Some Effects of the 

Larger Types of 

\quatic Vegetation on 

Iron Content of Water

y EUGENE T. OBORN and JOHN D. HEM

:HEMISTRY OF IRON IN NATURAL WATER

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1459-1

rnvestigation of factors affecting 

olution of iron in natural water

NITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington 25, D.C.
CONTENTS

	Page 

Abstract________________________________________________________ 237

Introduction._____________________________________________________ 237

Materials and methods,____________________________________________ 239

Federal Center Lake study____________________________________ 239

Greenhouse study- _--__-_-------_--___________________________ 239

Experimental procedure__--_-_-_-----_-____________________________ 239

Lake study. __________________________________________________ 240

Greenhouse study_____________________________________________ 243

Interpretation of results____________________________________________ 245

Month to month changes in greenhouse tanks_____________________ 247

Lake study observations________________________________________ 251

Comparisons of data from greenhouse and lake studies _____________ 253

Data classified by plant growth habit ____________________________ 258

Iron content of water in tanks containing soil and water-sedge. _____ 263

Amounts of water used by plants.___________________________________ 265

Summary and conclusions __________________________________________ 266

Status of knowledge of the chemistry of iron._________________________ 267

Literature cited___________________________________________________ 267

ILLUSTKATIONS

Page 

FIGURE 23. Lake, showing sampling locations.-.-.---------------.---.- 240

24. Measuring pH and Eh. Top, on lake; bottom, in greenhouse.- 242

25. Dissolved oxygen, iron and Eh of greenhouse tank waterstargrass)______-_-_---_----______________-__-._____-_ 248

26. Dissolved oxygen, iron and Eh of greenhouse tank (parrotfeather). __-____-------_---___________-_--__--__----- 249

27. Dissolved oxygen, iron and Eh of greenhouse tank (western

waterweed)______---_-_-_--__-_____________---__----- 250

28. Dissolved oxygen, iron and Eh of greenhouse tank (waterhyacinth)..-, ________ __--__-____________________---..-- 252

29. Water surface blanketing effect. Top, American pondweed;

bottom, lesser duckweed _______________________________ 254

30. Lake and greenhouse submerged-plant growth. Top, leafy

pondweed; bottom, sago pondweed_ _______________------ 256

31. Lake bloom. Top, microscopic view; bottom, habitat view. __ 257

32. Greenhouse submerged-plant growth. Top, needle spikerush ; middle, waterweed; bottom, water-stargrass______-_-- 259

33. Lake and greenhouse emergent-plant growth. Top, waterhyacinth; middle, parrotfeather; bottom, broad-leaved 

cattail._____________________________________________ 261

34. Coexistence of lesser duckweed and broad-leaved cattail at

lake________________________________________________ 262

35. Greenhouse canal-bank plant, water-sedge._._____-____--_- 264

in
IV CONTENTS

TABLES

Page 

TABLE 1. Chemical analyses of water samples from inlet and outlet of

Federal Center Lake, July 23, 1956- ____________________ 243

2. Plant species grown in greenhouse------------------------ 246

3. Characteristics of water affected by American pondweed in

greenhouse tanks and in the lake________________________ 255

4. Characteristics of water affected by lesser duckweed in greenhouse tanks and in the lake____________________________ 255

5. Characteristics of lake water during and after period in which

red waterbloom was present- ._____--____--_---__---___ 258

6. Characteristics of water affected by submerged soil-rooted

plants in greenhouse tanks and in the lake.-------------- 260

7. Characteristics of water affected by emergent aquatic plants

in greenhouse tanks and in the lake.____________________ 263

8. Characteristics of water percolating through tank containing 

bare canal-bank soil and from tank containing similar soil 

and water-sedge_____________-_---_-_-_-___-------_-_- 263
CHEMISTRY OF IRON IN NATURAL WATER

SOME EFFECTS OF THE LARGER TYPES OF AQUATIC 

VEGETATION ON IRON CONTENT OF WATER

By EUGENE T. OBORN and JOHN D. HEM

ABSTRACT

Complex antagonistic factors affecting solution of iron in natural water were 

investigated by correlating data from field and laboratory studies of aquaticplants.

As blanketing type of water-plant growth increases, oxygen in the water is 

generally depleted, principally through respiratory processes; furthermore, the 

normal exchange of oxygen at the air-water interface is inhibited if vegetation 

forms a complete blanket at the water surface.

A gradual accumulation of iron in the bottom mud of the Federal Center Lake 

seems to result from additive effects of oxygen entry into lake water from the 

air and from photosynthesis of the water plants growing in the lake. In both 

greenhouse and lake, water with submerged soil-rooted plants had highest concentrations of iron in solution when growth was most conspicuous Wateremergent soil-routed plants, such as parrotfeather and broad-leaved cattail 

permitted the additional blanketing effect by allowing the additional growth 

of duckweed or pond scum; this growth further decreased the exchange of 

oxygen at 'the air-water interface. Water-hyacinth leaves shade the water 

surface and do not permit the additional duckweed or pond-scum growth, but do 

permit exchange of oxygen at the air-water interface of the water body. As a 

result, dissolved oxygen and Eh remained high, and iron in water continued 

low throughout the growing season of water-hyacinth.

Pasteurization or sterilization of soil caused additional iron to go into water 

solution. Water percolating through soil may dissolve 10 or more times the 

amount of iron normally present in water at a lake bottom.

Water usage, particularly by the water-emergent soil-rooted plants, varies 

considerably with the morphologic differences of the different speciesi. Transpiration by such plants seems in general to be proportional to leaf surface area 

exposed per unit of water or to soil area upon which the plants grow.

INTRODUCTION

The general relation of plant growth to the chemistry of iron in 

natural waters has been noted earlier (Oborn, 1960a). The plan of 

the present report is to correlate observations of changes in dissolved

237
238 CHEMISTRY OF IRON IN NATURAL WATER

iron in a small lake with those in greenhouse tanks. The causative 

agents in both locations are common types of aquatic vegetation 

easily visible to the naked eye. Two small plants (duckweed and 

waterbloom) collectively have an effect equal to or exceeding that 

of larger plants and accordingly are included. Because the growth 

and normal development of larger plants is dependent on the presence 

and activity of a microflora, no attempt was made to separate the two; 

nevertheless, emphasis is here placed on the effects of the larger 

aquatic plants.

Seasonal fluctuation of plant growth in water has been known 

for thousands of years. Anyone acquainted with swamp or marsh 

areas has witnessed the sudden seasonal appearance and subsequent 

disappearance of waterblooms. Other planktonic and benthonic 

forms are less conspicuous but are nonetheless seasonally present. 

