Hydrochemical and environmental isotope analysis of groundwater and surface water in a dry mountain region in Northern Chile

Environmental context Iron (Fe) isotope analysis is a powerful tool to understand the transport of Fe within and from soils to rivers. We determined Fe isotopes and Fe concentrations of soil solutions at different depths and found that the Fe isotope compositions are modified owing to adsorption onto Fe oxides, especially in the subsoil. Hence Fe-rich capillary rising groundwater or seeping Fe-rich surface water are depleted in Fe and potentially other metals in Fe oxide-rich soil horizons. Abstract The mobility of iron (Fe) in soils is strongly affected by redox conditions, which also affect Fe input into groundwater and rivers. Stable Fe isotope analyses allow further investigation of Fe translocation processes within, into and out of soils. Soil solutions taken from a Gleysol in a lowland area (NW Germany) at different depths revealed that Fe concentration and isotope ratios strongly varied with abundance of solid Fe oxides. Low δ56Fe values of –1.7 ‰ and minimum Fe concentrations of ~0.2mgL–1 were recorded in soil solutions of Fe-rich horizons. Soil solutions of a Fe-poor horizon, however, yielded higher δ56Fe values (–0.39 ‰) and Fe concentrations of up to 68mgL–1. The water of an adjacent drainage ditch featured δ56Fe values of –1.1 ‰, in strong contrast to +0.60 ‰ of short-range ordered Fe oxide deposits in the ditch bed. We attribute the coupled low δ56Fe values and Fe concentrations to combined adsorption and atom exchange between dissolved Fe and Fe oxides. Consequently Fe oxide-poor horizons had higher δ56Fe values and dissolved Fe concentrations. Outflow of Fe-rich groundwater and surface water during rainfall into rivers is responsible for high δ56Fe for Fe-oxide precipitates and low riverine δ56Fe values.

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Interaction between Surface Water and Groundwater in Yinchuan Plain

Water ◽

10.3390/w12092635 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2635

Author(s):

Zizhao Cai ◽

Wenke Wang ◽

Ming Zhao ◽

Zhitong Ma ◽

Chuan Lu ◽

...

Keyword(s):

Numerical Simulation ◽

Surface Water ◽

Flow System ◽

Isotope Analysis ◽

Integrated Approach ◽

Field Investigation ◽

Circulation System ◽

Regional Flow ◽

Flow Systems ◽

Yinchuan Plain

The interaction of surface water (SW) and groundwater (GW) is becoming more and more complex under the effects of climate change and human activity. It is of great significance to fully understand the characteristics of regional SW–GW circulation to reveal the water circulation system and the effect of its evolution mechanism to improve the rational allocation of water resources, especially in arid and semi-arid areas. In this paper, Yinchuan Plain is selected as the study area, where the SW–GW interaction is intensive. Three typical profiles are selected to build two-dimensional hydrogeological structure models, using an integrated approach involving field investigation, numerical simulation, hydrogeochemistry and isotope analysis. The SW–GW transformation characteristics are analyzed with these models, showing that geological structure controls the SW–GW interaction in Yinchuan Plain. The SW–GW flow system presents a multi-level nested system including local, intermediate and regional flow systems. The runoff intensity and renewal rate of different flow systems are evidently different, motivating evolution of the hydro-chemical field; human activities (well mining, agricultural irrigation, ditch drainage, etc.) change the local water flow system with a certain impacting width and depth, resulting in a variation of the hydrological and hydro-chemical fields. This study presents the efficacy of an integrated approach combining numerical simulation, hydrogeochemistry and isotope data, as well as an analysis for the determination of GW-SW interactions in Yinchuan Plain.

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