Investigating organic matter in Fanno Creek, Oregon, Part 3 of 3: identifying and quantifying sources of organic matter to an urban stream

Journal of Hydrology
By: , and 

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Abstract

The sources, transport, and characteristics of organic matter (OM) in Fanno Creek, an urban stream in northwest Oregon, were assessed and quantified using: (1) optical instruments to calculate transported loads of dissolved, particulate, and total organic carbon, (2) fluorescence spectroscopy and stable isotope ratios (δ13C, δ15N) to elucidate sources and chemical properties of OM throughout the basin, and (3) synoptic sampling to investigate seasonal and hydrologic variations in the characteristics and quantity of OM. Results from this study indicate that of the roughly 324 (±2.9%) metric tons (tonnes, t) of organic carbon exported from the basin during March 2012 to March 2013, most of the OM in Fanno Creek was dissolved (72%) and was present year-round at concentrations exceeding 3–4 milligrams of carbon per liter, whereas particulate carbon typically was mobilized and transported only by higher-flow conditions. The isotopic and fluorescence characteristics of Fanno Creek OM indicate that the carbon originates primarily from terrestrial inputs, most likely riparian vegetative biomass that enters the stream via litterfall and overland transport and then travels through the system episodically as a result of hydrologic processes. The amount of OM exported from the Fanno Creek drainage over the course of a year in this study is consistent with previous estimates of annual riparian litterfall in or near the creek. Although the creek channel is actively eroding, most bank material has too little OM for that to be a dominant source of OM to the stream. Fluorescence data revealed that the OM contains primarily humic and fulvic-like components that become less aromatic as the OM moves downstream. The most significant seasonal variation was associated with OM transported in the first storms of the autumn season (fall flush). That material was characteristically different, with a larger fraction of microbially derived OM that probably resulted from an accumulation of easy-to-mobilize and decomposing material in the streambed during previous months of summertime low-flow conditions. The first fall flush produced the highest concentrations of OM of the entire year, and the resulting load of mobilized and decomposing OM resulted in a significant oxygen demand immediately downstream in the Tualatin River.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Investigating organic matter in Fanno Creek, Oregon, Part 3 of 3: identifying and quantifying sources of organic matter to an urban stream
Series title Journal of Hydrology
DOI 10.1016/j.jhydrol.2014.07.033
Volume 519
Issue Part D
Year Published 2014
Language English
Publisher Elsevier
Contributing office(s) Oregon Water Science Center
Description 14 p.
First page 3028
Last page 3041
Country United States
State Oregon
Other Geospatial Fanno Creek
Datum North American Datum of 1983
Projection Universal Transverse Mercator projection
Online Only (Y/N) N
Additional Online Files (Y/N) N