Stable isotopes of deep soil water retain long-term evaporation loss on China's Loess Plateau

Abstract. Knowledge about the long-term average soil evaporation, especially the ratio of evaporation to precipitation (f), is important for assessing the total available water resources. However, determining the long-term f remains technically challenging because soil evaporation is highly dynamic. Here we hypothesize that the stable isotopes (2H and 18O) of deep soil water preserve the long-term evaporation effects on precipitation and can be used to estimate long-term f. Our results showed that the deep soil water (2–10 m) had a mean line-conditioned excess (lc-excess) less than zero (−13.1 ‰ to −3.8 ‰) at the 15 sites across China's Loess Plateau, suggesting that evaporation effects are preserved in the isotopic compositions of the deep soil water. We then estimated f by the new lc-excess method that combines lc-excess and the Rayleigh fractionation theory, because it does not require the initial source isotopic values of soil water, which has a distinct advantage over traditional isotope-based methods (e.g. Craig-Gordon model) that require such information a priori. The estimated f of the 15 sites varied from 11 % to 30 %, and over 60 % of the variability of f was explained by the well-known Budyko dryness index. These data are also comparable with available annual estimates under similar climate regions of the world. Furthermore, these data represent a long-term average value because soil water tritium profile shows that deep soil water has a long residence time on the order of years to decades. Our work suggests that isotopic compositions of deep soil water can be used to calculate long-term average f where water flow within the unsaturated zone is piston-like flow predominantly, and the new lc-excess method provides an effective tool to estimate f.

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Severe depletion of available deep soil water induced by revegetation on the arid and semiarid Loess Plateau

Forest Ecology and Management ◽

10.1016/j.foreco.2021.119156 ◽

2021 ◽

Vol 491 ◽

pp. 119156

Author(s):

Binbin Li ◽

Wantao Zhang ◽

Shujie Li ◽

Ju Wang ◽

Guobin Liu ◽

...

Keyword(s):

Soil Water ◽

Loess Plateau ◽

Deep Soil ◽

Arid And Semiarid

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Interaction of soil water storage and stoichiometrical characteristics in the long-term natural vegetation restoration on the Loess Plateau

Ecological Engineering ◽

10.1016/j.ecoleng.2018.02.026 ◽

2018 ◽

Vol 116 ◽

pp. 7-13 ◽

Cited By ~ 4

Author(s):

Yong-wang Zhang ◽

Zhou-ping Shangguan

Keyword(s):

Soil Water ◽

Loess Plateau ◽

Water Storage ◽

Vegetation Restoration ◽

Natural Vegetation ◽

Soil Water Storage ◽

The Loess Plateau

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Quantify Piston and Preferential Water Flow in Deep Soil Using Cl− and Soil Water Profiles in Deforested Apple Orchards on the Loess Plateau, China

Water ◽

10.3390/w11102183 ◽

2019 ◽

Vol 11 (10) ◽

pp. 2183 ◽

Cited By ~ 1

Author(s):

Zhiqiang Zhang ◽

Bingcheng Si ◽

Huijie Li ◽

Min Li

Keyword(s):

Soil Water ◽

Water Flow ◽

Loess Plateau ◽

Preferential Flow ◽

Chloride Ions ◽

Apple Orchards ◽

The Loess Plateau ◽

Deep Soil ◽

Soil Water Profiles ◽

Preferential Water

Piston and preferential water flow are viewed as the two dominant water transport mechanisms regulating terrestrial water and solute cycles. However, it is difficult to accurately separate the two water flow patterns because preferential flow is not easy to capture directly in field environments. In this study, we take advantage of the afforestation induced desiccated deep soil, and directly quantify piston and preferential water flow using chloride ions (Cl−) and soil water profiles, in four deforested apple orchards on the Loess Plateau. The deforestation time ranged from 3 to 15 years. In each of the four selected orchards, there was a standing orchard that was planted at the same time as the deforested one, and therefore the standing orchard was used to benchmark the initial Cl− and soil water profiles of the deforested orchard. In the deforested orchards, piston flow was detected using the migration of the Cl− front, and preferential flow was measured via soil water increase below the Cl− front. Results showed that in the desiccated zone, Cl− migrated to deeper soil after deforestation, indicating that the desiccated soil layer formed by the water absorption of deep-rooted apple trees did not completely inhibit the movement of water. Moreover, there was an evident increase in soil water below the downward Cl− front, directly demonstrating the existence of preferential flow in deep soil under field conditions. Although pore water velocity was small in the deep loess, preferential water flow still accounted for 34–65% of total infiltrated water. This study presented the mechanisms that regulate movement of soil water following deforestation through field observations and advanced our understanding of the soil hydrologic process in deep soil.

