Use of stable isotopes of carbon and nitrogen to identify sources of organic matter to bed sediments of the Tualatin River, Oregon / by Bernadine A. Bonn and Stewart A. Rounds.

Format:

Book

Government document

Author/Creator:

Bonn, Bernadine, author.

Rounds, Stewart, author.

Contributor:

Geological Survey (U.S.), issuing body.

Clean Water Services (Washington County, Or.)

Series:

Scientific investigations report ; 2010-5154.

Scientific investigations report ; 2010-5154

Language:

English

Subjects (All):

River sediments--Oregon--Tualatin River.

River sediments.

Detritus--Oregon--Tualatin River.

Detritus.

Carbon--Oregon--Tualatin River.

Carbon.

Nitrogen--Oregon--Tualatin River.

Nitrogen.

Oregon--Tualatin River.

Physical Description:

1 online resource (vi, 58 pages) : illustrations (some color), color maps.

Place of Publication:

Reston, Virginia : U.S. Department of the Interior, U.S. Geological Survey, 2010.

Summary:

The potential sources of organic matter to bed sediment of the Tualatin River in northwestern Oregon were investigated by comparing the isotopic fractionation of carbon and nitrogen and the carbon/nitrogen ratios of potential sources and bed sediments. Samples of bed sediment, suspended sediment, and seston, as well as potential source materials, such as soil, plant litter, duckweed, and wastewater treatment facility effluent particulate were collected in 1998-2000. Based on the isotopic data, terrestrial plants and soils were determined to be the most likely sources of organic material to Tualatin River bed sediments. The [delta]¹³C fractionation matched well, and although the [delta]¹⁵N and carbon/nitrogen ratio of fresh plant litter did not match those of bed sediments, the changes expected with decomposition would result in a good match. The fact that the isotopic composition of decomposed terrestrial plant material closely resembled that of soils and bed sediments supports this conclusion. Phytoplankton probably was not a major source of organic matter to bed sediments. Compared to the values for bed sediments, the [delta]¹³C values and carbon/nitrogen ratios of phytoplankton were too low and the [delta]¹⁵N values were too high. Decomposition would only exacerbate these differences. Although phytoplankton cannot be considered a major source of organic material to bed sediment, a few bed sediment samples in the lower reach of the river showed a small influence from phytoplankton as evidenced by lower [delta]¹³C values than in other bed sediment samples. Isotopic data and carbon/nitrogen ratios for bed sediments generally were similar throughout the basin, supporting the idea of a widespread source such as terrestrial material. The [delta]¹⁵N was slightly lower in tributaries and in the upper reaches of the river. Higher rates of sediment oxygen demand have been measured in the tributaries in previous studies and coupled with the isotopic data may indicate the presence of more labile organic matter in these areas. Results from this study indicate that strategies to improve oxygen conditions in the Tualatin River are likely to be more successful if they target sources of soil, leaf litter, and other terrestrially derived organic materials to the river rather than the instream growth of algae.

Notes:

"Prepared in cooperation with Clean Water Services."

Includes bibliographical references (pages 23-24).

Description based on online resource; title from PDF title page (USGS, viewed Nov. 8, 2021).

OCLC:

903697196