干旱区生态环境知识资源中心

The development of a simple and low-cost portable weighing microlysimeter that makes use of a load cell for automated recording and for studying daily dew formation, rate of accumulation, and subsequent evaporation in arid or semiarid regions during rainless seasons is presented. The sampling cup is 3.5 cm deep, with the load cell itself situated at 20-cm depth to minimize temperature effects. The device was tested in a sand dune experimental station situated near Nizzana, northwest Negev Desert, Israel, during which extensive micrometeorological measurements were collected. One microlysimeter was placed in a playa and a second was installed on the stabilized midslope of an adjacent linear sand dune. To assess the performance of the load cell microlysimeters (LCM), one pair of manual microlysimeters was installed next to each LCM. A third pair was installed at a point between the LCMs and a fourth pair above the midslope LCM. Sixteen overnight measurements were carried out within a 6-week period. The LCM could measure dew with an error of +/- 0.02 mm. The daily dew variation in the samples during the 16 overnight measurements ranged up to 0.2 mm on stable dune slopes but up to 0.4 mm on the playa. This difference is attributed to the playa’s high silt and clay content and salinity. Dew formation and accumulation were found to occur long before the soil-surface temperature reached the dewpoint temperature of the air. The cost of building this microlysimeter, excluding labor, is about $175 (U.S.).