Data on Natural Organic Substances in Dissolved, Colloidal, 

Suspended-Silt and -Clay, and Bed-Sediment Phases in the 

Mississippi River and some of its Tributaries, 1987-90

by J.A. Leenheer, T.I. Noyes, and P.A. Brown

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 93-4204

Denver, Colorado 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For additional information write to: Copies of this report can be purchased from:

Chief, Branch of Regional Research U.S. Geological Survey

U.S. Geological Survey Earth Science Information Center

Box 25046, MS 418 Open-File Reports Section

Denver Federal Center Box 25286, MS 517

Denver, CO 80225 Denver Federal Center

	Denver, CO 80225
CONTENTS

	Page

Abstract 1

Introduction 1

Acknowledgments 2

Sampling cruise 1, July-August 1987 3

Objectives and approach 3

Dissolved organic matter 3

Organic matter in suspended-sediment fractions 10

Sampling cruise 2, November-December 1987 13

Objectives and approach 13

Dissolved organic matter 13

Organic matter on suspended-sediment fractions 17

Sampling cruise 3, May-June 1988 22

Objectives and approach 22

Dissolved organic matter 23

Organic matter in suspended-sediment fractions 29

Sampling cruise 4, March-April 1989 34

Objectives and approach 34

Dissolved organic matter 34

Organic matter in suspended-sediment fractions 37

Sampling cruise 5, June 1989 44

Objectives and approach 44

Dissolved organic matter 44

Organic matter in suspended-sediment fractions 48

Sampling cruise 6, February-March 1990 54

Objectives and approach 54

Dissolved organic carbon 54

Organic matter in suspended-sediment fractions 55

Sampling cruise 7, May-June 1990 63

Approach and objectives 63

Dissolved organic carbon 63

Organic matter in suspended and bed sediments 64

Conclusions 69

- 70

FIGURES

1. Sampling locations on the Mississippi River and some of its tributaries 4

2. 1H-nuclear magnetic resonance spectra of dissolved humic substances in samples 

from (A) the Mississippi River near St. Francisville, La., and (B) Ohio River at 

Olmsted, 111., sampled July-August 1987 8

3. 13C-nuclear magnetic resonance spectrum of dissolved humic substances isolated

from the Mississippi River near St. Francisville, La., sampled July-August 1987 9

4. Infrared spectrum of dissolved humic substances isolated from the Mississippi River

at St. Louis, Mo., sampled July-August 1987 10

CONTENTS Hi
FIGURES (Continued)

5. Solid-state 13C-nuclear magnetic resonance spectra of colloids isolated from the: 

(A) Arkansas River at Mile 55.9, (B) Mississippi River below Vicksburg, Miss., and 

(C) Mississippi River at St. Louis, Mo., sampled July-August 1987 12

6. Flow chart of procedures for water and suspended-sediment sampling,

sampling cruise 2, November-December 1987 14

7. 1H-nuclear magnetic resonance spectra of dissolved humic substances from 

samples from the (A) Illinois River below Meredosia, 111., (B) White River 

at Mile 11.5, Ark., and (C) Mississippi River below Belle Chasse, La. 18

8. 1H-nuclear magnetic resonance spectra of (A) dissolved humic substances and 

(B) dissolved hydrophilic substances from the Mississippi River near 

St. Francisville, La., June 1988 26

9. Infrared spectra of (A) dissolved humic substances and (B) dissolved

hydrophilic substances from the Mississippi River near St. Francisville, La., 

and (C) infrared spectrum of organic colloids from the Mississippi River at 

Fulton, Term., June 1988 27

10. Scanning electron micrograph of organic colloids isolated from the

Mississippi River at Thebes, ID., May 1988 28 

11-13. 1H-nuclear magnetic resonance spectra of dissolved humic substances from the:

11. (A) Mississippi River at Thebes, 111., (B) Ohio River at Olmsted, 111.,

and (C) Mississippi River below Hickman, Ky., sampled March 1989 36

12. (A) White River at Mile 11.5, Ark., (B) Yazoo River below Steele Bayou,

Miss., and (C) Mississippi River below Belle Chasse, La., sampled

March-April 1989 38

13. (A) Illinois River at Hardin, 111., (B) Arkansas River at Pendleton, Ark.,

and (C) Mississippi River below Belle Chasse, La., sampled June 1989 46

14. H-nuclear magnetic resonance spectra of dissolved hydrophilic substances from the:

(A) Illinois River at Hardin, 111., (B) Arkansas River at Pendleton, Ark.,

and (C) Mississippi River below Belle Chasse, La., sampled June 1989 47

15. Infrared spectra of organic substances extracted from suspended silt and clay 

from the Mississippi River at Helena, Ark. Spectrum A is from methylisobutyl 

ketone extraction; spectrum B is from acid pyrophosphate extraction; spectrum C is 

from acid dimethylsulfoxide extraction; spectrum D is the organic residue after 

destroying the inorganic substances with a mixture of hydrochloric and 

hydrofluoric acids 53

16. 1H-nuclear magnetic resonance spectra of methylisobutyl ketone extracts of

suspended silt and clay sampled from the: (A) Mississippi River near Cache, 111.,

and from (B) Wabash River near New Haven, 111., sampled February-March 1990 62

17. Flow chart of procedures used to prepare sediment samples for solid-state

13 C-nuclear magnetic resonance spectral analysis 66

18. Solid-state 13C-nuclear magnetic resonance spectra of (A) untreated and

(B) treated for iron removal of suspended silt and clay sampled from the

Mississippi River at St. Louis, Mo., in June 1990 68

iv
TABLES

1. Dissolved organic-carbon concentrations and transport for sampling cruise 1, 

July-August 1987

2. Acidity, isotopic, molecular-weight, and yield data of dissolved humic substances 

in the Mississippi River, July-August, 1987

3. Elemental analyses of dissolved humic substances isolated from water samples

collected during sampling cruise 1, July-August 1987 7

4. Organic-carbon and nitrogen transport on the silt and clay and colloid fractions

for sampling cruise 1, July-August 1987 11

5. Dissolved organic-carbon concentrations and transport for sampling cruise 2,

November-December 1987 15

6. Acidity, molecular-weight, and yield data of dissolved humic substances in the

Mississippi River sampled November-December 1987 16

7. Elemental analyses of dissolved humic substances isolated from water samples

collected during sampling cruise 2, November-December 1987 17

8. Organic-carbon and nitrogen contents of silt and clay and colloid fractions of

suspended sediment from sampling cruise 2, November-December 1987 19

9. Organic-carbon and nitrogen transport on the silt and clay and colloid fractions

for sampling cruise 2, November-December 1987 20

10. Concentrations of particulate organic carbon for sampling cruise 2,

November-December 1987 21

11. Dissolved organic-carbon concentrations and transport for sampling cruise 3,

May-June 1988 23

12. Elemental analyses of dissolved and colloidal organic substances isolated from

water samples collected during sampling cruise 3, May-June 1988 24

13. Relative percentages1 of silt and clay, mineral colloids, and organic colloids in the

Mississippi River and some of its tributaries for the May-June 1988 sampling cruise 29

14. Organic-carbon and nitrogen contents of silt and clay, mineral-colloid, and 

organic-colloid fractions of suspended sediment from sampling cruise 3, 

May-June 1988 -30

15. Organic-carbon and nitrogen transport on silt and clay, and colloid fractions

of suspended sediment from sampling cruise 3, May-June, 1988 

16. Concentrations of colloidal organic carbon for sampling cruise 3, May-June 1988

17. Dissolved organic-carbon concentrations and transport for sampling cruise 4,

March-April 1989 - - 35

18. Relative percentages of silt and clay, mineral colloids, and organic colloids in 

the Mississippi River and some of its tributaries for the March-April 1988 

sampling cruise 39

19. Organic-carbon content, nitrogen content, and atomic C:N ratio of silt and clay, 

and mineral-colloid fractions of suspended sediment from sampling cruise 4, 

March-April 1989 40

20. Organic-carbon and nitrogen transport of silt and clay, and colloid fractions of

suspended sediment from sampling cruise 4, March-April 1989 42

21. Concentrations of colloidal organic carbon for sampling cruise 4,

March-April 1989 43

22. Dissolved organic-carbon concentrations and transport for sampling cruise 5,

June 1989 45

23. Relative percentages of silt and clay, mineral colloids, and organic colloids in the

Mississippi River and some of its tributaries for the June 1989 sampling cruise 48

CONTENTS v
TABLES (Continued)

24. Organic-carbon content, nitrogen content, and atomic C:N ratio of silt and clay, 

mineral-colloid, and organic-colloid fractions of suspended sediment from 

sampling cruise 5, June 1989. Fluorine content of silt and clay fraction 

also is included 50

25. Organic-carbon and nitrogen transport of silt and clay, and colloid fractions of

suspended sediment from sampling cruise 5, June 1989 51

26. Concentrations of silt and clay, and colloidal organic carbon for sampling cruise 5,

June 1989 52

27. Dissolved organic-carbon concentrations and transport for sampling cruise 6,

February-March 1990 55

28. Recovery study of suspended-sediment fractions from the Ohio, Mississippi, and

Tennessee Rivers during sampling cruise 6, February-March 1990 56

29. Recovery percentages of silt and clay, mineral colloids, and organic colloids in the 

Cumberland, Ohio, Mississippi, Tennessee, and Wabash Rivers during 

sampling cruise 6, February-March 1990 58

30. Organic-carbon and nitrogen percentages of the suspended-silt and-clay fraction

from sampling cruise 6, February-March 1990 59

31. Transport of silt and clay organic carbon and nitrogen and silt and clay

organic-carbon concentrations from sampling cruise 6, February-March, 1990 r60

32. Relations between methylisobutyl ketone (MIBK) extract yields and organic 

carbon and nitrogen on suspended silt and clay from sampling cruise 6, 

February-March 1990 60

33. Dissolved organic-carbon concentrations and transport for sampling cruise 7,

May-June 1990 64

34. Composition, concentrations, and transport of carbon and nitrogen in the

suspended-silt and -clay fractions for sampling cruise 7, May-June 1990 65

35. Effect of selective mineral dissolution treatments on suspended silts and clays

and bottom muds on organic matter recoveries and composition 67

vi
CONVERSION FACTORS AND RELATED INFORMATION

Multiply By To obtain

liter (L) 1.2642 gallon

micrometer (\im) 0.00003937 inch

metric ton per day 1.102 short ton

centimeter (cm) 0.3937 inch

cubic meter per second (m3/s) 35.31 cubic foot per second

microsiemen per centimeter at 1.000 micromho per centimeter

25 degrees Celsius (uS/cm) at 25 degrees Celsius

Degree Celsius may be converted to degree Fahrenheit by using the following equation:

°F = 9/5(°C)+32 

The following terms also are used in this report:

milligrams per liter (mg/L)

millimoles per gram

dalton

parts per million (ppm)

CONTENTS vii
DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED,

COLLOIDAL, SUSPENDED-SILT AND -CLAY, AND BED-SEDIMENT

PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS

TRIBUTARIES, 1987-90

By J.A. Leenheer, T.I. Noyes, and P.A. Brown

ABSTRACT

The Mississippi River and some of its tributaries were sampled for natural organic substances 

dissolved in water and in suspended and bed sediments during seven sampling cruises from 

1987-90. The sampling cruises were made during different seasons, in the free-flowing reaches of 

the river from St. Louis, Missouri, to New Orleans, Louisiana. The first three cruises were made 

during low-water conditions, and the last four cruises during high-water conditions. The purpose 

for sampling and characterizing natural organic substances in the various phases in the river was 

to provide an understanding of how these substances facilitate contaminant transport and 

transformations in the Mississippi River.

Significant conclusions of this study were: (1) Natural organic substances appear to stabilize 

certain colloids against aggregation; therefore, these colloids remain in suspension and can act as 

transport agents that are not affected by sedimentation. Bacteria were found to be a significant 

fraction of organic colloids. (2) A new class of organic contaminants (polyethylene glycols) 

derived from nonionic surfactant residues was discovered dissolved with natural organic 

substances in water. These polyethylene glycols have the potential to affect both organic and 

inorganic contaminant transport in water. (3) The entire dissolved organic-matter component 

under varying hydrologic and seasonal conditions was characterized. (4) A method was

developed to characterize organic matter in sediment by solid-state, 13C-nuclear magnetic 

resonance spectrometry. (5) The organic matter in suspended sediments was characterized by a 

variety of spectral and nonspectral methods. The protein component (significant in trace-metal 

binding) and lipid component (significant in organic-contaminant binding) were found to be 

major constituents in natural organic matter in suspended sediment. (6) Pools are reservoirs 

acting as traps of sedimentary organic matter of allochthonous origin and export material of 

autochthonous origin that is rich in nitrogen. (7) A major portion of the mass of organic colloids 

in transport consisted of bacterial cells.

INTRODUCTION

Most contaminants in rivers have some degree of association with natural organic substances 

in the dissolved and particulate phases in the water (Leenheer, 1991,1994). These associations 

may either facilitate or retard contaminant transport in rivers, and may transform contaminants 

into different phases or different compounds, depending on the operative degradative processes.

The broad objectives of the Mississippi River project are to investigate the movement, mixing, 

and storage processes of sediment-associated pollutants (Moody and Meade, 1993). Some specific 

objectives are to:

1. Understand the compartmentalization of synthetic organic and inorganic agrochemicals 

between and water, sediment, and biotic phases.

ABSTRACT 1
2. Investigate the mixing, partitioning, and redistribution processes of the various pollutants 

downstream from major river confluences.

3. Understand the movement, storage, and remobilization of suspended sediment and associated pollutants at seasonal or longer time scales.

4. Predict the location and travel time of water masses and the associated sediment and 

pollutants; and

5. Examine the geochemistry of the suspended silt, clay, colloidal material, and dissolved 

phases of river water.

This report summarizes the research on natural organic matter conducted from July 1987 to 

June 1990 on the Mississippi River and some of its tributaries. Water and sediment samples were 

collected during seven cruises. Two general objectives of all seven cruises was to quantify the 

organic substances in dissolved and suspended-sediment phases, and to characterize the organic 

matter in the various phases through spectrometric and elemental measurements. Each cruise 

had specific objectives that required slightly different approaches. In order to adequately describe 

these differences, this report is organized chronologically by cruise and includes a discussion of 

the objectives and approach, as well as the results, for each cruise.

The location of the sampling sites on the lower Mississippi River and some of its tributaries is 

shown in figure 1. Integration of the research presented in this report with the research on metal 

and organic contaminants in the lower Mississippi River will provide an understanding of how 

natural organic substances affect contaminant transport and transformations.

Acknowledgments

The data presented in this report are the result of a group effort in sampling the Mississippi 

River and some if its tributaries, processing the samples to fractionate and isolate the various 

dissolved and sediment phases, and sharing data and assisting in data interpretation.

The authors wish to acknowledge the crew of the research vessel ACADIANA Lee Black, 

Wayne Simoneaux, Chuck Guidry, Steve Rabalais, Craig LeBoeuf, Ken Oliver, and Wilton 

Delaune who have accommodated our unusual requests and who have ensured the maintenance of proper scientific operations.

We also wish to acknowledge the Mississippi River project chief, Robert Meade, who along 

with John Moody attempted to teach a boatload of chemists the fundamentals of surface-water 

hydrology.

We wish to acknowledge our colleagues who assisted in measuring river discharge, collecting 

and processing large volumes of water for water and sediment sampling, performing field and 

laboratory measurements, and performing miscellaneous boat operations. These people include 

Ellen Axtmann, Terry Brinton, Wes Campbell, Phyllis Campbell, Daphne Frilot, John Garbarino, 

Tom Kraemer, Tom Leiker, Debby Martin, Dick Martin, Brent McKee, Dale Peart, Willie Periera, 

Jim Ranville, Terry Rees, Colleen Rostad, Jim Seely, Herb Stevens, Bob Stallard, Dick Tagg, and 

Howard Taylor and Tim Willoughby.

Lastly, we wish to thank Luis Cifuentes of Texas A & M University for determining stable 

carbon isotope ratio determinations of dissolved humic substances. We also thank Jim Ranville 

for performing scanning electron microscopy of organic colloids and for reviewing this report.

Robert L. Wershaw determined the 13C-NMR spectrum of dissolved humic substances.

2 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
SAMPLING CRUISE 1, JULY-AUGUST 1987

The sampling of cruise 1 began on the Missouri River (fig. 1) at Hermann, Missouri, on 

July 20,1987, and ended on the Mississippi River below Belle Chasse, Louisiana, on August 9, 

1987. Samples were collected in a Lagrangian scheme (Moody, 1993) that tried to follow the same 

mass of water downriver.

Objectives and Approach

The objectives of sampling cruise 1 were to: (1) Develop a sampling and fractionation procedure for organic substances in the suspended and dissolved phases that also was compatible for 

trace-metal studies; (2) characterize dissolved organic substances by elemental, spectral, and titrimetric analyses; (3) characterize suspended-sediment fractions by carbon and nitrogen analyses; 

and (4) determine loads of organic carbon transported in the various phases.

The approach was to obtain 70-100 L of water by depth-integration at 5-40 locations across 

the river from the research vessel Acadiana, (owned and operated by the Louisiana Universities' 

Marine Consortium) transfer this depth-integrated composite sample to a mobile field laboratory, 

and fractionate the sediment by a combination of sieving to isolate sand, continuous-flow centrifugation to isolate silt and clay, tangential-flow ultrafiltration to isolate colloids, and resin adsorption to isolate the fulvic-acid fraction of dissolved organic carbon (Leenheer, Meade, and others, 

1989). This approach was successfully followed except that the continuous-flow centrifuge broke 

down after the second sampling was completed at Mississippi River near Winfield, Mo., and gravitational settling in 46-L carboys for 8-12 hours was used to separate the silt and clay from the 

colloid fractions.