Microbiota and macrobiota usually exist in the same area. Some 

microspecies frequent areas that are almost devoid of direct light, but 

larger forms require sunlight and tend to concentrate in the quiet 

shallow and shoreward recesses of rivers, lakes, and reservoirs.

Major features of the environment control the forms of life that 

exist, but living organisms can modify their environments appreciably. After death of aquatic plants, the organic matter is consumed 

by animals or is decomposed by the action of micro-organisms. 

Decomposition of organic matter alters the structure of compounds 

in plant tissues that contain iron. As a result of partial decomposition, a soluble organic complex containing iron may be produced. 

Ultimately, however, if ample dissolved oxygen is available, organic 

matter and iron may be completely oxidized and the iron deposited 

as ferric hydroxide.

Iron in organic complexes derived from dead organisms may be 

available for plant metabolism even in alkaline solution. Shapiro 

(1957) described a complex of ferrous iron of high molecular weight 

(straight-chain organic acid) which he extracted from lake water. 

Hem (1960a) obtained a ferrous complex with tannic acid. Although 

both complexes were oxidized slowly in water that was in contact 

with air, both retained dissolved ferrous iron in appreciable quantity 

for more than a month at pH values considerably above neutrality. 

In the field and laboratory studies here described, both lake-bottom 

and canal-bank soils subjected to heat treatments, showed evidence of 

ferrous iron complex formation.

Iron solubility and concentration in water where vegetation is 

growing are evidently subject to many continually changing factors. 

These factors, which include vertical and horizontal currents, 

diffusion, stratification, and the diurnal variation of dissolved oxygen 

were recognized by Welch (1935), Ruttner (1953), and others.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 239

Variations in concentration of iron in water as affected by the 

natural microbiota or maerobiota present were discussed by Moore 

and Maynard (1929) Baas-Becking and others (1957), Hutchinson 

(1957),Ruttner (1953) and Steinberg (1946).

MATERIALS AND METHODS

Thomas Carlyle years ago said, "A world * * * exists by the 

balance of antagonism." This statement is applicable to the interrelated factors that control the iron content of natural waters. A 

correlation of field and laboratory studies seemed the best approach 

to a better understanding of these complex and sometimes antagonistic factors.

FEDERAL CENTER LAKE STUDY

The Federal Center Lake is near the east-central edge of the Denver 

Federal Center; it has a surface area of about 3 acres. The small 

reservoir has been in existence for about 20 years and, with the exception of a few short intervals, has been kept full of water. It receives 

some water from the industrial-waste treatment plant of the Federal 

Center; objectionable matter, including organic wastes, are removed 

from this effluent and do not enter the lake.

In comparison to the crested wheatgrass soil surrounding the lake, 

the lake-bottom soil is relatively rich in organic matter (Oborn 1960b, 

p. 201), and the lake supports an abundant growth of a wide assortment of aquatic vegetation during the warm months of each year. 

The lake was selected as a convenient field location to study the relation of occurrence and behavior of native species of aquatic vegetation 

to presence of dissolved iron in natural water.

GREENHOUSE STUDY

Most lake phenomena are affected by variables that cannot be controlled; therefore, some of the same species of vegetation that were 

present in the lake were used in the laboratory studies. These studies 

were made in a greenhouse, where temperature was thermostatically 

controlled. Dormancy of some species was delayed and of others was 

eliminated by use of fluorescent lighting.

EXPERIMENTAL PROCEDURE

So far as practicable, sampling and sample analyses were performed 

in a similar manner for lake and greenhouse samples. Care was exercised to keep variables at a minimum. Technique differences peculiar 

to lake or to greenhouse studies are discussed on pages- 240 and 243.
240 CHEMISTRY OF IRON IN NATURAL WATER

LAKE STUDY

Conditions in the Federal Center Lake were averaged on a monthly 

basis by using data collected weekly during the 1958 growing season. 

Water samples were collected near the inlet, near the outlet, and at one 

to five other locations in the lake. Sampling stations, numbered 1 to 

7 in figure 23, were in areas of different kinds of actively growing 

vegetation and are described in the table below. The red waterbloom

FIGURE 23. Aerial photograph of Federal Center Lake showing sampling locations.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 241

was identified by C. Norton, Colorado State University, the other 

plants by the senior author. The percent water-surface cover is not 

reported for lake stations because of the presence of inherently 

uncontrollable variables.

Station Location in lakf 

Southwest near 

inlet.

3_______ Northeast near

outlet. 

4_______ North_______

5_-_____ Northwest.

6_______ Northwest _

?_______ South_____

Approximate

water depth

(feet)

2>.-3

12-14

2/2-3 

7-9 

2%

2/2 2)2-

Predominant vegetation

Potamogeton nodosus Poir (American 

pondweed).

P.foliosus-P.pectinatus (leafy pondweed 

and Sago pondweed in approximately 

equal parts).

Potamogeton foliosus Raf. (leafy pondweed) .

Potamogeton pectinatus L. (sago pondweed) .

Typha latifolia L. (broad-leaved cattail)

Lemna minor L. (lesser duckweed).

Euglena rtibra Hardy (red waterbloom)

Some plant succession and variability in predominant lake-plant 

growth took place through the growing season. Ten to fifteen percent of the lake-water surface was covered by red waterbloom in 

July through August and by duckweed in August through October. 

All lake samples were obtained from a boat with an open-tube (Kemmerer) sampler. The sampler was fitted with stoppers that could be 

closed to entrap the sample at any desired depth below the water surface. A messenger weight, which was sent down the line suspending 

the sampling tube, triggered the closing mechanism. The samples 

were obtained from as near the lake-bottom mud-water interface as 

practical, and most were clear or only slightly turbid. Sampling 

operations on the lake are shown in figure 24. Temperature, pH, 

and Eh of each sample were immediately measured and recorded 

at the time of sampling.

Dissolved oxygen was determined in the laboratory within 2 hours 

after sample collection; the Rideal-Stewart modification of the 

Winkler procedure was used. .The iron content of each sample was 

analyzed after filtration through medium-porosity (Whatman) filter 

paper; the 2,2 bipyridine procedure was used. Ferrous iron and 

ferric iron were determined separately. In most samples, most of the 

iron was in the ferric form. At the pH of the samples, (between 

7.1 and 9.1) oxidation of ferrous iron, unless organically complexed, 

is rapid; therefore, at time of sampling more ferrous iron may have 

been present.

