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Use of Stable Isotopes of Carbon, Nitrogen, and Sulfur to Identify Sources of Nitrogen in Surface Waters in the Lower Susquehanna River Basin, Pennsylvania

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Use of Stable Isotopes of Carbon, Nitrogen, and Sulfur to Identify Sources of Nitrogen in Surface Waters in the Lower Susquehanna River Basin, Pennsylvania Use of Stable Isotopes of Carbon, Nitrogen, and Sulfur to Identify Sources of Nitrogen in Surface Waters in the Lower Susquehanna River Basin, Pennsylvania By CHARLES A. CRAVOTTA III Prepared in cooperation with the PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL PROTECTION U.S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER 2497 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, 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. For sale by the U.S. Geological Survey, Branch of Information Services Box 25286 Denver, CO 80225-0286 Library of Congress Cataloging-in-Publication Data Cravotta, Charles A. Use of stable isotopes of carbon, nitrogen, and sulfur to identify sources of nitrogen in surface waters in the lower Susquehanna River Basin, Pennsylvania / by Charles A. Cravotta III. p. cm. -- (U.S. Geological Survey water-supply paper : 2497) “Prepared in cooperation with the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation.” Includes bibliographic references (p. - ). Supt. of Docs. no.: I 19.13:W2497 1. Nitrogen--Environmental aspects--Susquehanna River Watershed. 2. Water--Pollution--Susquehanna River Watershed--Point source identification. 3. Radioactive tracers in water pollution research-Susquehanna River Water- shed. I. Pennsylvania. Bureau of Soil and Water Conservation. II. Title. III. Series. TD427.N5C73 1997 97-10381 628.1'61--dc21 CIP ISBN 0-607-87207-1 CONTENTS Abstract.................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................... 2 Purpose and Scope....................................................................................................................................................... 2 Acknowledgments ....................................................................................................................................................... 2 Terminology and Principles of Isotopic Measurements ........................................................................................................ 4 Isotopic Mass Balance ................................................................................................................................................. 6 Isotopic Fractionation .................................................................................................................................................. 6 Use of Stable Isotopes as Tracers .......................................................................................................................................... 7 Carbon ......................................................................................................................................................................... 7 Nitrogen ....................................................................................................................................................................... 9 Sulfur ........................................................................................................................................................................... 9 Data Collection and Analysis ................................................................................................................................................ 10 Study-Site Selection .................................................................................................................................................... 10 Sample Collection and Processing .............................................................................................................................. 10 Laboratory Analysis .................................................................................................................................................... 11 Statistical and Graphical Analytical Methods ............................................................................................................. 12 Intrasample Variations ........................................................................................................................................................... 13 Method Precision and Accuracy.................................................................................................................................. 16 Sample Components.................................................................................................................................................... 16 Organic and Inorganic ....................................................................................................................................... 16 Dissolved and Particulate .................................................................................................................................. 17 Characterization of Nitrogen Sources and Associated Soils and Waters .............................................................................. 18 Characterization of Nitrogen Sources.......................................................................................................................... 18 Precipitation....................................................................................................................................................... 18 Forest Leaf Litter ............................................................................................................................................... 38 Synthetic Fertilizer ............................................................................................................................................ 38 Manure............................................................................................................................................................... 38 Human Septic and Sewage Waste...................................................................................................................... 44 Isotopic Differences Among Nitrogen Sources........................................................................................................... 45 Characterization of Soil and Water Samples from Different Land-Use Areas............................................................ 46 Forest: Stony Creek and Upper Dogwood Run ................................................................................................. 46 Fertilizer: Monroe Creek and Bald Eagle Creek ............................................................................................... 51 Manure: Brush Run and Conestoga River Field Sites ....................................................................................... 52 Septic: Middle Dogwood Run and Berkshire Hills........................................................................................... 52 Sewage: Lower Dogwood Run and Codorus Creek .......................................................................................... 53 Estimation of Nitrogen Loads in Stream Waters ................................................................................................................... 53 Point Sources ............................................................................................................................................................... 58 Nonpoint Sources ........................................................................................................................................................ 58 Estimation of N-Isotopic Fractionation ................................................................................................................................. 59 Practicality of Using Stable Isotopes of Carbon, Nitrogen, and Sulfur to Identify Sources of Nitrogen in Surface Waters......................................................................................................................................... 61 Measurements.............................................................................................................................................................. 61 Computations............................................................................................................................................................... 61 Summary and Conclusions .................................................................................................................................................... 61 Selected References............................................................................................................................................................... 63 Appendix A: Descriptions of Subbasins and Sample Sites in the Lower Susquehanna River Basin, Pennsylvania...................................................................................................... 69 Appendix B: Field, Chemical, and Isotopic Data for Nitrogen-Source and Associated Soil and Water Samples from the Lower Susquehanna River Basin, Pennsylvania, 1988–90 ....................................... 75 Contents III ILLUSTRATIONS 1. Map showing location of sample-collection sites in the Lower Susquehanna River Basin ....................................... 3 2–3. Schematic diagrams showing: 2. Biochemical cycles
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