Dissolved Organic Matter

Dissolved organic carbon (DOC) concentrations were determined on the permeate from the 

ultrafilter by high-temperature oxidation of DOC to CO2 with a Beckman 915B1 total organic 

carbon analyzer (Van Hall and Stenger, 1967). The pore size of the cellulose filters used for ultrafiltration was 0.005 urn. DOC transport was computed using water-discharge measurements 

reported by Moody and Meade (1992). DOC concentrations and transport at 17 sampling sites are 

presented in table 1.

DOC concentrations were low in comparison to the National Stream Quality Accounting 

Network (NASQAN) average (6.0 mg/L in data averaged from 1972-1977) at Belle Chasse, La., 

(Leenheer, 1982). These low concentrations might result from low terrestrial carbon inputs to the 

river during this low-water cruise, from ultrafiltration that eliminates colloidal carbon from the 

data, and from instream biodegradation of DOC. Water temperatures were near 30°C during the 

entire cruise, and these warm temperatures likely accelerated the biodegradation of DOC.

Only the humic-substance component of dissolved organic matter was isolated from the river 

for characterization (Leenheer, Brown, and others, 1989). Various characterization data are listed 

in table 2.

SAMPLING CRUISE 1, JULY-AUGUST 1987 3
r-r -- --

Meredosia

Valley City

infield Hardjn

Hartford

St. Charles

St. Louis

£

Chester

New Haven 

(, \ rOlmstedt" Uniontown

Smithland 

Calvert City

Memphis 

elena 

Mile 11.5 Pendleton 

Arkansas City

4 

Mile 10

Vicksburg

100 200 Miles

0 100 200 Kilometers

Figure l.-Sampling locations on the Mississippi River and some of its tributaries.

DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 1.-Dissolved organic-carbon concentrations and transport for 

sampling cruise 1, July-August 1987

[Transport was computed using water-discharge data reported by 

Moody and Meade (1992)]

Sampling site

Water

discharge

(cubic meters

per second)

Dissolved 

organiccarbon 

concentration 

(milligrams 

per liter)

Transport

(metric tons

per day)

Mississippi River near Winfield, Mo. 1,370 4.2

Illinois River at Naples, 111. *312 2 10.5

Mississippi River at Hartford, 111. 1,500 3.2

Missouri River at Hermann, Mo. 2,640 3.8

Mississippi River at St. Louis, Mo. 3,940 3.7

Mississippi River at Chester, 111. 4,250 3.9

Ohio River below Smithland Locks and 652 235

Dam, Ill.-Ky.

Ohio River at Olmsted, 111. 2,070 1.7

Mississippi River below Hickman, Ky. 6,270 1.9

Mississippi River at Helena, Ark. 6,850 2.0

White River at Mile 11.5, Ark. 332 1.1

Arkansas River at Mile 55.9, Ark. 790 1.0

Mississippi River above Arkansas City, 7,630 1.9

Ark.

Mississippi River below Vicksburg, Miss. 7,750 2 14.6

Old River Outflow Channel near 2,050 3.1 

Knox Landing, La.

Mississippi River near St. Francisville, La. 6,190 2.3

Mississippi River below Belle Chasse, La. No discharge data 1.7

498

275

416

864

1,245

1,435

No discharge 

data

304

1,030

1,185

32

68

1,254

Dissolved 

organic-carbon 

data invalid 

552

1,230

No discharge 

data

1 Illinois River water discharge measured below Meredosia, Illinois. 

2Dissolved organic-carbon data were believed to be contaminated by organic-carbon bleed 

from ultrafilter membranes.

SAMPLING CRUISE 1, JULY-AUGUST 1987 5
Table 2.-Acidity, isotopic, molecular-weight, and yield data off dissolved humic 

substances in the Mississippi River, July-August, 1987

[813C, stable carbon isotope ratio, Mn/ number average molecular weight; 

Mw weight average molecular weight; ND, not determined]

Sampling site

Mississippi River near 

Winfield, Mo.

Illinois River at Naples, 111.

Mississippi River at 

Hartford, El.

Missouri River at Hermann, Mo.

Mississippi River at 

St. Louis, Mo.

Ohio River below

Smithland Locks and Dam, El Ky.

Ohio River at Olmsted, 111.

Mississippi River at 

Helena, Ark.

White River at

Mile 11.5, Ark.

Arkansas River at

Mile 55.9, Ark.

Mississippi River above 

Arkansas City, Ark.

Mississippi River below 

Vicksburg, Miss.

Old River Outflow Channel

near Knox Landing, La.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

Percent 

yield off 

dissolved 

organic 

carbon

44

ND

59

71

67

ND

83

63

81

ND

75

ND

53

60

86

1»13C 

(parts per 

thousand)

-26.0

-25.7

-25.6

-24.9

-27.2

-26.5

-26.3

-25.7

-27.0

-25.2

-25.6

-24.7

-25.6

-26.9

-25.6

Acidity2 

(miliimoles 

per 

gram)

3.2

4.5

5.0

4.9

5.8

ND

4.9

5.1

4.1

5.4

4.9

4.8

4.7

ND

5.1

3M

l¥in

865

568

606

506

496

521

318

716

409

886

438

957

352

443

986

Mw

919

992

919

803

805

677

453

907

908

1,111

799

1,154

768

681

1,041

Degree 

off polydispersity 

(IMWIn)

1.06

1.75

1.52

1.59

1.63

1.30

1.42

1.27

2.22

1.25

1.82

1.21

2.18

1.53

1.06

a 813C values were determined by Luis Cifuentes, Department of Oceanography, Texas 

A & M University.

2 Acidity determined by base titration to pH 8.5.

3 Molecular weight determinations were by equilibrium ultracentrifugation in tetrahydrofuran 

(Leenheer, Meade, and others, 1989).

6 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
An average of two-thirds of the DOC was isolated and characterized as humic substances. 

The relatively low molecular weights and moderately high acidity values typify these dissolved 

humic substances as predominantly fulvic acids. No discernible trends are apparent in the acidity 

or molecular weight data to indicate source or instream degradation processes. The isotopic

(813C) data indicated slightly heavier values than normally are observed for dissolved humic 

substances in temperate river waters (Malcolm, 1990). Input of humic substances from sewage, 

known to give heavy 813C values, is a possible cause for these sightly heavy values. In freshwater 

environments, allochthonous sources of humic substances cannot readily be distinguished from 

autochthonous sources by 813C values because the source term signatures are too similar (Mook 

and Tan, 1991).

Elemental analyses of dissolved humic substances at selected sites are shown in table 3. No 

significant trends in elemental composition were apparent between sampling sites. The isolated 

humic substances were exceptionally well separated from inorganic constituents, as shown by the 

low ash contents. The elemental composition of the Mississippi River isolates differed from 

humic substances isolated from the black water of the Suwannee River (Averett and others, 1989) 

in having greater carbon, hydrogen, and nitrogen contents and lower oxygen content. The greater 

hydrogen and nitrogen contents are especially significant on an atomic basis of comparison. The 

hydrogen content denotes that humic substances from the Mississippi River have a greater 

aliphatic character, and the nitrogen content indicates autochthonous sources are more significant 

in the Mississippi River than in the Suwannee River.

Spectral characterizations of dissolved humic substances were performed with H-nuclear 

magnetic resonance (NMR) spectrometry, 13C-NMR spectrometry, and infrared spectrometry (IR).

Two types of spectral patterns were obtained for the 1H-NMR spectra as shown in figure 2. Most 

of the spectra were similar to the Mississippi River near St. Francisville, La., sample (fig. 2, spectrum A), however, samples from the Ohio River at Olmsted, 111., Mississippi River at Helena, Ark.,

Table 3.-Elemental analyses of dissolved humic substances isolated from 

water samples collected during sampling cruise 1, July-August 1987

[<, less than]

Sampling site Percent Percent Percent Percent Percent 

carbon hydrogen oxygen nitrogen ash

Mississippi River near Winfield, Mo.

Missouri River at Hermann, Mo.

Ohio River at Olmsted, 111.

Mississippi River at Helena, Ark.

Arkansas River at Mile 55.9, Ark.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

55.34

54.86

56.60

57.86

55.92

54.76

55.94

5.07

5.05

5.48

4.60

5.07

5.44

4.92

35.11

36.40

33.27

33.04

34.92

36.44

34.86

2.70

2.52

2.46

2.43

2.37

2.24

2.43

0.74

.84

<.l

<.l

<.l

.86

<.l

SAMPLING CRUISE 1, JULY-AUGUST 1987 7
and the White River gave H-NMR spectra similar to spectrum B in figure 2. Spectral intensities 

at points 2 (methylene protons adjacent to a carboxyl group), 3 (protons associated with carbohydrates), and 4 (aromatic ring protons adjacent to phenolic groups) are diminished in spectrum B 

compared to spectrum A. The three samples similar to spectrum B also gave lower molecular 

weights, lower DOC values, and greater carbon and hydrogen contents than the remainder of the 

samples. All of these data indicate that these three samples are the result of a greater degree of 

degradation (humification) than the remainder of the samples.

CO

CD

z

CO

<

LLJ 

CC 

O

Z

Numbers denote peaks where peak height: 

were measured

10

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 2.~1H-nuclear magnetic resonance spectra of dissolved humic substances in samples 

from the (A) Mississippi River near St. Francisville, La., and (B) Ohio River at Olmsted, 111., 

sampled July-August 1987.

DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
The sharp peak at 3.6 ppm was found to be related to polyethylene glycol contaminants from 

nonionic surfactants (Leenheer and others, 1991). Polyethylene glycols cannot be analyzed by 

conventional solvent extraction, gas chromatographic, or mass spectrometric analyses. These 

contaminants were found in nearly all the samples from the first two sampling cruises, and they 

probably represent the most abundant organic contaminant found in the river during sampling 

cruise 1.

A 13C-NMR spectrum acquired under quantitative conditions for dissolved humic substances 

isolated from a sample from the Mississippi River near St. Francisville, La., is shown in figure 3. 

The spectrum is typical of an aquatic fulvic-atid sample with the exception that in spectral regions 

near 115 ppm and from 140 to 160 ppm, both of which are indicative of phenolic substituents, are 

depleted relative to these spectral regions for fulvic acid isolated from the Suwannee River

(Thorn, 1989). A second 13C-NMR spectrum for humic substances isolated from a sample from 

the Mississippi River at St. Louis, Mo., gave nearly identical results.

An infrared spectrum of dissolved humic substances isolated from a sample from the Mississippi River at St. Louis is shown in figure 4. The spectrum is dominated by hydroxyl (3,600-

2,500 cm"1) and carboxyl (1,720 cm"1) group absorbances. Infrared spectra were run on all of the 

humic-substance isolates, but no trends or information of particular geochemical significance 

were found.

LLJ 

CC 

CJ

300 250 200 150 100 50 0 -50

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 3. 13C-nuclear magnetic resonance spectrum of dissolved humic substances isolated 

from the Mississippi River near St. Francisville, La., sampled July-August 1987.

-100

SAMPUNG CRUISE 1, JULY-AUGUST 1987 9
100

80

LLJ 

U

m so 

cc 

O C/3 00

< 40 

(3

Z

2i 20

cc

U

4,000 3,500 3,000 2,500 2,000 1,800 1,600 1,400 1,200 1,000 800 600 400 200

WAVENUMBER, IN RECIPROCAL CENTIMETERS

Figure 4. Infared spectrum of dissolved humic substances isolated from a sample from the 

Mississippi River at St Louis, Mo., sampled July-August 1987.

Organic Matter in Suspended-Sediment Fractions

Differences in organic composition between colloid and silt and clay fractions were published 

in the report by Leenheer, Brown, and others (1989). Organic carbon percentages were consistently greater in the colloid fraction than in the silt fraction. Atomic carbon-nitrogen (ON) ratios 

were consistently less in the colloid fraction than in the silt and clay fraction. These consistent 

differences occurred throughout a wide range of organic-carbon compositions from 1.5 to 20.1 

percent and organic-nitrogen compositions from 0.2 to 3.7 percent. The small ON ratios in the 

colloid fraction were caused by large amounts of phytoplankton and related low-density organic 

matter that coisolate with colloid-size material.

Organic-carbon and nitrogen transport in the silt and clay and colloid fractions are listed in 

table 4. The transport in the Mississippi River was dominated by input from the silt and clay fraction in the Missouri River. The Mississippi River at Hartford, 111., and the Ohio, White, and 

Arkansas Rivers were at low stages and had greater transport on the colloid fractions than on the 

silt and clay fractions. The organic-carbon transport on the colloid fraction was slightly less than 

the dissolved organic carbon (table 1), but the organic-carbon transport on the silt and clay greatly 

exceeded the dissolved organic-carbon transport for sampling sites containing silt and day 

derived from the Missouri River. The reason for the significant transport in the colloid fraction is 

that the settling procedure did not remove suspended-mineral colloids greater than 1-2 um in 

diameter or low-density phytoplankton. Therefore, material that normally is removed by filtration or centrifugation was included in the colloid fraction.

Organic materials in the colloid fraction were characterized by solid-state C-NMR spectrometry by Professor Gary Maciel of the Regional NMR Center at Colorado State University, 

Ft. Collins, Colo. These were the first spectra of aquatic colloids characterized in this manner, and 

the relatively low carbon content of the colloids resulted in the spectra being of low intensity and 

poor quality. Only general qualitative significance should be attached to the spectra. Three of the 

spectra are shown in figure 5.

10 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 4.-Organic-carbon and nitrogen transport on the silt and clay and colloid fractions

for sampling cruise 1, July-August 1987

[Water-discharge and suspended-sediment concentration data used for computing 

transport reported by Moody and Meade (1992)]

Sampling site

Mississippi River at Hartford, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Chester, 111.

Ohio River below Smithland Locks

and Dam, 111. Ky.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Arkansas River at Mile 55.9, Ark.

Mississippi River above

Arkansas City, Ark.

Mississippi River below

Vicksburg, Miss.

Old River Outflow Channel near

Knox Landing, La.

Mississippi River near

St. Francisville, La.

Organiccarbon 

transport 

on silt and 

clay 

(metric 

tons per 

day)

92

7,145

4,019

4,454

20

96

1,625

2,975

44

71

2,018

2,585

508

2,086

Nitrogen 

transport 

on silt and 

clay 

(metric 

tons per 

day)

12

693

408

456

3

10

160

298

8

10

191

296

49

170

Organiccarbon 

transport 

on colloids 

(metric 

tons per 

day)

129

829

867

1,107

44

151

789

985

23

82

1,114

1,033

276

671

Nitrogen 

transport 

on colloids 

(metric 

tons per 

day)

25

107

124

167

6

24

121

153

4

15

164

166

40

_

113

The best spectrum, which had 20.1 percent carbon, was obtained on the colloid fraction from 

the Arkansas River (fig. 5 A). The lipid/hydrocarbon peak near 25 ppm and the carbohydrate 

peak near 70 ppm are of equal intensity, and the carbonyl peak associated with proteins, esters, 

and acids is near 170 ppm. A small aromatic carbon peak exists near 130 ppm. Most of the Mississippi River and tributary sites gave spectra similar to spectrum B (fig. 5) in which the lipid/hydrocarbon peak seemed to be diminished in intensity relative to the Arkansas River sample. Two 

exceptions were the colloids from samples from the Mississippi River at St. Louis, Mo.,

SAMPLING CRUISE 1, JULY-AUGUST 1987 11
(spectrum C, fig. 5) and from the Mississippi River at Chester, 111., immediately downriver. The 

lipid/hydrocarbon peak is enriched in these colloid fractions and might represent hydrocarbon

contamination from the St. Louis area. The 13C-NMR spectra of the colloid fraction (fig. 5) is 

markedly different than the dissolved mimic-substance fraction (fig. 3) in which the carbonyl and 

aromatic carbon are greater and the carbohydrate carbon is much less. The enhanced lipid/ 

hydrocarbon component on the colloid fraction relative to the dissolved humic-substance fraction 

should make the colloids better carriers of nonionic, nonpolar, organic contaminants.

LLI

LLI

oc 

o

350 300 250 200 150 100 50 0 -50

CHEMICAL SHIFT, IN PARTS PER MILLION

-100 -150 -200 -250

Figure 5.~Solid-state 13C-nuclear magnetic resonance spectra of colloids isolated from the: 

(A) Arkansas River at Mile 55.9, (B) Mississippi River below Vicksburg, Miss., and 

(C) Mississippi River at St. Louis, Mo., sampled July-August 1987.

12 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
SAMPLING CRUISE 2, NOVEMBER-DECEMBER 1987

The sampling of cruise 2 began on the Illinois River below Meredosia, Illinois, on 

November 29,1989, and ended on the Mississippi River below Belle Chasse, Louisiana, on 

December 20,1987. Sampling site changes from the first cruise were: (1) Sites on the Mississippi 

River at Hartford, Illinois, the Ohio River below Smithland Lock and Dam, and the Arkansas 

River at Mile 55.9 were eliminated. (2) The site on the Mississippi River at Chester, Illinois, was 

changed to Mississippi River at Thebes, Illinois, the site on the Missouri River was changed from 

Hermann, Missouri, to St. Charles, Missouri, and the site on the Illinois River at Naples, Illinois, 

was changed to below Meredosia, Illinois. (3) New sites were added on the Mississippi River at 

Fulton, Tennessee, and the Yazoo River at Mile 10, Mississippi.

Objectives and Approach

The major objective of sampling cruise 2 was to repeat the research investigations of the first 

cruise during the late fall, when water temperatures that affect the biological production and 

degradation processes are much lower. The nature of dissolved and suspended organic matter in 

the Mississippi River should be altered compared to the summer conditions of the first trip. 

Secondary objectives were to move the sample processing and sediment fractionation procedures 

to a laboratory mounted on the stern of the boat and to evaluate continuous-flow centrifugation 

and gravitational settling as a means of separating the silt and colloid fractions.

A flow chart of procedures for water and suspended-sediment fractionation of the depthintegrated composite sample is shown in figure 6 (Leenheer, Meade, and others, 1989). A Sharpies 

Model AS-12 continuous-flow supercentrifuge was borrowed from the Great Lakes Research 

Institute of the University of Wisconsin and was installed on the Acadiana at Alton, 111. For the 

gravitational settling procedure, the silt and clay in the composite B fraction (fig. 6) was settled in 

a carboy suspended in a custom-made gimbal on the boat. The gimbal minimized the rocking 

motion of the boat; an air-filled plenum on which the carboy was placed also minimized vibrations from the boat.

