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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

water-resources investigations report

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