Water chemistry samples were collected every three weeks beginning in 1969 for four small watersheds within the South Umpqua Experimental forest (Coyote Creek). Three of these adjacent watersheds were harvested in summer 1971. Water sampling was discontinued in 1981. Stream discharge was measured throughout the study duration. Watershed 1 was was logged as preparation for creating a shelterwood stand, watershed 2 was patch clearcut in 20 small units from 1.6 to 3.3 acres, watershed 3 was cut as one large clearcut, and watershed 4 was left undisturbed as a control.
Concurrently, water chemistry samples were collected every three weeks beginning in 1969 on three adjacent watersheds in the Fox Creek drainage within the Mt. Hood Experimental Forest. Two of these watersheds were logged in patches and one was left as an unlogged control. In FC-1, timber was clearcut in four units of 3-4 ha in late spring of 1969, and high-lead yarding was completed in July. Logging residue in the four logged units was burned in the fall of 1970. Logging in FC-3 occurred over a 3-year period; cutting in two units of 8-10 ha began in the summer of 1970, and yarding was completed in August 1972. Logged area in each watershed constitutes 25 percent of the total watershed.
Harr, R. Dennis; Fredriksen, Richard L.; Rothacher, Jack. 1979. Changes in streamflow following timber harvest in southwestern Oregon. Res. Pap. PNW-249. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 22 p.
Harr, R. Dennis; Fredriksen, Richard L. 1988. Water quality after logging small watersheds within the Bull Run Watershed, Oregon. Water Resources Bulletin. 24(5): 1103-1111.
Streamwater is sampled from each stream at a rate proportional to the streamflow rate. Samples are collected in 5 gal. polyethylene carboys and stored in an insulated housing or cabinet at the gaging station. Composite samples, collected proportionally to streamflow over approximate 3-week periods, contain representative sampling of the sediment and dissolved constituents carried by the stream over the collection period. Samples remained at the gage houses until transported to Corvallis for analysis.
Samples were collected using a battery powered, in-house constructed sampler designed by Richard Fredriksen (Fredriksen 1969). The interface between the sampler and the recorders was an array of magnetic reed switches which were activated by magnets attached to the counter weights of the recorders. There were 20 segmented proportions equal to discharge increases of 1/20th of the expected maximum discharge. For each proportional increase in flow, the number of samples taken in the base time period increased by one. Streamflow is measured continuously with Leopold-Stevens A-35 recorders
All samples are assigned sample type codes (TYPE). The rules for combining samples and assigning sample type codes are as follows:
Successful operation of the sampler over the 3 week period represents a complete or full (TYPE="F") sample. When the sampler failed or was out of operation for the entire 3 week period, a grab (TYPE='G') sample was taken to represent the entire period. When the sampler failed or was out of operation for part of the 3 week period, the sample is designated as partial (TYPE="P"). When the partial samples contained insufficient water for analysis, they were "augmented" (TYPE="A") with a grab sample to a level considered sufficient for conducting all analytical measurements. There are 5 cases when the sample contained insufficient water and were saved (TYPE='S') and combined (TYPE='C') with the following sample for analysis. In these cases, there are no independent analytical values for the saved samples (TYPE='S'). Flux values are created for the saved sample interval using streamflow from this interval and using the analytical values from the combined sample representing the 6-week interval.
Date and times listed as data_time in the data files refer to the end date of a collection period. Data is summarized by water year: October 1 to September 30. To allow summarization by water year, an artificial end-of-year sample point (TYPE="YE") is inserted on Sept 30 every year (Entity 2 flux data only) but is not an actual sample. Nutrient concentrations from the next analyzed sample (in October) are used with the streamflow total ending Sep 30, the end of the wateryear, to calculate flux for this interval, which is designated TYPE="YE". Similarly, the flux value for this first sample of the new wateryear in October is calculated based on concentration values from the October sample and on streamflow beginning Oct 1.
Official compilation of water analyses begins with the WY 1969 (10/1/68). Originally, samples are analyzed for suspended sediment, alkalinity, pH, ammonia nitrogen, nitrate, nitrite, dissolved kjeldahl nitrogen, ortho (reactive soluble) and total dissolved phosphorus, sodium, potassium, calcium, magnesium, and silica. Sulfate was determined for WY 1972 and sulfate and chloride in WY 1979. Analysis of specific conductivity was added in Dec 1974 and total P on an unfiltered samples in Oct 1974. Analysis of total kjeldahl N on an unfiltered sample was started in June 1978. Total N is calculated from the total Kjeldahl and NO3-N. In general, duplicates were run on all analyses.
Note: Results flagged as below detection prior to 1979 were assigned based on documentation of methods and an evaluation of analytical instrument responses produced during and after 1979 and may not reflect actual analytical performance for results produced prior to 1979.
Other notes on analyses: 1) From 1969 - 1973 samples were analyzed for free ammonia (FNH3) prior to being digested for total nitrogen (DON). The FNH3 was driven off and collected and analyzed separately. Then the sample was digested and analyzed for DON. For these years TKN represents the sum of DON and FNH3. 2) Silica: Historic records indicate that many, if not all, of the samples prior to that date were frozen prior to analysis for silica. Freezing samples prior to analysis for silica will reduce the final analyzed concentration of reactive silica (the form we have historically determined). Another complicating factor is that the methodology changed about this same time. Until 1982, a stannous chloride method was used to determine silica, and this method is more prone to variability due to reagent instability.
The CCAL lab analyzed for total dissolved Kjeldahl nitrogen (TKN) and also for total Kjeldahl nitrogen (UTKN), which is performed using an unfiltered sample and includes any particulates (sediment, biota) present. All dissolved results exclude particulates of 0.7 microns or greater. TKN includes NH3-N, but does not include NO3-N. The following are mathematically calculated in the data set and coded as 'D' when this occurs:
All samples are filtered upon arrival at the Corvallis lab (CCAL) and pH, alkalinity, conductivity, and autoanalyzer runs (NO3-N, NH4-N, SI) are made immediately. All analyses are completed within 6 weeks. Generally, samples are stored at 0 degrees C if not analyzed immediately.
Citations for all Cooperative Chemical Analytical Lab (CCAL) procedures are shown here: CCAL Methodology
The Coyote Creek watersheds originally supported a mixed conifer forest containing approximately 50,000 board feet per acre (440 cubic meters per ha). Douglas-fir (Pseudotsuga menziesii), grand fir (Abies grandis), incense-cedar (Libocedrus decurrens), and sugar pine (Pinus Zambertiana) predominated in the old growth. Occasional ponderosa pines (Pinus ponderosa) and western hemlocks (Tsuga heterophylla) were also present. Occupying adjacent drainages, the four watersheds comprise 171, 169, 123, and 120 acres (69.2, 68.4, 49.8 and 48.6 ha).
The Fox Creek watersheds are 59 ha, 253 ha, and 71 ha in size. Sideslope gradients of the watersheds average only 5-9 percent but range up to 60 percent near the watersheds' outlets. The relatively gentle topography is representative of perhaps 25-30 percent of the Bull Run Municipal Watershed. Elevation ranges from 840 m to 1070 m.