621977 O-J62
242 CHEMISTRY OF IRON IN NATURAL WATER

FIGURE 24. Measuring pH and Eh of water. Top, on Federal Center Lake ; bottom, in

greenhouse tank.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 243

Ferrous iron in small concentrations was usually present at the 

more shallow lake stations. At stations 1 and 3 it was definitely 

in higher concentrations during the period of most conspicuous plant 

growth. No ferrous iron was found in most of the samples from 

greenhouse tanks. Because oxidation after samples were collected 

may have influenced the results, separate ferrous and ferric iron 

concentrations are not reported.

Table 1 shows the chemical analyses of single lake inlet and outlet 

samples collected during the 1956 growing season, before the present 

study was begun. The loss of iron and silica and the gain in pH 

from the inlet to the outlet are probably due to influence of vegetation 

in the lake. Lake samples taken among vegetative growth in the 

immediate area of inflow and outflow indicate the overall gain or 

loss of iron in this lake water; observations at other sites indicate 

alterations caused by the other kinds of lake vegetation.

TABLE 1. Chemical analyses of water samples from inlet and outlet of Federal 

Center Lake, July 23, 1956

[Results in parts per million, except as indicated]

Inlet (18:30

p.m. slight Outlet (18:45 

turbidity) p.m. clear)

Silica (SiO2 )________________________________________ 11 1.0

Aluminum (Al)____________________________________ 1.1 .0

Iron (Fe)__-____-_-________________________________ .30 .00

Manganese (Mn)__________________________________ .00 .00

Calcium (Ca)______________________________________ 16 16

Magnesium (Mg)_____________:___________________ 1.9 3.9

Sodium (Na) _____________ __________________________ 83 39

Potassium (K) ___________ _ ________________________ 2. 8 1. 2

Bicarbonate (HCO3 )______________________________ 42 43

Carbonate (CO3 )_ _. ________________________________ 0 5

Sulfate (SO4 )- -_---------------_-_-_-.----------- 186 66

Chloride (Cl)__-__--__________-_________-_--_-____- 10 17-

Fluoride (F) __________ _ ______________________._._ .4 .4

Nitrate (NO8 )-------------------------------------- .8 .4

Phosphate (PO4 )----__------------------ ---------- 2.2 1.8

Dissolved solids (residue on evaporation at 180°C)______ 365 198

Specific conductance (micromhos per cm at 25°C) ______ 512 301

pH____ ______________________________________ 6.6 9.0

Temperature (°F)__________________________________ 68 74

GREENHOUSE STUDY

A series of greenhouse tests provided a more detailed study of the 

effects of individual plant species on the dissolved iron of water in 

which the plants grew. A greenhouse adjacent to the laboratory was 

used for the study, and earthenware crocks were used as test tanks. 

Four inches of bottom soil from the Federal Center Lake was placed
244 CHEMISTRY OF IRON IN NATURAL WATER

in each tank; the total iron content of this soil was 3.45 percent of its 

air-dry weight. A selected test species was planted to cover about 5 

percent of the soil area, and the tank was filled with tapwater containing 0.01 to 0.05 ppm of iron. After weekly sampling, tapwater was 

added to restore the original water volumes.

One 30-gallon, one 15-gallon, and one 5-gallon container were used 

for each test plant species. Control tanks, containing the same types 

of water and soil but no vegetation, were maintained during the study.

Emergent and submerged aquatic plants having widely diverse 

physiological methods of growth were selected for the tests. Thus, 

information could be obtained on increase or decrease in dissolved 

iron caused by different growth habits of different vegetation.

For comparisons, plants were physically removed from certain tanks 

for various periods of time. For further comparisons, soils of certain 

tanks were subjected to pasteurizing and ultimately to sterilizing 

temperatures. However, none of the heat-treated soils were sterile. 

Use of sterile soil would have defeated the purpose of the study.

In nature, water-sedge has more the growth habit of phreatophytes 

than of true aquatic plants. This common species was transplanted 

into a tank that was filled with the same soil in which the field plant 

had been growing. Another tank of similar soil from which watersedge had been removed served as the control. Water additions to 

these two tanks was sufficient to keep the soil surface moist (but not 

water submerged) at all times.

For several months after the initial plantings were made in the 

tanks, growth was relatively slow. However, the rate of growth 

increased during the spring and summer and coincided with natural 

growing-season trends. Most of the plants were still growing 

vigorously at the end of the study in December, 1958.

All the species except the water-sedge were planted December 9, 

1957; the water-sedge was planted November 19, 1957. As might 

be expected, through the year some plant succession and variability 

in predominant greenhouse plant growth took place. For example, 

sago pondweed, leafy pondweed, stonewort, and duckweed, not visible 

at first, appeared in some of the greenhouse tanks later in the year. 

Seeds and other materials capable of propagation were present in the 

lake-bottom soil.

Some algal plant and other microbiological species no doubt were 

introduced by waterborne and airborne spore reseeding in all the 

greenhouse tanks. This reseeding continued for the duration of the 

study.

Table 2 lists the plant species that were studied in the greenhouse 

and follows a classification based on growth habit (Oborn, 1960b).
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 245

The table indicates the months during which growth was most 

vigorous.

After plants were established, the tanks were sampled each week. 

Water temperature, pH, and Eh in each tank were measured at the 

time of sampling. The glass, calomel, and platinum electrodes required for the measurements were mounted in a rubber stopper, which 

in turn was fixed in the lower part of a 3-foot plastic tube. The 

leads were thus protected from contact with water when the tube 

was immersed in the tanks. Readings were made with a batteryoperated pH meter (fig. 24). A sample of water was then withdrawn 

for dissolved-oxygen and iron analysis. Samples were taken from 

the mud-water interface of the tank bottom by siphoning through 

glass tubing. The amount of water lost from each tank, including 

organism metabolic and transpiration requirements as well as water 

lost through tank-surface evaporation, was measured. The percentage of water surface covered by vegetation was recorded, and pertinent 

growth changes and physical phenomena occurring both at lake 

stations and in greenhouse tanks were noted each week. Sampling 

was discontinued at the end of December 1958.

The weekly measurements for each set of tanks containing the same 

species were averaged for each month. The results were further 

averaged to contrast the effects of plants during periods of vigorous 

growth with effects during1 periods of relative dormancy. Most of the 

interpretation is based on the averaged measurements.

Thermograph records showed that some deviations from constant 

temperature occurred in the greenhouse. However, the effects of 

these deviations were minor compared with the effects of other factors.