Dissolved Organic Matter

DOC concentrations and transport are listed in table 5. DOC transport for sampling site on 

the Mississippi River downriver from Helena, Arkansas, are approximately double the transport 

measured for the first sampling cruise (table 1). This transport increase is due to the combined 

effect of a discharge increase (38-percent average increase for Mississippi River sites upstream 

from the Old River Outflow) and a 24-percent DOC increase (all sites averaged on the Mississippi 

River) over equivalent data for sampling cruise 1. The Ohio River had a DOC transport increase 

of 3.8 times the DOC transport for the first sampling cruise, and DOC transport in the Mississippi 

River downriver from the Ohio River is proportionately increased. Water temperatures were 

much cooler for the second cruise near 5°C for sites near St. Louis and increasing to 10°C for sites 

near New Orleans. The most likely explanation for the greater DOC concentrations in the Lower 

Mississippi River during sampling cruise 2 is that there is less biodegradation when water 

temperatures are cooler in late fall. During both sampling cruises, DOC concentrations generally 

decreased in the downstream direction; this observation supports the biodegradation hypothesis.

SAMPLING CRUISE 2, NOVEMBER-DECEMBER 1987 13
70 to 100 liters of sample in two composites 

Composite A Composite B

Pass through 63-micrometer-pore-size nickel-wire sieve

Sand Sand 

Measure volume in 2-liter glass graduated cylinders

Apportion measured volumes into 20-liter churn splitters

H h

Split portion of each composite into 8-liter churn splitters

Recombine sample split

Pass through continuous-flow 

centrifuge

Recombine sample split

Settle silt in 46-liter 

carboy for 6-12 hours

I

Silt on FEP 

Teflon centrifuge bowl linear

I

Rinse off linear,

centrifuge, freeze

dry, dry silt

I

Pass:through

tangential-flow

ultrafilter

Pass:through

tangential-flow

ultrafilter

Silt suspension

in 500-1,000 milliliters H 2O

Laboratory centrifugation

Retentate colloid suspension

in 600-1,000 milliliters

H2O

Laboratory centrifugation

Moist colloid

Freeze dry

I 

Dry colloid

H2O

Recombine permeate 

composites

I

Acidify to 

pH 2 with HCI

Pass through 10-liter 

column Amberlite XAD-8

I

Retentate colloid 

suspension in 

600-1,000 milliliters H2O

Laboratory centrifugation

H2O

H2 0 

Discard

Moist colloid 

Freeze dry 

Elute Dry colloid column with 

75 percent CH3CN 

and 25 percent H2O

Laboratory evaporation 

of solvents, freeze dry

I 

Dissolved organic matter

Figure 6. Flow chart of procedures for water and suspended-sediment sampling, 

sampling cruise 2, November-December 1987.

14 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 5.~Dissolved organic-carbon concentrations and transport for sampling cruise 2,

November-December 1987

[Transport was computed using water-discharge data reported by 

Moody and Meade (1992)]

Sampling site

Mississippi River near Winfield, Mo.

Illinois River below Meredosia, 111.

Missouri River at St. Charles, Mo.

Mississippi River at St. Louis, Mo. 

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below Vicksburg, Miss. 

Old River Outflow Channel near Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water 

discharge 

(cubic 

meters per 

second)

2,040

262

2,810

5,440 

5,190

4,200

8,770

519

9,920

177

10,410 

1,830

8,180

9,560

Dissolved 

organiccarbon 

concentration 

(milligrams 

per liter)

3.8

4.3

3.4

3.9 

5.8

3.2

3.1

3.2

4.4

2.7

2.4 

2.5

2.7

2.7

Transport 

(metric 

tons per 

day)

670

97

822

1,833 

2,598

1,160

2,349

143

3,683

41

2,159 

359

1,908

1,982

Acidity, molecular-weight, and yield data of dissolved humic substances in the Mississippi 

River sampled during sampling cruise 2 are shown in table 6. Dissolved humic substances 

constituted an average of 63 percent of the DOC for all the sites. This average was very similar to 

the data from sampling cruise 1 (table 2).

Elemental analyses of dissolved humic substances isolated from samples obtained during 

sampling cruise 2 are shown in table 7. The only significant difference from humic-substance 

samples obtained during the first cruise (table 3) is the lower nitrogen content of the samples 

obtained from the river during the late fall season. The lower nitrogen content is hypothesized to 

result from greater allochthonous (terrestrial) inputs to stream humic substances during the fall 

when instream (autochthonous) productivity is decreased relative to the summer. Elemental 

analyses during both sampling cruises indicated the samples from the Mississippi River near 

Winfield, Mo., gave the greatest nitrogen content. The Winfield samples represent water 

discharged from the Upper Mississippi River where instream productivity should be the greatest 

because of the extensive series of pools above the locks and dams in this reach of the river.

SAMPUNG CRUISE 2, NOVEMBER-DECEMBER 1987 15
Table 6.-Acidity, molecular-weight, and yield data of dissolved humic substances in the 

Mississippi River sampled November-December 1987

[Mn, number average molecular weight; Mw weight average molecular weight;

ND, not determined]

Sampling site

Mississippi River near Winfield, Mo.

Illinois River below Meredosia, 111.

Missouri River at St. Charles, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow Channel

near Knox Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Percent 

yield of 

dissolved 

organic 

carbon

63

59

62

57

38

44

ND

ND

47

63

50

91

84

82

71

68

Acidity1 

(millimoles 

per gram)

5.4

5.7

5.2

ND

5.3

4.8

5.9

4.7

5.5

4.8

5.2

4.5

5.0

4.4

4.7

4.2

2Mn

823

596

580

ND

262

876

378

404

439

734

721

909

586

679

361

664

Mw

1,066

1,003

713

ND

593

1,003

528

948

829

1,142

1,091

1,126

992

951

455

856

Degree of 

polydispersity 

(Wkv/Mn)

1.30

1.68

1.23

ND

2.26

1.14

1.40

2.34

1.89

1.56

1.51

1.23

1.69

1.40

1.26

1.29

1 Acidity determined by base titration to pH 8.5.

2Molecular-weight determinations were by equilibrium ultracentrifugation in 

tetrahydrofuran (Leenheer, Meade, and others, 1989).

16 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table /.-Elemental analyses of dissolved humic substances isolated from water samples 

collected during sampling cruise 2, November-December 1987

[<, less than]

Q .. Percent Percent Percent Percent Percent 

sampling sue carbon hydrogen oxygen nitrogen ash

Mississippi River near Winfield, Mo.

Missouri River at St. Charles, Mo.

Ohio River at Olmsted, 111.

White River at Mile 11.5, Ark.

Mississippi River below

Belle Chasse, La.

55.03

56.44

55.86

55.48

50.97

5.04

5.22

5.12

4.90

5.00

36.18

35.07

34.86

35.87

33.17

2.27

2.07

2.05

1.81

1.83

0.17

.14

<.l

<.l

7.33

Proton NMR spectra of dissolved humic substances isolated from water at three sites during 

the late fall cruise are shown in figure 7. Humic substances isolated from the Illinois River (fig. 6, 

spectrum A) appear to be extensively contaminated with petroleum hydrocarbons as indicated by 

sharp peaks at 0.9,1.1,1.4,1.8, and 2.2 ppm. Lesser amounts of these contaminants were found 

in the Mississippi River near Winfield, Mo. Perhaps the cool water temperatures (4-6°C), which 

retard hydrocarbon volatilization losses, low suspended-sediment concentrations (Illinois River, 

79 mg/L; Mississippi River near Winfield, Mo., 31 mg/L), which limit hydrocarbon sorption 

losses, and decreased biologic activity in cold water may lead to a buildup of hydrocarbon

contaminants in the dissolved phase at certain times of the year. Most of the 1H-NMR spectra also 

contained indications of polyethylene glycol contaminants (Leenheer and others, 1991).

Humic substances isolated during the late fall cruise (fig. 7, spectra B and C) differed from 

humic substances isolated during the summer cruise (fig. 2) in having higher peak height ratios 

of peaks 2,3, and 4 to peak 1. Because these peaks represent the structural moieties that are the 

most likely to be biodegraded or sorbed onto sediment constituents, it is not surprising that these 

peaks are greater during the fall cruise than during the summer cruise. The dissolved humic 

substances isolated from the White River had the greatest increase in peaks 2,3, and 4 (fig. 7, spectrum B). Humic substances from the White River site also had the lowest nitrogen content 

(table 7), so spectrum B represents the allochthonous "end member" for dissolved humicsubstances studies for the fall 1987 sampling cruise.

Organic Matter on Suspended-Sediment Fractions

Recoveries of silt and clay and colloids comparing the gravitational settling and continuousflow centrifugation methods are presented in the report by Leenheer, Meade, and others (1989). 

The centrifuge recovered material about one order of magnitude (down to 0.3 um in diameter) 

smaller than did the gravitational settling technique, and there was an average 20-percent shift of 

colloids into the silt and clay fraction with centrifugation, based on the percentage of colloids 

recovered after centrifugation.

SAMPLING CRUISE 2, NOVEMBER-DECEMBER 1987 17
£

CO

LU

z

CD 

c?5

LU

rr 

o

Numbers denote peaks where peak heights 

were measured

10

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 7. 1H-nuclear magnetic resonance spectra of dissolved humic substances from 

samples from the: (A) Illinois River below Meredosia, 111., (B) White River at 

Mile 11.5, Ark., and (C) Mississippi River below Belle Chasse, La., sampled 

November-December 1987.

18 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Percentages of carbon and nitrogen measured on the silt and clay and colloid fractions are 

given in table 8. The carbon and nitrogen percentages on the silt and clay and colloid fractions on 

which the centrifuge was used were generally greater than for the fractions that were separated 

by gravitational settling. Apparently, inclusion of smaller particles into the operationally defined 

"silt and day" fraction separated by centrifugion resulted in greater carbon percentages than for 

silt and clay separated by gravitational settling. The samples highest in organic-matter content 

were from the Mississippi River near Winfield, Mo., and the organic-matter content of the settled 

silt and clay fraction generally decreased in the downriver direction.

Table 8.-Organic-carbon and nitrogen contents of silt and clay and colloid fractions of 

suspended sediment from sampling cruise 2, November-December 1987

[ND, not determined]

Sampling site

Mississippi River near

Winfield, Mo.

Illinois River below

Meredosia, 111.

Missouri River at

St. Charles, Mo.

Mississippi River at

St. Louis, Mo.

Mississippi River at

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at

Fulton, Tenn.

Mississippi River at

Helena, Ark.

White River at

Mile 11. 5, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River at

Mile 10, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow

Channel near

Knox Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Percent 

carbon 

on silt and 

clay

Settled

5.86

2.86

1.44

ND

1.86

1.83

1.87

1.66

1.88

1.18

1.75

1.05

1.64

1.44

1.83

ND

Centrifuged

ND

ND

ND

ND

2.01

2.40

2.15

2.10

2.24

1.61

2.42

1.58

3.03

2.21

1.99

ND

Percent 

nitrogen 

on silt and 

clay

Settled

0.84

.31

.15

ND

.22

.23

.22

.20

.21

.13

.21

.13

.17

.17

.21

ND

Centrifuged

ND

ND

ND

ND

0.22

.26

.24

.25

.25

.19

.28

.24

.41

.24

.25

ND

Percent 

carbon 

on colloid

Settled

14.99

6.71

2.75

4.72

4.13

6.67

5.21

4.32

4.58

3.07

3.54

2.56

4.01

3.66

3.99

ND

Centrifuged

ND

ND

7.25

7.28

7.26

8.09

7.25

8.75

4.67

4.47

5.63

4.01

8.72

7.77

8.33

6.52

Percent 

nitrogen 

on colloid

Settled

2.21

.94

.29

.53

.46

.64

.45

.50

.35

.35

.45

.33

.52

.41

.44

ND

Centrifuged

ND

ND

0.60

.53

.70

.81

.47

.90

.43

.43

.56

.37

.65

.73

.63

.68

SAMPLING CRUISE 2, NOVEMBER-DECEMBER 1987 19
Organic-carbon and nitrogen transport for the November-December 1987 sampling are 

presented in table 9. Only the data for the gravitational settling experiment were computed as this 

data set is more complete, and it allows direct comparison with the data in table 4. The major 

input to the organic-carbon and nitrogen transport on the silt and clay fraction was again the 

Missouri River, but this input is not nearly as substantial as for the July-August 1987 sampling 

(table 4).

Table 9.-Organic-carbon and nitrogen transport on the silt and clay and colloid fractions 

for sampling cruise 2, November-December 1987

[Water-discharge and suspended-sediment concentration data used to compute 

transport are reported by Moody and Meade (1992); ND, not determined]

Sampling site

Mississippi River near

Winfield, Mo.

Illinois River below

Meredosia, 111.

Missouri River at

St. Charles, Mo.

Mississippi River at

St. Louis, Mo.

Mississippi River at

Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at

Fulton, Tenn.

Mississippi River at

Helena, Ark.

White River at

Mile 11.5, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River at

Mile 10, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow Channel

near Knox Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Organiccarbon 

transport on 

silt and clay 

(metric tons 

per day)

223

35

761

ND

1,299

155

1,388

1,004

1,108

28

1,051

12

1,072

173

1,078

ND

Nitrogen 

transport on 

silt and clay 

(metric tons 

per day)

32

4

79

ND

154

19

163

121

124

3

126

1

111

20

123

ND

Organiccarbon 

transport on 

colloids 

(metric tons 

per day)

225

38

306

561

708

308

1,289

843

1,009

57

1,024

37

783

184

882

'401

Nitrogen 

transport on 

colloids 

(metric tons 

per day)

33

5

32

63

79

30

111

98

77

6

130

5

159

21

97

'42

Colloid recovered from centrifuge effluent.

20 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Organic-carbon and nitrogen transport on the colloid fraction (table 9) exceeded the silt and 

clay transport for the tributary rivers (Missouri River excepted) and the Mississippi River near 

Winfield, Mo., and the colloid carbon and nitrogen transport were within a factor of 2 of the silt 

and clay carbon and nitrogen transport for the Mississippi River sites. These data show the 

importance of colloids as a transport medium for contaminants that are associated with natural 

organic substances in water.

Concentrations of particulate organic carbon for the November-December 1987 sampling 

are shown in table 10. The concentrations were determined in two independent manners: 

(1) Computed as the difference between total organic-carbon and DOC concentrations on whole 

and filtered water samples injected into a high-temperature combustion furnace of the Beckman 

915B carbon analyzer, and (2) computed from the organic-carbon transport (table 9) divided by 

the discharge volume reported by Moody and Meade (1992). The two sets of concentrations are 

similar, but the set derived from the transport is much less variable than the set from the difference 

determination. Additivity of errors associated from the difference determination is believed to be 

the cause of the greater variability.

Table 10.-Concentrations of particulate organic carbon for sampling cruise 2,

November-December 1987

Sampling site

Particulate

organic carbon

determined by total

organic carbon

minus dissolved

organic carbon

(milligrams per

liter)

Particulate

organic carbon

determined form

carbon analysis of

isolated 

suspendedsediment fractions 

(milligrams per 

liter)

Mississippi River near Winfield, Mo.

Illinois River below Meredosia, 111.

Missouri River at St. Charles, Mo.

Mississippi River at Thebes, 111.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near Knox Landing, La.

Mississippi River near St. Francisville, La.

3.5

4.2

4.4

1.6

1.3

1.3

1.7

3.4

2.3

3.1

3.1

2.5

3.2

4.4

4.4

2.7

1.9

2.5

3.2

2.1

2.4

2.8

SAMPLING CRUISE 2, NOVEMBER-DECEMBER 1987 21
SAMPLING CRUISE 3, MAY-JUNE 1988

The sampling of cruise 3 began on the Illinois River below Meredosia, Illinois, on 

May 16,1988, and ended on the Mississippi River below Belle Chasse, Louisiana, on June 7,1988. 

The one sampling site change from cruise 2 was that the Missouri River was sampled at Hermann, 

Missouri instead of St. Charles, Missouri.

Objectives and Approach

The major objective of sampling cruise 3 was to repeat the research investigations of the first 

two cruises during a high-flow period during the spring; unfortunately, flow was at record low 

levels during this cruise. Another objective was to obtain a more complete characterization of the 

dissolved and colloidal fractions that were not recovered for analysis during the previous two 

cruises. The hydrophilic fraction (dissolved organic matter that does not adsorb on Amberlite 

XAD-8 resins) was studied, and an organic colloid fraction that was not recovered by laboratory 

supercentrifugation was also characterized.

The approach to isolating and characterizing the dissolved organic-matter fractions was 

modified significantly. The large 10-L column of Amberlite XAD-8 resin was removed from the 

boat, and 20-L samples of ultrafilter permeates were collected in cubitainers, preserved with chloroform, and shipped back to the laboratory. In the laboratory, the samples were acidified to pH 4 

with HC1 and vacuum evaporated to 500 mL to 1L (the point of salt saturation), the pH adjusted 

to 2 with HC1, and the sample concentrates passed through a 500-mL column of Amberlite 

XAD-8. Dissolved organic matter that adsorbed on the resin was eluted with 75 percent acetonitrile and 25 percent water acidified to pH 2. This modification of the procedure increased the 

recovery of dissolved organic matter that adsorbed on the resin. The procedure used in the first 

two sampling cruises recovered solutes whose column capacity factor (k1 ) was 10 or greater 

(Leenheer, 1981); the modified procedure recovered solutes of k' equal to 1 or greater.

Hydrophilic organic solutes that did not adsorb on the resins were collected in the eluent from 

the XAD-8 column, the eluent was vacuum evaporated to the point of salt crystallization, then 

glacial acetic acid was added to double the volume of the concentrate. Successive additions of 

acetic acid and separation of inorganic salts by centrifugation served to separate hydrophilic 

organic solutes from water and inorganic salts. After no more inorganic salts could be separated, 

the residue was dissolved in water and passed through a cation-exchange column in the hydrogen 

form to convert hydrophilic organic salts to acids.

