Humic Substances in the Suwannee River, Georgia: Interactions, Properties, and Proposed Structures
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Humic Substances in the Suwannee River, Georgia: Interactions, Properties, and Proposed Structures United States Geological Survey Water-Supply Paper 2373 Humic Substances in the Suwannee River, Georgia: Interactions, Properties, and Proposed Structures Edited by R.C. AVERETT, J.A. LEENHEER, D.M. McKNIGHT, and K.A. THORN This volume is published as chapters A-R These chapters are not available separately. U.S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER 2373 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U. S. Government. UNITED STATES GOVERNMENT PRINTING OFFICE: 1994 For sale by U.S. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Humic substances in the Suwannee River, Georgia : interactions, properties, and proposed structures / edited by R.C. Averett [et al.] p. cm. (U.S. Geological Survey Water-Supply Paper; 2373) Includes bibliographical references. Supt.ofDocs.no.: 119.13: 2373 1. Humic acid. 2. Water chemistry. 3. Hydrology Okefenokee Swamp (Ga. and Fla.) I. Averett, R.C. II. Geological Survey (U.S.) III. Series. GB857.2.043H86 1995 551.48 dc20 93-27314 CIP FOREWORD Humic substances as a collective term and humic and fulvic acids as spe cific terms are not household words. For about a century, these terms belonged to the domain of the soil scientist. Even though their chemical structures remained elusive, they were recognized as important entities in soil. During the past decade or so, there has been a renewed interest in humic substances in soil and water. Such interest has resulted from improved analytical instrumentation and by a need to understand the structure and function of natural organic substances in water. A responsibility of the U.S. Geological Survey is to assess the Nation's water resources; this includes assessing water quality, which is the study of mate rial in water. Such material may be suspended, colloidal, or in true solution. Because humic substances are a major carbon source in water, they have received attention by Geological Survey scientists. This attention has been a major focus by members of the Geological Survey's organic chemistry group. For more than a decade, this group has collected samples, made analyses, and worked toward determining the structure and function of humic substances in water. Their work has brought worldwide recognition to the field and, through Geological Survey support, in 1981 they helped organize the International Humic Substances Society, which held its first meeting in Estes Park, Colorado, in August 1983. At the second meeting of the Society in Birmingham, England, in August 1984, it became apparent that Geological Survey scientists were rapidly advancing the study of the chemistry of humic substances. It is appropriate, therefore, to pub lish this Water-Supply Paper on humic and fulvic acids from the Suwannee River in Georgia because these results represent the Survey's most definitive findings to date (1986). Though this work is not conclusive, it is state-of-the-science. Hope fully, the reporting on this work will aid in advancing the science of humic substances. Philip Cohen Chief Hydrologist ui PREFACE This Water-Supply Paper is concerned with for this reason that the study of the Suwannee River state-of-the-science chemistry of humic and fulvic began it is rich in organic matter as a result of flowing acids from the Suwannee River in Georgia. Humic and from the Okefenokee Swamp. Organic-matter produc fulvic acids are specific entities in the broad category tion is the driving force for all ecosystems; it controls, of humic substances. Although the broad subject in the through bacterial decomposition, dissolved-oxygen chapters that follow concerns humic substances, the resources in aquatic systems. But there are other primary focus will be on fulvic acids from the Suwan reasons to study humic substances in water. Humic nee River. After a decade of study, there is an im substances interact with contaminants, such as pesti proved understanding of the interactions, properties, cides. Moreover, humic substances chelate and trans and structures of fulvic acids that comprise the major port trace metals and are a source or sink for these fraction of dissolved organic substances in water. metals. Humic substances also are a source or sink for Most of the authors of the chapters that atmospheric carbon dioxide, which is a buffer against follow are research hydrologists with the U.S. Geo acidic precipitation. Finally, they have great effect on logical Survey located in Denver, Colorado. As the fertility and moisture-holding capacity of soil. project personnel, they work on specific facets of Modern instrumentation, especially nuclear-magnetic- organic chemistry, primarily natural organic matter in resonance spectrometers, gas chromatographs, and water. As a group, they devote some of their time mass spectrometers, has aided in advancing the deter and skill to the study of humic substances in water. mination of structural models of humic substances. This group focus on humic substances is not acciden Proposed structural models are presented in this Water- tal: it is an organized effort to understand the struc Supply Paper. As the "black box" of humic-substance ture and to improve definition of the function of chemistry is opened, our understanding of the inter humic substances in nature. actions, properties, and structures of humic substances The study of humic substances is not a new increases this aids our understanding of water chem scientific activity with regard to soil chemistry; it is, istry and, ultimately, of aquatic ecosystems. however, a relatively new field with regard to aquatic However, science continues to evolve, and the systems. Soil textbooks written before the turn of the findings in this Water-Supply Paper are part of the evo 20th century discuss humic substances and fulvic and lution of humic-substance chemistry. Because the humic acids. These discussions are brief: descriptions authors of the following chapters are at the forefront of of chemical properties are limited to color and solubil the science, it is time to share the information they have ity. Only during the past decade or so has the study of gathered and the knowledge they have gained share, humic substances provided a much clearer understand that is, with the full realization that, in this rapidly ing of the chemistry and economic and ecological changing field, the ideas and concepts presented here importance of these substances. may one day may be outdated or determined to be The authors of the chapters in this Water- incorrect. But that, too, is a characteristic of science. If Supply Paper have contributed extensively to the this Water-Supply Paper serves only as a historical understanding of humic substances in water. To fur benchmark, it will have served its purpose. If it helps ther expand the understanding of humic substances in the science of humic-substance chemistry to progress water and soil, the International Humic Substances by stimulating other scientists, or if it provides others Society was established with the support of the U.S. with a greater appreciation of this field of science, it Geological Survey. will have accomplished more than we had planned. Why do we study humic substances in water? That question would have been simple to answer a decade or so ago because we knew then only that they R.C. Averett were important components of the soil. Today, as our J.A. Leenheer knowledge expands, there are numerous reasons to D.M. McKnight study humic substances in water. Perhaps most impor K.A. Thorn tantly, humic substances constitute a large proportion Editors of the organic matter (carbon) in aquatic systems. It is IV ACKNOWLEDGMENTS Professor Michael A. Mikita, California State University at Bakersfield, deserves credit for stressing the importance of spatial relations of functional groups in structural models of fulvic acid from the Suwannee River. His partici pation with the research group of authors in this volume and his technical review of several reports in this volume were invaluable. Professor Jacob A. Marinsky, State University of New York, Buffalo, contributed his understanding of the pro- tonation and metal-ion complexation equilibria of fulvic acid from the Suwannee River. Professors Stephen Cabaniss, Harvard University, and E. Michael Perdue, Georgia Institute of Technology, deserve special thanks for the difficult task of reviewing the summary chapter of this volume (chapter P). CONTENTS [Letters designate chapters] Foreword......................................................................................................^ Ill Preface .................................................................._^ IV Acknowledgments......................................................................................^^ V Conversion Factors ..................................................................................................................~^ VIII A. History and Description of the Okefenokee Swamp Origin of the Suwannee River By R.L. Malcolm, D.M. McKnight, and R.C. Averett.............................................................................................. 1 B. Isolation of Fulvic and Humic Acids from the Suwannee River By R.L. Malcolm, G.R. Aiken,