The initial measurement of iron concentration was made 24 hours 

after planting was completed. The iron concentration at the mudwater interface at that time was uniformly very low (about 0.04 

ppm); nevertheless, the iron content of water samples collected in the 

first month after planting was commonly considerably greater. The 

high reading for the first month following planting was attributed 

to the soil disturbance caused by the planting and accordingly was 

not included in any of the tabulated average values.

INTERPRETATION OF RESULTS

Any phenomenon affected by seasonal fluctuation of growth is itself subject to continuous change dependent on kind and amount of 

influencing factors present; thus, both the form and the amount of 

iron in water could be seasonally altered.
bOrf*.

OS

TABLE 2. Plant species grown in greenhouse O

[Higher (vascular) plant nomenclature according to Fernald (1950) with the exception of Eichhornia (Kobuski, written communication, 1958). Algal (nonvascular) plant H

nomenclature according to Smith (1950) ] g

Months of growth M

Plant species Growth habit Sparse Abundant 2

Carex aquatilis Wahlenb. (water-sedge)_______ Land-water,_________-_---_ ________________________ February-December. ^

Lemna minor L. (lesser duckweed) ___________ Water emergent, water roots. ________________________ September-December. _

Eichhornia, crassipes (Mart.) Solms (water- Water emergent, soil roots._. February-July.-.__._____ August-December. ^

hyacinth). «

Myriophyllum brasiliense Camb. (parrot- Water emergent, soil roots. _. February-April __________ May-December. o

feather). ^

Cladophora sp. Kiitzing (pond scum)_________ Water submerged, water ________________________ August-December. H

roots.

Potamogeton nodosus Poir. (American pond- Water submerged, soil roots. February-April, August- May-July. f£

weed). December. £_|

Elodea nuttallii (Planch.) St. John (western Water submerged, soil roots_ February-July___________ August-December. »

waterweed). tr1

Heteranthera dubia (Jacq.) MacM. (water- Water submerged, soil roots_ February-July___________ August-December. <j

stargrass). >

Eleocharis acicularis (L.) R. and S. (needle Water submerged, soil roots. February-July___________ ^

spikerush). ^
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 247 

MONTH TO MONTH CHANGES IN GREENHOUSE TANKS

The four chemical variables measured in the lake and in the greenhouse tanks dissolved iron, pH, Eh, and dissolved oxygen are 

interrelated (Oborn, 1960a). For example, the amount of iron that 

can be retained in solution is directly related to pH, Eh, and dissolved 

oxygen in the absence of complexing and excessive amounts of certain 

anions (Hem, 1960a, 1960b). The Eh of water in contact with air 

is generally a function of the effects of oxygen in solution. The 

amount of oxygen dissolved is, in turn, affected by temperature, wind 

action, freedom of exchange between air and water at their interface, 

and the chemical or biologic oxidative processes going on in the water.

As plant metabolic-growth rates increase, the oxygen in the water 

is generally depleted, particularly at night when processes of respiration exceed those of photosynthesis. The exchange of oxygen at 

the air-water interface is inhibited if the vegetation forms a sufficiently dense blanket at the water surface. Depletic/n of oxygen 

lowers the Eh and makes iron more soluble. Hence, rapid respiration, 

coupled with a complete blanketing of leaves or other cover on the 

water surface, causes more iron to go into solution; furthermore, an 

apparent increase in soil solutes, of 1-3 ppm iron, frequently made 

available in the partial decomposition of plant materials, may be 

retained in solution indefinitely as an organic complex under 

anaerobic conditions.

Interrelations of dissolved iron, dissolved oxygen, and Eh are 

shown in figures 25-27 for greenhouse-grown water-stargrass, parrotfeather, and western waterweed, respectively. These three plants are 

all soil rooted. Water-stargrass and western waterweed have a watersubmerged type of growth, and parrotfeather has a water-emergent 

type of growth. Figures 25-27 consistently show that preceding 

rapid plant growth, Eh and dissolved oxygen were high and dissolved 

iron was low. During the most vigorous growth, Eh and dissolved 

oxygen decreased and iron increased.

Most of the available iron supply in the tanks was in the soil. 

As previously mentioned, iron was dissolved from the soil when the 

plantings were made, but most of this iron was returned to the soil 

from solution during the initial 30-day period of growth adjustment. 

In another study (Oborn, 1960b) it was pointed out that direct 

extraction of water-dissolved iron by the commonly iron-rich aquatic 

plants depends mainly on whether the plants are water-rooted or soilrooted species. The amounts of iron retained in solution during 

vigorous plant growth reflect the sum results of the several interrelated factors such as pH, Eh, temperature, dissolved oxygen, kind 

and amount of organic matter present, and method of iron extraction 

by the plants.
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EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 251

Data shown in figures 25-27 suggest that the supply of iron made 

available for solution by aquatic plants fluctuates seasonally. During 

and immediately after the growing season, iron in water solution is 

in excess of the amount that will be present in solution during other 

months of the year. The low Eh, its associated oxygen depletion, 

and available complexing organic matter probably are the principal 

controlling factors. The high iron values generally occur in conjunction with low Eh and low dissolved oxygen.

Figure 28 is a graph, similar to figures 25-27, for a tank containing 

water-hyacinth. The water in this tank did not have sufficiently low 

Eh and dissolved-oxygen values to permit much iron to go into 

solution.

The great importance of water-blanketing effect has been brought 

out in this study and is shown in figures 26 and 28. Both plants 

(parrotfeather and water-hyacinth) are water emergent and soil 

rooted. Even when growing at maximum density, parrotfeather 

(fig. 33) did not exclude light from the water surface and so duckweed 

or pond scum developed and coexisted as a heavy blanketing growth 

on the water surface of the tanks. The dense, thick (nonincised) 

leafage of water-hyacinth (fig. 33) does not allow adequate light for 

duckweed or pond scum to develop and coexist on the water surface 

of the tanks. Throughout the growing season, the additional blanketing effect of the growth of duckweed or pond scum (as in the parrotfeather tanks) and lack of it (as in the water hyacinth tanks) brought 

about the differences between low and high dissolved oxygen and Eh 

and between high and low iron in water at the soil-water interface in 

the tanks. The dissolved oxygen and Eh in the water-hyacinth tank 

decreased slowly during the summer, but never became as low as the 

dissolved oxygen and Eh in water in the parrotfeather tank (fig. 26). 

Water-hyacinth, for the reasons stated, did not exert any pronounced 

effect on iron content of the water.

