Suction Lysimeters

Description:

Suction lysimeters collect pore water from unsaturated soil. After installation below ground level, vacuum is applied to the lysimeter through tubing leading from the lysimeter to the ground surface. The negative air pressure created inside the lysimeter draws pore water into the lysimeter through the porous, stainless steel section of the lysimeter. The pore water is transported to the surface by applying positive pressure to the lysimeter through a second tube. At the surface the pore water is collected in a collection bottle. Suction lysimeters perform best in moist soil and below the water table. Pore water collection from relatively dry formations (pressure potential less than -500 mbar) is difficult.

Models:

Features:

• All welded 304 stainless steel construction
• No glue or plastics
• Suitable for organics and most inorganics
• Separate upper chamber for sample storage (models SW-070 and SW-070A)
• One way stainless steel valve prevents back flow from storage chamber to sample chamber (models SW-070 and SW-070A)
• Strong and durable.
• Suitable for installation at great depths (models SW-070 and SW-070A)
• 600 mbar bubbling pressure
• Optional battery powered vacuum pump (SW-073)

Dual chamber models only:

• Separate upper chamber for sample storage
• One-way stainless steel valve prevents back flow from upper storage chamber to sample chamber
• Suitable for installation at great depths 

Specifications:

Frequently asked questions:

Question 1: How deep can I install the lysimeters?

Answer:

The dual chamber models can be installed at depths of up to several hundred meters (500 feet or more). The single chamber models should be installed no deeper than six meters (about 20 feet).

Question 2: Should I use a contact material to ensure good contact between the porous section of the lysimeter and the surrounding soil or sediment?

Answer:

Many researchers use sifted fine sand removed from the depth of lysimeter installation as contact material. If such sand is not available, silica flour may be used as contact material. It is best to add water to the contact material first, resulting in a slurry that can be poured down a plastic pipe temporarily placed in the access hole.

Question 3: Are vacuum and pressure sources required for operation of the lysimeters?

Answer:

Model SW-074 requires a vacuum source (i.e. a vacuum pump) to draw pore water from the surrounding medium into the lysimeter, and from there up into a collection bottle, located on the soil surface.

Model SW-071 can also be operated with just a vacuum source, if it is placed at a relatively shallow depth (i.e. less than 3 to 4 meter), and if a collection bottle is located on the soil surface, as for model SW-074.

However, SW-071 models are usually operated such that the pore water is collected in the lysimeter itself. In that case a pressure pump (hand pump or electric pump) is needed to apply pressure to the vacuum/pressure tube of the lysimeter. This forces the water from the lysimeter up into the collection bottle. A good bicycle can be used for this purpose.

The dual chamber models SW-070 and SW-070A need both vacuum (to draw the pore water into the lysimeter and into the upper chamber of the lysimeter), and pressure. Pressure is needed to force the pore water sample up through the fluid return tube to the collection bottle at the soil surface. For a lysimeter placed at a depth of 30 meters (98 feet) one needs an air pump that can deliver a pressure of at least 30 meters, equivalent to 3 bars or about 45 psi. Note that most bicycle pumps can deliver at least 100 psi or 6.6 bars.

 ©2006. SOIL MEASUREMENT SYSTEMS