limnologists have defined distinct zones in lakes 

based upon the extent of light penetration in the wate; 

(fig. 1 ). The littoral zone is the shallow-water area where 

light reaches the bottom. At times, wave action may 

cause shoreline erosion and bring materials into suspension in the water. These suspended materials may cause a 

"turbid" condition and reduce the penetration of light 

and thus the depth of the littoral zone. Emersed (above 

water) and submersed (below water) rooted green plants 

grow in the littoral zone. 

The limnetic zone is the open-water area of a lake that 

extends from the surface to the depth where light 

intensity is reduced to about one percent of the surface 

light (Odum, 1971, p. 301). In theory, the lower 

boundary of this zone is the compensation level, which 

is the depth at which oxygen uptake by bacteria, plant, 

and animal respiration equals photosynthetic oxygen 

release by green plants. The depth of the compensation 

level depends upon the light-scattering and absorbing 

material in the water. The limnetic zone is inhabited by 

free-floating and swimming organisms, such as plankton 

and fish. The combined littoral and limnetic zones are 

referred to as the euphotic zone, the area where there is 

sufficient light for photosynthesis. 

The profunda/ zone is the deepwater area where only 

respiration and decomposition· occur. Ught intensity is 
water surtace 

II 

I I 

Lrf\OR~LlONE t.rnersed p\ants 

f\oat\ng \eai p\ants 

3 
DEGREES CELSIUS 

LATE AUTUMN EARLY SPRING 

0 5 10 15 20 25 0 5 10 15 20 25 

I I I I 

\ WIND DIRECTION DEGREES CELSIUS I DEGREES CELSIUS 

SUMMER STRATIFICATION 

0 10 15 20 25 

~ L---~----~-_j_--~----- Direction of circulation DEGREES CELSIUS 

Figure 2.-Seasonal thermal proftles of a warm monomictic lake. 

stratification, which limits wind mixing to the upper 

water layer. The result is the formation of three water 

layers. The upper water layer, the epilimnion, is thermally uniform and contains the warmest water in the 

lake. The lower water layer, the hypolimnion, is usually 

thermally uniform and contains the coldest and most 

dense water in the lake. Between these two layers is the 

metalimnion, a water mass with a temperature that 

rapidly decreases with depth. When these three water 

layers are distinct, the lake is thermally stratified and is 

referred to as being in the summer stagnation period 

(Welch, 1952, p. 59). With the cooler air of autumn, the 

surface water of the lake begins to cool, and the annual 

thermal cycle repeats itself. 

There are many variations in the thermal cycle. In 

colder areas, the surface water freezes in the winter. 

Once the lake surface is frozen, circulation by wind 

action is prevented, and further loss of heat to the 

4 

atmosphere is reduced. The water just below the ice is 

near freezing, but the water at greater depths may only 

cool to the temperature of maximum density ( 4°C). 

Thus, inverse thermal stratification may occur in these 

lakes during the winter. 

Many shallow lakes become stratified during periods 

of calm, but may be completely mixed by moderate 

winds. Moreover, shallow lakes of small surface area are 

more quickly heated or cooled by atmospheric or other 

external influences than deep lakes of relatively larger 

surface area. Other lakes are continuously mixed and 

thermal stratification never occurs. 

There are several schemes for the classification of 

lakes, but that proposed by Hutchinson (1957, p. 438) is 

perhaps the most useful. His classification is based upon 

the thermal and circulation patterns of lakes. For 

example, the San Francisco Bay area lakes would be 

classified as warm monomictic lakes. This classification 
refers to lakes in warmer latitudes where the temperature of the water is never below 4°C at any depth, 

complete circulation occurs once a year in late autumn 

or winter, and thermal stratification occurs during the 

summer. 

SUSPENDED SEDIMENT 

The amount of suspended sediment in water is very 

important from a water-quality standpoint. Streams 

entering lakes carry suspended sediment, which rapidly 

settles and fills the lake basin. If the streamborne 

sediment has a high organic content, it may also increase 

oxygen demand in the bottom water. Moreover, several 

minor chemical constituents and plant nutrients are 

commonly adsorbed by suspended material, especially 

clay. Consequently, suspended sediment transports 

many substances essential for plant growth. Suspended 

sediment may also enter the lake from runoff or wave 

action. 

MORPHOLOGY 

Light, temperature, and suspended sediment are 

important physical characteristics of lakes. However, 

other characteristics also provide meaningful information, and are frequently measured during lake surveys. 

These include: 

Flow-through or retention time--The time 

necessary for the volume of a lake to be 

replaced by inflowing water. 

Maximum depth--The greatest vertical distance 

between the surface and the bottom of a lake. 

Mean depth--The volume of a lake divided by its 

surface area. 

Maximum length--The longest straight-line 

distance over the surface of a lake. 

Maximum width (breadth)--The longest straightline distance perpendicular to the long axis of a 

lake. 

Shoreline length--Circumference of a lake. 

Stage--The elevation of a lake surface. 

Surface area--The total water surface enclosed 

within a lakeshore. 

Volume--The amount of water in a lake basin at 

any given time. Maximum volume refers to total 

capacity of a lake. 

Watershed (drainage area)--The total land and 

water surface area that is drained through the 

outlet of a lake. 

CHEMICAL CHARACTERISTICS 

Chemical constituents in water consist of dissolved 

solids, such as calcium and magnesium, gases, such as 

oxygen and carbon dioxide, and organic compounds. 

5 

The chemical characteristics of lakes are very important 

from the standpoint of water quality. Useful categories 

for discussing the chemical properties of water are (1) 

major chemical constituents, (2) minor chemical constituents, (3) major plant nutrients, and ( 4) dissolved gases. 

A complete <iiscussion of the individual constituents in 

these categories is given in Hem (1970). 

In the analyses of water for chemical constituents and 

major plant nutrients, the constituents may be in 

solution or sorbed {taken up) by particulate matter. The 

separation of dissolved and particulate materials is 

accomplished by flltration. Usually a filter having a pore 

size of 0.45 micrometre is used. However, some of the 

materials that pass through a fllter of this pore size may 

be colloidal and not truly in solution {Hem, 1970, 

p. 87-88). But from a practical standpoint, dissolved 

materials are those not removed when the water is 

flltered. 

MAJOR CHEMICAL CONSTITUENTS 

The major chemical constituents of dissolved solids in 

freshwater are listed below. The concentration of major 

chemical constituents is usually expressed in mg/1 

{milligrams per litre). Simple and accurate methods are 

available for their analysis, and for this reason, they are 

commonly determined in most lake studies. Under 

natural conditions, the concentrations of these constituents are related primarily to the minerals in the 

surrounding rocks. However, man's waste materials may 

add significant amounts of these constituents to water. 

An analysis of major chemical constituents is of value in 

assessing pollution and eutrophication problems in lakes. 

Most, if not all, of the major chemical constituents are 

essential for the growth of plants. 

Major chemical constituents 

Silica (Si02 ) 

Calcium (Ca) 

Magnesium (Mg) 

Sodium (Na) 

Potassium (K) 

Bicarbonate (HC03 ) 

Carbonate (C03 ) 

Sulfate (S04 ) 

Chloride (Cl) 

Fluoride (F) 

Nitrate (N03 ) 

MINOR CHEMICAL CONSTITUENTS 

The minor chemical constituents occur in low concentrations in water (generally less than 1 mg/1). Their 

concentrations are usually expressed in J.J.g/1 (micrograms 

per litre), which is one thousandth of 1 mg/1. Minor chemical constituents are important in water, as most of them 

are essential plant nutrients. Moreover, when found in 

even modest concentrations, some may be toxic to plants 

and animals. Some of the minor chemical constituents 

found in freshwater are listed on page 6. 
Aluminum (AI) 

Iron (Fe) 

Manganese (Mn) 

Boron (B) 

Arsenic (As) 

Bismuth (Bi) 

Cadmium (Cd) 

Chromium (Cr) 

Cobalt (Co) 

Minor chemical constituents 

Copper (Cu) 

Lead (Pb) 

Mercury (Hg) 

Molybdenum (Mo) 

Nickel (Ni) 

Titanium (Ti) 

Vanadium (V) 

Zinc (Zn) 

MAJOR PLANT NUTRIENTS 

A nutrient is any substance necessary for the promotion of growth, repair of tissue, or energy needs of an 

organism (Fruh, 1967). Nitrogen, phosphorus, and 

carbon (in their several forms) are considered to be the 

major plant nutrients because their concentrations in 

water are most likely to be exhausted by phytoplankton 

and limit further growth (Tailing, 1962). However, a 

literature review by Greeson (1971, p. 75) revealed that 

there are at least 21 elements, in some chemical 

combination, essential for the growth of phytoplankton 

(table 1 ). Most of these elements do not become limiting 

in water. 