Actual total quantities of iron circulated from the soil into the 

plants and thence into the water and back to the soil cannot be readily 

determined from the data obtained. The experiments were stopped 

before the greenhouse plants had run a full cycle of growth and dormancy; nevertheless, the mechanisms of iron extraction from and 

return to submerged soils are clearly indicated.

LAKE STUDY OBSERVATIONS

Average composition of the water samples from the lake stations 

are presented in tables 3-7. The averages for iron, pH, Eh, and dissolved oxygen represent seasonal periods of growth and dormancy for 

the different and predominant plant species present at the seven
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JAN.

* »

^

FEB.

~\

«.

^^

MAR.

\,

\

 -

APR.

. *''

"\

/

- 

MAY

*«,

~~\

x -

JUNE

*»

*" . *.

*^^^\

--^^

JULY

.......

*"

^^^ 1. ^^^

^>s

AUG.

"* -..

^

 ~ ~~

SEPT.

/

OCT.

.....

/\

NOV.

\

^

DEC.

to 

to

g

%

%^

0

M 

ft)

§

%

I

3 

ft)

> 

f 

<J

§ 

rt

FIGURE 28. Monthly average dissolved oxygen, Iron content, and Eh in greenhouse tank 201 (water-hyacinth). ft)
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 253

sampling points. Data in the tables show a pronounced tendency for 

iron in solution to be highest in late summer or early fall (August 

through October). This same tendency was observed in the greenhouse experiments.

A lake normally accumulates iron because of oxidation of the iron 

in the incoming water. Data in table 1 and a comparison of data for 

station 1 (table 3) with those for station 3 (table 6) show these results 

to occur at the Federal Center Lake. An additional indication is the 

fact that the iron content of the organically rich lake-bottom soil is 

greater than that of the soil of the surrounding area (Oborn, 1960b).

COMPARISONS OF DATA FROM GREENHOUSE AND LAKE STUDIES

Averaged measurements for the greenhouse-lake study were compiled from weekly readings. They show amounts of iron present 

in the water during the season of maximum growth as contrasted 

with amounts present at other times. The data also permit comparisons of changes of iron in water caused by plants of similar 

growth habit, regardless of whether growth takes place in lake or 

greenhouse. These data are presented in tables 4-8.

Vegetative surface cover for greenhouse tanks is reported to the 

nearest 5 percent. Figure 29 illustrates two plants that have dense 

leafy or leaflike growth at the surface of the water. Both in lake 

and in tanks, these plants tend to increase dissolved iron when watersurface cover is complete or nearly so. Table 3 summarizes the 

effect of American pondweed on iron content of water supporting 

the growth of this species and clearly indicates a seasonal trend. In 

greenhouse and lake, high dissolved iron content (accompanied by 

dense surface-water leaf growth) was both preceded and followed 

by lower iron concentrations (and pronounced decrease in amount 

of surface-water leaf growth).

Iron hi the greenhouse tank water reached a maximum earlier in 

the season than did iron in the lake water, probably because a higher 

temperature was maintained in the greenhouse. Iron content of 

water in the tanks did not increase significantly until about 85 percent 

of the surface area of the water was covered by plants. The cover 

in the tanks with American pondweed and with some other plants 

used in the greenhouse experiments was not always a pure stand of 

the initial planting. Plant competition and to some extent plant 

succession resulted in the establishment of mixtures of species and 

sometimes of genera.

Table 3 does not show the usual relation of iron content of water 

to pH and Eh; however, dissolved oxygen was lower in both greenhouse and lake when iron was high.
254 CHEMISTRY OF IRON IN NATURAL WATER

 

FIGURE 29. Plants whose floating leaves or leaflike parts completely cover the water' 

surface. Top, American pondweed ; bottom, duckweed.

Lesser duckweed growth in the greenhouse was all volunteer. Data 

for this species are presented in table 4. This water-rooted plant 

frequently forms a dense cover on organically rich, quiet waters during 

the late summer and fall (fig. 29). In contrast to American pondweed, duckweed was conspicuous in greenhouse tanks several weeks 

after its natural disappearance from the lake. Cooler temperatures 

combined with effects of wind on the lake likely were important 

contributing factors in the disappearance of duckweed from the lake.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 255

TABLE 3. Characteristics of water affected ~by American pondweed in greenhouse

tanks and in the lake

Sampling points

Greenhouse tanks

103,203,503.

Do-- _

Lake station 1 _______

Do. 

Period of average (1958)

February-April and

August-December.

May- July. ------ _

March- August and

November.

September-October. - .

0

d.

1

EH

20.4

21.8

17.4

18.5

K

a

8.0

7.5

7.2

O O. 1 1

^

"g

>

f.

W

0.19

.23

.29

.30

1ft 

a

|

0.17

.30

.74

1.15

&

~o!

o

4.8

1.8

3.1

2.4

Plant species

American pondweed.

Stonewort '_ _-.-

Algal scum --

Duck weed. __-

Total cover. _.

American pondweed.

Sago pond weed. . -

Algal scum .. -.

Total cover ...

American pondweed.

 do-.- 

^ t> w

w ^ a

^ tt ^ ^ «^«

10

15

15

10

50

80

10

5

95

(S!)

(2\

1 Chara sp.

2 Percent water-surface cover not reported for lake stations because of presence of inherently uncontrollable variables.

TABLE 4. Characteristics of water affected toy lesser duckweed in greenhouse

tanks and in the lake

Sampling points

Greenhouse tanks

103, 504 (without

vegetation) .

Greenhouse tanks

104, 205 (containing Duckweed).

Do _

Do 

Period of average (1958)

September-DecemberSeptember-October- ._

I^ovember December

O

d

£

20.5

21.9

21.1

24.0

16.4

H 

a

8.0

7.9

8

1

7 ^

7.8

_.

"3

&

0.07

.02

.05

.05

.02

1

1

t-H

0.29

.39

9fi

V)

.42

a

a 

&

6

3.7

.6

2.4

1.2

1.7

Plant species

Vascular plants

continuously

removed.

Lesser duckweed- -

- do 

... ..do -

 do 

s_il

1$|4S*

100

90

(')

1 Percent water-surface cover not reported for lake stations because of presence of inherently ilhcon - 

trollable variables.

Duckweed growth caused increase in iron in both greenhouse and 

lake water during the months of September and October. Iron in 

water in the greenhouse tanks was highest when the water surfaces 

were most nearly covered with vegetation.