Organic colloids that were not recoverable by centrifugation of the colloid fraction were recovered by placing the supernatant from the centrifugation in a 10,000-dalton pore-size dialysis bag, 

removing the salts by dialysis against distilled water, and freeze-drying the colloids remaining 

inside the dialysis bag.

A Sharpies Model AS-12 continuous-flow centrifuge was acquired by the project for use 

during this and subsequent sampling cruises. It was decided to use centrifugation to separate the 

silt and clay and colloid fractions rather than gravitational settling because centrifugation was 

much more time efficient with regard to the amount of water processed and the amount of silt and 

clay recovered. A pumped composite sample (see Moody and Meade, 1993) consisting of 300 to 

700 liters was collected in addition to the depth-integrated composite sample.

22 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Dissolved Organic Matter

DOC concentrations and transport for sampling cruise 3 are listed in table 11. Organic-carbon 

concentrations and transport are similar in the Mississippi River and tributary sites upstream 

from the Ohio River compared to the first cruise (table 1), where similar low-flow conditions 

existed; but concentrations and transport for sites downstream from the Ohio River are 50-80 

percent greater than the values for sampling cruise 1. The only significant difference between 

these cruises is water temperature near 30°C for the first cruise and 20-25°C for the third cruise. 

There may have been less instream degradation of DOC during the moderate temperatures of the 

third cruise than during the first cruise.

Table 11.-Dissolved organic-carbon concentrations and transport for sampling cruise 3,

May-June 1988

[Transport was computed using water-discharge data reported 

by Moody and Meade (1992)]

Sampling site

Mississippi River near Winfield, 111. 

Illinois River below Meredosia, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near

Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water 

discharge 

(cubic 

meters per 

second)

1,740 

332

1,480

3,350

3,590

3,230

6,790

7,170

7,050

438

8,160

73

7,950

2,150

5,700

5,570

Dissolved 

organic-carbon 

concentration 

(milligrams per 

liter)

4.8 

4.4

3.5

4.1

3.9

2.3

3.1

3.2

3.1

2.0

2.9

3.5

3.5

3.5

3.7

3.2

Transport 

(metric 

tons per 

day)

699 

126

456

1,004

1,260

639

1,827

1,997

1,883

76

2,083

21

2,412

663

1,802

1,543

Organic elemental analyses and yields of dissolved and colloidal organic substances isolated 

from water samples collected on the May-June 1988 sampling cruise are tabulated in table 12. 

Yields of the humic-substance fraction did not appreciably improve compared to data from the 

previous two cruises. The humic-substance fraction constitutes an average of about two-thirds of 

the DOC, and this fraction was quantitatively isolated in all three procedures. However, the ash 

content of the humic-substance fraction was much greater with this modified procedure because

SAMPLING CRUISE 3, MAY-JUNE 1988 23
Table 12.-Elemental analyses of dissolved and colloidal organic substances isolated from 

water samples collected during sampling cruise 3, May-June 1988

[ , no data]

Sampling site

Illinois River below

Meredosia, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at

Helena, Ark.

Mississippi River below

Vicksburg, Miss.

Fraction

Dissolved

humic

substances

Dissolved

hydrophilic

substances

Organic

colloids

Dissolved

humic

substances

Dissolved

hydrophilic

substances

Organic

colloids

Dissolved

humic

substances

Dissolved

hydrophilic

substances

Organic

colloids

Dissolved

humic

substances

Dissolved

hydrophilic

substances

Organic

colloids

Percent 

yield of 

dissolved 

organic 

carbon

75.8

7.1

61.1

12.4

69.5

12.7

58.4

9.1

Percent 

carbon 

(ashfree)

42.06

(49.9)

20.31

(30.4)

45.51

(47.4)

38.33

(50.7)

31.73

(39.1)

40.64

(45.8)

47.81

(51.3)

34.09

(39.4)

42.89

(46.5)

43.67

(50.3)

31.44

(38.1)

25.16

(40.4)

Percent 

hydrogen 

(ashfree)

4.10

(4.9)

2.54

(3.8)

6.13

(6.4)

3.49

(4.6)

3.37

(4.2)

5.54

(6.2)

4.34

(4.7)

3.58

(4.1)

5.96

(6.5)

4.01

(4.6)

3.26

(4.0)

2.94

(4.7)

Percent 

oxygen 

(ashfree)

29.29

(34.8)

41.03

(61.4)

38.21

(39.8)

29.32

(38.8)

32.09

(39.6)

35.04

(39.5)

33.53

(36.0)

38.39

(44.6)

34.32

(37.2)

32.38

(37.3)

31.97

(38.7)

33.58

(53.9)

Percent 

nitrogen 

(ashfree)

2.44

(2.9)

6.56

(9.8)

3.77

(3.9)

2.26

(2.9)

4.02

(5.0)

3.66

(4.1)

2.68

(2.9)

4.11

(4.8)

3.59

(3.9)

2.60

(3.0)

3.26

(4.0)

2.60

(4.2)

Percent 

ash

15.78

33.17

3.94

24.46

18.94

11.33

6.85

13.55

7.83

13.22

17.49

37.75

24 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
of incomplete removal of dissolved inorganic salts. This high ash content obviated the molecular 

weight and acidity determinations. The humic-substance fraction (ash-free data) has small shifts 

toward lower carbon, greater oxygen, and greater nitrogen percentages than for humic isolates 

from the previous two cruises. These elemental shifts indicate the modified procedure added 

small quantities of more hydrophilic substances to the dissolved humic-substance fraction.

The hydrophilic-substance fraction yields average only 10.3 percent, but it is likely the procedural yields are only 50 percent because of losses during precipitation, centrifugation, washing, 

drying, and weighing steps in the procedure. Therefore, the actual percentage of this fraction 

probably is closer to 20 percent or greater. The hydrophilic-substance fraction has lower carbon 

and hydrogen percentages and greater oxygen and nitrogen percentages than the dissolved 

humic-substance fraction. The ratio of carbon to oxygen is similar to carbohydrate substances. 

The high percentage of nitrogen suggests amino and amide substituents in the mixture. Nitrate 

ion also was not completely separated by the desalting process.

The organic-colloid fraction has a unique elemental signature compared to the dissolvedsubstance fraction. The high hydrogen percentage is unusual for a degraded fraction; therefore, 

the colloidal organic material may not be appreciably degraded.

Spectrometric characterizations of the dissolved and organic colloid fractions isolated from

the Mississippi River during sampling cruise 3 are shown in figure 8 (1H-NMR) and figure 9 (IR). 

Dissolved hydrophilic substances are very different from dissolved humic substances, as shown 

in figure 8 and 9. Dissolved hydrophilic substances are predominantly carbohydrates (peak 3 in 

spectrum B, fig. 8). In the IR spectrum of the dissolved hydrophilic-substance fraction (spectrum 

B, fig. 9), the presence of a carboxylic acid peak near 1,720 cm"1 , and the shape of the carbohydrate 

peak near 1,100 cm'1 indicate that the hemiacetal linkage in carbohydrates has been partially

oxidized to acid carboxyl groups. The small peak at 2.8 ppm in the 1H-NMR spectrum and the 

peak at 1,650 in the IR spectrum are probable indicators of amide structures in the dissolved 

hydrophilic-substance fraction.

The dissolved humic-substance fraction is similar to humic-substance fractions isolated from 

the Mississippi River during the previous two sampling cruises. The alteration of the isolation 

procedure in which the column capacity factor (k1 ) of recovered solutes was lowered by a factor 

of 10 caused a small increase in peaks 2 and 3 (fig. 8, spectrum A) that is related to more hydrophilic structures, but the changes in overall character of the spectrum were relatively minor. The 

character of the fulvic acid, determined by calculating the peak height ratio of peaks 2,3,4, and 5 

to peak 1 (spectrum A, fig. 8) is more similar to the fulvic acids characterized for sampling cruise 

2 than sampling cruise 1. The high water temperatures of cruise 1 may have resulted in exceptionally degraded humic substances with unique 1H-NHR spectral features.

The infrared spectra of organic-colloid fraction indicate a material composed of undegraded 

carbohydrates (peaks at 3,400 and 1,040 cm"1 ), hydrocarbons (peak at 2,930 cm"1 ), and proteins

(peaks at 1,650 and 1,550 cm"1) (fig. 9). Chemically, the colloid can be described as a glycolipoprotein. A scanning electron micrograph of the organic-colloid fraction (fig. 10) shows that the material consists predominantly of bacteria cells. Therefore, the interpretation of the spectral data of 

the colloid as being an undegraded glycolipoprotein is correct, as bacteria are glycolipoproteins.

SAMPLING CRUISE 3, MAY-JUNE 1988 25
W)

z

LU

z

Crt

<

LU

cc 

u

Numbers denote peaks where peak height 

were measured

76543

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 8. ^-nuclear magnetic resonance spectra of (A) dissolved humic substances and 

(B) dissolved hydrophilic substances from the Mississippi River near St. Francisville, La.,

June 1988.

26 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
4,000 3,500 3,000 2,500 2,000 1,800 1,600 1,400 1,200 1,000 800 600 400

WAVENUMBERS, IN RECIPROCAL CENTIMETERS

Figure 9. Infared spectra of (A) dissolved humic substances and (8) dissolved hydrophilic 

substances from the Mississippi River near St. Francisville, La., and (C) infrared spectrum 

of organic colloids from the Mississippi River at Fulton, Tenn., June 1988.

The significance of the comparative spectra of figures 8 and 9 and the comparative elemental 

analyses of table 12 is that these data show there are two distinct components of the dissolved 

organic-substance phase and a distinct organic-colloid phase that has properties intermediate 

between dissolved and particulate materials. Each of these components and phases should have 

unique contaminant interactions that affect contaminant fate and transport.

SAMPLING CRUISE 3, MAY-JUNE 1988 27
Figure 10.~Scanning electron micrograph of 

organic colloids isolated from the 

Mississippi River at Thebes, 111., May 

1988. The micrograph was taken by 

James F. Ranville (U.S. Geological 

Survey).

28 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Organic Matter In Suspended-Sediment Fractions

The relative percentages of silt and clay, mineral colloids, and organic colloids in water 

samples collected during the May-June 1988 sampling cruise are given in table 13. As mentioned 

previously, use of the centrifuge rather than gravitational settling shifted the relative percentage 

of silt to 90 percent or greater for most samples. The Yazoo River, in which most of the colloids 

are disaggregated, contained a lower percentage of silt and clay, and the Mississippi River below 

Belle Chasse, La., contained a lower percentage of silt and clay because of sedimentation loss of 

the silt and clay fraction, which occurred during this low-flow period. The mineral-colloid 

fraction ranged between 1.6 to 9.2 percent of the total suspended-sediment weight, and the 

organic-colloid fraction ranged from 0.3 to 3.6 percent.

Table 13.-Relative percentages1 of silt and clay, mineral colloids,

and organic colloids in the Mississippi River and some of its tributaries

for the May-June 1988 sampling cruise

[ND, not determined]

Sampling site

Mississippi River near Winfield, Mo.

Illinois River below Meredosia, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near

Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Percent silt

and clay 

(centrifuged)

91.3

97.3

96.4

95.0

94.7

93.0

96.3

97.3

95.3

91.2

94.3

87.2

94.0

94.0

95.9

81.6

Percent 

mineral

colloids

(ultrafiltered 

and

centrifuged)

ND

2.1

3.3

3.5

3.4

4.6

2.9

1.6

4.0

7.7

4.2

9.2

4.1

4.1

2.9

16.6

Percent

organic

colloids 

(ultrafiltered

and dialyzed)

ND

0.5

.3

1.5

1.9

2.4

.8

1.1

.7

1.1

1.5

3.6

1.9

1.9

1.2

1.7

1 See table 29 for method of determining relative percentages.

SAMPLING CRUISE 3, MAY-JUNE 1988 29
The organic-carbon and nitrogen contents of the silt and clay and colloid fractions are given 

in table 14. The organic-carbon and nitrogen percentages are greater than most of the data for the 

centrifuged samples in table 8 for sampling cruise 2. Possibly autochthonous production was 

greater during this late spring cruise than during the previous late fall cruise; this production may 

be indicated by the greater carbon and nitrogen contents of the silt and clay and colloid fractions. 

The carbon and nitrogen contents of the mineral colloid fractions in table 14 appear to be especially sensitive to sites where autochthonous production should be significant such as the Ohio 

River at Olmsted, m.

Table 14.-Organic-carbon and nitrogen contents off silt and clay, mineral-colloid, and 

organic-colloid fractions of suspended sediment from sampling cruise 3, May-June 1988

[ND, not determined]

Sampling site

Mississippi River near 

Winfield, Mo.

Illinois River below

Meredosia, 01.

Missouri River at

Hermann, Mo.

Mississippi River at 

St. Louis, Mo.

Mississippi River at 

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below 

Hickman, Ky.

Mississippi River at 

Fulton, Tenn.

Mississippi River at 

Helena, Ark.

White River at

Mile 11.5, Ark.

Mississippi River above 

Arkansas City, Ark.

Yazoo River at

Mile 10, Miss.

Mississippi River below 

Vicksburg, Miss.

Old River Outflow

Channel near

Knox Landing, La.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

Silt and clay fraction

Carbon 

(percent)

13.43

8.67

3.52

5.21

3.82

3.67

3.28

3.25

3.71

3.13

3.45

3.29

3.80

2.93

1.97

4.48

Nitrogen 

(percent)

2.22

1.31

.50

.64

.57

.54

.47

.49

.54

.53

.49

.53

.53

.40

.25

.56

Mineral-colloid 

fraction

Carbon 

(percent)

23.22

20.07

10.76

15.04

14.47

19.01

14.52

12.71

12.20

8.61

9.63

12.48

11.02

10.49

7.52

14.01

Nitrogen 

(percent)

ND

2.60

1.05

1.59

1.87

2.36

1.77

1.59

1.47

1.15

1.28

1.16

1.49

.96

.89

1.75

Organic-colloid 

fraction

Carbon 

(percent)

ND

45.51

ND

ND

ND

ND

40.64

ND

34.09

ND

ND

ND

25.16

ND

ND

ND

Nitrogen 

(percent)

ND

3.77

ND

ND

ND

ND

3.66

ND

4.11

ND

ND

ND

1.87

ND

ND

ND

30 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
The low carbon to nitrogen ratios of the silt and clay fractions (7.2 to 9.5) was noted to be only 

slightly larger than the Redfield ON ratio for phytoplankton, which may indicate a large 

percentage of autochthonous carbon in the silt and clay fraction (Leenheer, 1991). The amide II

band at 1,550 cm"1 in infrared spectra of silt and clay, mineral-colloid, and organic-colloid 

fractions (Leenheer, 1991) is direct evidence that suspended sediments from sampling cruise 3 

contain large amounts of proteinaceous matter.

The organic-carbon and nitrogen transport of the silt and clay and colloid fractions are given 

in table 15. The bulk of the organic-carbon and nitrogen transport occurs with the silt and clay 

because the bulk (about 95 percent) of the sediment is in the sUt and clay fraction. The carbon 

transport in the colloid fractions generally differ by less than a factor of 2. A major portion of the 

silt and clay carbon and nitrogen transport is lost by sedimentation to the riverbed between 

St. Francisville and Belle Chasse, La. There also is a greater proportion of the carbon and nitrogen 

transport in the colloid fractions at the Belle Chasse site.

SAMPLING CRUISE 3, MAY-JUNE 1988 31
Table 15.-Organic-carbon and nitrogen transport on silt and clay and colloid fractions of 

suspended sediment from sampling cruise 3, May-June 1988

[Water-discharge and suspended-sediment-concentration data used to compute transport 

are reported by Moody and Meade (1992); ND, not determined]

Sampling site

Mississippi River near

Winfield, Mo.

Illinois River below

Meredosia, 111.

Missouri River at

Hermann, Mo.

Mississippi River at

St. Louis, Mo.

Mississippi River at

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at

Fulton, Tenn.

Mississippi River at

Helena, Ark.

White River at

Mile 11. 5, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River at

Mile 10, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow

Channel near Knox

Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Organiccarbon 

transport 

on silt 

and clay 

(metric 

tons per 

day)

613

135

339

891

832

286

1,074

1,297

1,626

100

1,936

13

1,893

375

1,965

310

Nitrogen 

transport 

on silt 

and clay 

(metric 

tons per 

day)

101

20

55

109

124

42

154

195

237

17

275

2.0

264

51

249

39

Organiccarbon 

transport 

on 

mineral 

colloids 

(metric 

tons per 

day)

ND

7.0

36

95

113

73

143

83

224

23

241

5.1

239

58

227

197

Nitrogen 

transport 

on 

mineral 

colloids 

(metric 

tons per 

day)

ND

0.9

3.5

10

15

9.1

17

10

27

3.1

32

.5

33

5.4

27

25

Organiccarbon 

transport 

on 

organic 

colloids 

(metric 

tons per 

day)

ND

3.6

*12

 i

76

1 175

'81

110

hso

110

hs

357

'6.3

253

hos

1499

'58

Nitrogen 

transport 

on 

organic 

colloids 

(metric 

tons per 

day)

ND

.3

1 1.2

1-7 f. /.o

1 1.8

'8.1

10

h8

13

h.5

36

1 .6

19

ho

'50

'5.8

1 An estimate of 40 percent was made for the organic-carbon content and 4 percent for the 

nitrogen content.

32 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Concentrations of colloidal organic carbon determined by two independent methods for 

sampling cruise 3 are given in table 16. The difference determination of the left column is erratic 

because the variance of the organic-carbon determination (+0.1 mg/L) is large relative to the 

magnitude of the data values. There is not a large degree of variability for colloid organic-carbon 

concentrations at various sampling sites.

