Premium
Temporal dynamics of groundwater‐dissolved inorganic carbon beneath a drought‐affected braided stream: Platte River case study
Author(s) -
Boerner Audrey R.,
Gates John B.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg002950
Subject(s) - groundwater , water table , weathering , surface water , carbonate , hydrology (agriculture) , environmental science , carbonate minerals , total inorganic carbon , carbon cycle , geology , carbon dioxide , calcite , geochemistry , chemistry , ecosystem , ecology , environmental engineering , geotechnical engineering , organic chemistry , biology
Impacts of environmental changes on groundwater carbon cycling are poorly understood despite their potentially high relevance to terrestrial carbon budgets. This study focuses on streambed groundwater chemistry during a period of drought‐induced river drying and consequent disconnection between surface water and groundwater. Shallow groundwater underlying vegetated and bare portions of a braided streambed in the Platte River (Nebraska, USA) was monitored during drought conditions in summer 2012. Water temperature and dissolved inorganic carbon (dominated by HCO 3 − ) in streambed groundwater were correlated over a 3 month period coinciding with a decline in river discharge from 35 to 0 m 3 s −1 . Physical, chemical, and isotopic parameters were monitored to investigate mechanisms affecting the HCO 3 − trend. Equilibrium thermodynamic modeling suggests that an increase of p CO 2 near the water table, coupled with carbonate mineral weathering, can explain the trend. Stronger temporal trends in Ca 2+ and Mg 2+ compared to Cl − are consistent with carbonate mineral reequilibria rather than evaporative concentration as the primary mechanism of the increased HCO 3 − . Stable isotope trends are not apparent, providing further evidence of thermodynamic controls rather than evaporation from the water table. A combination of increased temperature and O 2 in the dewatered portion of the streambed is the most likely driver of increased p CO 2 near the water table. Results of this study highlight potential linkages between surface environmental changes and groundwater chemistry and underscore the need for high‐resolution chemical monitoring of alluvial groundwater in order to identify environmental change impacts.