A total cover of algal scum would probably have an effect on dissolved iron similar to that produced by a total cover of duckweed: 

A blanketing effect would result and upon disintegration of the plants, 

organic iron would be released. Data from a greenhouse tank that 

contained only a partial cover of algal scum showed no significant 

variation, and so the data are not included here. Algal scum, illustrated in the upper left area of figure 30, top, is primarily Cladophora 

sp.
256 CHEMISTRY OF IRON IN NATURAL WATER

FIBUEE 30. Submerged aquatic plants present In lake and greenhouse tanks. Top, leafy 

txmdwecd; bottom, sago pondweed (aerial view of water surface).
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 257

During July and August, a blood-red algal bloom, consisting of 

many unicellular organisms, appeared in the lake (fig. 31). Each 

cell of the bloom consists almost entirely of protoplasm and conducts 

its own independent iron metabolism. The blood-red algal bloom 

probably is very active in altering iron content of water because each 

plant cell is alive and metabolically very active.

FIGTJRE 31. Unicellular organism producing Wood-red bloom on lake. Top, microscopic 

view ; bottom, habitat view (organism is concentrated within the lined area).
258 CHEMISTRY OF IRON IN NATURAL WATER

Euglena polymorpha Dangeard (Johnson, 1944) commonly produces a pea-green waterbloom in the greenhouse. Denver laboratory 

analysis showed this plant to have 4.08 milligrams of iron per gram of 

blotter-dry plant material. Euglena rubra Hardy, the organism 

responsible for red waterbloom, is a different species but closely 

related in morphology and physiology.

TABO; 5. Characteristics of lake water during and after period in which red

waterbloom was present

Sampling points

Lake station 7 __ 

Do.. 

Period of average (1958)

July- August (bloom) _

Temp. (°C)

23.2

on c

pH

7.8 

7.4

Eh 

(volts)

0.28 

34

Iron 

(ppm)

0.48 

1.0

02

(ppm)

1.9

.5

Plant species

Red waterbloom. 

Do. i

1 Note this is actually the postbloom period.

Waterblooms make considerable amounts of iron available suddenly 

when their individual cells disintegrate. Data in table 5 shows that 

the iron content of the water during the postbloom period was about 

double the iron content during the most flourishing growth of the 

organism. After cessation of the bloom, the plant decays rapidly, 

and organic iron is released to the water.

DATA CLASSIFIED BY PLANT GROWTH HABIT

Aquatic vegetation has been classified for this study into waterrooted and soil-rooted, submerged and emergent types. Comparisons 

of data from greenhouse and lake studies of similar aquatic plants 

having submerged soil-rooted habits of growth are presented in table 

6.

Submerged plants growing at lake stations 2, 3, and 4 (fig. 23) 

are illustrated in figure 30. Both kinds of plants also grew in small 

volunteer amounts in several of the greenhouse tanks. Submerged 

plants, observed in the greenhouse but not present in the lake in 

appreciable amount, are illustrated in figure 32. Iron concentrations 

of about 0.3 ppm were measured for most of the water-submerged 

soil-rooted plants summarized in table 6. At the three lake stations, 

more iron was present in the water during August through October 

than during June, July, and November. Thus, the pondweeds had 

the same effect on the iron content of the water as the waterblooms; 

decaying vegetation made iron available for solution during and after 

periods of vigorous growth. At the three lake stations, the higher 

concentrations of iron in August through October were accompanied 

by lower pH, Eh, and dissolved oxygen.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 259

FIGURE 32. Aerial views of submerged aquatic plants grown in greenhouse. Top. needle 

spikerush (usually completely submerged) ; middle, waterweed (breaks the water surface 

occasionally) ; bottom, water stargrass (breaks the water surface frequently).
260 CHEMISTRY OF IRON IN NATURAL WATER

TABLE 6. Characteristics of water affected by submerged soil-rooted plants in 

greenhouse tanks and in lakes

Sampling points

Greenhouse tanks

104, 204, 504.

Do..............

Greenhouse tanks

105, 205, 505. 

Do.... ...... .

Do......... ..

Do 

Do .-....

Period of average (1958)

A ust Dec m

November.

November.

November.

D

it e

20.6

no o

20.2

15.6

1O 3

17.7

19.2

14 9

1C Q

wft

7.9

7.8

8.0

8.1

9.0

7.8

9.1

8.0

R 4

7 Q

1

a fS

0.36

.03

.36

.08

.29

.24

.28

.25

.28

.27

1

3 

|

0.15

.32

.06

.32

.18

.39

.23

.33

.30

.39

I

6

6.8

.5

7.1

2.5

7.4

3.3

7.8

6.3

6.0

4.6

Plant species

weed.

Total cover. _ _

weed.

Lesser duckweed..

Total cover. _ _

Lesser duckweed.. 

Sago pondweed. _ _

-__..do. _

 do.- 

and Sago pondweed equal 

parts, 

 ..do. __ 

Water surface cover-(percent) ed 

30

5

35

0

10

85

95 

40

65

5

10

5

85

(')

0)

CO

(1)

0)

(')

i Percent water-surface cover not reported for lake stations because of presence of inherently uncontrollable variables.

The averages of the iron content in the tank water during the 

growing season were comparable to the averages observed in the lake; 

however, decreases of the oxygen content and Eh during the growing 

season were more noticeable in the tank water than in the lake.

Emergent aquatic plants used in the water-iron study are illustrated 

in figure 33. Table 7 shows average characteristics of water affected 

by three emergent species two that grew in the greenhouse tanks and 

one that grew only in the lake.

Presence or absence of duckweed growth depends, among other 

things, on availability of adequate light at the water-surface growth 

site. Cattail and parrotfeather growth sites permit such suitable 

light conditions for duckweed to grow and coexist (figs. 33 and 34, respectively) ; the water-surf ace area may thus seasonally be completely 

covered by coexisting plant growths. Conversely, water-hyacinth 

growth sites do not permit suitable light conditions for duckweed 

growth, and water-surface areas are open between plants; thus, 

oxygen can more readily interchange between atmosphere and hydrosphere. This fact is demonstrated by the higher dissolved-oxygen
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 261

FIGURE 33. Emergent aquatic plants. Top, water-hyacinth, in greenhouse; middle, 

parrot-feather, in greenhouse ; bottom, broad-leaved cattail, in late.
262 CHEMISTRY OF IKON IN NATURAL WATER

FIGURE 34. Coexistence of duckweed and cattail growth at Federal Center Lake.

and lower dissolved-iron content of the water affected by waterhyacinth compared with the oxygen and iron content of the water 

affected by parrotfeather.

