American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 274601 bytes)    Cited by

WATER RESOURCES RESEARCH, VOL. 38, NO. 1, 1005, doi:10.1029/2001WR000269, 2002

In-stream sorption of fulvic acid in an acidic stream: A stream-scale transport experiment

Diane M. McKnight

Institute of Arctic and Alpine Research and Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, Colorado, USA


George M. Hornberger

Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA


Kenneth E. Bencala

U.S. Geological Survey, Menlo Park, California, USA


Elizabeth W. Boyer

College of Environmental Science and Forestry, State University of New York, Syracuse, New York, USA


Abstract

The variation of concentration and composition of dissolved organic carbon (DOC) in stream waters cannot be explained solely on the basis of soil processes in contributing subcatchments. To investigate in-stream processes that control DOC, we injected DOC-enriched water into a reach of the Snake River (Summit County, Colorado) that has abundant iron oxyhydroxides coating the streambed. The injected water was obtained from the Suwannee River (Georgia), which is highly enriched in fulvic acid. The fulvic acid from this water is the standard reference for aquatic fulvic acid for the International Humic Substances Society and has been well characterized. During the experimental injection, significant removal of sorbable fulvic acid occurred within the first 141 m of stream reach. We coinjected a conservative tracer (lithium chloride) and analyzed the results with the one-dimensional transport with inflow and storage (OTIS) stream solute transport model to quantify the physical transport mechanisms. The downstream transport of fulvic acid as indicated by absorbance was then simulated using OTIS with a first-order kinetic sorption rate constant applied to the sorbable fulvic acid. The “sorbable” fraction of injected fulvic acid was irreversibly sorbed by streambed sediments at rates (kinetic rate constants) of the order of 10−4–10−3 s−1. In the injected Suwannee River water, sorbable and nonsorbable fulvic acid had distinct chemical characteristics identified in 13C-NMR spectra. The 13C-NMR spectra indicate that during the experiment, the sorbable “signal” of greater aromaticity and carboxyl content decreased downstream; that is, these components were preferentially removed. This study illustrates that interactions between the water and the reactive surfaces will modify significantly the concentration and composition of DOC observed in streams with abundant chemically reactive surfaces on the streambed and in the hyporheic zone.

Published 29 January 2002.

Index Terms: 1806 Hydrology: Chemistry of fresh water; 1871 Hydrology: Surface water quality; 1055 Geochemistry: Organic geochemistry.

Read Full Article (file size: 274601 bytes)    Cited by

Citation: McKnight, D. M., G. M. Hornberger, K. E. Bencala, and E. W. Boyer (2002), In-stream sorption of fulvic acid in an acidic stream: A stream-scale transport experiment, Water Resour. Res., 38(1), 1005, doi:10.1029/2001WR000269.