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

McHugh TA, Morrissey EM, Reed SC, Hungate BA, Schwartz E - Sci Rep (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, USA.

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 (18)O-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.

No MeSH data available.


Atmospheric relative humidity (a) soil gravimetric moisture content (b) and soil water 18O atom percent excess (c) in response to atmospheric water vapor addition. Error bars are standard error for means (n = 3). Significant differences as determined by one-way ANOVA and Tukey’s post-hoc test are indicated using lowercase letters (α = 0.05).
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f1: Atmospheric relative humidity (a) soil gravimetric moisture content (b) and soil water 18O atom percent excess (c) in response to atmospheric water vapor addition. Error bars are standard error for means (n = 3). Significant differences as determined by one-way ANOVA and Tukey’s post-hoc test are indicated using lowercase letters (α = 0.05).

Mentions: To test for the occurrence of water vapor adsorption and examine the conditions under which it occurs, we conducted two sets of laboratory experiments. First, 18O-enriched water vapor was added to the atmosphere of sealed jars containing field dry soil from a semiarid grassland. Temperature and relative humidity were monitored over a three-day period as soils experienced simulated diurnal temperature fluctuations (23 °C for 4 h, 40 °C for 8 h, 23 °C for 4 h, and 10 °C for 8 h) typical for an arid region. Through the addition of 18O-enriched water vapor to the atmosphere (0, 50, 100, or 500 μg fully evaporated into ~1 L headspace), we were able to trace the movement of water vapor into the soil. Addition of water vapor to the atmosphere increased the atmospheric relative humidity (Fig. 1a) and soil gravimetric water content (Fig. 1b). 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). Further, the amount of water vapor adsorbed (calculated from 18O APE) was linearly related to the gravimetric moisture content of the soil (r2 = 0.91, p < 0.00001). Across all treatments, 35–50% of the water added to the atmosphere was adsorbed. 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 globe28. Because soil temperatures were well above dewpoint temperatures, the transfer of water from the atmosphere to the soil could not have occurred through dew.


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

McHugh TA, Morrissey EM, Reed SC, Hungate BA, Schwartz E - Sci Rep (2015)

Atmospheric relative humidity (a) soil gravimetric moisture content (b) and soil water 18O atom percent excess (c) in response to atmospheric water vapor addition. Error bars are standard error for means (n = 3). Significant differences as determined by one-way ANOVA and Tukey’s post-hoc test are indicated using lowercase letters (α = 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561883&req=5

f1: Atmospheric relative humidity (a) soil gravimetric moisture content (b) and soil water 18O atom percent excess (c) in response to atmospheric water vapor addition. Error bars are standard error for means (n = 3). Significant differences as determined by one-way ANOVA and Tukey’s post-hoc test are indicated using lowercase letters (α = 0.05).
Mentions: To test for the occurrence of water vapor adsorption and examine the conditions under which it occurs, we conducted two sets of laboratory experiments. First, 18O-enriched water vapor was added to the atmosphere of sealed jars containing field dry soil from a semiarid grassland. Temperature and relative humidity were monitored over a three-day period as soils experienced simulated diurnal temperature fluctuations (23 °C for 4 h, 40 °C for 8 h, 23 °C for 4 h, and 10 °C for 8 h) typical for an arid region. Through the addition of 18O-enriched water vapor to the atmosphere (0, 50, 100, or 500 μg fully evaporated into ~1 L headspace), we were able to trace the movement of water vapor into the soil. Addition of water vapor to the atmosphere increased the atmospheric relative humidity (Fig. 1a) and soil gravimetric water content (Fig. 1b). 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). Further, the amount of water vapor adsorbed (calculated from 18O APE) was linearly related to the gravimetric moisture content of the soil (r2 = 0.91, p < 0.00001). Across all treatments, 35–50% of the water added to the atmosphere was adsorbed. 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 globe28. Because soil temperatures were well above dewpoint temperatures, the transfer of water from the atmosphere to the soil could not have occurred through dew.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, USA.

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 (18)O-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.

No MeSH data available.