Table 16.-Concentrations of colloidal organic carbon for sampling cruise 3,

May-June 1988

[ND, not determined]

Sampling site

Colloidal organic

carbon determined by

total organic carbon of

centrifuge effluent

minus dissolved

organic carbon of

ultrafilter permeate

(milligrams per liter)

Colloidal organic

carbon determined

from carbon analysis

of isolated colloid

fractions 

(milligrams per liter)

Mississippi River near Winfield, Mo.

Illinois River below Meredosia, 111.

Missouri River at Hermann, Mo.

Mississippi River St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River at Mile 10, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel

near Knox Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below Belle Chasse, La.

1.0

1.0

.2

.4

.5

.5

ND

.3

.5

.2

.4

.4

0.0

0.0

0.0

.6

ND

0.4

.4

.7

.9

.6

.4

.4

.5

1.0

.9

1.9

.7

.8

1.5

.5

SAMPLING CRUISE 3, MAY-JUNE 1988 33
SAMPLING CRUISE 4, MARCH-APRIL 1989

The sampling of cruise 4 began at Hardin, Illinois, on March 9, 1989, on the Illinois River and 

ended on the Mississippi River below Belle Chasse, Louisiana, on April 1,1989. The two sampling 

site changes from cruise 3 is that the Illinois River was sampled at Hardin, Illinois, instead of 

below Meredosia, Illinois, and the Arkansas River was sampled at Pendleton, Arkansas.

Objectives and Approach

The major objective of the fourth sampling cruise was to intercept high-discharge conditions 

during the early spring runoff from the Ohio River and determine what effects high discharge had 

upon the nature and properties of natural organic substances in various phases. For the first time 

in four cruises, high-discharge conditions were observed in the Ohio River and sampling sites 

downstream.

A secondary objective was to investigate particle-size distributions and chemical fractionations that were occurring between the continuous-flow centrifugation and tangential-flow ultrafiltration steps. The approach was to process a separate set of water samples through the 

centrifuge and ultrafilter during the upriver part of the sampling cruise. Samples were collected 

from the Mississippi River at Memphis, Term., the Ohio River at Cairo, HI., the Illinois River at 

Grafton, 111., and the Missouri River at Hermann, Mo. Results of this study were published in a 

report by Rees and others (1991).

Dissolved Organic Matter

DOC concentrations and transport at the various sampling sites are presented in table 17. The

high discharge (20,410 m3/s) dominated the DOC transport, although the DOC concentration (of 

the Ohio River at Olmsted) was only one-half the DOC concentration of the Mississippi River just 

upstream from the confluence at Thebes, HI. The low DOC concentration of the Ohio River is 

likely due to the fact that the river stage was falling during sampling. Peak of the DOC, which 

generally occurs during rising stage, had passed and DOC on the falling limb of the hydiograph 

was diluted by the large volume of water in the system. The organic-carbon transport downstream from the Ohio River confluence and downstream from the White and Arkansas River 

confluences are additive, which means at this particular sampling, DOC is a conservative constituent in the system. The cool waters of early spring (3-15°C) likely retarded the rate of instream 

biodegradation of DOC.

34 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 1/.-Dissolved organic-carbon concentrations and transport for sampling cruise 4,

March-April 1989

[Transport was computed using water-discharge data reported by Moody

Meade (1993); ND, not detected]

and

Sampling site

Mississippi River near Winfield, 111.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Arkansas River at Pendleton, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss. 

Old River Outflow Channel near Knox Landing, Miss.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water 

discharge 

(cubic 

meters per 

second)

850

410

1,480

3,940

4,890

20,400

24,700

24,800

25,900

1,500

1,900

26,800

1,500

26,600 

6,160

23,100

22,500

Dissolved 

organiccarbon 

concentration 

(milligrams 

per liter)

ND

ND

3.4

4.7

4.2

2.1

2.8

2.8

2.7

2.6

3.5

3.0

4.9

2.9 

2.9

2.9

3.0

Load 

(metric 

tons per 

day)

ND

ND

435

1,600

1,774

3,703

5,970

6,002

6,042

337

574

6,957

635

6,652 

1,541

5,793

5,827

The effect of allochthonous inputs upon the constitution of DOC in the Mississippi River is

illustrated by the 1H-NMR spectra of figure 11. The spectrum of the Mississippi River at Thebes, 

HI. (spectrum A, fig. 11), is typical for humic-substance spectra from the Mississippi River at low 

flow (figs. 2,7, and 8). However, dissolved humic substances isolated from the Ohio River (spectrum B, fig. 11) have greater spectral peak-height ratios of peaks 3 and 4 to peak 1 than were 

observed previously. These spectra ratio increases represent increases in the carbohydrate (peak 

3) and phenol (peak 4) components of the dissolved humic-substance mixture. The source of these 

carbohydrate and phenol components arises from cellulose and lignin constituents of degraded

plant materials washed into the river by surface runoff. The 1H-NMR spectrum of dissolved 

humic substances isolated from the Mississippi River below Hickman, Ky. (spectrum C, fig. 11), is 

similar to spectrum B (the Ohio River sample), which indicates the humic-substance load is dominated by the Ohio River input as data from table 17 indicate.

SAMPLING CRUISE 4, MARCH-APRIL 1989 35
en

2 

C/3 

<

LU 

DC 

O

Numbers denote peaks where peak heights 

were measured

76543

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 11. 1H-nuclear magnetic resonance spectra of dissolved humic substances from the: 

(A) Mississippi River at Thebes, 111., (B) Ohio River at Olmsted, 111., and (C) Mississippi 

River below Hickman, Ky., sampled March 1989.

36 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Additional allochthonous inputs of dissolved humic substances occurred downstream from 

the Ohio River confluence on this fourth sampling cruise. High discharges from the White, 

Arkansas, and Yazoo Rivers added additional humic substances derived from allochthonous

sources. The 1H-NMR spectra of dissolved humic substances isolated from the White River, the 

Yazoo River, and the Mississippi River below Belle Chasse, La., are shown in figure 12. The 

greatest spectral ratios of peaks 2,3,4, and 5 to peak 1 for dissolved humic substances characterized from the Mississippi River and its tributaries were observed for the White River and Yazoo 

River samples. The sample from the Mississippi River at Belle Chasse, La., (spectrum C, fig. 12) 

had greater spectral ratios of peaks 2,3,4, and 5 to peak 1 than the sample from the Mississippi 

River below Hickman, Ky. (spectrum C, fig. 11). These increases in spectral ratios clearly indicated 

increasing inputs of humic substances from allochthonous sources as sampling proceeded downstream in the Mississippi River.

Dissolved hydrophilic organic substances were also isolated and characterized during 

sampling cruise 4. No significant differences were observed for either the proportion (yield) or

nature (1H-NMR spectra) of these dissolved hydrophilic substances isolated during sampling 

cruise 4 from those isolated and characterized during sampling cruise 3.

Organic Matter in Suspended-Sediment Fractions

The relative percentages of silt and clay, mineral colloids, and organic colloids in the Mississippi River for the March-April 1989 sampling cruise are given in table 18. Because of the coarse 

silt and clay fraction lost from the centrifuge during the shutdown procedure, suspended-sediment weights for the silt and clay fraction from the pumped composite sample rather than the 

depth-integrated composite sample were used for the calculations in table 18. Because of the 

smaller volume processed, the depth-integrated composite sample had a larger loss of the coarse 

silt fraction than the pumped composite sample, and the silt and clay percentages were 1-2 

percent lower for the depth-integrated composite fraction.

The relative size distribution of silt and clay and colloid fractions was similar to data from 

sampling cruise 3 (table 13), with two exceptions: (1) The organic-colloid percentage from the 

Mississippi River near Winfield, 111., was exceptionally high compared to other sites. These data 

indicate a large bacteria population in the river at this point. (2) The mineral-colloid percentages 

were high for the White and Yazoo Rivers. High discharge and low specific conductance (White 

River, 150 nS/cm at 25°C; Yazoo River, 80 nS/cm at 25°C) may have disaggregated clay-mineral 

aggregates that normally isolate in the silt and clay fraction (Rees and others, 1991), so that they 

are recovered in the mineral-colloid fraction. Most silt and clay in Mississippi River samples was 

found to be aggregated colloidal material (Rees and others, 1991).

Organic-carbon, nitrogen, and fluorine contents of the silt and clay and mineral-colloid fractions from the March-April 1989 sampling cruise are shown in table 19. Fluorine determinations 

were run on the silt and clay fraction because infrared analyses of this fraction suggested the presence of Teflon in the silt and clay fraction; the Teflon contamination may have occurred because 

of wear of a Teflon bushing and nozzle in the continuous-flow centrifuge. Fluorine was detected, 

but levels were low enough so that effects on carbon contents were minor, as carbon is only 

31 percent of the fluorine content in Teflon.

SAMPLING CRUISE 4, MARCH-APRIL 1989 37
g

I?°^

o>« 

m O

i

is

INCREASING INTENSITY r

20 

1^

M O

m ^

il

Is 

igm O

3D O

iio S I
Table 18.-Relative percentages1 of silt and clay, mineral colloids, and

organic colloids in the Mississippi River and some of its tributaries

for the March-April 1988 sampling cruise

Percent silt 

Sampling site and clay 

(centrifuged)

Mississippi River near Winfield, 111.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near

Knox Landing, La.

Mississippi River near 

St. Francisville, La.

Mississippi River below Belle Chasse, La.

82.6

95.5

91.1

93.0

89.1

91.8

91.1

90.2

89.4

51.1

68.1

86.0

88.2

87.1

89.5

Percent mineral 

colloids 

(ultrafiitered 

and centrifuged)

4.1

2.7

8.0

5.4

9.5

7.7

9.5

9.0

10.1

45.4

27.0

12.4

11.2

12.4

9.8

Percent 

organic 

colloids 

(uitrafiltered 

and diaiyzed)

12.7

1.8

0.9

1.6

1.4

0.5

0.4

0.8

0.5

3.5

4.9

1.6

0.6

0.5

0.7

1See table 29 for method of determining relative percentages.

SAMPLING CRUISE 4, MARCH-APRIL 1989 39
Table 19.-Organic-carbon content, nitrogen content, and atomic C:N ratio of

silt and clay and mineral-colloid fractions of suspended sediment from

sampling cruise 4, March-April 1989.

[Fluorine coment or silt imd clay rraction is a][so includec

Silt and clay fraction

Sampling site

Mississippi River near 

Winfield, Mo.

Illinois River at

Hardin, 111.

Missouri River at

Hermann, Mo.

Mississippi River at 

St. Louis, Mo.

Mississippi River at 

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below 

Hickman, Ky.

Mississippi River below 

Fulton, Tenn.

Mississippi River at 

Helena, Ark.

White River at

Mile 11. 5, Ark.

Arkansas River at

Pendleton, Ark.

Mississippi River above 

Arkansas City, Ark.

Yazoo River below

Steele Bayou, Miss.

Mississippi River below 

Vicksburg, Miss.

Old River Outflow

Channel near

Knox Landing, La.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

Organic 

carbon 

(percent)

15.93

3.32

2.50

5.01

4.09

2.35

2.56

2.44 

2.35

1.95

3.08

2.24

1.42

2.23

1.76

2.18

1.85

Nitrogen 

(percent)

2.59

.29

.24

.74

.51

.19

.26

.25 

.23

.18

.31

.23

.19

.22

.18

.19

.18

Atomic 

C:N 

ratio

7.2

13.4

12.4

7.8

9.4

14.7

11.6

11.3 

12.1

12.3

11.8

11.6

8.8

11.6

11.5

13.8

11.8

Fluorine 

(percent)

0.36

.15

.87

.10

.08

.08

.10

.10

.17

.28

.42

.07

.13

.06

.30

.12

.52

I; ND, not d<2terminedJ1

Mineral-colloid fraction

Organic 

carbon 

(percent)

28.96

8.83

7.15

10.67

7.35

3.39

4.76

4.27 

4.51

3.03

ND

ND

2.32

4.14

3.22

3.84

3.62

Nitrogen 

(percent)

4.74

1.05

.85

1.67

1.10

.48

.55

.53 

.60

.44

ND

ND

.40

.52

.48

.54

.51

Atomic 

C:N 

ratio

7.1

9.8

9.8

7.5

7.8

8.2

10.1

9.4 

8.8

8.0

ND

ND

6.8

9.3

7.8

8.3

8.28

40 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
The contrast between allochthonous inputs and autochthonous inputs to carbon and nitrogen 

in the silt and clay and colloid fractions is especially apparent among the different sampling sites. 

Sites where autochthonous inputs dominate (Mississippi River near Winfield, at St. Louis, and at 

Thebes) are characterized by high contents of carbon and nitrogen on the suspended-sediment 

fractions and by low C:N ratios (table 19). The tributaries and other sites have low carbon and 

nitrogen contents and high C:N ratios except for the low C:N ratio of the Yazoo River sample. The 

high discharges on the Ohio, White, Arkansas, and Yazoo Rivers resulted in the organic fraction 

of suspended sediment in the Lower Mississippi River being derived from allochthonous inputs. 

In contrast, autochthonous inputs from the Upper Mississippi River dominated the suspendedsediment characteristics downstream to the confluence with the Ohio River.

Organic-carbon and nitrogen transport of the various suspended-sediment fractions for 

sampling cruise 4 are presented in table 20. The transport is dominated by sediment inputs from 

the Ohio River. The organic fraction that appears to be the most conservative with discharge is 

the mineral-colloid fraction. Even inputs of tributaries whose discharge is small compared to the 

discharge of the Mississippi River, such as the White and Yazoo Rivers, can be detected by 

increases in the mineral-colloid fraction. The Upper Mississippi River has the greatest relative 

amount of transport in the organic-colloid fraction, whereas the Lower Mississippi and Ohio 

Rivers have most of the transport in the silt and clay and mineral-colloid fractions.

The colloid transport is converted into organic-carbon concentrations in table 21. Colloidal 

organic-carbon concentrations were slightly greater for the early spring period of sampling cruise 

4 than for the late spring period of sampling cruise 3 (table 16). The greater total suspendedsediment concentration during the fourth cruise also likely increased the colloidal organic-carbon 

concentrations. The difference method (left column, table 21) appears to underdetermine the 

colloidal organic-carbon concentration compared to concentrations determined from carbon analysis of the isolated colloids (right column, table 21), although there is a high degree of analytical 

variance in the difference method. Colloidal organics may not be efficiently determined by the 

persulfate oxidation method in freshwater systems, as was found previously for marine systems 

(Sugimura and Suzuki, 1988).

SAMPLING CRUISE 4, MARCH-APRIL 1989 41
Table 20.-Organic-carbon and nitrogen transport of silt and clay and colloid fractions of 

suspended sediment from sampling cruise 4, March-April 1989

[Water-discharge and suspended-sediment concentration data used to compute 

transport are reported by Moody and Meade (1993)]

Silt and clay

transport

Sampling site

Mississippi River near

Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at

Hermann, Mo.

Mississippi River at

St. Louis, Mo.

Mississippi River at

Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River below

Fulton, Tenn.

Mississippi River at

Helena, Ark.

White River at

Mile 11. 5, Ark.

Yazoo River below

Steele Bayou, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow

Channel near Knox

Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Organic 

carbon 

(metric 

tons 

per day)

222

111

213

1,079

1,617

5,782

6,614

6,463

6,253

56

187

5,367

1,322

4,400

4,695

Nitrogen 

(metric 

tons per 

day)

36

9.7

20

110

202

468

672

609

612

5.1

25

529

135

383

457

Mineral-colloid

transport

Organic 

carbon 

(metric 

tons 

per day)

20

8.4

53

133

310

700

1,282

1,129

1,356

77

121

1,437

307

1,103

1,006

Nitrogen 

(metric 

tons per 

day)

3.3

1.0

6.3

21

46

99

148

140

180

11

21

180

51

155

141

Organic-colloid

transport1

Organic 

carbon 

(metric 

tons 

per day)

86

25

34

148

248

536

453

940

595

78

378

1,791

204

463

794

Nitrogen 

(metric 

tons per 

day)

8.6

2.5

3.4

15

25

54

45

94

60

7.8

38

180

20

46

79

1 Organic-carbon and nitrogen transport calculations for the organic-colloid fraction were 

made by estimating 40 percent organic carbon and 4 percent for organic nitrogen.

42 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 21 .-Concentrations of colloidal organic carbon for sampling cruise 4,

March-April 1989

[ND, not determined]

Colloidal organic

carbon determined by Colloidal organic 

total organic carbon of carbon determined

« _ ,. ... centrifuge effluent from carbon analyses Sampling site m|nu8 d|88O|ved of |so|ated co||oid

organic carbon of fractions 

ultrafllter permeate (milligrams per liter) 

(milligrams per liter)

Mississippi River near Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Arkansas River at Pendleton, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near

Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

ND

ND

0.2

.2

.6

.5

.2

.2

.4

.6

.4

.3

1.5

.4

.3

.4

.2

3.0

.9

.7

.7

1.3

.7

.8

.9

.9

1.2

ND

ND

3.8

1.4

1.0

.8

.9

SAMPLING CRUISE 4, MARCH-APRIL 1989 43
SAMPLING CRUISE 5, JUNE 1989

The sampling of cruise 5 began on the Illinois River at Hardin, Illinois, on June 4,1989, and 

ended on the Mississippi River below Belle Chasse, Louisiana, on June 28,1989. No significant 

changes in sampling sites were made from cruise 4.

Objectives and Approach

An objective in the scheduling of this cruise was to determine herbicide transport in the lower 

Mississippi River after the spring application of herbicides. In this objective, only partial success 

was achieved because only the lower part of the river system was affected by rising stage resulting 

from runoff from agricultural lands.

Another objective was to finish the characterization work on dissolved organic substances. 

Sufficient data on dissolved organic substances were collected throughout the five cruises to 

predict its properties based upon the season and flow regimes of the rivers at various sampling 

sites. A continuing objective during each cruise was to quantify the carbon and nitrogen transport 

in the various phases at the various sites. This work was repeated during sampling cruise 5.

