Suction Lysimeters - Leachate Collection

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Abstract

The collection and analysis of soil solution (leachate) provides information on nutrient availability and hydrologic loss (leaching) from a given system. To collect soil solution in situ, low-tension quartz suction lysimeters (also called soil water samplers) are installed at ~1.2m depth, which at KBS is below most roots and in the Bt2 horizon of unconsolidated sand and gravel. The lysimeters are connected to the surface via a small diameter tube, to which suction (-0.5 atm) is applied. Over a 24h period enough soil water is pulled through the tube to measure nitrate and other solutes. Leachate samples are then filtered with glass fiber filters (pore size < 0.4 um) and frozen until analyzed.

Sampling frequency: Depends on experiment, time of year, and research purpose. Soil leachate is collected as part of our sampling program of the LTER Main Cropping System Experiment on a biweekly basis throughout the growing season or as allowed by precipitation and soil frost.

Protocol

Overview

Quartz (e.g., Prenart) and ceramic (e.g., Eijkelkamp) lysimeters are designed to pull soil solution at low suction (-0.5 atm or 38 cm Hg). The soil solution is harvested by attaching an evacuation flask to small diameter tubing connected to the lysimeter. Suction is applied to the lysimeter via the evacuation flask; the pressure differential between the soil solution and the flask draws the leachate from the soil into the flask until a state of equilibrium is reached. After 24 hours, flasks containing leachate are collected, transported to the laboratory, and the leachate volume measured. The leachate is then filtered with glass fiber filters, stored in polyethylene vials, and immediately frozen until thawed for analysis of inorganic N and other species using flow spectrophotometry or ion chromatography. See Protocol 42 for lysimeter installation instructions (https://lter.kbs.msu.edu/protocols.42).

Materials

  • Site maps
  • Avery 5160 Laser labels
  • 500 mL Erlenmeyer flasks
  • Manual vacuum pump
  • Parafilm squares
  • 20 mL polyethylene scintillation vials

Procedure

  1. Cover lysimeter flasks with parafilm to reduce particulate contamination during transport to field.
  2. Place flasks in storage boxes and transport to field. Invert the center flasks to fit 6 flasks per box. Each lysimeter has a specific flask to be used for leachate collection.
  3. The buried lysimeter is connected via sample tubing to a stopper in the enclosure box. Securely fit the stopper assembly into the neck of the flask. Connect the vacuum pump to the free end of the second piece of tygon tubing in the stopper. This tubing is used to create a vacuum.
  4. Create a vacuum of 38 cm Hg, as measured on the pump gauge.
  5. Create an air tight seal in the flask by folding the vacuum tubing and securing the fold in place with a clip.
  6. Record time and date of evacuation.
  7. After 24 hours, flasks are collected in the same order as evacuated.
  8. Remove the stopper from the flask and listen for a hissing sound which indicates a vacuum was present inside the flask.
  9. Securely cover the flask opening with parafilm. Place flasks in the storage boxes right side up for transport back to lab.
  10. Weigh flasks and record total weight; subtract the flask tare weight (in database) from this value to estimate the amount of leachate collected.
  11. Filter leachate samples of 20 mL or more into plastic scintillation vials. Discard samples of less than 20 mL.
  12. Filter leachate samples of 20 mL or more into plastic scintillation vials.
  13. Freeze leachate samples for analysis and/or archival.


Note: During freezing temperatures, the leachate in the Erlenmeyer flasks may freeze and crack the glass. This may be avoided by tilting flasks in the enclosures so the leachate can expand across the length of the flask as it freezes.

Date modified: Monday, Jul 20 2020

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    JS: Updated and name change; 20 July 2020

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