DISSOLVED GASES 

The dissolved gases that are commonly measured in 

water are oxygen and carbon dioxide. While carbon 

dioxide is the end product of respiration, it is also a 

form of carbon that green plants can use in photosynthesis to form organic compounds used for cell 

structure and metabolism. During the photosynthetic 

process plants consume carbon dioxide and produce 

oxygen. This oxygen may be reused by plants and 

animals in respiration. 

Usually the carbon dioxide concentration in water is 

not measured directly because of analytical difficulties. 

Dissolved oxygen, however, can be accurately determined using field techniques. As a result, oxygen is the 

gas commonly measured during lake surveys. 

BIOLOGICAL CHARACTERISTICS 

Lakes support a great variety of bacteria, plankton, 

higher plants, insect and fish species (fig. 3). These 

organisms can be placed into three broad categories: 

plankton (drifters and some swimmers), benthos (bottomdwellers), and nekton (swimmers). The relationships and 

interactions among these various groups of organisms 

must be considered if a lake is to be successfully managed 

for aquatic crop production or fo:t: the control of 

biological nuisances. 

Plant and animal life are affected by changes in water 

quality. Lakes are relatively closed systems, and interacting organisms remain in balance only in suitable 

6 

water-quality conditions. The introduction of excessive 

amounts of inorganic and organic materials in the water 

disrupts the organism balance. This may lead to an 

unstable ecosystem, often resulting in conditions adverse 

to man's use of the water. 

PLANKTON 

The planktonic community is composed of organisms 

that inhabit all the water zones of a lake. Two major 

categories of plankton are recognized--phytoplankton 

(plants) and zooplankton (animals). Phytoplankton are 

mostly microscopic, whereas zooplankton can frequently be seen with the unaided eye. Phytoplankton 

usually drift with the currents, while some zooplankton 

are strong swimmers. Phytoplankton growth depends 

upon solar radiation and nutrient elements, while zooplankton feed on phytoplankton, bacteria, or dead 

organisms. 

The phytoplankton community (primary food producers) includes several major groups of plants collectively known as algae. The most common groups of 

free-floating algae are the diatoms, green algae, and 

blue-green algae. Usually it is the blue-green algae that 

become overabundant and cause esthetic, taste, and odor 

problems in lakes. 

Other types of plants which may inhabit lakes are the 

algae attached to solid surfaces (periphyton) and rooted 

submersed and emersed higher plants. Rooted plants are 

found in the littoral zone of lakes, where sufficient 

sunlight for photosynthesis reaches the bottom. 

The zooplankton community (primary consumers) is 

dominated by small crustaceans and rotifers. Typically 

the zooplankton spend the daylight hours in the deeper 

water and rise toward the surface in late afternoon and 

early evening. The kinds and numbers of zooplankton in 

a lake are closely controlled by the available food supply 

and by grazing of predators such as fish. 

BENTHOS 

The benthic community (consumers and decomposers) includes a number of different types of organisms, such as bacteria, insect larvae and nymphs, snails, 

clams, and crayfish. These organisms are an integral part 

of the food chain of an aquatic environment. Benthic 

organisms feed on both plants and animals, and they in 

turn are fed upon by higher organisms. The bacteria and 

fungi are especially abundant on the lake bottom and 

decompose the organic materials that settle there. 

NEKTON 

The nektonic community (consumers) consists of 

relatively large free-swimming organisms. This community consists primarily of fish and certain insects. 

Nektonic organisms feed on benthos and plankton in the 

lake. In most lakes, fish are at the end of the food chain 
-....] 

Table I.--Common forms, minimum requirements, and some sources of elements essential for the growth of algae 

[The minimum nutrient requirements of algae in the aquatic environment are difficult to determine, and this uncertainty is shown by the wide range of concentrations in the 

table. "Trace" quantities generally refer to concentrations less than 1 mgfl, and more exact concentration requirements for these elements have not been determined. 

"Quantities always sufficient in surrounding medium" refers to those elements that are never below minimum concentrations so as to limit algal growth] 

Element1 Symbol Some common forms Minimum Examples of natural sources1 4 Examples of manmade sources 5 6 7 

in water 1 2 requirements 3 

Aluminum .... AI Al +3 , AlS04 , Al02 , Probably trace Clay minerals, silicate rock minerals Domestic sewage, industrial wastes, mine drainage. 

(salts of aluminum) quantities 

Boron ....... B B,H3 B03 100 #lg/1 Evaporite deposits, igneous rock minerals, springs, Cleaning aids, detergents, industrial wastes, 

volcanic gases irrigation, sewage. 

Calcium ..... Ca Ca +:z, CaC03 , CaS04 20 mg/1 Igneous rock minerals, rainwater, sedimentary Industrial wastes (metallurgy, steelmaking), treatrocks, soil ment plant wastes. 

Carbon ...... c C02 , C03 , HC03 , Quantities always Atmosphere, organic compounds and decay pro- Industrial wastes (carbonation, metallurgy, pulp and 

H2 C03 , CaC03 sufficient in ducts, rainwater, soil paper, soda, and steelmaking), domestic sewage. 

surrounding 

medium 

Chlorine ..... Cl Cl- 1 , (oxides of Trace quantities Evaporite deposits, igneous rock minerals, ocean Chlorinated hydrocarbon process, cleaning aids, 

chlorine) water, rainwater, sedimentary rocks, volcanic industrial wastes (petroleum and refining), 

gases irrigation, salt mining. 

Cobalt ....... Co Co 500 #lg/1 Coal ash, soil, ultramafic rocks Manufacturing wastes (tools and instruments), 

metallurgy. 

Copper ...... Cu Cu+2 ,Cu,CuS04 6.0 #lg/1 Crustal rocks, ground water, marine animals Industrial wastes (fabrication of pipes, refining, 

smelting), manufacturing wastes (electrical, 

foods), mill tailings, mine wastes, ore dumps, 

treatment plant wastes. 

Hydrogen .... H H+, H2 S, H2 0, HC03 , Quantities always Atmosphere, oxidation processes, rainwater, Industrial wastes (hydrocarbon process), oils. 

H2C03 ,0H sufficient in volcanic activity 

surrounding 

medium 

Iron ......... Fe Fe+2 , Fe+3 , FeS04 , 0.65-6,000 #lg/1 Ground water, igneous rock minerals, iron Acid drainage from mines, industrial wastes (steelFe(OH)2 minerals, organic decomposition, soil making), iron ore mining, manufacturing 

wastes, oxides of iron metals (car bodies, 

refigera tors). 

Magnesium ... Mg Mg+2 , MgS04 Trace quantities Igneous rock minerals, ground water, rainwater, Irrigation, manufacturing wastes (transportation 

sedimentary rocks vehicles). 

Manganese ... Mn Mn+2 , Mn02 5.0 #lg/1 Ground water, plants, rocks, soil, tree leaves Acid drainage from coal mines, industrial wastes 

(steelmaking). 
Table I.--Common forms, minimum requirements, and some sources of elements essential for the growth of algae--Continued 

Element 1 Symbol Some common forms Minimum Examples of nfltural sources 1 4 Examples of manmade sources 5 6 7 

in water 1 2 requirements3 

Molybdenum .. Mo Mo, Mo04 Trace quantities Ground water, rocks, soil Industrial wastes (electrical devices, metallurgy, 

steelmaking), manufacturing wastes (alloys). 

Nitrogen ..... N N, N02, N03 , organic Trace quantities to Atmosphere, bacterial and plant fixation, lime- Agricultural wastes (feedlots, fertilizers), domestic 

nitrogen, NH3 5.3 mg/1 stone, rainwater, soil sewage, industrial wastes, storm drainage. 

Oxygen ...... 0 0 2, H2 0, oxides Quantities always Atmosphere, oxidation processes, photosynthe- Industry (metallurgy). 

sufficient in sis, rainwater 

surrounding 

medium 

Phosphorus ... p p+S' P04' HP03' 0.002-0.09 mg/l Ground water, igneous and marine sediments, Agricultural wastes {feedlots, fertilizers), domestic 

organic phosphorus rainwater, soil, waterfowl sewage (detergents), industrial wastes. 