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Effect of planting density on deep soil water and maize yield on the Loess Plateau of China

Agricultural Water Management ◽

10.1016/j.agwat.2019.05.039 ◽

2019 ◽

Vol 223 ◽

pp. 105655 ◽

Cited By ~ 2

Author(s):

Yuanhong Zhang ◽

Rui Wang ◽

Shulan Wang ◽

Fang Ning ◽

Hao Wang ◽

...

Keyword(s):

Soil Water ◽

Loess Plateau ◽

Maize Yield ◽

Planting Density ◽

The Loess Plateau ◽

Deep Soil

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Dynamics of Soil Water Content Across Different Landscapes in a Typical Desert-Oasis Ecotone

Frontiers in Environmental Science ◽

10.3389/fenvs.2020.577406 ◽

2020 ◽

Vol 8 ◽

Author(s):

Guohua Wang ◽

Qianqian Gou ◽

Yulian Hao ◽

Huimin Zhao ◽

Xiafang Zhang

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Groundwater Resources ◽

Time Lag ◽

Northwest China ◽

Deep Soil ◽

Deep Layers ◽

Desert Oasis

An understanding of soil water content dynamics is important for vegetation restoration in an arid desert-oasis ecotone under different landscapes. In this study, the dynamics of soil water content under three typical landscapes (i.e., desert, sand-binding shrubland, and farmland shelter woodland) were investigated in the Hexi Corridor, northwest China, during the growing season from 2002 to 2013. The results showed that the soil water content in the deep layers decreased from 20–30% to a stable low level of 3–5% in the desert and shrubland. For the farmland shelter woodland, the soil water content at the deep layers also decreased, but the decrease rate was much smaller than the desert and shrubland. The decrease of soil water content in the deep soil layers among desert–shrubland–woodland was strongly associated with the increase of groundwater depths. The greatest increase of groundwater depths mainly occurred during 2008–2011, while the largest decrease of soil water content took place during the years 2009–2011, with a time-lag in response to increase in groundwater depths. This study provides new insight into the long-term dynamics of soil water content in a typical desert oasis ecotone under different landscape components from the influence of overexploiting groundwater that cannot be inferred from a short-term study. The findings demonstrate that the sharp increase of groundwater depths could be the main reason behind the reduction of soil water content in the clay interlayers, and sustainable development of groundwater resources exploitation is very important for the management of desert-oasis ecotone from a long-term perspective.

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Changes of deep soil desiccation with plant growth age in the Chinese Loess Plateau

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-9-12029-2012 ◽

2012 ◽

Vol 9 (10) ◽

pp. 12029-12060 ◽

Cited By ~ 13

Author(s):

Y. Q. Wang ◽

M. A. Shao ◽

Z. P. Liu ◽

C. C. Zhang

Keyword(s):

Soil Water ◽

Loess Plateau ◽

Turning Point ◽

Chinese Loess Plateau ◽

Root Depth ◽

Vegetation Types ◽

Deep Soil ◽

Chinese Loess ◽

Soil Desiccation ◽

The Chinese Loess Plateau

Abstract. Negative water balance in soil can lead to soil desiccation and subsequent the formation of a dried soil layer (DSL). Essential progress on DSL temporal change has been hampered by difficulty in collecting deep soil water samples (i.e. > 1000 cm), which are necessary to quantify the real extent of DSL. We collected soil samples up to a depth of 1800 cm and investigated the evolution of soil water content (SWC) and DSL under three vegetation types (C. korshinskii, R. pseudoacacia, apple) in three zones (Ansai, Luochuan, and Changwu) of the Chinese Loess Plateau. As plant growth age increased, SWC, available soil water (ASW), SWC within DSL (DSL-SWC), and quantity of water deficit for DSL (DSL-QWD) showed similar change trends of decreasing at first and then increasing, whereas DSL thickness (DSLT) showed an increasing trend over time. A turning point in soil water change was found for the three vegetation types. In Changwu zone, the turning point, both in and out of DSL, was corresponded to the 17-year-old apple orchard. The period from 9 to 17 yr was vital to maintain the buffering function of deep soil water pool and to avoid the deterioration of soil desiccation because the highest mean decline velocity of ASW and the maximum mean forming velocity of DSLT were 165 mm yr−1 and 168 cm yr−1, respectively. Significant correlations were found between DSLT and growth age and root depth, and between DSL-QWD and root depth, whereas mean DSL-SWC had no significant correlation with either growth year or root depth. Soil water condition was highly dependent on the growth year of the plants. This information provides pertinent reference for water resource management in the Chinese Loess Plateau and possibly in other water-limited regions in the world.

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