Sammanfattning

Large proportions of rainwater and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time-varying processes. Chlorofluorocarbon (CFC)-based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km(2) forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from nine different wells with depths of 2-18 m close to the stream network. Immediately below the water table, CFC-based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age-depth-relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity.

Nyckelord

CFCs; groundwater age stratification; groundwater recharge; hillslope storage Boussinesq equations; Krycklan; subsurface discharge; subsurface hydrological connectivity

Publicerad i

Hydrological Processes
2020, Volym: 34, nummer: 10, sidor: 2176-2189
Utgivare: WILEY

SLU författare

• Kolbe, Tamara

  • Institutionen för vatten och miljö, Sveriges lantbruksuniversitet
    
  • Technische Universität Bergakademie Freiberg

• Bishop, Kevin

  • Institutionen för vatten och miljö, Sveriges lantbruksuniversitet
    

Associerade SLU-program

Försurning


Globala målen

Säkerställa tillgången till och en hållbar förvaltning av vatten och sanitet för alla


UKÄ forskningsämne

Oceanografi, hydrologi, vattenresurser


Publikationens identifierare

DOI: https://doi.org/10.1002/hyp.13753

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/105692