Potassium .... K K + {salts of potassium) Trace quantities Evaporite deposits, igneous rock minerals, plant Agricultural wastes {feedlots, fertilizers), industrial 

ash, sedimentary rocks wastes {preservatives, pulp ash). 

Silicon ....... Si Si+4,Si02 0.5-0.8 mg/l Diatom shells, igneous rock minerals, metamor- Domestic sewage, industrial wastes. 

phic rocks . Sodium ...... Na Na+, Na salts (NaCl, 5.0 mg/l Ground water, igneous rock minerals, ocean Industrial wastes (paper and pulp, rubber, soda, 

00 NaC03 water, soil water softeners), manufacturing wastes {dyes 

and drugs). 

Sulfur ....... s S02, Hs, H2 s, S04 5.0 mg/l Animal and plant decomposition, igneous rocks, Agricultural wastes {fertilizers), industrial wastes 

rainwater, sedimentary rocks, springs, (fuels, paper and pulp). 

volcanic activity 

Vanadium .... v y+2, y+3, y+4, y+s Trace quantities Ground water, plant ash Industrial wastes. 

(salts and oxides of 

vanadium) 

Zinc ......... Zn Zn +2 (salts of zinc), 10-100 #Lg/1 Igneous and carbonate rock minerals Industrial wastes (piping, refining), mine wastes. 

Zn02 

1. Hem {1970). 5. Gurnham { 196 5). 

2. McKee and Wolf(1971). 6. Nebergall, Schmidt, and Holtzclaw { 1963}. 

3. Greeson(1971}. 7. Sawyer and McCarty (1967). 

4. Reid {1961 ). 
Diatom Green alga Blue-green alga Dinoflagellate 

A. PHYTOPLANKTON 

Rotifer Water flea (crustacean) 

B. ZOOPLANKTON 

Mayfly nymph Caddi~fly larva 

, 

Diving beetle larva 

/ 

Midge larva ~ 

C. BENTHIC INVERTEBRATES 

Spiny-rayed fish (sunfish) Soft-rayed fish (trout) 

D. NEKTON 

Figure 3.-Representative lake organisms. 

and are often the most economically important 

organisms to man. 

PROCESSES IN LAKES 

Most of the properties and materials of lakes are easy 

to measure and describe. In contrast, their interactions 

as they relate to plants and animals are somewhat more 

difficult to describe, and measurements of these processes often more difficult to make. As a result, some of 

the processes in lakes are not well understood. Energy 

and material transport between plants and animals, and 

between animals themselves, is among several of the 

9 

poorly understood biological processes in lakes. Other 

processes, such as photosynthesis, respiration, eutrophication, and basic geochemical cycles are somewhat 

better known, and can be described in general terms. 

PHOTOSYNTHESIS AND RESPIRATION 

Photosynthesis is carried out only by green 

(chlorophyll-containing) plants and some bacteria. 

Respiration is carried out by both plants and animals. 

Both processes are essential to life and have a profound 

effect upon water quality in lakes. 

As mentioned earlier, photosynthesis is the process 

whereby green plants take up carbon and synthesize 
carbon compounds, while producing oxygen. When 

plants take up carbon, generally as carbon dioxide, they 

combine hydrogen, sulfur, nitrogen, or phosphorus with 

the carbon, to form cellular materials such as carbohydrates, proteins, and fats. The oxygen produced 

during this process goes into solution. 

Respiration is the process whereby organisms obtain 

their energy by oxidizing food (organic material) to 

carbon dioxide and water. Because their energy need is 

continuous, all organisms respire throughout their lives. 

Plants emit oxygen as a result of photosynthesis, but 

they must also use oxygen for respiration. 

Photosynthesis and respiration result in daily and 

seasonal fluctuations of dissolved oxygen and carbon 

dioxide levels in lakes. As a result, the carbon dioxide 

and dissolved oxygen concentrations are not always in 

balance. These imbalances have a significant effect upon 

the quality of water. For example, all lakes contain some 

algae, but in the presence of sufficient sunlight and plant 

nutrients, photosynthesis by phytoplankton may result 

in an excessive production of oxygen. At this time, the 

phytoplankton may increase to concentrations of a 

million cells per litre, a condition known as an algal 

bloom (Lee, 1970, p. 19). 

Respiration removes dissolved oxygen from the water. 

For example, in a thermally stratified lake during the 

summer, respiration by bacteria may oxidize organic 

materials at such a rapid rate in the bottom water that 

the dissolved oxygen becomes drastically depleted. Thus, 

when large quantities of decomposable organic wastes 

are introduced into natural water, severe oxygen 

depletion can occur. 

Decreases in oxygen concentration also affect the 

solubilities of compounds contained in sediment. For 

example, iron in natural water is found in either the 

ferrous (Fe+2 ) or the ferric (Fe+3 ) state. Under aerobic 

(oxygenated) conditions, iron is in the ferric (or highly 

oxidized) form as a complex with other inorganic 

constituents, and as simple decomposition products 

(Reid, 1961, p. 193). Under anaerobic conditions, the 

insoluble ferric complex in the lake sediment loses 

oxygen and is reduced to the more soluble ferrous state. 

This not only puts more iron in solution, but also 

releases other combined constituents, such as silicate, 

phosphate, and bicarbonate. The ions that go into 

solution all act as plant nutrients. 

EUTROPHICATION 

Eutrophication is the enrichment of lakes by nutrients 

and filling by sediment. Although eutrophication is a 

natural phenomenon, recent concern has been with the 

acceleration of this process by man's activities. Presently, 

it is a major problem of many lakes and reservoirs. 

10 

The aging process of a lake begins with its formation 

in a basin. As the lake accumulates plant nutrients and 

sediment deposits, plant production increases and shoreline vegetation invades the lake. As the depth of the lake 

decreases and emergent vegetation increases, the lake 

becomes a bog and is referred to as a dystrophic system. 

Eventually the original lake becomes land. 

Unenriched lakes are classified as oligotrophic. 

Oligotrophic lakes have high concentrations of dissolved 

oxygen at all depths, low concentrations of dissolved 

substances, and usually clear waters. Although sufficient 

oxygen is available to support life throughout the water 

mass of oligotrophic lakes, the low quantity of dissolved 

materials and plant nutrients limits plant production and 

thereby restricts the abundance of animal life. Many 

newly created real-estate lakes and reservoirs are 

oligotrophic. However, many older reservoirs and natural 

lakes, such as Lake Tahoe, may still be considered 

oligotrophic because they contain minimal plant 

nutrient concentrations (Goldman and Carter, 1965; 

Crippen and Pavelka, 1970). 

The second enrichment stage of a lake is mesotrophy. 

This stage is characterized by increased concentrations 

of dissolved materials and plant nutrients, and thus 

increased plant production. A mesotrophic lake may 

support a large plant population but generally plant 

production is not so excessive as to be undesirable, in 

terms of human use of the water, nor to seriously 

deplete the dissolved oxygen concentration. 

The third stage of the enrichment process is called 

eutrophy (hence eutrophication). This is the final stage 

of the lake before filling and extinction are complete. 

The symptoms of a eutrophic lake are high concentrations of dissolved materials, excessive numbers of 

phytoplankton represented by only a few tolerant 

species, and oxygen depletion in the deeper water. The 

reduction of oxygen is caused by bacterial decomposition of organic matter (Redfield and others, 1963, 

p. 27) and may result in fish kills. Other characteristics 

of eutrophic lakes may be discolored water from 

excessive algae production and unpleasant odors attributable to decay. 

The effect of man on the eutrophication process is 

shown in figure 4. The diagram shows the effect of 

nutrient enrichment upon the natural eutrophication of 

lakes. Regardless of the enrichment status of lakes, 

nutrient inputs by man can hasten lake extinction. 

However, the rate of eutrophication, and thus the 

extinction of lakes, can be retarded by nutrient removal. 

THE BIOGEOCHEMICAL CYCLE 

Materials that enter a lake from tributaries or from 

the atmosphere may settle in the lake basin, be removed 
Extinction 

........ --- , .... --- ,- ,, ,, I 

/~ I 

~Effect of artificial enrichment --i I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I I 

I 

I 

I 

Effect of \ --------------- t-- nutrient------" .... ____ _ I 

f 1 removal 

I 

I 

I 

I -· ' ---- \ ---- \ ---- ' ' ------ ....... ___ ,.,. 

