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The organic carbon load during 1969-70 of each of the six rivers in this study is substantial. The 3.4-billion-kilogram (3.7-million-ton) and 47-million-kilogram (52-thousandton) annual organic carbon loads of the Mississippi River and the Brazos River (Tex.), respectively, were approximately equally distributed between dissolved and suspended phases, whereas the 725-million-kilogram (79.8-million-ton) organic load of the Missouri River was primarily in the suspended phase. The major portion of the 6.4-million-kilogram (7.3thousand-ton) and the 19-million-kilogram (21-thousand-ton) organic carbon loads of the Sopchoppy River (Fla.) and the Neuse River (N.C.), respectively, was in the dissolved phase. DOC (dissolved organic carbon) concentrations in most rivers were usually less than 8 milligrams per litre. SOC (suspended organic carbon) concentrations fluctuated markedly with discharge, ranging between 1 and 14 percent, by weight, in sediment of most rivers. DOC concentrations were found to be independent of discharge, whereas SOC and SIC (suspended inorganic carbon) concentrations were positively correlated with discharge. Seasonal fluctuations in DOC and SOC were exhibited by the Missouri, Neuse, Ohio, and Brazos Rivers, but both SOC and DOC concentrations were relatively constant throughout the year in the Mississippi and Sopchoppy Rivers. The carbon-nitrogen ratio in the sediment phase of all river waters averaged les~ than 8 : 1 as compared with 12:1 or greater for most soils. This high nitrogen content shows a nitrogen enrichment of the stream sediment over that in adjacent soils, which suggests tha* different decomposition and humification processes are operating in streams than in the soils. The abundance of organic material in the dissolved and suspended phase of all river waters in this study indicate a large capacity factor for various types of organic reactivity within all streams and the quantitative importance of organic constituents in relation to the water quality of rivers and streams. INTRODUCTION Organic substances in river waters and river sediments are very diverse in quality, quantity, and source. Hundreds of new organic compounds are synthesized each year, with many of them finding their way into the streams and other surface waters as a result of man's activities. Some of the Fl F2 ORGANIC SUBSTANCES IN WATER major sources of these organic substances include plant and animal debris deposited in a stream from terrestrial sources, wastes from municipal treatment facilities, industrial wastes, and eutrophic activity within the stream itself. This complex assemblage of carbonaceous organic material has been found to significantly influence water quality. Organic substances found in stream water can affect the distribution of ions between water and sediment phases carried in the stream (Baas-Becking and Moore, 1959; Jenne and Wahlberg, 1968; Jenne, 1968; Glenn, 1973; Jenne, 197f). Organic substances can solubilize clay minerals (Malcolm and others, 1969), can strongly complex certain trace metals (Malcolm and others, 1969; Malcolm, 1972; Schnitzer and Kahn, 1972), and can have a high cationexchange capacity as compared with clay minerals (Kennedy, 1965; Malcolm and Kennedy 1970; Schnitzer and Kahn, 1972). Organic materials are food sources for the diversity of heterotrophic microorganisms which thrive in streams. The nitrogen and phosphorous components of organic substances on sediment partirles and dissolved in water are significant sources of nutrients for alga~ and other autotrophic organisms. DOC (dissolved organic carbon) has also been associated with nuisance algae blooms (Wright and Mills, 1967; King, 1970; Forester, 1972). Because of the various roles and reactivity of organics within the stream, the amount of these substances must be determined in representative streams such that the magnitude of the preceding reactions can be established. The carbon content of surface water has not been studied in a systematic manner, largely because of the poor accuracy and the lack of precision of chemical methods. Recent advances in technology with various types of carbon analyzers has enabled the accurate determination of all organic carbon in the dissolved and sediment phases in water. Brooks (1970) found that the DOC concentrations in the Brazos River ranged from 2.8 to 7.0 mg/1 during the spring of 1970. POC (paniculate organic carbon) varies between 1 and 16 mg/1, but was generally less than DOC concentrations. During a 1-year study, Weber and Moore (1967) reported that the DOC of the Little Miami River at Cincinnati, Ohio, averaged 6.4 mg/1 and showed no seasonal cycle. Fredericks and Sackett (1970) determined the mean DOC and POC concentrations in the Gulf of Mexico to be less than 1 mg/1 and 0.2 mg/1, respectively. PO^l (particulate organic carbon) and SOC (suspended organic carbon) are essentially synonomous terms, except for method dependency. POC has been associated with glass-fiber filtration, whereas SOC has