Initial work was begun on development of methodology for spectrometric characterization of 

organic substances in suspended sediments and bottom sediments. Bottom sediments were 

collected with a pipe dredge in relatively quiescent sections of the river where fine material accumulated. These bottom samples were subjected to a series of chemical and physical separation 

procedures to separate the organic material for spectrometric characterization. Suspended-silt 

and -clay samples also were collected from the Illinois River at Hardin, HI., the Missouri River at 

Hermann, Mo., and the Mississippi River at Helena, Ark., for the initial evaluations of organic 

extraction methodologies for sediment characterization.

Dissolved Organic Matter

DOC concentrations and transport at the various sampling points for the June 1989 sampling 

cruise are presented in table 22. The DOC concentrations and transport inputs to the Lower 

Mississippi River system are unique in that a greater proportion of the DOC transport, as 

measured at Vicksburg, comes from both the Upper Mississippi River, as measured near Winfield, 

Mo., and from the Arkansas River. Each of these rivers contributes about 18 percent of the DOC 

transport, whereas the transport contributions were significantly less on the previous sampling 

cruises. The DOC concentration measured in the Upper Mississippi River near Winfield, Mo., was 

the highest measured for any sample collected up to this point. These significant DOC concentrations may be related to the fact that samples were collected as the river stage was rising. Although 

the stage rise was fairly small, elevated DOC concentration is related to initial increases in stream 

discharge (McDowell and Likens, 1988). The DOC transport is about additive at the Upper 

Mississippi River-Illinois River-Missouri River confluence, at the Upper Mississippi River-Ohio 

River confluence, and at the Arkansas River-Lower Mississippi River confluence.

44 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 22.-Dissolved organic-carbon concentrations and transport for sampling cruise 5,

June 1989

[Transport was computed using water-discharge data reported by Moody and

Meade (1993)]

Sampling site

Mississippi River near Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

Arkansas River at Pendleton, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water WTCfLtfff

discharge 

(cubic

meters per 

second)

2,320

780

1,760

4,760

5,230

8,760

14,100

15,300

16,900

3,600

23,300

1,070

24,800

4,890

19,000

20,100

Dissolved

organiccarbon 

concentration

(milligrams 

per liter)

6.4

4.5

3.7

5.0

5.1

3.2

3.7

3.8

3.8

4.3

3.5

4.7

3.3

3.3

3.2

3.4

Transport 

(metric 

tons per

day)

1,263

303

562

2,056

2,300

2,422

4,504

5,023

5,562

1,334

7,058

435

7,077

1,278

5,264

5,893

The nature of humic substances in the Mississippi River and its tributaries is similar to what 

was observed on previous cruises. At the beginning of the cruise where river stages were low to

average, dissolved humic substances were typified by the 1H-NMR spectrum of figure 13, spectrum A. In this spectrum, the ratio of peak 5 to peak 1 indicated a predominantly allochthonous 

source, but the small ratio of peak 4 to peak 5 indicated that phenolic substances had been 

removed through degradation or sorption onto sediments. As the cruise proceeded downriver, 

inputs of fresh allochthonous humic substances from tributaries at high river stage, such as the 

Arkansas River (fig. 13, spectrum B), increased the proportion of fresh humic substances until the 

Mississippi River near Belle Chasse, La., contained predominantly humic substances of minimal 

alteration (fig. 13, spectrum C).

The process of how dissolved humic substances are altered in the Mississippi River system 

was indicated by examining the hydrophilic-substance fraction of these samples presented in 

figure 13. The results are shown in figure 14. Spectrum A, the Illinois River at Hardin, HI., is 

significantly different from the hydrophilic fractions of the Arkansas River (spectrum B) and the 

Mississippi River below Belle Chasse, La., (spectrum C). The acid metabolites of degraded humic 

substances were captured in the hydrophilic fraction of the Illinois River sample. Degradation of 

carbohydrates to carbohydrate acids is shown by the additional peak in figure 14 spectrum A at 

4.2 ppm, and degradation of aromatic rings is shown by shift of aromatic protons from 7.4 ppm 

(spectrum A, fig. 13) to 7.7-8.0 ppm (spectrum A, fig. 14). This aromatic proton shift results from 

the buildup of carboxyl groups on aromatic rings during oxidation.

SAMPLING CRUISE 5, JUNE 1989 45
en

en 

<

LLJ 

CC

o

Numbers denote peaks where peak heights 

were measured

10

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 13.-1H-nuclear magnetic resonance spectra of dissolved humic substances from the: 

(A) Illinois River at Hardin, 111., (B) Arkansas River at Pendleton, Ark., and 

(C) Mississippi River below Belle Chasse, La., sampled June 1989.

46 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
(0

 o

o o

30i

in 

<n

»-H §
These results do not rule out selective sorption processes in altering the nature of dissolved 

humic substances but definitely confirm the importance of oxidative degradation processes 

(possibly both biotic and abiotic) in changing the character of dissolved humic substances. The 

low DOC values and their decrease downriver during sampling cruise 1 (table 1) also indicate 

instream degradation of dissolved humic substances as a significant process when river stage is 

low and water temperatures are warm.

Organic Matter In Suspended-Sediment Fractions

The relative percentages of silt and clay, mineral colloids, and organic colloids in the Mississippi River and some of its tributaries for sampling cruise 5 are given in table 23. A typical distribution of relative percentages for the various sampling sites was found. The Upper Mississippi 

River sampled near Winfield, Mo., had the highest percentage of organic colloids, and the 

Arkansas, White, and Yazoo Rivers had the highest percentages of mineral colloids. Inputs of 

mineral colloids from the Arkansas, White, and Yazoo Rivers in the lower part of the Mississippi 

River are indicated by small increases in the mineral-colloid percentages at the below Vicksburg 

and Old River Outflow Channel sites.

Table 23.-Relative percentages1 of silt and clay, mineral colloids, and organic colloids in 

the Mississippi River and some of its tributaries for the June 1989 sampling cruise

[ND, not determined]

Sampling site

Mississippi River near Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River at Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Arkansas River at Pendleton, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Percent siit

and clay 

(centrifuged)

89.5

98.7

96.1

93.2

92.7

94.1

94.2

93.5

93.7

84.6

83.0

92.2

81.7

88.9

88.8

92.1

93.2

Percent

mineral

coiioids

(ultrafiltered 

and

centrifuged)

7.9

1.0

3.5

5.9

6.7

5.9

5.2

6.1

6.1

14.9

15.6

7.2

17.3

10.3

10.9

7.6

6.4

Percent

organic

colloids 

(ultrafiltered

and diaiyzed)

2.6

.3

.4

.9

.6

ND

.6

.4

.2

.5

1.4

.6

1.0

.7

.3

.3

.4

1 See table 29 for method of determining relative percentages.

48 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
The elemental composition of the various suspended-sediment fractions is given in table 24. 

Fluorine percentages in the silt and clay fraction were lower than for the previous sampling cruise 

because a Teflon drag bushing in the continuous-flow centrifuge, which probably was the source 

of much of the fluorine content, was replaced by a treated wood bushing.

Typical increases in organic-carbon content of suspended sediment fractions were observed in 

proceeding from the silt and clay fraction (about 2-4 percent) to the mineral-colloid fraction 

(about 4-11 percent) to the organic-colloid fraction (about 25-40 percent). The atomic C:N ratio 

was somewhat elevated for most sites sampled on sampling cruise 5 compared to previous 

cruises; this elevated ratio indicates sediment contained a significant proportion of allochthonous 

material, which is consistent with the moderate to high stages of the river during cruise 5.

The organic-carbon and nitrogen transport for the various sediment-size fractions are 

presented in table 25. The transport of organic carbon in the mineral-colloid fraction are remarkably additive compared to the silt and clay transport when proceeding downriver. Especially 

remarkable is the additivity of the mineral-colloid transport at St. Louis for inputs from the Illinois 

River, the Upper Mississippi River, and the Missouri River. The organic carbon in the silt and clay 

fraction at these sampling points is not at all additive. Furthermore, the total masses of the 

mineral colloids are not additive; only the organic-carbon component is additive.

To gain further insight into the independent variations in the organic-carbon component of the 

silt and mineral-colloid fractions, the transport was converted into organic-carbon concentrations 

in table 26. The maximum variation between colloidal organic carbon concentrations was a factor 

of 3.2, whereas there was more than an order of magnitude variation between silt and clay organic 

carbon concentrations. The variations in colloidal organic-carbon concentrations in table 26 tend 

to parallel the variations in dissolved organic-carbon concentrations in table 22; the colloidal 

organic-carbon concentrations were 16-40 percent of the dissolved organic-carbon concentrations. The independent variations in the silt and clay and colloidal organic-carbon concentrations 

were among the most significant findings of this study, and the various mechanisms responsible 

for colloidal organic carbon acting as a conservative, dissolved constituent in water merits additional research.

Results of the work involving infrared spectral characterization of organic substances 

extracted from suspended silt and clay collected from the Mississippi River at Helena, Ark., are 

shown in figure 15. The initial extraction of sediment was by methylisobutyl ketone (MIBK) 

under both acid and alkaline conditions (Rice and MacCarthy, 1989). The MIBK extract after 

drying is shown in spectrum A. This extract appears to consist of aliphatic hydrocarbons, 

aliphatic alcohols, and aliphatic ester lipids. The next extraction in the sequence was by acid pyrophosphate designed to extract adsorbed fulvic acid from soils and sediments (Gregor and Powell, 

1986). The spectrum of this extract (spectrum B, fig. 15) has a peak pattern typical for fulvic acid. 

The next extract was by a mixture (95 percent dimethyl sulfoxide, 4 percent water, and 1 percent 

HC1) recommended by Hayes (1985) for extraction of soil humic substances. This extract, after 

removal of the dimethylsulfoxide by dialysis and the silica by hydrofluoric acid (HF), gave the 

spectrum shown in spectrum C (fig. 15). This spectrum indicated a protein-rich substance that 

also contained lipids and humic substances.

SAMPLING CRUISE 5, JUNE 1989 49
Table 24.-Organlc-carbon content, nitrogen content, and atomic C:N ratio of 

silt and clay, mineral-colloid, and organic-colloid fractions of suspended sediment

from sampling cruise 5, June 1989.

[Fluorine content of silt fraction also is included]

Silt and clay fraction

Sampling site

Mississippi River near

Winfield, Mo.

Illinois River at

Hardin, 111.

Missouri River at

Hermann, Mo.

Mississippi River at

St. Louis, Mo.

Mississippi River at

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River at

Fulton, Tenn.

Mississippi River at

Helena, Ark.

White River at

Mile 11. 5, Ark.

Arkansas River at

Pendleton, Ark.

Mississippi River above

Arkansas City, Ark.

Yazoo River below

Steele Bayou, Miss.

Mississippi River below

Vicksburg, Miss.

Old River Outflow

Channel near Knox

Landing, La.

Mississippi River near

St. Francisville, La.

Mississippi River below

Belle Chasse, La.

Organic

carbon

(percent)

4.38

2.60

2.87

3.50

3.58

2.63

2.78

2.30

2.17

1.86

2.68

2.33

1.20

2.16

2.32

1.97

1.90

Nitrogen

(percent)

0.57

.24

.26

.36

.39

.26

.31

.26

.23

.26

.35

.24

.14

.20

.23

.21

.20

Atomic

C:N

ratio

9.0

10.8

13.1

11.3

10.6

11.8

10.6

10.4

10.9

8.3

8.9

11.3

10.6

12.5

11.7

8.2

11.6

Fluorine

(percent)

0.11

.05

.06

.08

.08

.06

.07

.08

.06

.06

.09

.06

.06

.08

.08

.07

.06

Mineral-colloid 

fraction

Organic

carbon

(percent)

11.29

6.34

2.51

7.76

6.61

7.20

5.12

4.36

4.42

4.36

5.42

4.54

2.85

4.57

4.27

4.07

4.58

Nitrogen

(percent)

0.63

1.67

.38

1.00

.83

.99

.46

.48

.44

.44

.37

.54

.54

.39

.47

.44

.72

Atomic

C:N

ratio

20.9

4.5

7.7

9.1

9.1

8.5

13.2

10.6

11.7

11.6

17.1

9.8

6.2

13.7

10.6

10.8

7.4

Organiccolloid 

fraction1

Organic

carbon

(percent)

40

30

20

35

40

40

35

35

35

30

30

25

20

30

30

30

30

Nitrogen

(percent)

4.0

3.0

2.0

3.5

4.0

4.0

3.5

3.5

3.5

3.0

3.0

2.5

2.0

3.0

3.0

3.0

3.0

1 Carbon and nitrogen percentages on organic colloids were estimated using infrared spectral 

data.

50 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 25.-Organic-carbon and nitrogen transport on silt and clay and colloid fractions of 

suspended sediment from sampling cruise 5, June 1989

[Water-discharge and suspended-sediment-concentration data used to compute 

transport are reported by Moody and Meade (1993); ND, not determined]

Silt and clay 

transport

Sampling site

Mississippi River near 

Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at

Hermann, Mo.

Mississippi River at 

St. Louis, Mo.

Mississippi River at 

Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below 

Hickman, Ky.

Mississippi River at 

Fulton, Tenn.

Mississippi River at 

Helena, Ark.

White River at

Mile 11. 5, Ark.

Arkansas River at

Pendleton, Ark.

Mississippi River above 

Arkansas City, Ark.

Yazoo River below

Steele Bayou, Miss.

Mississippi River below 

Vicksburg, Miss.

Old River Outflow Channel

near Knox Landing, La.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

Organic 

carbon 

(metric 

tons per 

day)

572

1,224

1,975

1,636

1,751

2,154

4,112

5,145

6,280

106

469

7,321

245

6,300

1,390

4,596

5,218

Nitrogen 

(metric 

tons 

per day)

70

113

176

169

192

213

454

579

674

15

61

755

27

590

139

481

536

Mineral-colloid 

transport

Organic 

carbon 

(metric 

tons per 

day)

123

30

63

230

234

370

418

636

844

44

178

1,114

124

1,554

314

783

863

Nitrogen 

(metric 

tons 

per day)

69

7.9

9.5

30

29

51

38

70

84

4.4

12

132

23

138

35

85

136

Organic-colloid 

transport

Organic 

carbon 

(metric 

tons per 

day)

144

43

57

158

126

ND

293

334

219

10

89

511

50

689

61

228

314

Nitrogen 

(metric 

tons 

per day)

14.4

4.3

5.7

16

13

ND

29

33

22

1.0

8.9

51

5.0

69

6.1

23

31

SAMPLING CRUISE 5, JUNE 1989 51
Table 26.-Concentrations of silt and clay and colloidal organic carbon for

sampling cruise 5, June 1989

[ND, not determined]

Sampling site

Silt and clay

organic carbon

determined from

carbon analysis of

isolated silt and

clay fractions

(milligrams per

liter)

Colloidal

organic carbon

determined from

carbon analysis of

isolated colloid

fractions

(milligrams per

liter)

Mississippi River near Winfield, Mo.

Illinois River at Hardin, 111.

Missouri River at Hermann, Mo.

Mississippi River at St. Louis, Mo.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Hickman, Ky.

Mississippi River at Fulton, Tenn.

Mississippi River at Helena, Ark.

White River at Mile 11.5, Ark.

Arkansas River at Pendleton, Ark.

Mississippi River above Arkansas City, Ark.

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss.

Old River Outflow Channel near Knox Landing, La.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

2.9

18.2

13.0

4.0

3.9

2.8

3.4

3.9

4.3

1.4

1.5

3.6

2.7

2.9

3.6

2.3

3.0

1.4

1.1

.8

.8

.8.

ND

.6

.7

.7

.7

.9

.8

1.9

1.0

1.0

.6

.7

The last treatment was to destroy the inorganic constituents of the silt and clay with HC1-HF 

(Leenheer and Moe, 1969), leaving the remaining inorganic materials as an insoluble residue. This 

residue (spectrum D, fig. 15) consisted of proteins and Teflon powder (peaks at 1,220 and

1,169 cm ). The Teflon came from wear of Teflon components in the centrifuge and possibly the 

Teflon bellows pump. From weighing the extracts and residues of this sequential extraction 

procedure coupled with carbon and infrared spectral analyses, only about 50 percent of the total 

organic carbon was extracted by this series of selective extractions. The high protein content was 

believed to cause most of the difficulty in achieving greater extraction efficiencies.

As a result of these extraction experiments, a conceptual model of an organic coating on 

Mississippi River silt and clay was derived (Leenheer, 1991). The mechanistic means (including 

hydrogen-bonding, electrostatic, ligand exchange, and nonpolar partitioning interactions) by 

which a series of organic and inorganic contaminants associate with organic coatings on sediments are illustrated in this model. Lipid structures, into which nonionic organic contaminants 

such as polychlorinated biphenyls can partition, and appear to be important for nonpolar partitioning interactions. Proteins appear to be strongly bound to mineral surfaces through multiple 

interactions, and the proteins also appear to serve as a substrate for binding of humic substances 

and various contaminants.

52 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
4,000 3,500 3,000 2,500 2,000 1,800 1,600 1,400 1,200 1,000

WAVENUMBERS, IN RECIPROCAL CENTIMETERS

800 600 400 200

Figure 15. Infared spectra of organic substances extracted from suspended silt and clay from 

the Mississippi River at Helena, Ark. Spectrum A is from methylisobutyl ketone 

extraction; spectrum B is from acid pyrophosphate extraction; spectrum C is from acid 

dimethylsulfoxide extraction; spectrum D is the organic residue after destroying the 

inorganic substances with a mixture of hydrochloric and hydrofluoric acids.

SAMPLING CRUISE 5, JUNE 1989 53
SAMPLING CRUISE 6, FEBRUARY-MARCH 1990

The sampling of cruise 6 began on the Cumberland River near Southland, Kentucky, on 

February 23,1990, and ended on the Mississippi River below Belle Chasse, Louisiana, on 

March 14,1990. The Cumberland, Tennessee, and Wabash Rivers were sampled for the first time 

during this cruise. Other new sampling sites added during cruise 6 were the Mississippi River 

near Cache, Illinois, and the Ohio River at Uniontown, Kentucky. Sites sampled on cruise 5 that 

were not sampled on cruise 6 were the Mississippi River at Thebes, Illinois, and sites on the Illinois, Missouri, White, Arkansas, Yazoo, and Old Rivers.