I Eutrophic stage I 

-RELATIVE AGE OF LAKE~ 

Figure 4.-Effect of man upon the eutrophication of1akes. After Greeson, 1971; modified from Hasler, 1947. 

through the outlet, or remain in solution. Those that 

remain in solution, and that are required for plant 

production, may be incorporated into living tissue. 

SEDIMENTATION 

The major pathway for the flow of plant nutrients and 

other elements into a lake is sedimentation. Sedimenta· 

tion is the process whereby fragmental material originates 

from the disintegration of rocks and from other sources, is 

transported, and is deposited in layers or remains sus· 

pended in the water (Colby, 1963, p. A3). Lakes receive 

sediment from both inflowing water and from the wind. 

The sediment accumulates permanently in areas little 

affected by wave action. Because most lake·bottom sediments are relatively permanent deposits, sediment deposition is a major cause of the aging and extinction of lakes. 

Many lakes retard inflow sufficiently to trap all 

incoming coarse sediment, as well as part of the fine 

sediment. The trap efficiency of a lake depends in part 

upon the fall velocities of the sediment particles, the 

density of the water, and how much the water is slowed as 

it passes through the reservoir (Brune, 1953). As a lake fills 

with sediment, its trap efficiency usually decreases 

(Colby, 1963, p. A35). 

11 

Besides being a mechanism for lake filling, sedimentation introduces plant nutrients and dissolved materials 

into lakes. The quantity of plant nutrients sorbed by 

sediment particles may be high, and the nutrients can 

become more soluble upon entering the different chemical 

environment of a lake. Once in the lake,plant nutrients are 

subjected to cycling. 

NUTRIENT CYCLING 

A generalized scheme of element sources, losses, and 

cycling in lakes is shown in figure 5. Some elements, such 

as phosphorus, nitrogen, silicon, and perhaps soluble carbon, may undergo such extensive use by plants that these 

nutrients are virtually depleted in the water. Thus, they 

may become limiting nutrient elements to plants and 

restrict plant production until the elements are recycled or 

new supplies enter the lake. 

Many elements are cycled through a number of chemical forms. For example, nitrogen may be taken up by 

plants as the stable nitrate ion (N03 -). In the plant cell it 

is reduced and makes up an important part of plant and 

animal protein. Upon death of the organism, the nitrogen 

may be released either as ammonia gas (NH3 ), or the 
Atmospheric precipitation 

(water or ,dry fallout) Gaseous exchange with atmosphere 

~ 1 

Lake surface t t 

Uptake of constituents by 

plants from water 

Uptake of constituents by 

animals consuming plants 

Death of plants or animals 

Figure 5.-Sources and cycling of elements in a lake. 

ammonium ion (NI4 + ). Further oxidation of these forms 

by specific bacteria results in the unstable oxidized 

form, nitrite (N02 -). Further oxidation of the nitrite by 

other bacteria results in the stable nitrate form, thus 

completing the cycle. 

Phosphorus (P), inorganic phosphate (P04 - 3 ) , and 

organic phosphorus (OP--the fraction bound in plant 

and animal cells) follow a cycle similar to nitrogen. 

Carbon also occurs in several forms. In water it is found 

as carbon dioxide gas (C02 ), as the inorganic ions 

bicarbonate (HC03 -) and carbonate {C03 - 2 ), or as the 

solid compound calcium carbonate (CaC03 ). Organic 

carbon is that fraction of total carbon within plants and 

animals. 

The sorption {absorption and adsorption) of chemical 

elements and compounds by sediment is well known. 

Lake bottom sediment is often a rich source of plant 

nutrients. The release of these nutrients from the 

sediment is regulated by various factors, such as temperature, pH, and dissolved oxygen. For example, a lack of 

oxygen in the bottom water of lakes (hypolimnion) may 

trigger the release of phosphorus compounds from the 

sediment. When the bottom water becomes oxygenated 

again, the phosphorus compounds precipitate and 

reenter the sediment. There they are unavailable as plant 

nutrients until oxygen depletion again occurs in the 

hypolimnion. 

PLANNING AND MANAGEMENT OF 

WATERSHEDS AND LAKES FOR 

WATER-QUALITY CONTROL 

The foremost goals in lake management are to prevent 

or reduce the undesirable effects of eutrophication and 

12 

to provide water of high quality. Factors associated with 

eutrophication of lakes are excessive algal production, 

dissolved oxygen depletion in the hypolimnion, objectionable taste and odor, and general esthetic depreciation of the environment. In the past, management of 

lakes was commonly limited to volume manipulation 

and water releases. In recent years, intensified demands 

for water of high quality have caused more attention to 

be focused on lake-basin planning, watershed and lake 

management, and water-quality control (Keup and 

Mackenthun, 1970). 

LAKE BASIN PLANNING 

Good lake-basin planning can minimize water-quality 

problems. The selection of an appropriate site for a 

reservoir is of paramount importance. A preimpoundment survey of the physical, chemical, and biological 

characteristics of the proposed lake basin is most 

beneficial when done before construction begins. In 

addition, basin planning and dam construction should 

take seismic safety into consideration. This becomes 

especially important in fault regions like the San 

Francisco Bay area. 

A primary characteristic of a good reservoir is a high 

ratio of volume to surface area, which is desirable for 

land conservation and water-quality control {Linsley and 

Franzini, 1964, p. 168). For example, a deep reservoir is 

preferable to a shallow one because of lower land costs 

per unit of capacity, less evaporation loss, and less area 

for weed growth. The watershed, of course, must have a 

suitable damsite, and the reservoir site must have enough 

capacity for its intended use. If a reservoir site has 

tributaries which produce much sediment and plant 
nutrients, rapid eutrophication may result after construction of the reservoir. Therefore, a preimpoundment 

survey that includes a nutrient-loading estimate of at 

least nitrogen and phosphorus for all waters entering the 

planned impoundment will enable the planner to assess 

the eutrophication potential. Open mines in the basin 

may cause toxic water conditions. Reconnaissance 

surveys of reservoir sites can reveal such potential 

problems, so plans can be formulated to avoid or deal 

with them. 

An important step, after selection of an appropriate 

reservoir site, is to remove trees and vegetation from that 

part of the basin that will be inundated, because the 

decomposition of this organic material may cause 

oxygen depletion and undesirable taste and odor in the 

reservoir water. The ideal practice is to remove the 

topsoil and contained plant nutrients also, but the cost 

of such an operation may be prohibitive in large 

reservoir basins (Houghton, 1966, p. 180). If the topsoil 

is not removed when the reservoir is cleared, removal of 

vegetation from the site with as little disturbance of the 

soil as possible will reduce the amount of plant nutrients 

released from the soil and decrease the incidence of algal 

blooms (Houghton, 1966, p. 180). 

WATERSHED MANAGEMENT 

Effective watershed management can prevent or 

reduce the rate of eutrophication; thus attention must 

be given to the quality of in flowing water. 

The disturbance of soil in the watershed from natural 

events and human activities increases the transport of 

sediment and combined plant nutrients into the lake. 

Maintaining a good vegetative cover around the lake will 

help prevent excessive erosion of the watershed. However, if the soil in the watershed must be disturbed, 

construction of sediment traps (temporary debris basins) 

below the disturbance will minimize the amount of 

sediment entering the lake (Rickert and Spieker, 1971 ). 

Because fertilizer is a rich source of plant nutrients, its 

use should be limited within the lake basin. 

Control or diversion of all waste inflows (wastes high 

in biochemical oxygen demand or rich in nutrients) is 

probably the best way to control lake enrichment. This 

can be accomplished by re-routing the effluent to the 

outlet of the lake. Advanced methods of sewage treatment, rather than the use of septic tanks, reduce the 

seepage of nutrients into the lake. If sewage discharges 

into the lake cannot be avoided, then sewage that has 

had secondary treatment, but preferably tertiary treatment, will keep nutrients entering the lake to a 

minimum. Secondary and tertiary treatment of wastewater reduces the oxygen demand, disease potential, and 

nutrient levels of wastes. 

