科研之友
微信
新浪微博
Facebook
分享链接
摘要
A tide-influenced two-layer aquifer system in northern Germany was investigated using environmental dating tracers (H-3, Ar-39, C-14), the noble gas isotopes He-3, He-4 and Ne. The study area is a marshland at the River Ems estuary, exposed to regular flooding until AD 1000. The construction of dykes, artificial land drainage and groundwater abstraction define the hydraulic gradient. The aquifer depicts a pronounced age stratification with depth. Tritium concentrations above 0.03 TU are found only in the top 30 m. Two tritium-free samples between 20 and 30 m depth show Ar-39 ages of 130 and 250 years. Below a clay layer-about 50 m below surface level (mbsl)-all analysed samples are Ar-39 free and, thus, older than 900 years. The initial C-14 activities were about 70 pmC. Resulting C-14 ages increase with depth and increase up to 9,000 years, in agreement with minimal Ar-39 ages. Concentrations of radiogenic He-4 correlate with C-14 ages. Samples in a mid-depth range (20-70 mbsl) show significant gas loss. The gas loss is assigned to recharge in a methane producing environment. Deduced He-4 ages were used to assign this water to a infiltration period of about AD 1000.
- 出版日期2011-2
