hess-2016-555 :Soil water migration in the unsaturated zone of semi-arid region in China from isotope evidence

2016 ◽  
Author(s):  
Anonymous
2016 ◽  
Author(s):  
Yonggang Yang ◽  
BoJie Fu

Abstract. Abstract. Soil water is an important driving force of the ecosystems, especially in the semi-arid hilly and gully region of northwestern Loess Plateau in China. The mechanism of soil water migration in the reconstruction and restoration of Loess Plateau is a key scientific problem that must be solved. Isotopic tracers can provide valuable information associated with complex hydrological problems, which is difficult to obtain by other methods. In this study, the oxygen and hydrogen isotopes are used as tracers to investigate the migration processes of soil water in the unsaturated zone in the Loess Plateau of arid region in China. Samples of precipitation, soil water, plant xylems and plant roots are collected and analysed. The conservative elements D and 18O are used as tracers to identify variable source and mixing processes. The mixing model is used to quantify the contribution of each end member and calculate mixing amounts.The results show that the isotopic composition of precipitation in the Anjiagou River basin is affected by isotopic fractionation due to evaporation. The isotopic compositions of soil waters are plotted between or near the local meteoric water lines, indicating that soil waters are recharged by precipitation. The soil water migration is dominated by piston-type flow in the study area, but rarely preferential flow.Water migration exhibited a transformation pathway from precipitation to soil water to plant water. δ18O and δD are enrichment in the shallow (<20 cm depth) soil water in most soil profiles due to evaporation. The isotopic composition of xylem water is close to that of soil water at the depth of 40%–60 cm. These values reflect soil water signatures associated with caraganakorshinshiikom uptake at the depth of 40%–60 cm. Soil water from the surface soil lay (20%–40 cm) contributed to 6 %–12 % of plant xylem water, while soil water at the depth of 40%–60 cm is the largest component of plant xylem water (range from 60 % to 66 %), soil water below 60 cm depth contributed 8 %–14 % to plant xylem water, and only 5 %–8 % is derived directly from precipitation.This study investigates the migration process of soil water, and identifies the source of plant water, and finally provides a scientific basis for identification of model structure and parameter. It can provide a scientific basis for ecological water demand, ecological restoration, management of water resources and the improvement of water benefit on each scale.


Radiocarbon ◽  
2013 ◽  
Vol 55 (2) ◽  
pp. 932-942 ◽  
Author(s):  
I Carmi ◽  
D Yakir ◽  
Y Yechieli ◽  
J Kronfeld ◽  
M Stiller

A study of CO2 in soil gas was conducted in a bare plot in the unsaturated zone (USZ) of Yatir Forest, northern Negev, Israel. In 2006, 6 tubes for sampling of soil gas were inserted into the USZ to depths of 30, 60, 90, 120, 200, and 240 cm. Profiles of soil gas in the USZ were collected from the tubes 5 times between October 2007 and September 2008. Measurements of the collected profiles of soil gas were of CO2 (ppm), δ13C (′), and Δ14C (′). At all times, the concentration of CO2 in the soil gas was higher than in the air at the surface (CO2 ≃ 400 ppm; δ13C ≃ −9′). The main source of the CO2 in soil gas is from biotic activity released through roots of trees and of seasonal plants close to the surface. In the winter, the CO2 concentrations were lowest (6000 ppm) and the δ13C was −20′. In the spring and through the summer, the CO2 concentration increased. It was estimated that the major source of CO2 is at ≃240 cm depth (δ13C ≃ −22′; CO2 ≃ 9000 ppm) or below. Above this level, the concentrations decrease and the δ13C (′) become more positive. The 14C values in the measured profile are all less than atmospheric and biotic 14C. It was deduced that biotic CO2 dissolves in porewater to form carbonic acid, which then dissolves secondary carbonate (δ13C ≃ −8′; 14C ≃ −900′) from the sediments of the USZ. With the 14C data, the subsequent release of CO2 into the soil gas was then estimated. The 14C data, supported by the 13C and CO2 data, also indicate a biotic source at the root zone, at about 90 cm depth.


2022 ◽  
Vol 53 ◽  
Author(s):  
Marcos Makeison Moreira de Sousa ◽  
Eunice Maia de Andrade ◽  
Helba Araújo de Quairoz Palácio ◽  
Pedro Henrique Augusto Medeiros ◽  
Jacques Carvalho Ribeiro Filho

2018 ◽  
Vol 223 ◽  
pp. 41-47 ◽  
Author(s):  
Zeng Cui ◽  
Yu Liu ◽  
Chao Jia ◽  
Ze Huang ◽  
Honghua He ◽  
...  

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