KBS031: MCSE: Soil Leachate - Inorganic and Dissolved Organic Nitrogen

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Abstract

Sampling Frequency: biweekly 1996 to present

Soil leachate samples are collected from low-tension quartz lysimeters on a biweekly basis from March through November. Precipitation and soil frost levels dictate the time frame and frequency of collection. Three lysimeters are installed in the C horizon approximately 1 to 1.2 m deep under an undisturbed soil profile in three replicate blocks of each of the KBS LTER treatments. Suction (-0.5 atm) is applied to each lysimeter and the resulting leachate collected in Erlenmeyer flasks after a 24 h period. Soil leachate samples are filtered with glass fiber filters (pore size < 0.4 um) and immediately frozen. Samples are thawed and analyzed with flow spectrophotometry for inorganic N and dissolved organic N.

Protocol

Overview

The quartz lysimeters are designed to pull soil solution at low suction (-0.5 atm or 38 cm Hg). The soil solution (leachate) is harvested by attaching a sealed and evacuated flask to a small diameter sample line connected to the lysimeter. Over a period of 24 h, the pressure differential between the soil solution and leachate collected within the flask reaches a state of equilibrium. Flasks containing leachate are transferred to the laboratory. The leachate is filtered with glass fiber filters, stored in polyethelene vials, and frozen until analyzed for inorganic N and dissolved organic N using flow spectrophotometry.

Materials

  • Site maps
  • Avery 5160 Laser labels
  • 500 mL flasks
  • hand pump
  • parafilm squares
  • 20 mL scintillation vials

Procedure

  1. Cover lysimeter flasks with parafilm to reduce particulate contamination during transport to field.
  2. Place flasks in boxes and transport to field. The center flasks will need to be inverted in order to fit 6 flasks in a box. Each lysimeter will have specific flask to be used for leachate collection.
  3. There is tubing coming from the buried lysimeter that is attached to a stopper in the collection box. Place stopper assembly in flask. Connect hand pump to tygon tubing.
  4. Create a vacuum of 38 cm Hg with hand pump.
  5. Fold tygon tubing and place binder clip on tube to keep air tight seal.
  6. Record time and date of evacuation.
  7. After 24 hours collect flasks in same order as evacuated.
  8. Attach hand pump to tygon tubing.
  9. Release binder clip and record vacuum remaining in flask.
  10. Remove stopper and place parafilm over flask opening. Place flasks in boxes right side up for transport back to lab.
  11. Weigh flasks in order to estimate the amount of leachate.
  12. Filter leachate samples of 20 mL or more into plastic scintillation vials.
  13. Freeze leachate samples for analysis and archive.

During freezing temperatures, the leachate in the Erlenmeyer flasks may freeze and crack the glass flasks. This may be avoided by tilting the flasks in the cooler so the leachate can freeze and expand across the length of the flask.

Time required to complete sampling of all 90 KBS LTER quartz lysimeters

  • Prep: 1.5 h
  • Field placement: 4 h
  • Field collection: 4 h
  • Weigh leachate volumes in lab: 1 h
  • Filter:2.5 h
  • Wash flasks: 3 h
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