We will measure the velocity of water movement (saturated flow) through the hyporheic zone at different depths in the soil profile by a series of slotted (0.05 mm) 10 cm diameter PVC well pipes (Boart Longyear Company, Salt Lake City, Utah). Presently, three transects of wells 2 m below the soils surface have been installed (transect lengths = 1-2 km). We plan to install two new well transect in floodplain white spruce stands. Further, additional wells will be installed at varying depths (1, 3, and 5 m) to characterize vertical distribution of subsurface flow rates and solute concentrations in hyporheic flow. These additional wells will be installed at the upstream, middle and downstream ends of transects. Deeper wells will be slotted on the bottom 0.25 m only to characterize the vertical distribution of water chemistry. We have successfully used solute dilution methods in the past to estimate rates of saturated flow, but we have yet to measure water flow at the proposed greater depths within the hyporheic zone.

We will use small-diameter (3 cm) bucket augers to sample solute concentrations in the soil by depth on a monthly basis from June through September. We will install wells, as described above, to sample soil solutions at the depth of perennial water flow (3 m), at median river stage (1.5 m), high river stage typical of mid season (0.5 m), and flooding stage (0.1 m). The wells will be sampled using a peristaltic pump in the deep wells and a hand pump in the shallow wells.

We will not quantify the annual vertical flux of water from the hyporheic zone to the soil surface and to the atmosphere, but rather examine the potential for such water flux over a range of physical conditions at different times of the year. In order to quantify the thermal and water potential gradients that drive this process, we will measure soil temperatures and soil moisture at two different depths (-5 cm and -50 cm) using thermistors (HOBO H8, Onset Computer Corp, MA) and soil moisture probes, respectively (ECHO dielectric aquameter, Decagon Devices, Inc, Pullman, WA). >Surface temperatures and relative humidity will be measured using HOBO Temperature/RH Smart Sensors. These measurements provide a reasonable estimate of the energy gradients driving vertical water flux up through the soil profile to the surface, to which we can apply Darcy’s Law (Campbell and Norman 1998). We are in the process of experimentally estimating the hydraulic conductivity of the soil profile in the laboratory using standard methods (Klute 1986).

We will measure soil temperatures at each well transect with thermistors strings from the soil surface every 50 cm down to the depth of perennially flowing water (3 m depth). Coupled to our soil temperature measurements, from which we can estimate the length of the active season for biogeochemical processes, we will measure vertical heat flow through the soil profile using self-calibrating soil heat flux plates (Campbell Scientific, Inc). The heat flux plates will be installed at 10 cm depth at the same locations as the thermistors strings. Additionally we will install four heat flux plates in a representative upland white spruce stand of similar age to the spruce stands on the floodplain. These measurements will allow us to evaluate the relative importance of subsurface water flow as an advective (horizontal) and convective (vertical) agent of heat flow in the soil.

Electrical conductance and dissolved oxygen will be measured in river and ground water using conductivity and oxygen probes. Ammonium, nitrate, and other ions will be measured using a Dionex DX-320 ion chromatograph. Phosphate will be measured colorimetrically as soluble reactive phosphorus. Dissolved organic carbon (DOC) and dissolved organic nitrogen will be measured on a Shimaduz TOC-5000 carbon analyzer plumbed with an Antek nitric oxide detector. Protein and amino acid-nitrogen will be determined by fluorescence spectroscopy on a FL-600 microplate mutidetection reader (Bio-Tek, Wisconsin, USA).