Sediment Oxygen Demand in the Tualatin River Basin, Oregon, 1992-96
Entry ID:
WRIR_97_4103
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Summary
Abstract:
Sediment oxygen demand (SOD) rates were measured by U.S. Geological Survey (USGS) personnel at 20 stream sites in the Tualatin River Basin from 1992 through 1996 as part of an investigation into the sources and sinks of dissolved oxygen in the Tualatin River. During the low-flow summer periods of 1992 through 1994, 97 measurements were collected at 9 sites on the main stem of the river between ... river miles (RMs) 5.5 and 43.2. During the low-flow summer
periods of 1995 and 1996, 28 measurements of SOD were collected at 11 sites on
8 tributaries of the Tualatin River. All SOD rates were measured with in-situ
benthic chambers designed to monitor the loss of dissolved oxygen in a known
volume of water circulating above a known area of minimally disturbed stream
sediment. For main-stem Tualatin River sites, the observed SOD rate ranged
from 0.6 to 4.4 grams of oxygen per square meter per day (g/m 2 d) with a
median of 2.3 g/m 2 d. In the tributaries, the measured SOD rate ranged from
0.2 to 10.9 with a median of 3.6 g/m 2 d. These rates are in the range of those
reported for other sites in Oregon and across the United States. Most of the
variation in the measured SOD rates was likely due to heterogeneities in the
bed sediment. Statistical comparisons show that the rates measured at the
tributary sites are significantly larger than those measured in the main stem.
Within the main stem, the rates measured at sites in the meander reach of the
river were not significantly different from those measured in the reservoir
reach. Similarly, no difference was found when the sites affected by the cycle
of phytoplankton bloom and die-off were compared to those unaffected by
phytoplankton. Only one site on the main stem, RM 5.5, was found to have an SOD
rate that was significantly higher than that found at the other main-stem
sites. Algal detritus may contribute to the elevated rate at that site, but
other factors such as the rate of sediment accumulation could also account for
the increased rate.
This report discusses the USGS measurements of SOD in the Tualatin River Basin.
Specifically, this investigation of SOD in the Tualatin River Basin was
designed to determine the magnitude of the SOD rate in the main stem and the
tributaries, determine the spatial and temporal variability of the SOD rate in
the main stem, determine the influence of the river flow regime on the SOD
rate, and determine the influence of phytoplankton on the SOD rate. These
objectives were accomplished by measuring the SOD rate at various locations and
at different times during the low-flow summer period. Other measures of water
quality necessary to this study, such as chlorophyll-a concentrations, were
collected by USA as part of a routine monitoring program. The investigation was
restricted to the low-flow period between May 1 and October 31. Throughout this
report, all references to algae refer only to phytoplankton.
The area of study is the Tualatin River Basin in northwestern Oregon.
In-situ SOD chambers with recirculating flow are designed to isolate a a known
volume of water over a known area of bottom sediment so that the oxygen loss
over time may be monitored with minimal (a) disturbance and compaction of the
sediments, (b) disturbance of the biological community, and (c) alteration of
ambient conditions (Murphy and Hicks, 1986). The SOD chambers used in this
investigation (figs. 2 and 3) open-bottomed opaque plastic cylinders that are
designed to seat and seal on the river bottom. Scuba divers deployed SOD
chambers in the main stem of the Tualatin River where water depth at several
sites exceeded 15 feet. SOD measurements in the tributary streams did not
require divers. Once seated, each chamber isolates about 52 liters of river
water that is then slowly recirculated for at least 2 hours over 0.225 square
meters of bottom sediment. A calibrated HydrolabTM multiparameter probe, fitted
with a "Lo-Flow" dissolved oxygen membrane, is mounted vertically in the center
of the chamber (fig. 3). The chambers used in this study are based on a design
by the ODEQ, which in turn was based on a design by Murphy and Hicks (1986). In
1992, a closed-bottom, "blank" chamber was also used. This chamber was designed
to isolate a volume of near-bottom river water without allowing that water to
interact with the bottom sediments. The purpose of this closed-bottom chamber
was to measure the rate of oxygen depletion in the water column as a "blank"
correction. Any oxygen depletion measured in the blank would be subtracted from
the loss measured in the open-bottom chamber to correct for this water- column
oxygen demand. Due to the low water-column oxygen demand measured in 1992,
however, the subsequent use of a closed-bottom chamber was determined to be
unnecessary. Dimensions of the internal measuring part of the chamber are
provided in figure 3. The lower part of the open-bottom chamber has a
stainless-steel collar to assist in bed sediment penetration when seating the
chambers. The closed-bottom chamber has identical dimensions, except it has no
collar and has an opaque plastic bottom with two inspection ports which, when
opened, facilitated the lowering of the chamber through the water column to the
river bed. When the closed-bottom chamber was near but not on the river bed,
divers would close the inspection ports and then place it on the river bottom.
