Concentration, UV-spectroscopic characteristics and fractionation of DOC in stormflow from an urban stream, Southern California, USA
John A. Izbicki A D , Isabel M. Pimentel A , Russell Johnson A , George R. Aiken B and Jerry Leenheer CA U.S. Geological Survey, 4165 Spruance Road, Suite 200, San Diego, CA 92101, USA.
B U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303, USA.
C U.S. Geological Survey, Denver Federation Center, Denver, CO 80225, USA.
D Corresponding author. Email: jaizbick@usgs.gov
Environmental Chemistry 4(1) 35-48 https://doi.org/10.1071/EN06046
Submitted: 8 August 2006 Accepted: 9 November 2006 Published: 14 February 2007
Environmental context. There is concern that there may be public health issues associated with dissolved organic carbon (DOC) because of its unknown composition and reactivity to disinfection in water used for public supply. Here, changes in the concentration and composition of DOC in stormflow (1995–2004) in the Santa Ana River and its tributaries is evaluated based on its optical properties, molecular weight and solubility differences of the contributing DOC components. Such a study may allow improved water management in the future. Ongoing work in the study area has shown that DOC in surface water diverted for groundwater recharge degrades to near natural levels in underlying aquifers pumped for public supply.
Abstract. The composition of dissolved organic carbon (DOC) in stormflow from urban areas has been greatly altered, both directly and indirectly, by human activities and there is concern that there may be public health issues associated with DOC, which has unknown composition from different sources within urban watersheds. This study evaluated changes in the concentration and composition of DOC in stormflow in the Santa Ana River and its tributaries between 1995 and 2004 using a simplified approach based on the differences in the optical properties of DOC and using operationally defined differences in molecular weight and solubility. The data show changes in the composition of DOC in stormflow during the rainy season and differences associated with runoff from different parts of the basin, including extensive upland areas burned prior to the 2004 rainy season.
Samples were collected from the Santa Ana River, which drains ~6950 km2 of the densely populated coastal area of southern California, during 23 stormflows between 1995 and 2004. Dissolved organic carbon (DOC) concentrations during the first stormflows of the ‘winter’ (November to March) rainy season increased rapidly with streamflow and were positively correlated with increased faecal indicator bacteria concentrations. DOC concentrations were not correlated with streamflow or with other constituents during stormflows later in the rainy season and DOC had increasing UV absorbance per unit carbon as the rainy season progressed. DOC concentrations in stormflow from an urban drain tributary to the river also increased during stormflow and were greater than concentrations in the river. DOC concentrations in stormflow from a tributary stream, draining urban and agricultural land that contained more than 320 000 animals, mostly dairy cows, were higher than concentrations in stormflow from the river and from the urban drain. Fires that burned large areas of the basin before the 2004 rainy season did not increase DOC concentrations in the river during stormflow after the fires – possibly because the large watershed of the river damped the effect of the fires. However, the fires increased the hydrophobic neutral organic carbon fraction of DOC in stormflow from the urban drain and the tributary stream.
Acknowledgements
Funding for the study was provided by the Orange County Water District (OCWD) as part of their Santa Ana River Water Quality and Health (SARWQH) Study in cooperation with the USA Geological Survey. The authors thank Katherine Patel, Greg Woodside, Mike Weiner, Nira Yamachika, Susan Bradford, and the staff of the OCWD for their assistance with this study. The authors also thank the members of the scientific advisory panel of the SAWQH study for their technical advice during the study; Minoo Ghajar, Orange County Public Health Department, for the analysis of faecal indicator bacteria; Patricia Bigger, Orange County Flood Control, for permission to sample from the stormdrain at LaPalma Avenue; and Ed Nylund, City of Chino, for permission to sample from Mill Creek at Chino-Corona Road.
The use of tradenames in this manuscript is for identification purposes only and does not constitute an endorsement of any particular brand.
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