Objectives and Approach

An objective of sampling cruise 6 was to examine the Ohio River system in greater detail 

during early spring runoff. Large discharge occurred (about 16,000 m3/s) in the Ohio River as 

compared to an average discharge of 7,700 m3 /s (Moody and Meade, 1993).

With respect to specific project objectives, specific studies of the dissolved organic-carbon fractions in water were discontinued with the exception of measuring and interpreting dissolved 

organic-carbon concentrations. Data obtained on the nature of dissolved organic constituents 

were regarded as sufficient so that time and fiscal resources could be diverted to more specific 

studies of sedimentary organic substances.

All silt and clay fractions from this cruise were extracted with MIBK, and this extract was characterized by 1H-NMR spectrometry to determine if there were significant variations in the nature 

of lipids that act as carriers of organic contaminants on the sediment. The silt and clay fractions 

were not dried before their extraction, using the procedure of Rice and MacCarthy (1989).

Dissolved Organic Carbon

DOC concentrations and transport at the various sampling sites are presented in table 27. 

DOC transport in the Mississippi River downstream from the confluence of the Arkansas and 

White Rivers were about double the transport during the March-April 1989 sampling cruise 

(table 17), during which DOC transport was the highest of the previous cruises. The Arkansas 

and White Rivers, which were not sampled during sampling cruise 6, added significant amounts 

of carbon. Assuming conservative mixing of DOC transport, the DOC concentration inputs from 

the Arkansas and White Rivers were calculated to average 5.4 mg/L. Conservation of DOC transport was observed at the Olmsted, HI., sampling site on the Ohio River for inputs from the Ohio, 

Wabash, Cumberland, and Tennessee Rivers. This conservation of transport is somewhat 

surprising as it took 5 days to obtain samples at all these sites, and the same body of water was 

not being sampled because of the time interval. Conservation of DOC transport also was noted 

at the below Hickman, Ky., site for inputs from the Upper Mississippi and Ohio Rivers.

54 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 27.-Dissolved organic-carbon concentrations and transport for 

sampling cruise 6, February-March 1990

[Transport was computed using water-discharge data reported by Moody and

Meade (1991b)]

Sampling site

Ohio River at Uniontown, Ky.

Wabash River near New Haven, 111.

Cumberland River near Smithland, Ky.

Tennessee River near Calvert City, Ky.

Ohio River at Olmsted, 111.

Mississippi River near Cache, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

Mississippi River above Arkansas City, Ark.

Mississippi River below Vicksburg, Miss.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water 

discharge 

(cubic meters 

per second)

6,620

2,340

2,170

6,570

16,100

4,240

21,000

22,800

23,300

33,200

34,100

26,300

26,700

Dissolved

organiccarbon 

concentration 

(milligrams 

per liter)

3.3

5.0

2.9

2.5

3.4

5.3

3.6

3.7

3.7

4.2

4.2

4.1

3.8

Transport 

(metric tons 

per day)

1,887

1,011

544

1,419

4,730

2,079

6,529

7,292

7,462

12,048

12,381

9,324

8,776

Organic Matter in Suspended-Sediment Fractions

A recovery study was performed during sampling cruise 6 to determine where the significant 

losses were in the field and laboratory processing of suspended-sediment fractions. A coarse silt 

fraction, which was lost into the centrifuge sump during the backflow through the centrifuge 

bowl and bowl-bottom sealing unit during the shutdown procedure, was quantitated by flushing 

the sump with water, measuring the volume, and determining the suspended-sediment concentration by filtration, drying, and weighing. Losses of sediment during laboratory processing 

procedures (sample transfers, centrifugations, freeze-drying, and weighing) were estimated by 

taking a representative aliquot of the suspended silt and clay recovered from the centrifuge before 

laboratory processing and determining sediment concentrations (and mass) by filtration, drying, 

and weighing the filtrate. Comparison with silt and clay weights after laboratory processing gave 

an estimate of laboratory processing loss. The results for samples from nine sites where complete 

sets of data were obtained are presented in table 28.

The major source of suspended-sediment loss was to the centrifuge sump during the shutdown procedure; losses varied between about 8 and 21 percent, and the average loss was 

11 percent. The average loss due to laboratory processing of samples was 5.2 percent, but the variability of the data indicated that variance of the loss determinations was near the variance of the 

losses. The average total recovery for all nine sites was 98.1 percent; the completeness of recoveries, with the exception of the below Hickman, Ky, site for some unknown reason, indicates that 

the two major sources of sediment loss were identified. These results rule out significant losses, 

on a weight-percentage basis of total silt and colloid concentrations, of colloids recovered from the 

ultrafiltration process.

SAMPLING CRUISE 6, FEBRUARY-MARCH 1990 55
Table 28.-Recovery study of suspended-sediment fractions1 from the Ohio, Mississippi, and 

Tennessee Rivers during sampling cruise 6, February-March 1990

[ND, not determined]

Sampling site

Ohio River at

Uniontown, Ky.

Tennessee River near

Calvert City, Ky.

Ohio River at

Olmsted, 111.

Mississippi River below

Hickman, Ky.

Mississippi River below

Fulton, Tenn.

Mississippi River at

Helena, Ark.

Mississippi River above

Arkansas City, Ark.

Mississippi River below

Vicksburg, Miss.

Mississippi River near

St. Francisville, La.

Average recoveries

Percent of 

suspended

sediment1

determined by 

filtration, 

drying, snd 

weighing a 

representative 

siiquot of silt 

end clay 

suspension

recovered 

from

centrifuge

81.0

73.1

80.6

66.6

60.8

67.7

76.7

84.9

77.0

74.3

Percent 

of sus-

 nmjgnj

sediment1 

determined by 

froezedrying 

and 

weighing

a 

representative split

76.3

70.1

66.5

66.1

67.0

65.8

69.5

72.3

68.3

69.1

Percent

laboratory 

drying,

sample

 -- r>a<^«- iransieft 

end 

weighing 

losses 

determined 

by 

subtracting 

data In

second 

columnfrom

data In first

column

4.7

3.0

14.1

.5

-6.2

1.9

7.2

12.6

8.7

5.2

Percent of

suspended 

sediment1 

lost to 

waste 

sump in 

centrifuge 

during 

shutdown

procedure

13.8

7.5

11.3

9.2

20.7

14.8

8.3

8.2

12.4

11.8

Mineralcolloid 

fraction 

recovered

fmnjin. TrOfn

uHraflKer 

(percent of 

suspended

sediment1 )

6.8

20.6

9.3

9.2

10.1

7.4

11.5

11.9

11.6

10.9

Organiccolloid 

fraction 

(percent 

of suspended 

sediment1)

0.3

1.5

.6

.5

ND

.6

ND

.5

ND

.7

Total

accounted 

recovery 

of suspended 

sediment1, 

in

percent

101.9

102.7

101.8

85.5

97.8

90.5

96.5

105.5

101.0

98.1

The sand fraction was not included in suspended-sediment concentrations.

56 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
The findings of this loss study were applied to the calculation of carbon and nitrogen transport 

data from the previous cruises where sources of losses were not yet identified. Calculation of silt 

and clay and colloid distributions by taking silt and clay masses from pumped composite sample 

data and multiplying colloid masses obtained from the depth-integrated composite sample by a 

volume factor difference between the pumped and depth-integrated samples potentially can 

minimize these errors apparent in depth-integrated composite sample data because of the greater 

mass (about 5 times) of silt and clay in the pumped composite sample. This greater mass should 

minimize both the losses due to laboratory processing and the percent of silt and clay lost from 

the centrifuge during shutdown because of greater suspended-sediment loading of the centrifuge 

bowl. Comparison of recovery percentages on the composite sample (with losses figured into the 

appropriate fractions to give valid distributions) with relative percentages calculated from 

combining the pumped composite sample and depth-integrated composite data, as described 

above, are presented in table 29. Within the variance of the data set, the averages show there is no 

detectable bias when the data are calculated by combining pumped composite sample data for silt 

and clay percentages and depth-integrated composite sample data for colloid percentages. Therefore, data in tables 13,18, and 23 were calculated by combining pumped composite sample data 

for silt and clay percentages with depth-integrated composite sample data for colloid percentages.

A more significant error than calculation of sediment distribution percentages might be the 

analysis of carbon and nitrogen in the silt and clay fraction in which the coarse silt, which potentially has a lower organic matter percentage, has been lost. Organic carbon and nitrogen percentages on silt and clay from the pumped composite sample were consistently lower than these 

percentages from the depth-integrated composite sample because the pumped composite sample 

should contain a greater percentage of the coarse silt fraction. Therefore, organic-carbon data on 

the silt and clay from the pumped composite sample also were used for carbon transport calculations. As a result of these recovery studies, a new drain housing assembly was purchased for the 

continuous-flow centrifuge so that this coarse silt fraction could be recovered at the end of a 

centrifuge run without contaminating the sample by recovering it from the sump.

Organic-carbon and nitrogen data for the silt and clay fraction recovered from the FebruaryMarch 1990 sampling are presented in table 30. A significant finding is the abrupt decrease in C:N 

ratios in the Ohio River between Uniontown and Olmsted because of inputs of sedimentary 

organic materials derived from autochthonous sources by the Cumberland and Tennessee Rivers.

Even though the Cumberland and Tennessee Rivers were at high discharge (2,170 m3/s, for the

Cumberland River and 6,570 m3/s for the Tennessee River; Moody and Meade, 1993), it appears 

the reservoirs of the Tennessee Valley Authority (TVA) system were acting as a trap for allochthonous organic-sediment inputs and were exchanging these silts and clays for silts and clays with 

organic material from autochthonous sources, which had been accumulating in the reservoir 

during low-water periods. The Wabash and upper Ohio Rivers do not have significant reservoir 

systems like TVA where this process can occur, and C:N ratios from these rivers were much 

greater. As determined in previous cruises, the Upper Mississippi River also contributes sedimentary organic matter of low C:N ratios into the system. This situation appeared to be the case 

during this sampling of the Mississippi River near Cache, 111. The percent of carbon on the silt and 

clay fraction appeared to decrease downriver; this decrease might have been the result of instream 

mineralization processes of carbon. Resuspension of silt and clay from bottom sediments on 

which carbon mineralization had already occurred may also likely occur during high-water 

periods.

SAMPLING CRUISE 6, FEBRUARY-MARCH 1990 57
Table 29.-Recovery percentages of silt and clay, mineral colloids, and organic colloids in 

the Cumberland, Ohio, Mississippi, Tennessee, and Wabash Rivers during sampling

cruise 6, February-March 1990

[Data in parentheses are relative percentages computed by determining the relative

proportions of silt and clay from the pumped composite sample (plus mineral

colloid plus organic colloids from depth-integrated composite sample) times

(volume of pumped composite sample) divided by volume of depth-integrated

composite sample; ND, not determined]

Sampling site

<

Ohio River at Uniontown, Ky.

Wabash River near New Haven, 111.

Cumberland River near Smithland, Ky.

Tennessee River near Calvert City, Ky.

Ohio River at Olmsted, 111.

Mississippi River near Cache, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

Mississippi River above Arkansas City, Ark.

Mississippi River below Vicksburg, Miss.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Recovery percentage average

Relative percentage average

Percent silt 

and clay 

centrifuged)

94.9

(92.0)

89.7

(83.8)

(83.4)

80.5

(78.3)

91.9

(88.0)

(82.2)

75.8

(88.2)

81.5

(88.7)

82.6

(90.7)

85.1

(88.1)

93.1

(87.2)

89.4

(86.8)

80.3

87.2

(86.5)

Percent mineral 

colloids 

(ultrafiltered 

and centrifuged)

6.8

(6.8)

16.7

(16.8)

(14.4)

20.6

(20.3)

9.4

(11.3)

(16.4)

9.2

(11.2)

10.2

(11.2)

7.4

(8.7)

(11.9)

11.9

(12.3)

11.6

(13.2)

9.6

12.4

(11.5)

Percent 

organic 

colloids 

(ultrafiltered 

and dialyzed)

0.3

(.3)

.7

(.7)

(2.2)

1.5

(1.4)

.6

(.7)

(1.3)

.5

(.6)

ND

ND

.6

.6

ND

.5

.5

ND

ND

ND

.7

(-7)

58 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 30.-Organlc-carbon and nitrogen percentages of the suspended-silt and -clay 

fraction from sampling cruise 6, February-March 1990

Percent organic 

Sampling site carbon of siit 

and ciay fraction

Ohio River at Uniontown, Ky.

Wabash River near New Haven, HI.

Cumberland River near Smithland, Ky.

Tennessee River near Calvert City, Ky.

Ohio River at Olmsted, 111.

Mississippi River near Cache, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

Mississippi River above Arkansas City, Ark.

Mississippi River below Vicksburg, Miss.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

2.65

2.62

2.35

1.99

2.41

2.76

2.19

2.12

2.43

2.11

1.95

2.02

1.72

Percent 

nitrogen of siit 

and clay 

fraction

0.28

.30

.43

.30

.29

.47

.27

.26

.30

.27

.25

.27

.23

Atomic 

C:N ratio

11.04

10.2

6.4

7.7

9.7

6.9

9.5

8.2

8.1

9.1

9.1

8.7

8.7

Determinations of carbon and nitrogen transport on the silt and clay fraction and of the silt 

and clay organic-carbon concentrations are presented in table 31. Transport at the Ohio River sites 

are high, as would be expected during a high discharge period, but the relatively low transport 

and concentrations from the Cumberland and Tennessee Rivers compared to the fact that over 

half of the discharge of the Ohio River at Olmsted, 111., comes from the Cumberland and Tennessee 

Rivers show how efficient the reservoirs of the TVA system are as traps for sedimentary organic 

matter. The sum of the organic-carbon and nitrogen transport for the upper Ohio, Wabash, 

Cumberland, and Ohio Rivers agree moderately well with measured values for the transport in 

the Ohio River at Olmsted, 111. Inputs of silt and clay organic carbon and nitrogen from the White 

and Arkansas Rivers are not as apparent in the Lower Mississippi River as these inputs were for 

the dissolved organic-carbon data in table 27. This is additional evidence that organic carbon and 

nitrogen on the silt and clay fraction is not as conservative as dissolved organic carbon.

Research performed on sampling cruise 5 identified the importance of hydrocarbons, lipid 

esters, and fatty acids extracted by MIBK as carriers of organic contaminants on the suspendedsilt and clay fraction. Numerical relations between MIBK extract yields and organic carbon and 

nitrogen on suspended silt and clay are presented in table 32.

There appears to be an inverse relation trend between extract yield normalized to carbon 

content and the atomic C:N ratio for the first seven sampling sites in table 32. At sites farther 

downstream, this relation breaks down; instream mineralization of organic matter and resuspension of low-organic-carbon silts and clays may obscure the trends in this data set for the samples 

in the lower portion of the Mississippi River. The relation of extract yield with atomic C:N ratios 

indicates extractable hydrocarbons and lipids are related to the nature of the source of organic 

matter. To obtain additional characterization of these MIBK extracts, H-NMR spectra of the 

extracts were determined.

SAMPLING CRUISE 6, FEBRUARY-MARCH 1990 59
Table 31 .-Transport of silt and clay organic carbon and nitrogen and silt and clay 

organic-carbon concentrations from sampling cruise 6, February-March, 1990

[Water discharge and suspended-sediment-concentration data used to compute 

transport are reported by Moody and Meade (1991b)]

<

Sampling site

(

Ohio River at Uniontown, Ky.

Wabash River near New Haven, 111.

Cumberland River near Smithland, Ky.

Tennessee River near Calvert City, Ky.

Ohio River at Olmsted, 111.

Mississippi River near Cache, 111.

Mississippi River below Hickman, Ky.

Mississippi River below Fulton, Tenn.

Mississippi River at Helena, Ark.

Mississippi River above Arkansas City, Ark.

Mississippi River below Vicksburg, Miss.

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Organic-carbon 

transport on 

suspended silt 

and clay 

metric tons per 

day)

2,851

660

118

430

4,248

961

5,535

5,225

6,511

6,719

6,290

3,901

4,450

Nitrogen 

transport on 

suspended 

slit and clay 

(metric tons 

per day)

301

76

22

65

511

163

682

641

804

860

806

521

595

Organiccarbon 

concentration 

on suspended 

silt and clay 

(milligrams 

per liter)

5.0

3.3

.6

.8

3.1

2.4

3.0

2.7

3.2

2.3

2.1

1.7

1.9

Table 32.-Relations between methylisobutyl ketone (MIBK) extract yields and 

organic carbon and nitrogen on suspended silt and clay from sampling cruise 6,

February-March 1990

Sampling site

Ohio River at Uniontown, Ky. 

Wabash River near New Haven, 111. 

Cumberland River near Smithland, Ky. 

Tennessee River near Calvert City, Ky. 

Ohio River at Olmsted, 111. 

Mississippi River near Cache, 111.

Mississippi River below Hickman, Ky. 

Mississippi River below Fulton, Tenn. 

Mississippi River at Helena, Ark. 

Mississippi River above Arkansas City, Ark.

Mississippi River below Vicksburg, Miss.

Mississippi River near St. Francisville, La. 

Mississippi River below Belle Chasse, La.

Percent MIBK extract yield 

of silt organic carbon

2.5 

1.6 

5.1 

3.2 

2.2 

8.8

3.8

2.5 

1.4 

3.4

3.8

2.0 

1.2

Atomic C:N ratio

11.04 

10.2 

6.4 

7.7 

9.7 

6.9

9.5 

8.2 

8.1 

9.1

9.1

8.7 

8.7

60 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Two general types of 1H-NMR spectral patterns are shown in figure 16. Extracts from silts and 

clays with low C:N ratios (autochthonous source term) gave spectra similar to spectrum A, figure 

16, whereas extracts from silts and clays with high C:N ratios (allochthonous source term) gave 

spectra similar to spectrum B, figure 16. The composition of the extract of spectrum A appears to 

be straight chain acids, lipids, and hydrocarbons (peaks 1 and 2), with some olefinic hydrocarbons 

(peak 4) in the mixture. The extract of spectrum B differs from spectrum A in that the peak height 

ratio of peak 1 to peak 2 is greater, meaning there are more branched hydrocarbon components. 