13 

Inflowing streams, or lakes themselves, may receive 

heated effluent from industrial plants. Heat can greatly 

alter the chemistry and biology of the water. Thus, 

heated water should be cooled before its introduction 

into lakes and reservoirs. There are several cooling 

devices used in thermal industrial plants. The most 

effective is the dry-cooling tower. Cooling and spray 

ponds, although not as effective, are more economical 

and are used more frequently (Unsley and Franzini, 

1964). 

LAKE MANAGEMENT 

Although lake water-quality problems are best controlled by effective management of the watershed area, 

some within-the-lake management tools are often 

necessary. Multipenstock release systems on a reservoir 

allow for greater flexibility in releasing water from 

various depths, and hence reducing potential waterquality problems. For example, domestic wastewater 

containing undesirable chemical constituents, such as 

manganese and iron, can be passed through the lake by 

regulating the release of water at the dam. Mechanical 

aeration can be used to increase the oxygen in the water, 

to prevent the buildup of hydrogen sulfide concentrations (see p. 46), and to depress high levels of 

manganese or iron before the water enters the distribution system. Regulating recreation on the lake may 

help prevent accelerated eutrophication. Many recreational lake areas do not have adequate sanitary facilities, 

and drainage of human wastes into the lake may cause 

bacterial contamination. 

WATER-QUAUTY CONTROL 

Although preventive measures for water-quality 

control are always preferable, it is often necessary to 

manage a lake system to control after-the-fact waterquality problems. These problems generally arise as part 

of the eutrophication process, and are often accelerated 

by man. 

ALGAL BLOOMS 

Algal blooms are a troublesome problem in lakes. An 

algal bloom is an excessive amount of phytoplankton 

production which usually occurs during the spring and 

summer in nutrient-enriched lakes. Minimum conditions 

for an algal bloom are a sufficient concentration of plant 

nutrients in the water, adequate sunlight, and a water 

temperature suitable for growth. The concentration of 

algae that constitutes a bloom is not precise, and it 

depends upon the type of algae. Lee (1970) proposed 

that a concentration of ~ million to 1 million cells per 

litre indicates a bloom condition. 
When minimum conditions for algal growth are met, 

the growth of algae takes place at a more or less constant 

rate (fig. 6). If no property is limiting, the algae grows 

rapidly, causing a bloom. At some point, an essential 

condition becomes limiting and restricts further algal 

growth. The cell density may remain stable for a few 

days, but because of limiting materials for growth and 

tissue repair, the cells begin to die. As the algal cells die, 

they sink and are decomposed by bacteria, which results 

in the uptake of dissolved oxygen and release of cellular 

materials back to the water or lake sediment. 

Although algae are essential for other organisms to 

live, algal blooms may cause coloration or fouling of the 

lake water. Algae may clog sand fllters at water 

treatment plants. Recreational activities, such as boating 

and fishing, may be hindered by mats of floating algae, 

and water sports may prove harmful because of the 

presence of toxic algae (Mackenthun and Ingram, 1967, 

p. 157-166). 

Effective treatment and control of algae requires some 

knowledge of the number, kind, and distribution of 

algae in the water. The application of an algicide is the 

most frequent method of control. Copper sulfate is the 

most common and effective algicide used today, because 

it is toxic to many algae at comparatively low concentrations, has a relatively low toxicity to man and other 

animals, and is inexpensive (Gratteau, 1970, p. 25). The 

concentration of copper sulfate which is toxic to a 

particular type of algae varies with the abundance of the 

algae, the temperature, pH, alkalinity, and amount of 

organic matter in the water. Mackenthun and Ingram 

~ UJ 

m 

~ 

::> 

z 

...J 

...J 

UJ 

() 

Initial 

growth 

phase 

(1967, p. 258-260) present application rates for copper 

sulfate based on these variables. The most effective time 

for the application of an algicide is at the junction of the 

initial growth phase and the rapid growth phase. To 

determine the growth-phase junction, several algalgrowth curves are needed. These can be prepared by 

frequently collecting water samples and counting the 

algal cells. Once several growth curves are established for 

the algal species of the lake, it will be possible to predict 

with some reliability the growth-phase junction, and 

hence the best time to apply an algicide. Mechanical 

removal of algae may be an alternative control, 

especially in water where localized blooms occur 

(fhomas, 1965). The harvested material is usually 

hauled to shore and burned, or removed to a disposal 

site (Gratteau, 1970, p. 25). 

Higher aquatic plants may be killed with herbicides or 

removed by mechanical means. Livermore and 

Wunderlich {1969, p. 498-512) and Mackenthun and 

Ingram {1967, p. 264-273) discuss the removal of both 

submersed and emersed aquatic plants. If the plants are 

removed mechanically, they are usually hauled out of 

the watershed area so that their contained nutrients will 

not reenter the lake upon decomposition. 

ANAEROBIC CONDITIONS 

The quantity of available dissolved oxygen in a lake is 

often a limiting factor to productivity. When thermal 

stratification occurs in a lake, the lighter water at the 

surface forms a density barrier which prevents reaeration 

Stationary growth phase 

TIME 

Figure 6.-Typical growth pattern of blooming unicellular algae. 

14 
by atmospheric oxygen in the bottom waters. The 

sinking and decomposition of algae following a bloom 

may add to the depletion of dissolved oxygen in the 

lower water. The introduction of large amounts of other 

oxygen-demanding materials, such as organic wastes, 

raises the BOD (biochemical oxygen demand) of the 

water, and thus depletes the oxygen supply. 

Under anaerobic conditions, water quality often 

depreciates. For example, concentrations of hydrogen 

sulfide, soluble manganese, and iron may increase in the 

bottom water. Anaerobic conditions also can result in 

undesirable taste and odor from hydrogen sulfide buildup. Obviously, aquatic life will be adversely affected. 

Mechanical aeration of lakes has become a useful 

management tool in reducing anaerobic conditions. 

Pumping or drawing off the deoxygenated water, combined with recirculation of oxygenated water from the 

surface, will help to relieve hypolimnetic oxygen 

depletion (Thomas, 1962, p. 303; Irwin and others, 

1969). 

FISH KILLS 

Fish kills may become an important problem in some 

lakes. Fish are killed by exposure to toxins in waste 

discharges and by some algicides. Anaerobic conditions 

may suffocate fish. Rapidly changing or excessively high 

water temperatures may kill fish, or cause an increase in 

fish respiration. This means that more water passes 

through their gills, and hence introduces more toxins 

into their bloodstream. 

Fish kills can be prevented only by treating the cause, 

which involves proper planning and management of the 

lake. Obviously there are no after-the-fact control 

measures for fish kills. However, immediate cleanup of 

dead fish along the shores of lakes will reduce odors and 

improve recreation and the esthetic value of beaches. 

Chemical tests for the investigation of fish kills can be 

used on distressed or dead fish. Any conditions at the 

site of the kill that might help identify the cause of 

death should be investigated, such as oxygen depletion 

or evidence of toxicity (Burdick, 1965; Slack and others, 

1973, p. 158-159). 

SEDIMENT DEPOSITION 

Sediment deposition is one of the most prevalent 

problems with real-estate lakes (Rickert and Spieker, 

1971), and it has become increasingly evident in all 

lakes. Reservoirs in particular are depositories for sediment. Accelerated sediment deposition usually results 

from soil disturbances in the watershed. Common causes 

of soil disturbances are logging, road construction, 

farming, and overgrazing. Sediment deposits may fill the 

lake, introduce nutrients, or reduce the esthetic value of 

15 

the lake. Organic sediment may place an oxygen demand 

upon the lake water. 

Once deposition has occurred,.the life of the lake may 

be extended by dredging, or if the reservoir can be 

drained, the sediment can be removed with earthmoving 

equipment. Both sediment-removal techniques are 

expensive, and unless watershed-protection measures are 

undertaken, the success of these techniques may be 

shortlived. 

SUMMARY OF MANAGEMENT OPTIONS 

There are few management options available for 

reducing eutrophication once it occurs. The best 

management is prevention--choosing the reservoir site 

carefully, understanding the potential nutrient loads of 

the tributaries, and clearing the reservoir site completely 

and carefully. Most important, however, is the wise 

management of the watershed. The maintenance of a 

plant cover with a minimum of soil disturbance in the 

watershed is of prime importance. The removal or 

prevention of domestic and industrial waste is of course 

a desirable feature and a prerequisite for the reduction 

or prevention of eutrophication. 

