Diurnal Water Content Changes in the Bare Soil of a Coastal Desert

Abstract

The deposition of dew is a common meteorological phenomenon that has been recognized as an important ecosystem element, especially in arid areas. There is some evidence that indicates that there is an increase in the water content of the topsoil during nights in which no dew deposition was observed. The purpose of this study is to describe the daily pattern of changes in water content in the upper soil layers and to identify the mechanism by which water is added to the soil (deposition or direct absorption). Moreover, the gains in soil water content during the night are compared to the dew amounts recorded by the Hiltner balance, and the losses and gains of water in terms of easily measurable environmental parameters are parameterized.Nine 24-h field campaigns took place during the dry season of 2002. During each campaign, the 100-mm topsoil was sampled hourly, and water content at 10-mm increments was obtained. Micrometeorological measurements included incoming and reflected shortwave radiation; net radiation; wind speed at four levels; dryand wet-bulb temperatures at 1-m height; and soil heat flux. In addition, the changes in mass of an improved microlysimeter were recorded, and dew deposition amounts were measured using a conventional Hiltner dew balance.The results of this study indicate that in the area in which this study was carried out actual dew deposition on a bare soil surface is probably a rare occurrence. There is, however, a clear discernible daily cycle of water content in the upper soil layers. The lack of any evidence of soil surface wetting led to the conclusion that the main process responsible for the observed diurnal change in water content is the direct adsorption of water vapor by the soil. A strong and significant correlation was found between the total adsorption of water vapor by the soil during the period that begins in the early afternoon and ends at sunrise and the total potential evaporation between sunrise and sunset of the previous day. Based on this finding an empirical model is proposed in order to predict the total amount of water adsorbed by the soil during the absorption period. The proposed model is probably site specific but is very simple and easy to implement. An additional outcome of the present study is that, in the area in which it was carried out, artificial condensing plates are poorly correlated to water vapor absorption, and the deposition of dew on them is not indicative of dew deposition on bare soil.

Can water responses in Stipa tenacissima L. during the summer season be promoted by non-rainfall water gains in soil?

“…Other important factors that could explain why we found that the total average water gain in bare soil (1.42 mm day -1 ) was twice the daily average WVA found by Verhoef et al (2006) are: (i) the clay content in that study was somewhat lower than in ours (14.8% compared with 17.7%), (ii) our study plot is closer to the coast than the Coria area (17 km from the southern coast of the city of Alicante compared to 80 km), and there are no mountains between the coast and the ''El Ventó s'' area. The total average water gain we found is within the range of WVA detected by Kosmas et al (2001) (from 0.05 to 3.7 mm day -1 ) but higher than the mean WVA measured by Agam and Berliner (2004) in the Negev desert in Israel (0.25 mm day -1 ). Like Domingo et al (1999) in a Retama sphaerocarpa stand in Almería (Spain), we found good correspondence of transpiration from S. tenacissima calculated from the Clumped Model and transpiration measured by the porometer method (Fig.…”

“…In these environments, where rainfall is scarce and light, if any, there may be other important dry-season ''non-rainfall'' soil water input from fog and dew formation (Kidron 2000(Kidron , 2005Malek et al 1999;Seely 1976;Shanyengana et al 2002;Zangvil 1996) or soil water vapour adsorption (WVA) (Agam and Berliner 2004;Kosmas et al 1998Kosmas et al , 2001. These processes can supply vegetation with water vital for survival in seasons with a severe water deficit, giving rise to a close relationship between soil water dynamics and plant water response.…”

Dispersion modeling of particulate matter containing hexavalent chromium during high winds in southern Iraq

“…We therefore chose a value of 2%, still very dry but elevated slightly above minimum to reflect these adjacent sources of water. The value of 2% is in the low end of observations of soil moisture in desert soils reported in the literature (Scanlon, 1994;Agam (Ninari) and Berliner, 2004).…”

Impact of dew deposition on water flux dynamics at a tropical rainfed paddy field in the dry season

“…2), direct water vapor adsorption and soil internal evaporation are also thought to contribute to total daytime evaporation in the cool dry season. Furthermore, previous studies of arid and semiarid regions showed that actual dew deposition on a bare soil surface is probably rare because the dew-point temperature is lower than the soil surface temperature due to the lack of water vapor content (WVC) in the atmosphere (Agam and Berliner, 2004). In contrast, this study showed that the dew-point temperature is higher than or equal to the soil surface temperature.…”