The chamber would remain at the bottom of the river for the 2-hour measuring
period. During the measurement period, the water in each chamber is circulated
by a bilge pump, powered by a 12-volt rechargeable gel-cell battery, at a rate
of 1,360 liters per hour (23 liters per minute). Water is withdrawn from the
chamber by the pump and then injected into the chamber through three separate
diffuser tubes; this design allows for good mixing of the isolated water with
minimal suspension of the bottom sediments. A dye test within the chamber
confirmed complete mixing within 2 minutes and a circulating velocity within
the chamber of 0.1 to 0.2 ft/s. This range of mixing velocities resulted in
thorough mixing in the chamber with velocities on the order of those expected
in the study area. The "Lo-Flow" membrane on the HydrolabTM is minimally
affected by variations in sample flow and is suitable for velocities as low as
0.003 ft/s (Hydrolab Inc., 1991). A number of researchers have noted that the
actual SOD rate may depend on the degree of turbulence in the water column and
that the mixing velocity produced in an in-situ benthic chamber therefore
should be controlled to match that near the sediment/water interface outside
the chamber (Murphy and Hicks, 1986; NCASI, 1978 and 1979; Parkhill and
Gulliver, 1997). Although the mixing velocity can be important when the rate of
oxygen utilization in the sediment exceeds the rate at which oxygen in the
overlying water column can be delivered, it is also true that when the rate of
oxygen utilization in the sediment is low and the mixing velocity is sufficient
to eliminate concentration gradients near the sediment/water interface, the SOD
rate will not depend on the mixing velocity (Parkhill and Gulliver, 1997). The
effect of variations in the chamber mixing velocity will be studied in more
detail in future investigations, but preliminary data from the SOD measurements
in 1996 at several Tualatin River tributary sites indicate that velocity
variations below the normal operating range of 0.1 to 0.2 ft/s do not influence
the measured SOD rate.
The steps used to deploy an SOD chamber and monitor the dissolved oxygen loss
over time are as follows: 1.) A calibrated HydrolabTM multiparameter probe with
a " Lo-Flow" dissolved oxygen membrane is inserted in the chamber and clamped
to the stabilizing rod (fig. 3). 2.) Near the water surface, the submerged
chamber is inspected to check power, pump circulation, and tubing connections
to ensure that all air is removed from the chamber and its associated tubing.
3.) A valve on top of the chamber is adjusted to direct water from within the
chamber out into the stream. This step is done in preparation for purging the
chamber (step 5). 4.) With the pump off and inspection ports open, the chamber
is lowered and seated in the bottom sediment. For SOD measurements in the main
stem Tualatin River, this step is performed by divers. For SOD measurements in
the tributaries, an individual wearing chest waders and shoulder length gloves
can seat the chamber into the river bed. This step is done with care to
minimize disturbance to the bottom sediment. The chamber is left undisturbed
for 10 minutes to allow any suspended sediments to settle. 5.) After the
settling period, the pump is turned on. This purge cycle, with the inspection
ports open and the valve directing water from inside the chamber out into the
river, ensures that native, near-bottom water fills the chamber and that any
remaining suspended material, as well as water from the upper part of the water
column, is pumped out. 6.) After the chamber has been purged for at least 10
minutes (a time period sufficient to flush at least one chamber volume), the
ports are closed and the valves are adjusted to recirculate water within the
chamber. 7.) The starting time and initial readings of DO, pH, water
temperature, and specific conductance are noted. The HydrolabTM is programmed
to automatically record probe readings at 5-minute intervals for at least 2
hours. Instrument readings are also recorded manually at 10- to 20-minute
intervals. These seven steps are repeated for each chamber deployed; most SOD
measurements were obtained in triplicate at each site. For most of the
measurements, a 2-hour time period was used. Some of the data, however, were
collected over 5 hours to verify the linearity of the oxygen depletion curve
over an extended time period.In 1992, a closed-bottom chamber of identical
dimensions to the open-bottom chamber was used to measure water-column oxygen
demand as a "blank" correction. The oxygen depletion rate measured with this
closed-bottom chamber was minimal in comparison with that measured in the
open-bottom chambers. Half of these measured "blank" corrections (the
interquartile range) were between -0.1 and 0.4 g/m 2 d with a median of 0.1
g/m2d (n=17). The median correction was approximately 5 percent of the SOD rate
measured with the open-bottom chambers. It is likely, however, that some of the
higher "blank" rates were artifacts of oxygen demand from suspended bottom
sediment that was accidentally introduced into the "blank" chamber during its
placement on the river bottom. Given the relatively low water-column oxygen
demand measured with this chamber, and the potential error caused by the
accidental introduction of bottom sediments into these chambers, this " blank"
correction was not deemed to be large enough, or reliable enough, to continue
to measure in subsequent years. After 1992, a sample of water near the river
bottom was collected and the rate of oxygen depletion was measured to determine
the magnitude of the water-column oxygen demand over a 2-hour period. Water
samples were collected using 300-mL opaque BOD bottles. This near-bottom water
sample was placed in a water bath (and located in a shaded area) at river
temperature. DO readings were made using calibrated YSI model 57 and model 58
DO meters equipped with a YSI model 5420A self-stirring probe. DO
concentrations were measured at 15- to 20-minute intervals over a 2-hour time
period. Water-column oxygen demand measured in this manner was also small (< 3
percent) compared to the SOD measured with the open-bottom SOD chambers. As a
result, water-column oxygen demand was discounted as a significant source of
oxygen consumption in this procedure.