CONDUCTING LAKE STUDIES 

Studies of lakes are conducted for a number of 

reasons. Frequently, lakes are studied to determine 

present or changing water-quality conditions. Waterquality measurements can be made to assess physical, 

chemical, and biological factors. Morphological studies 

of lakes are designed to determine the bottom configuration, sediment deposits, or erosional processes resulting 

from wave action. 

For convenience and understanding, as well as for 

management direction, lake investigations can be 

separated into the three categories of reconnaissance, 

monitoring, and interpretative. 

Reconnaissance investigations are somewhat encompassing in design. They are not intensive studies, but are 

of sufficient detail to determine the physical arrangement of a lake and the distribution and abundance of 

materials (chemical or biological) in the lake basin at a 

particular time. The results of a reconnaissance study 

may be the end product of a lake study, or they may 

point the way toward more intensive investigations. In 

any event, a reconnaissance study is a prerequisite to the 

design of a monitoring program or an interpretative 

study. 

Monitoring studies or programs are designed to 

determine time-trend changes in a particular variable. 

Such studies usually determine the changes in abundance 

of materials in lakes, the distribution pattern having 

been determined during the reconnaissance study. 
Usually, but not always, monitoring takes place at the 

same site on a lake, at predetermined time intervals. 

Interpretative studies are designed to determine the 

processes that govern the distribution and abundance of 

materials in a lake. An effective interpretative study is 

usually designed after sufficient data are collected in a 

reconnaissance study. Interpretative studies are generally 

made to advance our knowledge of limnology, or to 

study a special type of lake or processes within a lake. 

From the standpoint of lake management, a reconnaissance study is often sufficient, and the measurements discussed below are those frequently made during 

reconnaissance investigations. 

MEASURING THE PROPERTIES OF LAKES 

The number of sampling sites on a lake will vary with 

the size and shape of the basin. In shallow lakes, having a 

circular basin, a single site in the deepest part of the lake 

may be sufficient to describe the distribution and 

abundance of the constituents in solution. In natural 

lakes, the deepest point is generally near the lake center, 

and in reservoirs, the deepest area is near the dam. In 

lakes with irregular shape and with several arms and bays 

that are protected from the wind, additional sampling 

sites may be needed to adequately define the water 

quality. The investigator can determine this need by 

comparing the thermal and specific-conductance proflles 

in the bays with those in the deepest area of the lake. If 

a significant difference exists, then additional sampling 

sites may be needed. 

A variety of equipment is available for the measurement of lake variables. A discussion of all the equipment 

and its use would be voluminous. Only general guidelines 

will be given here, and the reader is referred to the cited 

literature for more details. 

Many lake measurements are now made in-place with 

the use of sensor probes and automatic readout or 

recording devices. Single-parameter devices are available 

for measuring temperature, depth, pH, specific conductance, dissolved oxygen, chloride levels, light 

penetration, and turbidity. Recently, multiparameter 

units have become available for the in-place measurements of several of these at the same time. While 

expensive, such pieces of equipment are great timesavers 

if a number of surveys are to be made. Multiparameter 

units may be read directly, or attached to continuous 

recorders. As a rule, all surface-to-bottom (vertical) 

measurements made from a boat should be done while 

the craft is at anchor. 

While a number of publications describe lake survey 

techniques and methods, there is no recent publication 

addressed solely to the subject. The book entitled 

Limnological Methods (Welch, 1948) is the most recent 

16 

manual on the subject. While there have been advances 

in limnological equipment and techniques since Welch's 

book, many of the techniques he described are still 

commonly used. Other references useful for lake studies 

are Mackenthun and Ingram (1967), Committee on 

Oceanography, Biological Methods Panel (1969), Brown, 

Skougstad, and Fishman (1970), Edmondson and Winberg (1971), Holme and Mcintyre (1971), Goerlitz and 

Brown {1972), and Slack and others (1973). Only the 

important considerations of common measurements--what, why, and where--are discussed in detail 

here. References are given for detailed instructions on 

how a particular measurement is made. 

PHYSICAL MEASUREMENTS 

Mapping 

A map of the lake can be prepared from aerial 

photographs or topographic maps, or the lake can be 

surveyed using any of the methods given in Welch (1948, 

p. 3-24). Maps are an essential first step in designing a 

detailed lake study, and are quite useful when the 

bottom contours of the lake are included. Bottom 

configuration and depth of water are easily measured in 

large lakes with an echo sounder (Holme and Mcintyre, 

1971, p. 14-17). In small lakes, a sounding line and 

weight are sufficient. When a lake or reservoir is 

sounded, installation of a staff gage or other similar type 

marker, and recording of the water-surface elevation of 

the lake will make it possible to compute the estimated 

volume of the lake at any given surface elevation. A 

complete discussion of how to sound and plot lake 

contours and how to determine the volume of water is 

given in Welch (1948, p. 25-49, 77-98). In reservoirs, 

bottom contours and water depth may be estimated 

from topographic maps made before the reservoir was 

constructed. Many recent topographic maps give the 

depth contours of reservoirs. Shoreline configuration 

will point out areas where wind circulation is likely to be 

negligible (bays and arms); bottom contours will indicate 

the fteepest part of the lake, the shallow and shoal areas, 

and areas of sediment deposition. When the map is 

complete, a survey of the lake can begin. 

Temperature 

The temperature profile of a lake is determined by 

measurements at the deepest part of the lake and 

preferably in one or more shallow areas and in protected 

bays and arms. A thermistor attached to a readout 

device in the boat, with a cable marked in feet or metres, 

is the easiest way to obtain a temperature profile of a 

lake. However, other methods, most of which are not as 

convenient, are available (Welch, 1948, p. 101-125). 
The exact position of the metalimnion can be 

determined, and consequently the positions of the 

epilimnion and hypolimnion, when temperature 

measurements are made at intervals of 1 to 3 ft (0.3 to 

0.9 m). The temperature profile is then used as a guide 

for the collection of other limnological data. 

Light Penetration 

In some instances, especially for productivity studies, 

it is important to measure light penetration. This 

parameter is often not measured directly, but is 

estimated with a Secchi disk, a plate about 12 in. (30 

em) in diameter, with alternate black and white markings (Welch, 1948, p. 159). If light measurement is 

critical for a particular study, the discussion in Welch 

(1948, p. 159-167) and Holme and Mcintyre (1971, p. 

53-58) should be consulted. 

CHEMICAL MEASUREMENTS 

Dissolved Oxygen 

Dissolved oxygen is one of the most important 

variables measured during a lake investigation. A 

limnologist can tell more about the water quality and 

the well-being and activity of the biota in a lake with 

dissolved-oxygen data than with any other measurement 

(Hutchinson, 1957, p. 575). Measurements made at 

many depth intervals are needed because the dissolvedoxygen concentration may be altered locally. It is not 

unusual, for example, to find a subsurface oxygen 

maximum resulting from photosynthesis in the 

epilimnion of lakes and oxygen depletion due to 

bacterial decomposition of organic matter in the 

hypolimnion of enriched lakes in late summer. 

To accurately defme the distribution of dissolved 

oxygen, at least two dissolved oxygen measurements are 

needed in the epilimnion, one in the metalimnion, and at 

least two in the hypolimnion, one near its top and 

another near the lake bottom. Additional measurements 

may be necessary if the results show drastic changes in 

the dissolved oxygen concentration with depth. One 

advantage of measuring dissolved oxygen with a probe 

connected to a readout device is that measurements can 

be quickly made in-place at any depth in the lake. With 

the Winkler method (American Public Health Association and others, 1971, p. 474-488; Brown, Skougstad 

and Fishman, 1970, p. 126-129), the sample is 

collected at a particular depth with a sampling bottle, 

brought to the surface, and the dissolved oxygen level 

determined there. Regardless of how the dissolvedoxygen concentration is determined, its measurement is 

essential in a lake study. 

Alkalinity and pH 

Alkalinity is a measure of the capacity of water to 

resist a change in pH, and provides a measure of the 

17 

carbon dioxide (C02 ), bicarbonate (HC03 -), and carbonate (C03 - 2 ) in the water. The pH is a measure of the 

hydrogen ion (H+) concentration (actually the activity 

of the hydrogen ion). Alkalinity is a function of pH and 

cannot be determined without measuring the pH. While 

pH can be measured with indicator dyes, or in-place with 

an instrument (often included on multiparameter units), 

alkalinity must still be measured on water samples 

collected in the lake. The pH value is logarithmic, 

ranging from 0 to 14. Alkalinity is expressed in mg/1 of 

HC03-, C03 - 2 , or as CaC03 • 

Both alkalinity and pH are altered by photosynthesis 

and respiration. As a result, they should be measured at 

depths similar to those used for dissolved-oxygen determinations. Instructions for alkalinity and pH measurements are given in American Public Health Association 

and others (1971, p. 52-56, and p. 370-376 for 

alkalinity, and p. 276-281 for pH) and Brown, 

Skougstad, and Fishman (1970, p. 41-44 for alkalinity, 

and p. 129-130 for pH). 

