Wells and well transects:
Two types of wells were used in this study: observation wells to measure water table elevations and sample wells to collect interstitial water. Casings for observation wells were made from PVC pipe and screened by drilling 0.32 cm diameter holes into the bottom 50 cm of each PVC pipe, at an approximate density of 1 hole/cm2. Casings for sample wells were constructed from 45-cm lengths of 2.54-cm diameter, porous, high density polyethylene pipe (HDPE) with a mean pore diameter of 20 µm. A length of PVC pipe was added to extend the casing above the ground surface.
All wells were driven by hand because the study site had no road access. Large cobbles and boulders throughout the study site hindered well placement so that the deepest wells penetrated only 2.5 m below the ground surface. Wherever possible, wells were placed in holes driven at least 50 cm below the surface of the water table at summer baseflow. Holes were back filled with the soil originally removed and, if necessary, additional fill was taken from nearby soil pits or recent root-throw pits. Following installation of the wells, back fill was washed and entrained sediments were removed from the well casing by repeated pumping.
A single transect of wells was established during late summer in 1989 as a pilot study. Additional transects of wells were installed during the summer of 1990 and an additional 18 wells were established on, and adjacent to, the gravel bar during 1991 and 1992. Nine sample wells were placed adjacent to observation wells so that water table levels could be measured concurrently with the collection of water samples during storm events. During the summer of 1991, about half of the observation wells were retro-fitted with evacuation tubes so that water samples could be collected over a much larger area during base flow periods.
Water samples and chemical analyses:
Water samples were collected from wells to compare changes in dissolved nitrogen concentrations among seasons and within storm events. Sampling was concentrated from mid summer to early fall and during fall storms. Samples were also collected in mid winter, in early spring, and during a single late-winter storm. Water table depths were recorded from observation wells less then 24 h before collecting base flow water samples after which wells were pumped dry and allowed to refill before collecting samples. Dissolved oxygen and temperature were also measured in each observation well using a YSI Model 51A dissolved oxygen meter and a YSI probe in 1991 and 1992. Water samples were only collected from the sample wells during storms because observation wells were used to monitor changes in water table levels and withdrawing water to collect samples would have changed the water level in the wells. Twenty-four hours before a forecasted storm, all sample wells were pumped dry and allowed to refill. Wells were not re-evacuated between sample collections during a storm.
Surface water samples (stream, tributaries, and secondary channel) were collected as Agrab samples@, holding a clean, acid washed HDPE bottle just under the surface of the stream and allowing it to fill. Bottles were rinsed 3 times with water samples before collecting the final sample. Head space above the water sample was evacuated and samples were stored on ice. Water samples were collected from wells using a vacuum flask. All wells were instrumented with a permanent evacuation tube to limit contamination and the introduction of foreign materials into the wells when sampling during storms. To collect a sample, the evacuation tube was connected to the vacuum flask and a vacuum was applied using a small hand pump. The vacuum flask was never rinsed with sample water because if a small amount of water was evacuated from the well and used to rinse the flask, large amounts of sediment would be stirred up in the well. Thus, the entire sample was collected immediately. Samples were collected in clean, acid washed HDPE bottles that were rinsed with sample water from the vacuum flask before transferring the final sample to the bottle. Head space above the water sample was evacuated and samples were stored on ice. The vacuum flask was rinsed 3 times with D.I. water immediately before collecting a sample from the next well.
Samples were categorized by landform, season, and a storm index variable (FLOINDEX). Samples from wells were categorized by landform on which the well was located (STREAMBED, GRAVEL (gravel bar), FLOOD (flood plain), TERRACE, FAN (alluvial fan) and SEEP (a well located in a seep or spring at the base of the terrace). and grab samples of surface water were categorized as either STREAM, TRIB (tributary), or STLET (secondary channel). Samples from early fall, collected before the start of the rainy season, were considered summer samples. Each season was subdivided into periods of base flow or storm flow. The period of annual low flow in late summer was designated as LOW (low base flow) to distinguish from other base flow periods. Hydrographs of either stream discharge or well records of water table elevations were used to subdivided non-baseflow periods as either the RISE (rising leg), PEAK, and FALL (falling leg) of the hydrograph. Pre-storm samples were collected immediately before the storm and post-storm samples were collected once the stream returned to base flow conditions after the end of the storm. These samples were designated as PRE and POST, respectively, but were also used in analyses of base flow trends.
The following samples are flagged (variable name FLAG, coded XX) as non-typical in the data set. You can find a short description of each sample below:
Samples 117, 128, 129, 130, 181, 182, 197, 201, 202, 203, 216, 232, 263, 324, 398, 420, 421, 792, 795, 803, 804:
Samples 278-321 and 348-392 were collected in a well network located on Lookout Creek in conjunction with a stream fertilization experiment and are not included in this data set, despite sequential numbering. Additionally, samples 318-321 and 375-382 were collected for an experiment to test the effect of freezing on NH4 and NO3 concentrations.
Greenberg, A. E., J. J. Connors, and D. Jenkins (eds). 1980. Standard methods for the examination of water and wastewater. American Public Health Association, Washington D.C.15th edition. 1134 p.
Wondzell, S. M. and F. J. Swanson. 1996. Seasonal and storm dynamics of the hyporheic zone of a 4th-order mountain stream. I: Hydrologic processes. The J. of the North American Benthological Society 15:3-19
Wondzell, S., and F. J. Swanson. 1996. Seasonal and storm dynamics of the hyporheic zone of a 4th-order mountain stream. II: Nitrogen cycling. The Journal of the North American Benthological Society 15:20-34
Wondzell, S. 1994. Flux of ground water and nitrogen through the floodplain of a fourth-order stream. Ph.D. Thesis. Oregon State University, Corvallis OR.