Peak 3 is also much greater in spectrum B. Peak 3 may be indicative of methyl groups attached to 

a doubly-bonded carbon, as is found in plant pigments such as the carotene hydrocarbons. No

specific organic contaminants or classes of organic contaminants were detected in the 1H-NMR 

survey of MIBK extracts of suspended silts and clays.

SAMPLING CRUISE 6, FEBRUARY-MARCH 1990 61
Numbers denote peaks where peak height: 

were measured

76543 

CHEMICAL SHIFT, IN PARTS PER MILLION

Figure 16. 1H-nuclear magnetic resonance spectra of methylisobutyl ketone extracts of

suspended silt sampled from the: (A) Mississippi River near Cache, 111., and (B) Wabash 

River near New Haven, 111., sampled February-March 1990.

62 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
SAMPLING CRUISE 7, MAY-JUNE 1990

The downstream sampling leg of cruise 7 began on the Illinois River at Valley City, Illinois, on 

June 7,1990, and ended on the Mississippi River below Belle Chasse, Louisiana, on June 27,1990. 

The Mississippi River sites sampled during the downstream leg of cruise 7 were below Grafton, 

Illinois; a special sample at St. Louis, Mo.; at Thebes, Illinois; below Memphis, Tennessee; below 

Vicksburg, Mississippi; near St. Francisville, Louisiana; and below Belle Chasse, Louisiana. Tributary sampling sites were the Illinois River at Valley City, Illinois; the Ohio River at Olmsted, Illinois; and the Yazoo River below Steele Bayou, Miss.

Approach and Objectives

The primary purpose of the seventh sampling cruise was to conduct a study of dissolved 

trace-metal concentrations in the lower Mississippi River supported by the National Stream 

Quality Accounting Network. However, the general long-term studies of organic-carbon and 

nitrogen transport in the dissolved and particulate phases were also continued during this cruise.

The major specific objective of sampling cruise 7 was to develop improved methodology for 

the characterization of organic substances in bed and suspended sediments. Therefore, a number 

of bed-and suspended-sediment samples were obtained during this cruise for the development of 

methods for organic-substance characterization that can be related to contaminant fate and transport. Data on extraction of organic substances from suspended sediment obtained on sampling 

cruise 5 indicated that it was impossible to extract and characterize more than 50 percent of the 

carbon on the sediment fractions. Therefore, an alternative strategy begun on sampling cruise 7 

was to find a way of enriching the carbon on sediment fractions by dissolving the inorganic 

substances without altering the organic substances. The objective of this approach was to obtain

high-quality solid-state 13C-NMR spectra on the carbon in the various sediment fractions. These 

spectra could then be related to organic structure composition and variation in a manner analogous to the use of 1H-NMR to characterize the dissolved organic-substance fractions in water.

Dissolved Orosnic Csrbon

DOC concentrations and transport for the Mississippi River and some of its tributaries 

sampled in May-June 1990 are presented in table 33. This was the first sampling performed while 

the Upper Mississippi River and Missouri River were at high discharges. Organic-carbon transport at the Grafton, 111., and Thebes, 111., sites were the greatest for these locations on any sampling 

cruise. DOC inputs from the Missouri River doubled the transport on the Mississippi River 

between Grafton and Thebes. Based on this transport doubling and the increase in discharge, the 

DOC concentration of the Missouri River was computed to be 4.5 mg/L.

Not only were the transport values elevated for these high-discharge conditions, but the DOC 

concentrations were increased 1-3 mg/L over concentrations observed during the low-discharge 

conditions of the first three cruises. During sampling cruises 6 and 7, inputs of water high in DOC 

concentrations upstream from the Mississippi-Ohio Rivers confluence raised the DOC concentrations and transport in the Mississippi River downstream from this confluence. Instream degradation of DOC, observed during the first and third cruises, does not seem to be a significant process 

during high-discharge conditions.

SAMPLING CRUISE 7, MAY-JUNE 1990 63
Table 33.-Dissolved organic-carbon concentrations and transport for sampling cruise 7,

May-June 1990

[Water-discharge data used to compute transport were reported by 

Moody and Meade (1993)]

Sampling site

Illinois River at Valley City, 111.

Mississippi River below Grafton, 111.

Mississippi River at Thebes, 111.

Ohio River at Olmsted, 111.

Mississippi River below Memphis, Tenn.

Mississippi River below Arkansas City, Ark. 

Yazoo River below Steele Bayou, Miss.

Mississippi River below Vicksburg, Miss. 

Mississippi River near St. Francisville, La.

Mississippi River below Belle Chasse, La.

Water 

discharge 

(cubic meters 

per second)

1,230

5,040

12,600

9,550

20,800

25,500 

1,250

27,300 

23,200

23,300

Dissolved

organiccarbon 

concentration 

(milligrams 

per liter)

4.6

5.8

5.0

3.3

3.9

4.1 

5.0

3.9 

3.8

4.2

Dissolved

organiccarbon 

transport 

(metric tons 

per day)

489

2,526

5,443

2,723

7,009

9,019 

540

9,196 

7,617

8,455

Organic Matter in Suspended and Bed Sediments

A somewhat limited set of data on suspended-sediment composition, concentrations, and 

transport was available when this report was written. Available data are presented in table 34. 

Because of the high discharges encountered from the Upper Mississippi and Missouri Rivers, 

record-high transport and concentrations of carbon and nitrogen were measured at the Thebes, 

HI., sampling site on the Mississippi River. Most of this transport was input by the Missouri River 

between the Grafton, 111., and Thebes, 111., sites. The relatively high C:N ratio of 10.2 for organic 

matter on the suspended silt and clay at Thebes indicates an allochthonous origin. The decrease 

in transport in the downriver direction probably is not significant because this sampling cruise 

was not designed to sample the same body of water as it flows downstream (Lagrangian 

sampling).

The suspended- and bed-sediment samples collected during sampling cruise 7 were prepared

for solid-state 13C-NMR spectral analysis by dissolving interfering inorganic constituents (especially iron) without losing or altering sedimentary organic matter. A flow chart of selective 

mineral dissolution procedures is presented in figure 17.

The acid pyrophosphate procedure (Gregor and Powell, 1986) was placed first in the sequence 

to remove calcium and magnesium minerals that would form insoluble oxalates in the following 

extraction if they were not removed. Acid pyrophosphate solution also removes some of the iron. 

The next step, use of 0.15 molar oxalic acid at pH 3, was previously determined (Parfitt, 1989) to 

be the most efficient extractant for removing amorphous aluminum, iron, and silicon from soils.

64 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 34.-Composition, concentrations, and transport of carbon and nitrogen in the 

suspended-silt fractions for sampling cruise 7, May-June 1990

[Water-discharge and suspended-sediment-concentration data used to compute 

transport were reported by Moody and Meade (1993); ND, not determined]

Silt

Perce1

site Percent Atomic concenCarbon 

tr "8P°rt

Illinois River at 

Valley City, 111.

Mississippi River below 

Grafton, 111.

Mississippi River at 

Thebes, 111.

Ohio River at

Olmsted, 111.

Mississippi River below 

Memphis, Tenn.

Mississippi River below 

Arkansas City, Ark.

Mississippi River below 

Vicksburg, Miss.

Mississippi River near 

St. Francisville, La.

Mississippi River below 

Belle Chasse, La.

carbon

2.98

2.24

1.83

1.83

2.06

1.92

2.00

1.83

2.03

iiiuwycn

0.41

.28

.21

.24

.24

.24

.27

.24

.26

\S.I1 IdUVI

8.5

9.7

10.2

8.9

10.0

9.3

8.6

8.9

9.1

t 11 dllWI 1

(milligrams 

per liter)

2.6

9.7

19.2

2.9

ND

ND

5.1

2.9

3.2

tons per 

day)

280

4,233

20,918

2,395

ND

ND

12,024

5,905

6,375

tons per 

day)

39

528

2,400

314

ND

ND

1,398

774

816

The pyrophosphate and oxalate extractants also release adsorbed fulvic acid, which is recovered 

by adsorption chromatography on XAD-8 resin. The two hydrofluoric acid treatments were 

performed under dilute acid conditions at room temperature because a previous study (Preston 

and others, 1989) found that high concentrations (2.88 molar) and long reaction periods needed to 

completely remove silicates destroyed the carbohydrate portion of organic matter through acid 

hydrolysis. Dilute hydrofluoric acid destroys only hydrous silicates (clay minerals), but it does 

not attack silicon oxides (quartz).

Gentle mixing of the samples inside the dialysis tubing was achieved by placing the tubing 

inside a 1-L wide-mouth polyethylene bottle with the extracting solutions and rotating the bottle 

attached to the rim of a bicycle wheel at six revolutions per minute. This rotation resulted in a 

gentle inversion of the sediment inside the dialysis tubing so that the sediment mixed without 

physically abrading the tubing. The cellulose acetate dialysis tubing was chemically stable to all 

the extracting solutions, and it greatly facilitated the separation of colloidal sediments from the 

extracting solutions without filtration or centrifugation steps being necessary.

SAMPLING CRUISE 7, MAY-JUNE 1990 65
Rinse column with 

1 I of 0.01 mHCt

Solution phase {complexed

Ca2+, Mg 2+, Fe 2+, Fe3+ 

pyrophosphates, fulvic acid)

Solution phase (complexed

Fe 2+, Fe3+, AI3+ 

oxalates, fulvic acid)

Combine pyrophosphates and

oxalate extracts, adjust to

pH 2 with HCI

Elute fulvic acid from column with! 

500 ml of 75% acetonitrite, 

25% aqueous 0.01 m HCI

500 ml column Amberlite 

XAD-8 resin

Discard pyrophosphate and

oxalate eluent solutions

and water rinse

3 grams sediment in 10 ml water inside

1,000-dalton pore-size cellulose

acetate dialysis tubing

_L

24-hr treatment with 1 I of 0.1 M sodium 

pyrophosphate acidified to pH 2 with HCI

24-hr treatment with 1 I of 

0.15 m oxalic acid, pH 3

2-successive 24-hr treatments 

with 0.1 m HF

Sediment

24-hr treatment with 

1 I of distilled water

Discard HF solution 

(H 2 SiF6 &H2AIF6)

Fulvic acid eluted by 

acetonitrite, water mixture

Vacuum evaporate acetonitrite, 

dissolve fulvic acid in water

Combine

Discard water 

and rinse

Freeze-dry treated sediment

Figure 17. Flow chart of procedures used to prepare sediment samples for solid-state 

13C-nuclear magnetic resonance spectral analysis.

The effect of selective mineral-dissolution treatments on suspended silts and clays and bottom 

muds on organic-matter recovery and composition is presented in table 35. The treatments 

removed an average of 59 percent of the weight of the suspended-silt and -clay samples and an 

average of 48 percent of the weight of the bottom mud samples. An average of 12 percent of the 

organic carbon was lost by these treatments, and increases in the C:N ratios indicated selective 

loss of organic-nitrogen compounds. The loss may be caused by low-molecular-weight amines 

and amino acids, which are released during the dilute acid treatments and these nitrogen 

compounds are too small to be retained by the dialysis membrane. The organic-carbon content 

was approximately doubled by the treatments; this doubling of organic-matter content is advantageous for 13C-NMR spectral analysis. Infrared studies of these sediments after treatment indicated remaining mineral matter was largely quartz and mineral fluorides, such as magnesiumrich clays converted to insoluble magnesium fluorides.

66 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
Table 35.-Effect of selective mineral dissolution treatments on suspended-silts and -ciays 

and bottom muds on organic matter recoveries and composition

Sampling site and 

sample

Per- Percent cent 

carbon carbon 

before after 

treat- treatment ment

Per- Percent cent 

nitro- nitrogen gen 

before after 

treat- treatment ment

Percent Atomic Atomic 

or- C:N C:N

gen gen JT" ganic before after 

efore after W«*'SIU car. treat- treatbon 

ioss

Percent

loss

treatment

2.14 4.98

1.26 2.67

1.78 3.42

.14 .26 45.94 -12.8 10.5

treatment

10.0

.25 .56 63.47 15.0 10.0 10.4

12.0

Illinois River at 

Valley City, HI. 

Suspended silt 3.23 7.27 0.44 0.85 60.75 11.7 8.6

and clay

Mississippi River below 

Grafton, HI. 

Suspended silt

and clay 

Bottom mud 

Mississippi River at 

St. Louis, Mo. 

Suspended silt

and clay

Mississippi River at 

Thebes, HI.

Suspended silt 1.82 3.64 .21 .36 57.60 15.2 10.1 11.8 

and clay

Bottom mud 1.17 1.88 .16 .18 48.82 17.8 8.5 12.2 

Ohio River at 

Olmsted, 111.

.20 .32 52.11 8.0 10.4 12.5

Suspended silt 

and clay

Bottom mud

2.08

1.44

4.52

3.02

.24

.16

.46

.27

60.2

48.5

13.5

10.5

10.1

13.0

11.5

13.1

A recent advance in 13C-NMR spectrometry is the development of large-sample, magic-angle 

spinners that provide enhanced signal-to-noise ratios in the spectra (Zhang and Maciel, 1990). 

This new technology was applied to both treated and untreated suspended silts sampled at 

St. Louis, Mo. The results are shown in figure 18. Results on the untreated sample (spectrum A) 

are superior to previous results obtained with the small-volume, magic-angle spinner used for the 

colloids from sampling cruise 1 (fig. 5); and results on the treated sample (spectrum B) gave much 

better resolution of peaks than the untreated sample (spectrum A). The spectral band-broadening 

problem caused by iron in the untreated sample was solved by the treatment procedure, and the 

peak resolution and interpretation of the spectra were facilitated in spectrum B.

SAMPLING CRUISE 7, MAY-JUNE 1990 67
The organic matter of this silt and day fraction appears to be a mixture of aliphatic hydrocarbons (peak at 30 ppm), carbohydrates (peak at 80 ppm), aromatic hydrocarbons (peak at 130 

ppm), and carboxyl and amide functional groups (peak at 175 ppm) (fig. 18, spectrum B). Organic 

amines that occur near 45 ppm may have been lost from the sample by the treatment process. 

There was no detectable destruction of carbohydrates by acid hydrolysis during the treatment 

procedure in comparing the ratio of carbohydrate peaks to other peaks in the treated and 

untreated samples.

This knowledge of organic-matter structure can now be applied to studies of contaminant 

association with sediment. For example, nonionic, nonpolar organic contaminants such as PCB's 

are known to partition into aliphatic and aromatic hydrocarbon components of organic matter, 

and trace-metal contaminants are known to bind with carboxyl and amide functional groups.

CO

CO

<

LU 

QC 

O

I

400 350 300 250 200 150 100 50 0- -50

CHEMICAL SHIFT, IN PARTS PER MILLION

-100 -150 -200 -250

Figure 18.-Solid-state 13C-nuclear magnetic resonance spectra of (A) untreated and 

(B) treated for iron removal of suspended silt and clay sampled from the 

Mississippi River at St. Louis, Mo., in June 1990.

68 DATA ON NATURAL ORGANIC SUBSTANCES IN DISSOLVED, COLLOIDAL, SUSPENDED-SILT AND -CLAY, 

AND BED-SEDIMENT PHASES IN THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES, 1987-90
CONCLUSIONS

Following are seven significant conclusions from this study that are arranged in order of 

decreasing importance:

1. The organic-carbon component in both the mineral-colloid fraction and organic-colloid 

fraction appears to be transported conservatively in river reaches and at river confluences 

where there are significant gains or losses in carbon in the silt fractions. It appears that 

organic-matter content is the major component that prevents colloid aggregation in 

Mississippi River suspended particulates of colloidal dimensions.

2. The discovery of polyethylene-glycol residue as the major anthropogenic organic contaminant in the Mississippi River (Leenheer and others, 1991).

3. Characterization of the entire dissolved organic-matter component under varying hydrologic and seasonal conditions revealed it originated from a variety of allochthonous and 

autochtonous sources. The isolation and characterization of the hydrophilic component 

of dissolved organic matter indicated oxidized carbohydrates as the major component of 

hydrophilic acids. Dissolved organic matter is usually transported in a conservative 

manner except during low-water periods of the summer when biodegradation processes 

were significant.

4. Development of a method to obtain solid-state, 13C-NMR spectra of organic matter in sediments revealed that sedimentary organic matter consists of a mixture of lipids, carbohydrates, proteins, and humic substances. Progress in organic geochemical studies of 

sediments is partially dependent on advances in NMR spectrometry.

5. Characterization of sedimentary organic matter revealed that proteins, that are important 

in trace-metal binding, and lipids, that are important in nonpolar contaminant partitioning interactions, are major constituents of sedimentary organic matter. Proteins, in 

particular, are not generally recognized as being important as humic substances in aquatic 

sediments.

6. The data in the report provide extensive evidence that (A) Pools and reservoirs are traps 

for sedimentary organic matter of allochtonous origin, and (B) Navigation pools and reservoirs export organic material of autochthonous origin that is rich in nitrogen. These findings are not new and unique, but there is good quantitative transport data of organic 

carbon and nitrogen under varying hydrologic conditions that may help resource 

managers better understand the management of the Mississippi River system.

7. The quantisation of the bacterial organic colloid component of organic matter transported 

in the river. The magnitude of the mass of bacteria and bacterial organic carbon being 

transported is a significant finding. The bacterial carbon transport appears to be more 

conservative than the organic carbon associated with the silt fraction.

CONCLUSIONS 69
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Geological Survey Open-File Report 87-557,377 p.

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of Soil Science, v. 37, p. 577-585.

Hayes, M.H.B., 1985, Extraction of humic substances from soils: in Aiken, G.R., McKnight, D.M., 

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