Major Chemical Constituents and Specific Conductance 

The major chemical constituents make up the bulk of 

the dissolved solids in water. Because most of these 

dissolved constituents are in the ionic state, they 

conduct electricity. Therefore, a correlation between the 

dissolved solids and the specific conductance of the 

water can be made (Hem, 1970, p. 96-103). 

The major chemical constituents are important plant 

nutrients and are used in classifying water types and 

assessing enrichment (Beeton, 1969). Over short time 

periods and in the absence of outside influences, their 

concentrations change very little. Frequent measurement 

of the individual major constituents is usually not 

necessary, and concentration changes in dissolved solids 

(summation of the major dissolved constituents) can be 

detected by measuring the specific conductance of the 

water. 

Water samples are collected with a standard watersampling bottle, at the desired depth, and brought to the 

surface for filtering or other preanalysis treatment. 

General procedures for collection, preanalysis treatment, 

and analysis are found in Brown, Skougstad, and 

Fishman (1970, p. 4-18). Nonuniform vertical mixing 

of chemical constituents occurs because of wind and 

temperature changes, the shape of the lake basin, 

biological activity, and many other factors. Therefore, 

water samples for major chemical constituents collected 

at several depths in a lake will more accurately defme 

the distribution of major chemical constituents than a 

single point sample. One sample taken in each of the 

epilimnion, metalimnion, and hypolimnion in the 

summer and winter is usually sufficient to describe the 
concentration of the major chemical constituents. 

Estimates of the dissolved solids concentration can be 

made during other times of the year with specificconductance measurements. 

Specific conductance is a measure of the ability of 

water to conduct an electrical current. It is usually 

expressed in micromhos per centimetre at 25°C, a 

micromho being the reciprocal of ohms X 1 06 • Specific 

conductance may be measured in-place with a probe 

connected to a readout device, or it may be measured in 

a water sample collected at the desired depth in the lake. 

Wind movement of water masses often causes short-term 

changes in specific conductance. These changes are easily 

measured by towing a conductance probe behind a boat. 

Edmondson (1956) discusses the measurement of 

specific conductance. 

Minor Chemical Constituents 

The minor chemical constituents in water are often 

important plant nutrients and enzyme activators for both 

plants and animals. They are often transported with sediment. At times, particulary during rapid algal production, 

the minor chemical constituents in the water are effectively exhausted because of algal uptake. Too often, minor 

chemical constituents are not determined as a part of a 

lake-reconnaissance study. This is unfortunate because 

while their role in the ecosystem is not as well understood 

as that of the major chemical constituents, they are nonetheless important. More work on their specific relationships to algal production is needed. 

As is the case with major chemical constituents, water 

samples for minor chemical constituents should be collected from the epilimnion, metalimnion, and the lower hypolimnion. The chemical species to analyze for, and the frequency of collection, will depend upon the enrichment 

status and particular suspected problems of the lake. Iron, 

aluminum, copper, manganese, molybdenum, and zinc are 

the minor chemical elements that are commonly measured. In appropriate cases, mercury and lead levels should 

be determined as well. 

Water samples for minor chemical constituents are 

collected with a sampling bottle, using the procedures 

given in Brown, Skougstad, and Fishman (1970, p. 

4-18). This publication also presents procedures for 

their determination. Because minor elements occur in 

small or trace quantities, care must be taken in the 

collection and handling of water samples. Nonmetallic 

bottles must be used, and preanalysis procedures, including ftltering and acidification, must be followed carefully 

(Brown, Skougstad, and Fishman, 1970; American 

Public Health Association and others, 1971 ). 

Major Plant Nutrients 

Nitrogen, phosphorus, and carbon are the so-called 

major plant nutrients. Because they may limit the 

18 

growth of phytoplankton and other plants, their 

measurement is important in lake surveys. The concentrations of these nutrients are readily altered by 

biological activity, and even short-term storage of the 

water samples before analysis may result in drastic 

concentration changes. The total nitrogen concentration 

can be estimated by analyzing for nitrate and total 

Kjeldahl nitrogen (ammonia plus organic nitrogen) and 

summing the results. Usually nitrite, the transitory 

oxidized form, is not present in significant quantities 

and can be ignored. Summing the concentrations of 

nitrate and total Kjeldahl nitrogen still has an inherent 

error in that some ammonia may escape from the sample 

container before analysis. Thus the sum of these two 

forms may represent an underestimation of the true 

nitrogen concentration. A discussion of analytical 

methods for the several forms of nitrogen is given in 

Brown, Skougstad, and Fishman (1970, p. 116-124) 

and American Public Health Association and others 

(1971, p. 221-248 and p. 453-470). 

Phosphorus may be analyzed as a number of forms 

but is generally analyzed either as inorganic orthophosphate or total phosphorus (inorganic and organic). 

Usually a measure of the total phosphorus concentration 

is sufficient for reconnaissance studies. If the sample is 

to be filtered, care should be taken to rinse the filter 

with distilled water before collecting the sample. This is 

necessary because many commercial ftlters contain 

appreciable amounts of phosphorus. The analysis of 

phosphorus is described in Brown, Skougstad, and 

Fishman (1970, p. 130-133) and American Public 

Health Association and others (1971, p. 283 and p. 

518-534). 

Analysis of water for soluble and particulate carbon is 

a relatively new measurement. Some results and their 

significance can be found in Helms (1970) and Emery, 

Welch, and Christman (1971 ). Methods of collection and 

preanalysis treatment, as well as analytical techniques 

are given in Goerlitz and Brown (1972, p. 2-6). Silver 

ftlters are required for carbon analysis. 

The frequency, depth, and location for collection of 

water samples for nitrogen, phosphorus, and carbon 

analysis depend upon a number of factors. Usually, it is 

wise to collect some samples in the winter before algal 

production, and some during the growing season. It is 

often advantageous to collect nutrient samples just after 

the spring overturn in order to estimate the maximum 

concentrations that may be available for the summer 

production period. However, relations between plant 

nutrient concentrations and algal growth are difficult to 

evaluate, and the investigator should not always expect 

definitive results. It is often useful to collect a water 

sample for algal cell counts at the same time a 
measurement of major plant nutrient concentration is 

made. Much of the nitrogen, phosphorus, and carbon in 

a lake may be in or sorbed by the sediment, thus 

becoming a potential nutrient source for plants. However, measuring the nutrient concentration in the 

bottom material to evaluate potential sources for plant 

production is a difficult task, and is not a routine 

lake-reconnaissance measurement. As a rule, water 

samples for nitrogen, phosphorus, and carbon are collected at several depths in the euphotic zone because this 

is the zone of active biological uptake of plant nutrients. 

A single surface sample and several more in the zone of 

light penetration are usually sufficient. 

BIOLOGICAL MEASUREMENTS 

The biological measurements made on lakes commonly include phytoplankton and periphyton types, 

their population density, and biomass {dry and ash 

weights per unit volume or area). Plant pigments such as 

chlorophyll are often used to estimate the biomass of 

phytoplankton and periphyton. In addition, the primary 

production (carbon assimilation) of these organisms can 

be determined by measuring oxygen output or the 

uptake of carbon-14. Other important biological 

measurements include types and numbers of zooplankton and benthic invertebrates. 

Phytoplankton and Periphyton 

The most commonly made biological measurements 

are those of the phytoplankton and periphyton. 

Phytoplankton are the one-celled plants responsible for 

most biologically or biochemically caused water-quality 

problems. Blue-green algae are usually responsible for 

nuisance conditions in lakes. Periphyton are the attached 

algae of lakes, reservoirs, and streams. Periphyton may 

also have a profound effect upon water quality, and may 

cause tastes and odors, as well as coloration. A number 

of techniques for collecting phytoplankton and 

periphyton have been published. Mackenthun and 

Ingram (1967, p. 149-173) present an excellent discussion on the role of algae in the aquatic environment. 

