The hillslope study area was located on the south aspect of WS10, 91 m upstream from the stream gauging station. This site was reestablished from early 1970s era benchmark studies [Harr and Ranken, 1972; Harr, 1977; Sollins and McCorison, 1981; Sollins et al., 1981]. The slope is representative of the two main planar hillslopes that compose the overall v-shaped catchment (WS10). The 125 m long stream-to-ridge slope is slightly convex and its gradient averages 37°, ranging from 27° near the ridge to 48° adjacent to the stream. Elevation ranges from 480 to 565 m.
A 10 m long trench was constructed to measure subsurface throughflow at the location of a seep that had been previously gauged in the early to mid-1970s [Harr, 1977; Triska et al., 1984]. The trench was constructed by intercepting subsurface water from a natural seepage face, which was routed to a calibrated 15 degree V notch weir that recorded stage at 10 min time intervals using a 1 mm resolution capacitance water level recorder (TruTrack, Inc., model WT-HR).
Precipitation samples were collected weekly from January 2000 to February 2003 (about 1130 day period) in bulk collectors at two locations that coincided with a low (PRIMET, 430 m) and high (H15MET, 922 m) elevation meteorological station.
Harr, R. D., and D. W. Ranken (1972), Movement of water through forested soils in steep topography, Coniferous For. Biome Internal Rep. 117, 19 pp., Univ. of Wash., Seattle.
Harr, R. D. (1977), Water flux in soil and subsoil on a steep forested slope, J. Hydrol., 33(1–2), 37–58, doi:10.1016/0022-1694(77)90097-X.
Sollins, P., and F. M. McCorison (1981), Nitrogen and carbon solution chemistry of an old growth coniferous forest watershed before and after cutting, Water Resour. Res., 17(5), 1409–1418, doi:10.1029/ WR017i005p01409.
Sollins, P., K. J. Cromack, F. M. McCorison, R. H. Waring, and R. D. Harr (1981), Changes in nitrogen cycling at an old-growth Douglas-fir site after disturbance, J. Environ. Qual., 10, 37–42, doi:10.2134/ jeq1981.00472425001000010007x.
Discharge was measured from the trench from 1 September 2002 to 21 January 2003 and thereafter predicted using regression with WS10 discharge due to gauge failure. Precipitation was measured with a tipping bucket (15.39 cm diameter orifice, 0.2 mm resolution) and storage gauge (8.9 cm diameter orifice) observed on an event basis in a small canopy opening on the hillslope. The drainage area of the hillslope was delineated from a total station topographic survey of the entire hillslope (0.2 ha) and verified by a water balance calculation (i.e., compared similarly to the WS10 balance).
Precipitation samples were collected weekly from January 2000 to February 2003 (~1130 day period) in bulk collectors at two locations that coincided with a low (PRIMET, 430 m) and high (Hi-15, 922 m) elevation meteorological station. Precipitation samplers consisted of plastic funnels with drainage tubing attached to plastic bottles. To minimize evaporation, water traps were created by looping drainage tubes and protecting collection bottles in either a climate controlled shelter (Hi-15) or by burying the bottle beneath the soil surface below a small insulated shelter (PRIMET). Precipitation rates were determined using heated tipping bucket rain gauges at each station as part of HJA long-term data collection. Snowmelt sampling occurred weekly at Hi-15 during the 2001–2002 winter using a 0.25 m2 snow lysimeter that drained into a heated shelter to prevent the samples from freezing. Snowmelt rates were measured using tipping buckets (0.025 mm per tip) and a 5.52 m2 lysimeter. A network of small bulk rainfall collectors (N = 38) were used to assess input variations across the large basin scale for 3 rain storms in fall 2002. Seven stream sites (WS02, WS03, WS08, WS09, WS10, MACK, and LOOK) were sampled weekly (generally on the same day as precipitation sample collection).
Two line source tracers were applied to the hillslope immediately before a large winter rainstorm (66 mm, 49 h duration) that began on 9 December 2002 at 21:30 [see McGuire et al., 2007]. 20.9 g of amino G acid monopotassium salt (AGA), a fluorescent dye [Smart and Laidlaw, 1977], and 4.0 kg of bromide (as LiBr solution) were applied 19 and 33 m from the trench, respectively. Both tracers were monitored continuously at the trench for the first 9 days of the experiment. AGA was monitored using a field fluorometer (10-AU, Turner Designs, Inc., Sunnyvale, CA) equipped with along wavelength optical kit, temperature compensation, flow-through cell, and data logger. Bromide was also measured in situ with an ion-selective electrode for Br- (TempHion®, Instrumentation Northwest, Inc.) until 31 March 2003. Grab sampling extended the AGA breakthrough for 100 days and it provided additional samples for calibrating the Br- selective electrode (N = 107, R2 = 0.99). Both tracers were monitored until concentrations during storm events were at background levels (~100 days).
Oxygen-18 (18O) samples were collected weekly at the hillslope trench (1 November 2001 to 11 February 2003), WS10 (13 February 2001 to 4 February 2003), and as bulk precipitation (1 January 2000 to 11 February 2003). Soil water samples from the lysimeters were collected at time intervals between daily and weekly from 2 October 2002 until 11 February 2003. Storm samples were collected between 2 and 4 h intervals from the hillslope and WS10 for several storms during the fall 2002 to winter 2003 period. Rainfall was sampled sequentially (4.4 mm increments) over this period for 18O using samplers as described by Kennedy et al. [1979].
