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Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity

Kolbe, Tamara and Marcais, Jean and de Dreuzy, Jean-Raynald and Labasque, Thierry and Bishop, Kevin (2020). Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity. Hydrological Processes. 34 , 2176-2189
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Abstract

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.

Authors/Creators:Kolbe, Tamara and Marcais, Jean and de Dreuzy, Jean-Raynald and Labasque, Thierry and Bishop, Kevin
Title:Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity
Year of publishing :2020
Volume:34
Page range:2176-2189
Number of Pages:14
Publisher:Wiley
ISSN:0885-6087
Language:English
Publication Type:Journal article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Oceanography, Hydrology, Water Resources
Keywords:CFCs, groundwater age stratification, groundwater recharge, hillslope storage Boussinesq equations, Krycklan, subsurface discharge, subsurface hydrological connectivity
URN:NBN:urn:nbn:se:slu:epsilon-p-105692
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-105692
Additional ID:
Type of IDID
DOI10.1002/hyp.13753
Web of Science (WoS)000530491800002
ID Code:17097
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Dept. of Aquatic Sciences and Assessment
Deposited By: SLUpub Connector
Deposited On:22 Jun 2020 13:18
Metadata Last Modified:22 Jun 2020 13:18

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