Phytoplankton are collected with a water-sampling 

bottle. If the cells are to be kept alive for production 

studies, then a water bottle made of polyvinyl chloride 

(PVC) is recommended (Vollenweider, 1969, p. 5; 

Slack and others, 1973, p. 70). If a plankton net is used 

for collecting phytoplankton, then the mesh size 

(aperture of the net), diameter of the net orifice, and the 

amount of water passed through the net (length of tow) 

are needed with the results so that the number of 

organisms per unit volume can be calculated. Many small 

phytoplankton pass through the mesh; hence the use of 

19 

nets for collecting phytoplankton is usually discouraged. 

In most studies concerned with phytoplankton types 

and abundance, samples are collected at various depths 

in the euphotic zone. Generally the samples are collected 

at the same depths as dissolved-oxygen samples because 

phytoplankton production is directly related to the 

dissolved-oxygen concentration. 

After collection the samples are preserved in a dilute 

formaldehyde solution or Lugol's solution, or if analysis 

begins within 2 or 3 hours, the samples may be chilled at 

3-4°C (Slack and others, 1973, p. 71). In the laboratory, the samples can be examined for types and 

numbers of phytoplankton, using the Sedgwick-Rafter, 

inverted microscope, or membrane filter method. These 

are described in detail in American Public Health 

Association and others (1971, p. 729-737) and Slack 

and others (1973, p. 70-78). 

Usually periphyton is collected on artificial substrates 

(made of glass or Plexiglas) which have been placed in 

the lake. Measurements may also be made on periphyton 

attached to natural substrates. After sufficient time for 

colonization {4-6 weeks), the substrates are removed 

and the periphyton within a given area, for example 25 

cm2 (3.9 in2 ) is seraped off. If the samples are to be 

examined within 2 or 3 hours, no special treatment is 

necessary. Periphyton samples may be maintained for 24 

hours at 3-4°C. For extended storage of samples being 

examined for species identification and cell counts, the 

samples should be preserved with a dilute formaldehyde 

solution or Lugol's solution. Samples for biomass 

measurements should be air dried or frozen if oven 

drying cannot begin immediately after collection. 

Samples are examined for types and numbers in the 

laboratory, using a Sedgwick-Rafter counting cell or an 

inverted microscope. Biomass measurements may also be 

made in the laboratory. Slack and others (1973, 

p. 86-93) discusses procedures, instructions and technique limitations. 

Several taxonomic keys are available for identifying 

the phytoplankton and periphyton of a given area. In 

the absence of keys to local forms, the publications by 

Edmondson {1959), Needham and Needham {1962), and 

Prescott {1962) are useful. Algal taxonomy is best done 

by someone with training and experience in the science. 

However, in a given body of water, an untrained 

observer can often identify the common species with 

little trouble. 

Bio111Jlss. --Both phytoplankton and periphyton 

biomass may be estimated by measuring the amount of 

cellular chlorophyll extract. Chlorophyll is the green 

plant pigment essential to the photosynthetic process. 

The technique is particularly valuable since samples can 

be easily collected and inexpensively analyzed. 
A water sample containing phytoplankton or periphyton is filtered through a membrane filter, and the cells 

and filter placed in acetone or another extracting solvent. 

The chlorophyll content is determined spectrographically. 

A description of the method and a discussion of its 

limitations are found in Strickland {1960, p. 49-53), 

Vollenweider {1969, p. 21-40), American Public Health 

Association and others {1971, p. 746-747) and Slack 

and others (1973, p. 57-64). 

Primary production.--While not a common measurement in routine lake surveys, primary production is 

useful in classifying lakes and describing their enrichment status. In enriched lakes, the oxygen light- and 

dark-bottle test is often used, but in unenriched lakes, 

the method is frequently not sensitive enough, and the 

carbon-14 method is used. 

Samples of the water and associated phytoplankton or 

periphyton are collected at a given depth and put in 

suitable containers (usually 300-millilitre glass-stoppered 

bottles) for suspension at various depths. Before 

suspension, each sample container is either inoculated 

with radioactive carbon, in the carbon-14 method, or its 

initial oxygen concentration determined, in the oxygen 

light- and dark-bottle method. After being suspended at 

different depths for given periods of time, the sample is 

returned to the surface, and the amount of radioactive carbon taken up, or the change in oxygen concentration is 

measured. The techniques of primary production measurements are thoroughly discussed in Strickland (1960), 

Vollenweider (1969, p. 41-127), American Public Health 

Association and others (1971, p. 738-742), Janzer and 

others {1973),and Slack and others {1973,p. 93-122). 

Zooplankton 

Zooplankton, the animal part of the plankton, are an 

important part of the lake fauna. Some zooplankton are 

strong swimmers while others have weak powers of 

locomotion. A daily vertical migration of zooplankton is 

common. Zooplankton feed upon bacteria and algae, 

and under normal conditions may keep some algal 

populations under control. They are also an important 

food source for many fish. Because of their role in the 

aquatic environment, zooplankton types, numbers, and 

biomass are often measured in lake surveys. 

Zooplankton may be collected with a water-sampling 

bottle; usually, however, zooplankton are collected with 

a net (usually a 202-micrometre mesh). If a water bottle 

is used, the samples should be collected at the same 

depths as phytoplankton samples, because zooplankton 

feed on phytoplankton. If a net is used, the aperture of 

the net, diameter of net orifice, and the length and 

depth of tow should be recorded so the population 

density can be calculated. Zooplankton samples to be 

examined for species identification and counts are 

preserved with a dilute formaldehyde solution, and those 

for biomass determinations are preserved by freezing 

with dry ice. 

Methods for the collection and analysis of zooplankton are described in detail in Committee on Oceanography, Biological Methods Panel (1969, p. 47-59), 

Edmondson and Winberg (1971, p. 1-20 and 127-137), 

and Slack and others (1973, p. 78-86). Useful taxonomic 

keys for the identification of zooplankton are found in 

Edmondson (1959) and Needham and Needham (1962). 

These publications also provide lists of references to the 

literature on zooplankton. 

Benthic Invertebrates 

Benthic invertebrates are organisms that live on or 

within the bottom substrate of lakes and reservoirs. 

Many are permanent residents, completing their life 

history in the water. Others (insects such as mayflies, 

caddis flies, and damselflies) spend their immature stages 

in the aquatic environment but when near sexual 

maturity emerge from the water. After leaving the 

water, they mate, and the females lay their eggs over the 

water. The eggs then hatch in the water, and the cycle is 

repeated. Benthic invertebrates are important as a source 

of fish food and as consumers of algae and detritus. 

Some types (mayflies, gnats, and mosquitoes) may 

become nuisances around the lake or reservoir. When this 

occurs, chemical control is often necessary. Benthic 

invertebrates are also important indicators of the quality 

of the water. However, in their use as water-quality 

indicators, the type of substrate as well as the species must 

be considered (Mackenthun and Ingram, 1967 ,p. 38-42). 

The collection of benthic invertebrates in a lake can 

be made with a variety of devices. Usually a grab, 

lowered into the water, which closes upon contact with 

the bottom or is tripped with a messenger, is used for 

collection. In the soft mud or detritus of lake bottoms, a 

spring-loaded Ekman grab can be used. For hard 

bottoms, a weighted Peterson grab may be required. 

Artificial substrates are also used for collection of 

benthic invertebrates. After collection, the samples are 

preserved in 40-percent isopropyl alcohol or similar 

preservative. Benthic invertebrate samples may be analyzed as to types, numbers per unit area, biomass (dry 

weight), or for diversity. Detailed instructions for the 

collection and analysis of benthic invertebrates are 

found in American Public Health Association and others 

(1971, p. 761-771), Edmondson and Winberg 

(1971, p. 25-65), Holme and Mcintyre (1971, 

p. 80-168), and Slack and others {1973, p. 126-151). 

20 
The physical, chemical, and biological measurements 

given above are not complete, but cover most aspects of 

a reconnaissance study of a lake or reservoir. Other types 

of measurements are given in the cited references. For 

example, it may be desirable to survey the types of fish 

inhabiting a lake. Suggestions and references are given in 

American Public Health Association and others (1971, p. 

771-779) and Slack and others (1973, p. 151-160). 

For extensive interpretative lake studies, consultation of 

a limnologist, as well as other experts on lakes and water 

quality, may be required. Many State, Federal, and 

private agencies can provide such assistance. 

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21 

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