Why dew and fog measurements carried out by microlysimeters do not adequately reflect the intact soil? The role of temperature

Abstract

The assumption that microlysimeters (MLs) adequately reflect the soil conditions is widespread. Nevertheless, previous findings raised doubts regarding the reliability of MLs to adequately reflect the amounts of dew and fog of the intact soil (control, COT). We therefore hypothesized that the structure (whether a single cylinder inserted into the soil (ML-I), or a cylinder inserted within a large-diameter cylinder thus mimicking a weighing ML (ML-II)), the construction material (PVC and metal, i.e., iron), length (12, 50 cm) and height above ground (12, 30 cm), all will largely affect the thermal regime of the ML. A set of experiments were conducted during which the ML temperatures (1, 5 cm and more) and the dew and fog (using cloths attached to 10 × 10 × 0.2 glass plates located on the MLs) were measured. The findings indicate that (a) in comparison to COT, the minimum temperatures substantially decreased (by 2.0–2.5 °C) and dew and fog substantially increased (by a factor of 3.2–3.5) with height above ground (b) MLPVC-I and both types of MLs-II yielded higher dew and fog than COT, especially MLPVC-II, which yielded 2.1-fold higher amounts of dew and fog than COT (c) except for MLmetal-I that yielded similar temperatures and dew and fog to COT, all the remaining MLs exhibited lower nocturnal temperatures and higher dew and fog than COT. The higher amounts of dew and fog recorded by the MLs are explained by changes in the heat regime induced by the structure of the ML. The findings raise doubts on recent attempts to deduce the magnitude of vapor flux (dewrise, distillation) based on dew and fog measurements with MLs, and call for extra caution once arid ecosystem productivity is analyzed and predicted following ML-based dew and fog values.