The figure above represents typical instrumentation used at BBWM for measuring soil solutions. Tension lysimeters are composed of tubes that are either straight or at right angles (see picture below) that have a porous ceramic cup at the end. A vacuum is placed on the tube, and solutions are drawn into the tube for sampling under a “tension” against the pull of capillary forces in the soil. These solutions are thought to be closer to equilibrium with the solid soil materials. Zero-tension lysimeters are made of plastic pans placed within the soil that drain into collection bottles as water percolates through pores in the soil under the force of gravity. These solutions, often called gravitational water, are typically not in the soil long enough to achieve chemical equilibrium with solid soil materials, but these solutions are more representative of solutions leaching out of the soil under the force of gravity in freely drained soils. Since there is no tension pulling the solutions into these collectors, they are called “zero-tension”. Different designs have been used at BBWM at different times and for different purposes, but most are variations on these designs.
Below is a table of summary data from Fernandez et al. (1999) that give means of many solutes in soil solution from both TL and TZL collectors.
Soil solution chemistry by horizon, catchment and vegetation type for the treatment period 1990-1995
|East Bear||West Bear||East Bear||West Bear|
Upper case letters indicate significant differences between the catchments within vegetation type. Lower case letters indicate significant differences between vegetation types within a catchment. ‘*’ indicates a significant difference between the pre-treatment and treatment period chemistry using a standard t-test. Upper = upper tension lysimeter data; Lower = lower tension lysimeter data. Units are umol/L for Al and Si, umol C/L for DOC, and ueq/L for all others.
|More recently, Szillery (2003) studied soil solutions at BBWM and allowed us to see some longer-term temporal patterns noted in the figure below. Additional soil solution studies are being initiated in 2005.|
Long-term soil solution temporal trends in concentrations of (a) calcium (b) hydrogen (c) aluminum (d) aluminum by watershed and forest type (e) nitrate and (f) sulfate in the experimental (West Bear) and reference (East Bear) watersheds.