Precipitation chemistry samples were collected every three weeks beginning in 1969 in association with stream chemistry samples from for four small watersheds within the South Umpqua Experimental forest (Coyote Creek). Three of these adjacent watersheds were harvested in summer 1971. One watershed was left undisturbed as a control. Stream and precipitation sampling were discontinued in 1981. Precipitation and stream discharge was measured throughout the study duration.
Concurrently, precipitation and stream water chemistry samples were collected every three weeks beginning in 1969 in association with 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.
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.
Samples of precipitation for chemical analyses were collected in large openings in the forest. Stainless steel funnels caught the precipitation, which passed through plastic tubing to an acid-washed polyethylene carboy in an underground chamber to keep the sample cool. The carboys were collected after a 3-week interval. Precipitation samples were 3-week composite samples of bulk precipitation for each watershed. References to 'individual samples' refer to these 3-weeks composites. Methods of sample handling and chemical analyses were the same as for streamwater samples (See study database CF003). Precipitation was measured continuously with a Leupold-Stevens Q-12 snow-rain gauge and chart recorder.
All samples are assigned sample type codes (TYPE). The rules for combining samples and assigning sample type codes are as follows:
Successful collection of precipitation over the 3 week period represents a complete or full (TYPE="F") sample. When the collector failed from freezing, snow bridging or otherwise did not collect precipitation for part of the 3 week period, the sample is designated as partial (TYPE="P"). When the sample contained insufficient water they were saved (TYPE='S') and combined (TYPE='C') with following samples for analysis. In these cases, there are no independent analytical values for the saved samples (TYPE='S'). Flux values are created using precipitation from the combined interval and using the analytical values from the combined sample representing the 6-week or longer 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, 68.2, 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.
