Water from air: an overlooked source of moisture in arid and semiarid regions.

Theresa A. McHugh,Bruce A. Hungate,Egbert Schwartz,Ember M. Morrissey,Sasha C. Reed

doi:10.1038/srep13767

Theresa A. McHugh, Bruce A. Hungate + Show 3 more

Open Access

https://doi.org/10.1038/srep13767

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Abstract

Water drives the functioning of Earth’s arid and semiarid lands. Drylands can obtain water from sources other than precipitation, yet little is known about how non-rainfall water inputs influence dryland communities and their activity. In particular, water vapor adsorption – movement of atmospheric water vapor into soil when soil air is drier than the overlying air – likely occurs often in drylands, yet its effects on ecosystem processes are not known. By adding 18O-enriched water vapor to the atmosphere of a closed system, we documented the conversion of water vapor to soil liquid water across a temperature range typical of arid ecosystems. This phenomenon rapidly increased soil moisture and stimulated microbial carbon (C) cycling, and the flux of water vapor to soil had a stronger impact than temperature on microbial activity. In a semiarid grassland, we also observed that non-rainfall water inputs stimulated microbial activity and C cycling. Together these data suggest that, during rain-free periods, atmospheric moisture in drylands may significantly contribute to variation in soil water content, thereby influencing ecosystem processes. The simple physical process of adsorption of water vapor to soil particles, forming liquid water, represents an overlooked but potentially important contributor to C cycling in drylands.

Highlights

In the absence of precipitation, there are three primary mechanisms for the addition of water to surface soils: fog deposition, dew formation, and water vapor adsorption[15]
Strong water limitation in drylands means that soil water inputs from adsorption of atmospheric water vapor could be an important driver of soil biogeochemistry, yet whether the phenomenon is quantitatively significant and ecologically relevant is not known
Water vapor adsorption occurred at atmospheric relative humidity values ranging from 20–60% (Fig. 1a,b), which are consistent with humidity values reported for arid and semiarid lands across the globe[28]

Summary

Introduction

In the absence of precipitation, there are three primary mechanisms for the addition of water to surface soils: fog deposition, dew formation, and water vapor adsorption[15]. The increase in soil gravimetric water content was due to vapor adsorption, as the soil water 18O atom percent excess (APE) confirmed the transfer of moisture from the atmosphere to the soil (Fig. 1c).

Results

Conclusion