been associated with plastic or metal filtration. POC values should be slightly lower than SOC values because most glass fiber filters have a larger average pore size (typically 2 /im (micrometres)) whereas plastic and metal membrane ANNUAL ORGANIC CARBON LOAD OF SIX U.S. RIVERS F3 filters are typically 0.45 p.m with a narrow range of pore sizes. Therefore, POC values are usually lower than SOC values because some of the particulate organic material between 0.45 /urn and 2 /urn passes through the glass filter and is included in the DOC phase. DOC and SOC are quantitative organic water quality parameters, whereas CCE (carbon chloroform extract) and CAE (carbon clcohol extract) are only qualitative indices of organic water quality in the dissolved phase. Suspended sediment is not usually included in the CCE or CAE determination. The CCE and CAE methods are based upon the extraction of organic substances onto activated charcoal columns with subsequent elution from the charcoal with chloroform or alcoho1 . Such methods are only qualitative because the relative percentage of all the organic compounds in the water which are sorbed by the charcoal is not determined. The relative recovery of the sorbed organic compounds from the activated charcoal by solvent elution is also not determined. ACKNOWLEDGMENTS Appreciation is expressed to the many U.S. Geological Survey personnel who made this study possible. Included are Robert J. Steiert, Louisville, Ky,; Duane Everett, Baton Rouge, La.; Roy B. Stone, Tallahassee, Fla.; Howard E. Reeder and Rufuss J. Alien, Raleigh, N.C.; Guadalupe Ramos and Carl A. Heinrich, Houston, Tex.; and Sarford C. Down, Lincoln, Nebr., who collected and filtered the water samples from the various rivers of this study. APPROACH AND OBJECTIVES The Missouri, Mississippi, Ohio, Brazos (Tex.), Neuse (N.C.), and Sopchoppy (Fla.) Rivers are representative streams found within different climatic regions within the United States. Inorganic water chemistry, discharge, sediment load, and other hydrologic parameters of these rivers are routinely monitored by the U.S. Geological Survey. Because Surrey personnel must regularly visit these monitoring stations for equipment maintenance and water sampling, this situation enabled the periodic additional collection of suspended-sediment and water samples for organic analyses. The overall objective of this study is to learn more about the quantity and quality of organic matter as organic carbon and nitrogen that is transported by major streams of the United States. During the 1-year reconnaissance study, it was intended that sufficient data be collected fcr a given stream to establish changes in organic concentrations and load with season of the year and discharge, to evaluate the relative importanre of the dissolved organic load to the paniculate organic load, and to estimate the annual dissolved and suspended organic load of the river. F4 ORGANIC SUBSTANCES IN WATER EXPERIMENTAL METHODS SAMPLE COLLECTION The six participating U.S. Geological Survey District Offices were asked to collect a total of 15-20 composite ETR (equal transit rate) samples from each of the selected streams over a period of 1 year. Samples were to be taken whenever large changes in streamflow cr chemistry occurred such that possible changes in organic load and distribution would be detected. The sampling sites were as follows: Neuse River near Goldsboro, N.C. (ETR sample from bridge); Brazos River at Richmond, Tex. (ETR sample from bridge); Ohio River at Metropolis, 111. (ETR sample from Paducah Dam); Mississippi River near Luling Ferry, La., St. Francisville, La., and Belle Chasse, La. (ETR sample obtained by pumping from boat); and Missouri River at Nebraska City, Nebr. (pumping point sample from 4 ft above the bed at the quality water monitor); and the Sopchoppy River near Sopchoppy, Fla. (ETR sample from bridge). An index map giving the locaion of the six rivers and respective sampling sites is shown in figure 1. SAMPLE FILTRATION AND PRESERVATION A 4to 10-litre ETR sample was collected at each sampling. The exact volume of each sample, date and time of collection, river temperature and gage height, and name of collector were noted on the samp'e tag. The ETR sample was immediately pressure filtered at the site or taken to the laboratory with an elapsed transit time of less than 6 hours. The pressure filter used was as described by Skougstad and Scarbro (1958). The plexiglass barrel was fitted with a 4-inch 0.45 /Am vinyl metracel filter. Maximum filtration pressure by tire pump or compressed nitrogen never exceeded 40 lb/in2 (pounds per square inch). The pressure filter assembly was refilled with unfiltered sample as necessary and the first 75 percent of the sample filtrate was discarded. Then 65-75 ml of sample filtrate was collected in a 100-ml plastic bottle, labeled, and immediately frozen. The vinyl metrical membrane filter was leached with 2 or more

Organic carbon and nitrogen concentrations and annual organic carbon load of six selected rivers of the United States