Multiyear Increase in the Stable Isotopic Composition of Stream Water From Groundwater Recharge Due to Extreme Precipitation

Abstract

AbstractThe isotopic composition of surface and groundwater is impacted by many hydrologic processes. The long‐term stable water isotopic response of systems to hydrologic change is critical for interpreting isotopic information for streamflow generation, stream‐aquifer‐coupling, and recharge processes. To evaluate the response of stream‐aquifer systems to extreme precipitation events we use 743 surface and groundwater isotopes with drainage areas ranging from 0.1 to >800 km2. Results show multiannual trends from high to low isotopic compositions associated with increases in the composition of shallow groundwater. The year 2011 was one of the wettest years and the months of August and September were the wettest consecutive 2‐month period in the 123‐year record. This increase in the isotopic composition has long‐term impact on the isotopic composition of surface and groundwater highlighting the importance of groundwater sources of baseflow to streams and the transient storage and release mechanisms of groundwater at the catchment scale.