Dense root growth and nearly complete covering of the water 

surface by parrotfeather, as well as by lesser duckweed and (or) pond 

scum, interfered with absorption of oxygen by the water and promoted a low Eh in the tanks. The data in figure 26 show more clearly 

than the seasonal averages that the iron concentration in the tanks 

where parrotfeather was growing increased as oxygen and Eh 

decreased.

In the shallow lake water where broad-leaved cattail was growing, 

Eh and dissolved oxygen were low from July to October. Although 

Eh and dissolved oxygen increased considerably during November, 

iron in the organically rich shallow area remained high. Growth of 

lesser duckweed among the cattails during July through October 

indirectly increased iron by interfering with oxygen interchange at 

the air-water interface and by oxygen usage in respiration. Disintegration of the duckweed during November also contributed organic 

iron to the water.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 263

TABLE 7. Characteristics of water in greenhouse tanks and in lake affected by

emergent aquatic plants

Sampling points

Greenhouse tanks

101, 201, 501.

Do.............

Greenhouse tanks

102, 202, 502.

Do

Lake station 5.. .. .

Do. ... ...... .

Do.

Period of average (1958)

February- July. .

August-December .

February- April .

May-December _______

July- August .. _ ..

September- October. . .

November-. .......___

U

%1

20.9

21.7

19.3

22.3

24.1

16.6

7.1

wft

7.3

7.6

7.6

7.5

7.2

7.1

7.7

^^

"3

,C|

W

.38

.22

.37

.06

.04

.14

.31

1

P. 

3

g

ft

0.15

.11

.31

.34

.42

.60

.48

1 

 ©

C1

0

5.6

3.8

4.9

.2

.2

.5

6.8

Plant species

Water hyacinth...

 .do. 

Parrotfeather

(pond scum also

present) .

Panotfeather

(duckweed

and scum also

present).

Broad-leaved

cattail.

Broad-leaved cattail (duckweed

also present).

Broad-leaved

cattail.

H ^ O

||I^^"S

^

55

100

40

90

0)

0)

(0

i Percent water-surface cover not reported for lake stations because of presence of inherently uncontrollable variables.

IRON CONTENT OF WATER IN TANKS CONTAINING SOIL AND

WATER-SEDGE

Figure 35 shows the growth of a common ditch-bank phreatophyte, 

water-sedge, in a greenhouse tank. Data obtained from this study 

are presented in table 8.

Table 8 shows that water percolating through soil may pick up 

10 or more times the amount of iron normally present in water at the 

lake bottom. Soi] in the bare tank was kept saturated. After 2 

months of operation, the soil in the bare tank was removed and subjected to pasteurization heat treatment (65°C for 30 minutes) and then 

returned to the tank. Two months later the soil was again removed 

from the bare tank and subjected to sterilization heat (127°C for 15 

minutes). The soil then was returned to the tank, and the study 

continued.

TABLE 8. Characteristics of icater percolating through tank containing bare 

canal-bank soil and tank containing similar soil and icater-sedge

Tank containing Period of average (1958)

-___.do_ .... __ -_- 

. do _- 

Temp. (°C)

19.6

20.2

19.4

22.4

23.0

22.3

pH

7.0

7.0

6.8

7.2

7.3

Eh 

(volts)

0.16

.16

.08

.11

.07

Iron 

(ppm)

6.5

4.5

11

7.8

3.2

3.4

Os 

(ppm)

0.2

.2

.0

.0

.0
264 CHEMISTRY OF IRON IN NATURAL WATER

FIGURE 35. Common canal-bank water-sedge growth In greenhouse tank.

Pasteurization temperatures were not adequate to oxidize soil 

organic matter but did decrease particularly t'he non-spore-forming 

soil-microbe population. Sterilization temperatures had a greater 

killing effect on the soil microbiota. After soils were subjected to the 

pasturization and sterilization temperatures, no attempt was made 

to maintain sterile conditions; nevertheless, the heat treatments 

undoubtedly decreased the soil microbe population.

The iron in the protoplasm of microbes killed by heat treatment 

probably was released to the soil solutes as an organic complex. An 

important difference was noted in the amounts of iron released by 

lake-botom. and by canal-bank soils when subjected to the same 

sterilization temperatures. The effect of sterilization on lake-bottom 

soil was to increase soil solute iron tenfold. The same treatment on
EFFECTS OF LARGER TYPES OF .AQUATIC VEGETATION 265

canal-bank soil decreased soil solute iron by about half. Difference 

in results seems to be due to a more complete, disintegration of 

organic matter in the lake-bottom soil. In both the bare pasteurized 

and water-sedge unpasteurized canal-bank soils, iron release by soil 

microbes during April-June was about double what it was for other 

months of the year.

AMOUNTS OF WATER USED BY PLANTS

Records were kept of the amounts of water that were added to the 

tanks in the greenhouse. This was done mainly to know the amount 

of iron introduced in the weekly tap water additions. The influence 

of the iron in the added water was minor. Figures 25-28 show no 

tendency for iron content of the water in the tanks to increase until 

the time when plant growth became vigorous, although water was 

evaporated from all but two tanks at a uniform rate through the 

year.

The rates of water use in the tanks for the period July-December 

were as follows:

Average water use (gal per week per 

Type of vegetation sq ft of water or soil surface)

None (open water)--_ 0.93

Do ________________________ 1.0 (August-December)

Algal scum (mostly Cladophora sp.)______ .86 (August-October)

Lesser duckweed___________________ .86 (September-December)

Water-star^rass _________ . 94

Western waterweed________ --__ __ . 88

American pondweed________________ . 90

Parrotfeather ____________________ 1. 0

Water-hyacinth ______________ _ 2. 0

None (wetted1 canal-bank soil)_________ .56

Water-sedge in wetted canal-bank soil______ 3. 0

The submerged types of aquatic vegetation reduced evaporation 

slightly when a thick growth was present. Emergent types, however, 

permitted at least as much water loss as open-water surfaces. Waterhyacinth, which has broad thick leaves, transpired twice as much 

water as was lost by evaporation alone from an equivalent open-water 

area.

Use of a surprisingly large amount of water by water-sedge agrees 

with observations made by investigators of other phreatophytes. 

Water-sedge plants consumed three times as much water per unit of 

soil surface area as was evaporated from open-water and six times as 

much water as was evaporated from wetted surfaces of similar soil 

but which had no plant growth.
266 CHEMISTRY OF IRON IN NATURAL WATER

SUMMARY AND CONCLUSIONS

The average values of iron concentration observed in the lake and 

in the greenhouse tanks lead to some important conclusions regarding 

the effects of aquatic vegetation on the transport and deposition of 

iron in water. Even though amounts of iron entering the Federal 

Center Lake are not large, iron accumulates in the lake-bottom soil. 

