Evolution of chemical and isotopic composition of inorganic carbon in a complex semi-arid zone environment: Consequences for groundwater dating using radiocarbon

摘要: Abstract Estimating groundwater age is important for any resource assessment and radiocarbon ( 14 C) dating of dissolved inorganic carbon (DIC) can provide this information. In semi-arid zone (i.e. water-limited environments), there are a multitude reasons why C traditional correction models may not be directly transferable. Some include; (1) the complex hydrological responses these systems that lead to mixture different ages in aquifer(s), (2) varied sources, origins organic matter unsaturated (3) high evaporation rates. These all influence evolution DIC easily accounted models. study, we determined isotope data for; water, carbonate minerals sediments, sediment matter, soil gas CO 2 from zone, vegetation samples. The samples were collected after an extended drought, again flood event, capture varying regimes. A graphical method (Han et al., 2012) was applied interpretation geochemical isotopic data. Simple forward mass-balance modelling carried out on key processes involving agreed well with observed High values δ 13 , low could explained by simple mineral–CO dissolution process. Instead it suggested during water–sediment interaction leads ion exchange within top ∼10–20 m aquifer which promotes greater calcite saline groundwater. This process found contribute more than half DIC, mostly ‘dead’ source. also influenced between water 2 m zone. occurs because repeated dissolution/precipitation dependent salinity driven drought periodic flooding conditions. study shows although cannot as tool some circumstances, geochemical/isotopic useful investigations related identifying mixing relations, recharge processes, evolution, surface water.