Closing the Water Balance with a Precision Small-Scale Field Lysimeter.

Area of Science:

• Environmental Science
• Soil Science
• Hydrology

Background:

• Accurate measurement of bare soil evaporation is crucial for understanding hydrological processes in arid and semi-arid regions.
• Traditional methods may lack the precision needed to fully close the soil water balance.

Purpose of the Study:

• To develop and validate a set of precision, small-scale lysimeters for accurate measurement of bare soil evaporation.
• To assess the performance of these lysimeters in a semi-arid environment.

Main Methods:

• Two lysimeters were constructed with soil tanks, load cells, and wicking drainage systems to measure drained water.
• Fiberglass wicks maintained -60 cm tension, and soil water drainage was quantified to close the water balance.
• Lysimeters were calibrated, yielding mass change uncertainties of 3-8 g (0.02-0.05 mm water).

Main Results:

• Lysimeters were installed at a semi-arid site in northern Nevada, filled with construction sand and silt loam.
• Over six months, bare soil evaporation rates of 0.19 mm/day (sand) and 0.40 mm/day (silt loam) were recorded.
• Measured evaporation aligned with meteorological data and potential evapotranspiration models.

Conclusions:

• The developed lysimeters provide accurate measurements of bare soil evaporation, essential for closing the soil water balance.
• The design is adaptable for various research needs and site constraints.
• These instruments enhance the capability for precise soil water balance studies in water-limited environments.