How much information can soil solute profiles reveal about groundwater recharge?

The unsaturated zone is an important link between groundwater and the land surface, and can provide storage capacity for both water and contaminants. Consequently, the solute profile of the unsaturated zone can provide much information on groundwater recharge using tracers. This study takes a rain-fed agricultural area (Luochuan loess plain) in the Chinese Loess Plateau as an example to demonstrate how much recharge information in the thick unsaturated zone can be obtained from the solute profile. The results show that the recharge rate is 36–67 mm yr–1 and infiltration rate is 0.19 to 0.30 m yr–1, as obtained using three methods, i.e., evaluating the Cl-peak, chloride mass balance, and nitrate levels. The amount of time needed for annual precipitation to reach the water table is 133–316 years, and the groundwater is tritium free. The nitrate introduced by human activities is mainly distributed in the upper unsaturated zone (above 6 m), and the groundwater nitrate content (3.7 to 9.6 mg l–1 as NO3) remains at baseline level. The storage capacity of the unsaturated zone is found to delay the entrance of pollutants into the aquifer.

[1]  W. Edmunds,et al.  Unsaturated zones as archives of past climates: toward a new proxy for continental regions , 2002 .

[2]  Tianming Huang,et al.  Limits to recharge of groundwater from Tibetan plateau to the Gobi desert, implications for water management in the mountain front , 2009 .

[3]  J. F. Mann.  Wastewaters in the Vadose Zone of Arid Regions: Hydrologic Interactionsa , 1976 .

[4]  Zhifang Xu,et al.  Chemical and strontium isotope characterization of rainwater at an urban site in Loess Plateau, northwest China. , 2009 .

[5]  Li Ying,et al.  Origin and recharge estimates of groundwater in the ordos plateau, People’s Republic of China , 2010 .

[6]  Z. Zhang,et al.  Study of soil water movement and recharge rate of rainfall infiltration in aeration zone of loess by measuring natural tritium. , 1990 .

[7]  K. Wei,et al.  Tritium profiles of pore water in the Chinese loess unsaturated zone: Implications for estimation of groundwater recharge , 2006 .

[8]  I. Goni,et al.  Rainfall geochemistry in the Sahel region of northern Nigeria , 2001 .

[9]  W. Edmunds,et al.  Naturally high nitrate concentrations in groundwaters from the Sahel , 1997 .

[10]  Y. Li.  THE PROPERTIES OF WATER CYCLE IN SOIL AND THEIR EFFECT ON WATER CYCLE FOR LAND IN THE LOESS REGION , 1983 .

[11]  F. Phillips,et al.  Chlorine 36 and tritium from nuclear weapons fallout as tracers for long-term liquid and vapor movement in desert soils , 1988 .

[12]  G. Gee,et al.  Vadose-zone techniques for estimating groundwater recharge in arid and semiarid regions , 1994 .

[13]  W. Edmunds,et al.  A geochemical and isotopic approach to recharge evaluation in semi-arid zones; past and present , 1980 .

[14]  W. Edmunds.  Geochemistry's vital contribution to solving water resource problems. , 2009 .

[15]  Jinzhu Ma,et al.  Groundwater and lake evolution in the Badain Jaran Desert ecosystem, Inner Mongolia , 2006 .

[16]  B. Scanlon,et al.  Estimating groundwater recharge in a cold desert environment in northern China using chloride , 2008 .

[17]  D. Ronen,et al.  The unsaturated zone — a neglected component of nature , 2005 .

[18]  Jiazhong Qian,et al.  Distribution of nitrate and its implication for the contaminant source in groundwater of Huaibei Plain, Anhui Province , 2015, Geosciences Journal.

[19]  Fred M. Phillips,et al.  Environmental Tracers for Water Movement in Desert Soils of the American Southwest , 1994 .

[20]  J. Böhlke,et al.  Groundwater recharge and agricultural contamination , 2002 .

[21]  Daniel Hillel,et al.  Groundwater recharge in arid regions: Review and critique of estimation methods , 1988 .

[22]  Tianming Huang,et al.  Groundwater Baseline Quality in the Minqin Basin, NW China , 2012 .

[23]  Wei Zhang,et al.  Nitrate pollution of groundwater in northern China , 1996 .

[24]  R. Reedy,et al.  Inventories and mobilization of unsaturated zone sulfate, fluoride, and chloride related to land use change in semiarid regions, southwestern United States and Australia , 2009 .

[25]  D. K. Solomon,et al.  3H and 3He , 2000 .

[26]  Lu Zhang,et al.  Impacts of soil conservation on groundwater recharge in the semi-arid Loess Plateau, China , 2011 .

[27]  P. Cook,et al.  A new chloride leaching approach to the estimation of diffuse recharge following a change in land use , 1991 .

[28]  I. Winograd,et al.  Deep Oxygenated Ground Water: Anomaly or Common Occurrence? , 1982, Science.

[29]  Jacques Gallichand,et al.  Use of the SHAW model to assess soil water recovery after apple trees in the gully region of the Loess Plateau, China , 2006 .

[30]  Mingbin Huang,et al.  Pasture yield and soil water depletion of continuous growing alfalfa in the Loess Plateau of China , 2008 .

[31]  M. Hughes,et al.  The use of environmental chloride and tritium to estimate total recharge to an unconfined aquifer , 1978 .

[32]  Dongsheng Liu,et al.  Loess and the environment , 1985 .

[33]  W. Edmunds,et al.  Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6335 Global synthesis of groundwater recharge in semiarid andaridregions , 2022 .