The SOD rate is calculated from a graph of dissolved oxygen concentration
versus elapsed time. Two hours is usually a sufficient amount of time for a
representative oxygen consumption rate to be established in the chambers.
Sometimes in the first 10 to 20 minutes of the assay, a rapid and nonlinear
decrease in DO concentration is recorded within the chambers (fig. 4>. This
decrease is thought to be due to a small amount of bottom sediment that had
been suspended in the chamber during deployment and had not yet settled back to
the sediment surface. Whenever this occurred, the oxygen consumption curve
usually stabilized and became linear after the suspended sediment was given
time to settle. Only the data obtained after that initial period were used in
the calculation of SOD rates. The slope of the linear part of the oxygen
depletion line is determined through linear regression, and the following
equation is used to calculate the SOD rate: SODsubT (1.44) V/A b. (1) where
SOD T is the sediment oxygen demand rate in g/m2d at temperature T, b is the
slope of the oxygen-depletion curve in milligrams per liter per minute, V is
the volume of the chamber in liters, A is the area of bottom sediment covered
by the chamber in square meters, and 1.44 is a units-conversion constant.
Volume corrections were made when insertion of the chambers into the sediments
was less than or more than the ideal (insertion of the entire stainless-steel
collar on the chamber constituted an ideal seating, figs. 2 and 3). Measured
SOD rates were corrected to 200C using a standard van't Hoff equation: (2) SOD
to the base 20 SODsub T /1.065 super T-20 where SOD20 is the rate at 200C, and
T is in degrees Celsius (0C) (Thomann and Mueller, 1987). This correction does
not hold for temperatures less than 100C; however, temperatures in this study
ranged from 14.4 to 23.00C. Standard statistical tests were used in the
analysis of the SOD rate data, including on factor and nested analysis of
variance (ANOVA), the Mann-Whitney (Wilcoxon) test, and Tukey's multiple
comparison test (Helsel and Hirsch, 1992; Box and others, 1978; SAS Institute
Inc., 1989; Searle, 1987). Satterthwaite's approximate test procedure (Ostle
and Malone, 1988) was used in conjunction with nested ANOVA designs. Rank
transformations were used to increase the normality of the data distributions.
All tests forstatistical significance were made at the 95 percent confidence
level.
The information for this metadata was taken from the Online Publications of the
Oregon District at http://oregon.usgs.gov/pubs_dir/online_list.html. 
Related URL
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Description:
Metadata in National Biological Information Infrastructure format.
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Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
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N: 45.6
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S: 45.38
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E: -122.62
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W: -123.25
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Data Set Citation
Dataset Originator/Creator:
Stewart A. Rounds and Micelis C. Doyle
Dataset Title:
Sediment Oxygen Demand in the Tualatin River Basin, Oregon, 1992-96
Dataset Release Place:
Portland, Oregon
Dataset Publisher:
U.S. Geological Survey
Data Presentation Form:
database
Temporal Coverage
Start Date:
1992-01-01
Stop Date:
1996-01-01
Quality
All of the SOD rates measured by USGS personnel in the Tualatin River Basin
from 1992 through 1996 are shown both in table 1 and figure 5. Ninety-seven
rates were measured at nine main-stem sites from 1992 through 1994.
Twenty-eight rates were measured at 11 tributary sites from 1995 through 1996.
All of the measurements were made during the May ... through October low-flow
period, with a slight emphasis on the month of September, which is a critical
period for DO in the main-stem river. During each measurement, the amount of
oxygen in the chamber was not a limiting factor. The lowest initial and final
DO concentrations encountered were 4.9 and 3.9 mg/L, respectively. Most of the
measurements, however, were performed with DO concentrations well above 6.0
mg/L.
Access Constraints
None
Use Constraints
None
Data Set Progress
COMPLETE
Personnel
Role:
TECHNICAL CONTACT
Phone:
(503) 251-3280
Fax:
(503) 251-3470
Email:
sarounds at usgs.gov
Contact Address:
U.S. Geological Survey
10615 SE Cherry Blossom Dr.
City:
Portland
Province or State:
Oregon
Postal Code:
97216
Country:
USA
Role:
DIF AUTHOR
Phone:
(301) 614-6898
Fax:
301-614-5268
Email:
Tyler.B.Stevens at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Global Change Master Directory
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date:
2001-06-27
Last DIF Revision Date:
2012-12-12
Future DIF Review Date:
2002-06-27
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