Contact of lake-bottom accumulated iron with ground water having 

a low Eh likely would cause the ground water to become iron bearing. 

Geologic terranes formed under conditions where lakes commonly 

existed likely would have iron-bearing ground water.

Vegetation growing in water bodies recirculates iron from both 

water and the bottom deposits by absorbing iron into plant tissues 

during the growing season and releasing iron both in water solution 

and as bottom deposits when the season's growth decays. Iron bacteria, notoriously involved in this process, can produce major deposits 

of iron ore.

Observations in this study emphasize the fact that the amounts of 

iron recirculated by aquatic vegetation vary with the species and 

combination of species.

For comparable plant species, iron concentration in lake water was 

greater than in the greenhouse tanks. The water in tanks that supported plant growth averaged two times more iron content than the 

water in similar tanks that supported no vegetation. The wateremergent soil-rooted plant parrotfeather brought iron into"the water 

in a quantity comparable to that of the water-submerged soil-rooted 

and the water-emergent water-rooted groups. All these plants produce a dense and frequently solid cover of vegetation over the water 

surface during optimum growth conditions. In contrast, waterhyacinth, although it grows thickly, does not produce an asphyxiating 

cover over the water surface. Even when the water surface was-fully 

covered by water-hyacinth, the pH, Eh, and dissolved oxygen and 

iron content of the water were nearly the same as for water in which 

no vegetation was growing. Thick asphyxiating cover of other 

species resulted in a low Eh and low dissolved-oxygen content in the 

tanks and favored solution of iron from the water-submerged tank 

mud.

Water of highest iron content noted in this study was obtained when 

water was allowed to percolate through the soil in tanks containing 

canal-bank soil either bare or with a vigorous growth of water-sedge. 

Soil microbiota activity is known to be extremely effective in bringing 

soil iron into water solution (Oborn and Hem, 1961) and is most 

likely the major factor involved in the high iron concentrations 

observed in the samples from the soil-water drainage tanks.
EFFECTS OF LARGER TYPES OF AQUATIC VEGETATION 267 

STATUS OF KNOWLEDGE OF THE CHEMISTRY OF IRON

The research described in this chapter and in chapters A through H 

of Water-Supply Paper 1459 does not completely cover all possible 

aspects of iron chemistry in natural water. Work on some aspects has 

been done by others and much additional research still is desirable. 

As an example, Eh values observed in some ground waters are higher 

than expected considering the amount of iron the waters contain; 

several explanations have been suggested for this anomaly. One 

of the several possibilities worth exploring is the completing of ferrous 

iron with bicarbonate or carbonate ions. Such complexes have not 

been reported for ferrous iron.

Kinetics of the oxidation of inorganic ferrous iron by atmospheric 

oxygen were not extensively studied in this research. Recent work 

by Stumm and Lee (1960, 1961), has added to existing knowledge of 

this subject. Stumm and Lee found the oxidation to be a first-order 

reaction with respect to inorganic ferrous iron at a constant partial 

pressure of oxygen. The rate is highly dependent on pH; at pH 

levels between 6 and 7, the rate of inorganic iron oxidation is increased 

by a factor of 100 when the pH is raised by one unit. These experiments were done in water containing bicarbonate.

Before the problems involving iron or other impurities in water 

supplies can be effectively minimized, a more complete understanding 

of the chemical behavior of both organic and inorganic materials 

involved is needed. The research that has been summarized in this 

report and in the others of the series on iron chemistry are a step 

toward this understanding.

LITERATURE CITED

Baas-Becking, L. G. M., Wood, E. J. F., and KapLan, I. R., 1957, Biological 

processes in the estuarine environment, Xa-Xb. The place of the estuajine 

environment within the aqueous milieu: Koninkl. Nederlandse Akad. 

Wetensch. Proc., ser. B, Phys. Sei., v. 60, no. 2, p. 88-95, 96-102.

Fernald, M. L., 1950, Gray's manual of botany: 8th ed., New York, Am. Book 

Co., 1632 p.

Hem, J. D., 1960a, Complexes of ferrous iron with tannic acid: U.S. Geol. 

Survey Water-Supply Paper 1459-D.

 1960b, Restraints on dissolved ferrous iron imposed by bicarbonate, 

redox potential, and pH : U.S. Geol. Survey Water-Supply Paper 1459-B.

Hutchinson, G. E., 1957, A treatise on limnology, v. 1, Geography, physics 

and chemistry: New York, John Wiley and Sons, Inc., 1015 p.

Johnson, L. P., 1944, Euglenae of Iowa: Am. Microscopical Soc. Trans., v. 63, 

no. 2, p. 97-135.

Moore, E. S., and Maynard, J. E., 1929, Solution, transportation, and precipitation of iron and silica : Econ. Geology, v. 24, 896 p.
268 CHEMISTRY OF IRON IN NATURAL WATER

Oborn, E. T., 1960a, A survey of pertinent biochemical literature: U.S. Geol. 

Survey Water-Supply Paper 1459-F.

 1960b, Iron content of selected water and land plants: U.S. Geol.

Survey Water-Supply Paper 1459-G. 

Oborn, E. T., and Hem, J. D., 1961, Microbiologic factors in the solution and

transport of iron: TT.S. Geol. Survey Water-Supply Paper 1459-H. 

Ruttner, F., 1953, Fundamentals of limnology, translated, ~by D. G. Frey and

F. E. J. Fry : Toronto Univ. Press, 242 p. 

Shapiro, Joseph, 1957, Chemical and biological studies on the yellow organic

acids of lake water: Limnology and Oceanog., v. 2, no. 3, p. 161-179. 

Smith, G. M., 1950, Fresh-water algae of the United States: 2d ed., New York,

McGraw-Hill Book Co., 719p. 

Steinberg, R. A., 1946, Mineral requirements of Lemna minor: Plant Physiol.,

v. 21, p. 42-48. 

Stumm, Werner, and Lee, G. F., 1960, The chemistry of aqueous iron: Schweiz.

Zeitschr. fur Hydrologie v. 22, p. 295-319.

 1961, Oxygenation of ferrous iron: Ind. and Engr. Ghem. v. 53, p. 143-146. 

Welch, P. S., 1935, Limnology, New York, McGraw-Hill Book Co., 471 p.

U.S. GOVERNMENT PRINTING OFFICE: 1962 O 621977