Seasonal shifts in the solute ion ratios of vadose zone rock moisture from the Eel River Critical Zone Observatory

Abstract

One of the greatest challenges in critical zone studies is to document the moisture dynamics, water flux, and solute chemistry of the unsaturated, fractured and weathered bedrock that lies between the soil and groundwater table. The central impediment to quantifying this component of the subsurface is the difficulty associated with direct observations. Here, we report solute chemistry as a function of depth collected over a full year across the shale-derived vadose zone of the Eel River Critical Zone Observatory using a set of novel sub-horizontal wellbores, referred to as the vadose zone monitoring system. The results of this first geochemical glimpse into the deep vadose zone indicate a dynamic temporal and depth-resolved structure. Major cation concentrations reflect seasonal changes in precipitation and water saturation, and normalized ratios span the full range of values reported for the world's largest rivers.

Drainage from the Critical Zone: Lithologic Controls on the Persistence and Spatial Extent of Wetted Channels during the Summer Dry Season

“…By coupling our understanding of the subsurface hydrology of our sites (Dralle et. al, 2016;Druhan et al, 2017;Hahm et al, 2016Kim et al, 2017;Link et al, 2014;Oshun et al, 2016;Rempe & Dietrich, 2014;Rempe et al, 2010;Salve et al, 2012) with wetted channel observations at the beginning and end of the summer dry season, our study demonstrates the connection between critical zone structure and the extent and duration of wetted channels.…”

“…At Rivendell, data on groundwater table levels, groundwater and stream water chemistry, soil and rock moisture, water isotope dynamics, meteorology, sap flow, subsurface temperature and CO 2 have been continuously collected, with a principal focus of understanding the path and solute evolution of water through the critical zone (Druhan et al, 2017;Kim et al, 2014Kim et al, , 2017Link et al, 2014;Oshun et al, 2016;Rempe, 2016, Rempe & Dietrich, 2014Salve et al, 2012). At the start of the wet season, most of the infiltrating rain increases the moisture content in the soil and the underlying weathered bedrock.…”

Lithologically Controlled Subsurface Critical Zone Thickness and Water Storage Capacity Determine Regional Plant Community Composition

“…Angelo is part of the University of California Natural Reserve System and consists largely of steep‐sloped, old‐growth mixed broadleaf‐needleleaf evergreen forest (see map in supporting information Figure S1). It contains the Elder Creek watershed (Table ), a tributary to the South Fork Eel River, and Rivendell, an intensively instrumented hillslope that has been the site of numerous isotopic, geochemical, ecophysiological, and hydrologic studies (Dralle et al, ; Druhan et al, ; Kim et al, , ; Link et al, ; Lovill et al, ; Oshun et al, ; Rempe & Dietrich, ; Salve et al, ; Simonin et al, ). Rivendell (39.729°, −123.6451°) is ~15 km east of the Pacific Ocean, 430 m above sea level (a.s.l.…”

Mercury Sourcing and Sequestration in Weathering Profiles at Six Critical Zone Observatories

“…Soil carbon data were obtained for each CZO: Calhoun (Bacon et al, 2012;Fimmen et al, 2008), Eel River (Druhan et al, 2017), Luquillo (Buss et al, 2005), and Southern Sierra. Total organic C (TOC) concentrations in soil and regolith samples were measured for Boulder Creek and Shale Hills CZO samples using the Carlo-Erba NA 1500 Element Analyzer (Thermo Scientific, Waltham, MA, USA).…”